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EG35CH05-Schwarzenbach ARI 18 September 2010 7:4
Global Water Pollutionand Human HealthRene P. Schwarzenbach,1
Thomas Egli,1,2
Thomas B. Hofstetter,1,2 Urs von Gunten,1,2
and Bernhard Wehrli1,21Institute of Biogeochemistry and
Pollutant Dynamics (IBP), ETH Zurich, 8092 Zurich,Switzerland;
email: [email protected], Swiss Federal Institute of
Aquatic Science and Technology, 8600 Dubendorf,Switzerland
Annu. Rev. Environ. Resour. 2010. 35:10936
First published online as a Review in Advance onAugust 16,
2010
The Annual Review of Environment and Resourcesis online at
environ.annualreviews.org
This articles doi:10.1146/annurev-environ-100809-125342
Copyright c 2010 by Annual Reviews.All rights reserved
1543-5938/10/1121-0109$20.00
Key Words
agriculture, geogenic, micropollutants, mining, pathogens,
wastes
Abstract
Water quality issues are a major challenge that humanity is
facing in thetwenty-rst century. Here, we review the main groups of
aquatic con-taminants, their effects on human health, and
approaches to mitigatepollution of freshwater resources. Emphasis
is placed on chemical pol-lution, particularly on inorganic and
organic micropollutants includingtoxic metals and metalloids as
well as a large variety of synthetic or-ganic chemicals. Some
aspects of waterborne diseases and the urgentneed for improved
sanitation in developing countries are also discussed.The review
addresses current scientic advances to cope with the greatdiversity
of pollutants. It is organized along the different temporal
andspatial scales of global water pollution. Persistent organic
pollutants(POPs) have affected water systems on a global scale for
more than vedecades; during that time geogenic pollutants, mining
operations, andhazardous waste sites have been the most relevant
sources of long-termregional and local water pollution.
Agricultural chemicals and waste-water sources exert shorter-term
effects on regional to local scales.
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Improved sanitation:a safe way to handleexcreta, including
itscollection, treatment,and disposal or reuseto avoid
spreadingdiseases and pollution
Contents
INTRODUCTION . . . . . . . . . . . . . . . . . . 110AQUATIC
MICROPOLLUTANTS:
THE CHALLENGE OFDEALING WITH CHEMICALCOMPLEXITY . . . . . . . .
. . . . . . . . . . . 111
SELECTED TOPICS OFCHEMICAL WATERPOLLUTION . . . . . . . . . . .
. . . . . . . . . 113Persistent Organic Pollutants:
A Long-Term Global Problem . . 115Agriculture and Water Quality
. . . . . 116Geogenic Contamination Sources:
The Problem with Arsenic inGroundwater . . . . . . . . . . . . .
. . . . . . 117
Surface Water Contaminationfrom Mining Operations . . . . . . .
. 118
Groundwater Contamination bySpills and Hazardous WasteSites . .
. . . . . . . . . . . . . . . . . . . . . . . . . . 119
Pharmaceuticals in Wastewaterand Drinking Water . . . . . . . .
. . . . 121
VIRUSES AND MICROBIALPATHOGENS: THECHALLENGES
CONCERNINGWATERBORNE DISEASES . . . . . . 122Global Health Problems
Related to
Sanitation and Drinking Water . . 122Wastewater Treatment
and Water Reuse . . . . . . . . . . . . . . . 124Detecting
Pathogens
and Waterborne Diseases . . . . . . . 125The Multibarrier
Concept for
Improved Sanitation and SafeDrinking Water Supply . . . . . . .
. . 125
CONCLUSION . . . . . . . . . . . . . . . . . . . . . 126
INTRODUCTION
Many of the major problems that humanity isfacing in the
twenty-rst century are related towater quantity and/or water
quality issues (1).These problems are going to be more aggra-vated
in the future by climate change, result-ing in higher water
temperatures, melting of
glaciers, and an intensicationof thewater cycle(2), with
potentially more oods and droughts(3). With respect to human
health, the mostdirect and most severe impact is the lack
ofimproved sanitation, and related to it is the lackof safe
drinking water, which currently affectsmore than a third of the
people in theworld.Ad-ditional threats include, for example,
exposureto pathogens or to chemical toxicants via thefood chain
(e.g., the result of irrigating plantswith contaminated water and
of bioaccumula-tion of toxic chemicals by aquatic
organisms,including seafood and sh) or during recreation(e.g.,
swimming in polluted surface water).
This reviewdealswith the pollutionof fresh-water resources,
including lakes, rivers, andgroundwater. Because numerous reviews
haveappeared recently that cover the various aspectsof waterborne
diseases in a comprehensive way(4), more emphasis is placed on
chemical pollu-tion. More than one-third of Earths
accessiblerenewable freshwater is consumptively used
foragricultural, industrial, and domestic purposes(5). Asmost of
these activities lead towater con-tamination with diverse synthetic
and geogenicnatural chemicals, it comes as no surprise thatchemical
pollution of natural water has becomea major public concern in
almost all parts ofthe world. In fact, a recent Gallup poll taken
in2009 revealed that pollution of drinking wateris the primary U.S.
environmental concern (6).
Chemical water pollutants can be dividedinto two categories, the
relatively small numberof macropollutants,which typically occur at
themilligram per liter level and include nutrientssuch as nitrogen
(7) andphosphorous species (8)as well as natural organic
constituents (9). Thesources and impacts of these common classi-cal
pollutants are reasonably well understood,but designing sustainable
treatment technolo-gies for them remains a scientic challenge
(10).For example, high nutrient loads can lead toincreased primary
production of biomass, oxy-gen depletion, and toxic algal blooms
(11, 12).Increasing salt loads entering surface water viaroad salt
and excessive irrigation pose anotherlong-term problem (13). High
salt concentra-tions prevent the direct use as drinking water
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and inhibit crop growth in agriculture. Theproblem is
accentuated in many coastal areas,such as India and China, by
marine salt intru-sion into groundwater owing to overexploita-tion
of aquifers and sea level rise (14). Technicaland political
strategies to cope with these clas-sical problems have been
discussed extensivelyin the literature (15, 16) and are therefore
notaddressed here.
In this review, we focus on the thousands ofsynthetic and
natural trace contaminants thatare present in natural water at the
nanogramto microgram per liter level. Many of thesemicropollutants
may exert toxic effects evenat such low concentrations,
particularly whenpresent as mixtures. The large number andgreat
structural variety ofmicropollutantsmakeit, however, usually very
difcult to assess suchadverse effects, which often are not acute
but aresubtle, chronic effects (5). This contrasts withthe common,
acute health effects of the rathersmall number of well-known
pathogens thatmay be present in polluted water.
Therefore,considering the difculty of assessing the effectsof
micropollutants on aquatic life and humanhealth and that
appropriate, affordable watertreatment methods for their effective
removalare not available inmany parts of theworld,ma-jor efforts
(such as restricted use, substitutionor oxidative treatment) have
to be undertakento prevent these chemicals from reaching natu-ral
water. However, as should become evidentfrom the examples discussed
in this review, thistask often represents a formidable challenge
notonly from a technical but also from economic,societal, and
political standpoints.
The sources of micropollutants in naturalwater are diverse.
About 30%of the globally ac-cessible renewable freshwater is used
by indus-try andmunicipalities (17), generating togetheran enormous
amount of wastewaters containingnumerous chemicals in varying
concentrations.In many parts of the world, including emerg-ing
economies such asChina, these wastewatersare still untreated or
undergo only treatmentthat does not effectively remove the
majorityof the micropollutants present (18). The latteralso holds
for municipal wastewater in indus-
Macropollutants: therelatively smallnumber of mostlyinorganic
pollutantsoccurring at themilligram per literlevel
Micropollutants: thethousands of inorganicand organic
tracepollutants occurring atthe nanogram tomicrogram per
literlevel
trialized countries (see below). Other impor-tant sources of
micropollutants include inputsfromagriculture (19), which applies
severalmil-lion tons of pesticides each year; from oil andgasoline
spills (20); and from the human-drivenmobilization of naturally
occurring geogenictoxic chemicals, such as heavymetals
andmetal-loids. Additional naturalmicropollutants are bi-ologically
produced taste and odor compounds(21), which are not primarily a
toxicologicalproblem but are of great aesthetic concern.There are
also the millions of municipal and,particularly, hazardous waste
sites, includingabandoned industrial and former military sites,from
which toxic chemicals may nd their wayinto natural water,
especially into groundwater.Finally, when considering that more
than100,000 chemicals are registered and most arein daily use (22),
one can easily imagine numer-ous additional routes by which such
chemicalsmay enter the aquatic environment.
By addressing a series of very different typesof micropollutants
from different sources, weattempt to give a representative picture
of thescales and extent of this global water pollutionproblem,
without a claim of completeness. Asan introduction to these
selected topics, we startwith some general remarks on the
problemsand challenges in assessing micropollutants innatural
water.
AQUATIC MICROPOLLUTANTS:THE CHALLENGE OF DEALINGWITH CHEMICAL
COMPLEXITY
A proper assessment of any chemical pollu-tion of natural water
relies on ve elements:(a) knowledge of the type and origin of the
pol-lutants, (b) the availability of analytical methodsfor
quantication of the temporal and spatialvariability in
concentrations of the chemical(s)present, (c) a profound
understanding of theprocesses determining the transport and fateof
the chemical(s) in the system considered,(d ) mathematical
transport and fate modelsof appropriate complexity to design
optimalsampling strategies and to predict futuredevelopments of a
given pollution case, and
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Complexation: theinteraction between apositively chargedmetal
ion in solutionand a negativelycharged ion or amolecule with
anunshared electron pair
(e) methods for quantication of the adverseeffects of the
chemicals on aquatic life andhuman health. Notably, the same
analyticaltools and process knowledge are also pivotalfor the
design and operation of treatment tech-nologies and in situ
remediation procedures.In the following, we address some
fundamentalaspects related to these ve elements of anexposure
assessment of micropollutants.
Considering the large number of struc-turally diverse
micropollutants that may un-dergo numerous interactions with other
natu-ral or anthropogenic, dissolved or particulatechemical species
and materials (e.g., naturalorganic matter, mineral surfaces, redox
activespecies), with light, and even with living or-ganisms,
exposure assessment of aquatic micro-pollutants is commonly quite a
challenging taskand requires a broad interdisciplinary approach(5,
23).
For inorganic pollutants, including heavymetals (e.g., Cr,Ni,
Cu, Zn, Cd, Pb,Hg,U, Pu)andmetalloids (e.g., Se, As), themain
challengein assessing environmental risks is related totheir
contrasting behavior under different redoxconditions. These
elements are not subject todegradation like many of the organic
pollutants(see below); the major processes that determinetheir
transport and their bioavailability includeoxidation/reduction,
complexation, adsorp-tion, and precipitation/dissolution
reactions.Most metallic elements exhibit widely differentsolubility
in the presence of oxygen and underreducing conditions. Under oxic
conditions,the most abundant redox sensitive metalsiron and
manganeseform nely dispersedoxide particles, which strongly adsorb
heavymetals and metalloids (24). When oxygen isdepleted, these
oxide particles undergo reduc-tive dissolution and release their
adsorbed toxicload (25). The precipitation and dissolution ofsuch
reactive particles in the environment areoften governed by
microorganisms. Analyzingpathways and rates of iron and
manganesedispersal under environmental conditions re-mains a
challenging task, but recently, progressin mass spectrometry opened
new analyticalwindows to trace microbial processes via the
stable isotope signatures of metallic elements,such as iron
(26).
The large variety of different mineral phasesand possible
interactions between solutes,which are relevant for adsorption
processes,complicate the environmental assessment ofmetal pollution
and its health effects (27). Rapidprogress in X-ray spectroscopy
was instrumen-tal in elucidating the structure of metal ions
ad-sorbed on mineral surfaces because the methodallows identication
of the specic molecu-lar neighbors of metal ions in complex
min-eral environments (28). Such molecular-levelinformation helps
develop an understandingof the factors affecting the mobility of
toxicmetal ions. A precondition for biological ac-tion is the
potential ability of metal ions tocross cell membranes. Strong
bonds to mineralparticles and stable macromolecular
complexestypically prevent uptake. As a consequence, di-rect
methods have been developed to assess themobility and
bioavailability of metal contam-inants in complex media, e.g.,
soils or sedi-ments (29). To determine the fate and distri-bution
of metals in the environment, insightfrom molecular-level studies
and in situ eldobservations can then be scaled up using simpleor
more sophisticated reaction/transport mod-els (30), which combine
physical, chemical, and(micro)biological processes (26). The last
stepof an assessment procedure addresses the ef-fects of biological
uptake. The analysis of po-tential effects of nanoparticles
provides an il-lustrative example. In recent years, the
rapidlygrowing use of engineered nanoparticles forindustrial and
commercial applications causedconcern about the biological effects
of this typeof new anthropogenic pollutant for the
aquaticenvironment and human health. There is nowpreliminary
evidence that such particles do notonly release toxic metals at
constant rates butcould also exert direct specic harmful
effects,which require further research (31). So far,much progress
has been made in elucidatingmolecular mechanisms, relevant
geochemicaland microbial reactions, and integrating reac-tion and
transport pathways in biogeochemi-cal models. The most critical
knowledge gap
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relates to our limited ability to predict andquantify adverse
effects of inorganic pollutantson aquatic life and human
health.
When dealing with organic pollutants, themajor challenge is to
cope with the large num-ber and the great variety of chemicals
cover-ing a wide range in physical-chemical prop-erties and
reactivities (23). As an illustration,Figure 1 (see color insert)
shows the large dif-ferences in partitioning behavior
betweenwaterand air or water and an organic phase, respec-tively,
that may exist between different typesof chemical micropollutants.
For example, theapolar, hydrophobic polychlorinated biphenyls(PCBs)
partition reasonably well from waterinto air and extremely well
from water into anorganic phase, such as octanol, and are
thushighly bioaccumulative. In contrast, more po-lar, hydrophilic
compounds, such as the sul-fonamide antibiotics, partition very
poorly intoboth air and an organic phase. This
differentpartitioning behavior means that these com-pounds exhibit
a very different transport andphase transfer behavior in the
environment.Also, their analysis in environmental samples(e.g.,
air, water, sediment, soil) requires a differ-ent methodological
approach because usuallyseveral enrichment and separation steps are
in-volved, which rely on the partitioning behaviorof the compound.
Themajor analytical difcul-ties are encountered withmore complex,
multi-functional polar chemicals, which includemanyof the
biologically active compoundssuch asmodern pesticides, biocides,
and pharmaceuti-cals (32, 33). The same holds for the quanti-cation
of the environmental partitioning of or-ganic pollutants (e.g.,
sorption from water toparticles, soils, or sediments), which is
most dif-cult for polar, complex organic chemicalsincluding those
exhibiting ionizable functionalgroups (34, 35).
The major challenges in assessing orpredicting transformation
reactions of or-ganic micropollutants in the environmentare
presented by the biologically (micro-bially) mediated processes.
This is partlydue to the intrinsic difculty of classify-ing or even
quantifying biological activity
Persistent organicpollutants (POPs):the globallydistributed
pollutantsthat exhibit a highbioaccumulationpotential
in complex natural systems. Moreover, incontrast to models
describing homogeneouschemical or photochemical reactions (23),the
treatment of enzymatic and surface-mediated reactions, which are
often linkedto biological processes, is still in its
infancy.Depending on the environmental conditions(e.g., pH, redox
potential, type of surfacespresent), a given compound may react
byvarious pathways and/or at very different rates.Furthermore, even
compounds exhibiting onlyminor differences in their structures may
reactvery differently (23). Therefore, future researchshould be
directed more intensively toward de-veloping tools for assessing
(bio)transformationprocesses in environmental settings becausethese
processes represent the most powerfulremoval mechanisms for organic
pollutantsin natural water. In addition, predictivemodels for
biodegradability using structuralinformation need to be developed
(36).
Finally, there are a signicant number ofcases in which chemical
water pollution issuspected, but the types and sources of the
pol-lutants are not known and/or cannot be ex-haustively analyzed.
In such cases, a batteryof effect-oriented routine methods that
wouldallow one to assess whether or not action isneeded would be
useful to investigators. Al-though promising examples of
effect-orientedmethods have been reported (37, 38), there isstill
ample room for future developments.
SELECTED TOPICS OFCHEMICAL WATER POLLUTION
Table 1 gives an overview of the topics thatare discussed in the
following sections. Thesetopics address and illustrate various
aspectsof global water pollution, including importanttypes of
pollutant sources and pollutants as wellas different temporal and
spatial scales of waterpollution, ranging from long-term global
per-sistent organic pollutants (POPs) to long-termregional (e.g.,
geogenic pollutants, mining) tolong-term local (e.g., hazardous
waste sites) toshort-term regional (e.g., agriculture) to
short-term regional or even local (e.g., wastewater)
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Table
1The
discussion
ofwater
pollu
tion
issues
inthisreview
follo
wsthesequ
ence
ofpo
llutant
sourcesas
show
nin
thisoverview
oftopics
Pollutant
sources
Source
type
Pollutant
type
saddressed
Illustrative
exam
ples
aMainwater
quality
prob
lems
Major
challeng
esM
ultip
le(w
aste
sites,
spills,
agricu
lture,
combu
stion,
and
othe
rs)
Globa
llydistribu
tedpo
int
anddiffu
se
Persisten
torg
anic
pollu
tant
s(P
OPs)
PCBs,
PBDEs,
DDT,
PAH
s,PCDDs,
PCDFs
Biomag
nic
ationin
food
chain,
dive
rsehe
alth
effects
Pha
seou
texistingPOPs,
con
neex
istin
gso
urce
s,pr
even
tuse
ofne
wPOPs
Agr
icultu
reDiffus
ePestic
ides
Triaz
ines,
chlorace
anilide
s,DDT,
linda
ne
Con
taminationof
grou
ndan
dsu
rfac
ewater
with
biolog
ically
activ
ech
emicals;
accide
ntal
poison
ing(partic
ularly
inde
veloping
coun
tries)
Con
trol
ofpe
sticideru
noff
from
agricu
lturallan
d,pe
sticidemisus
e
Natur
alco
ntam
inan
tsGeo
genic
cont
aminan
tsBioge
nicco
ntam
inan
ts
Diffus
eIn
orga
nicco
ntam
inan
ts,
cyan
otox
ins,
tastean
dod
orco
mpo
unds
As,
F,Se
,U,m
icro
cystins,
geos
min
Can
cer,
uor
osis,h
uman
health
,aesth
etics(taste
andod
or)
Dev
elop
men
tofe
ffective
hous
eholdtrea
tmen
tsystem
s,co
ntro
l,eu
trop
hica
tion,
cons
umer
acce
ptan
ceM
ining
Mos
tlypo
int
Acids
,lea
chingag
ents,
heav
ymetals
Sulur
icac
id,c
yanide
,mercu
ry,c
oppe
rM
etal
remob
iliza
tion,
acut
eto
xicity,c
hron
icne
urot
oxicity
Acidne
utraliz
ation,
metal
remov
al,int
rodu
cing
effectiveno
ntox
icreag
ents
Haz
ardo
uswaste
Point
Diverse
U,tec
hnetium,
chro
mium,c
hlor
inated
solven
ts,n
itroa
romatic
explos
ives
Lon
g-term
cont
amination
ofdr
inking
water
reso
urce
s
Con
tainmen
tofp
ollutant
s,mon
itoring
ofmiti
gatio
npr
ocessesinclud
ingna
tural
attenu
ation
Urb
anwastewater
inindu
strialized
coun
tries
Point
Pha
rmac
eutic
als,
horm
ones
Dicloph
enac
,17-eth
inylestrad
iol
Eco
toxico
logica
leffe
ctsin
rive
rs,fem
inizationof
sh
Red
uctio
nof
micro
pollu
tant
load
sfrom
wastewater
bypo
lishing
trea
tmen
tUrb
anwastewater
inde
veloping
and
emerging
coun
tries
Point
Micro
orga
nism
san
dviru
ses
Cho
lera,typ
hoid
feve
r,diarrh
ea,h
epatiti
sA
and
B,s
chisto
somiasis,
deng
ue
Hum
anhe
alth
,child
mor
talit
y,malnu
triti
onIm
prov
ingsanitatio
nan
dhy
gien
e,safe
drinking
water,c
heap
adeq
uate
drinking
water
disinf
ectio
ntech
niqu
es
a Abb
reviations
:As,
arsenic;
F,u
orine;
PCBs,
polych
lorina
tedbiph
enyls;
PBDEs,
polybr
ominated
diph
enyl
ethe
rs;D
DT,d
ichlor
odiphe
nyltr
ichlor
oeth
ane;
PAH
s,po
lycy
clic
arom
atic
hydr
ocarbo
ns;P
CDDs,
polych
lorina
teddibe
nzo-
p-diox
ines;P
CDFs
,polyc
hlor
inated
dibe
nzofur
ans;
Se,s
elen
ium;U
,uranium
.
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pollutants. The examples should also illustratethat any
mitigation and adaptation strategies tosolve a givenwater pollution
problemhave theirown technical, economical, political, and
soci-etal boundary conditions.
Persistent Organic Pollutants:A Long-Term Global Problem
A group of chemicals that have been and con-tinue to be of
greatest environmental concernare denoted as POPs. They include a
diverse setof high-volume production compounds that
areintentionally produced as well as compoundsthat form as
accidental by-products of a vari-ety of combustion processes. A
compound iscommonly classied as a POP if it exhibits thefollowing
four characteristics:
1. Persistent in the environment, whichmeans that chemical,
photochemical, andbiological transformation processes donot lead to
a signicant removal of thecompound in any environmental
com-partment;
2. Prone to long-range transport, thus toglobal distribution,
even in remote re-gions where the compound has not beenused or
disposed, owing to the com-pounds physical-chemical properties;
3. Bioaccumulative through the food web;and
4. Toxic to living organisms, including hu-mans and
wildlife.
Some prominent classical POPs (also calledlegacy POPs or the
dirty dozen) have beenlisted and dealt with in two international
con-ventions (the Aarhus Protocol and the Stock-holm Convention)
with the goal to assess thePOPs global presence and to reduce their
emis-sions to the environment (39). They primar-ily encompass
highly chlorinated compounds[e.g., dichlorodiphenyltrichloroethane
(DDT),PCBs, polychlorinated dioxins and dibenzofu-ranes] and
polycyclic aromatic hydrocarbons(PAHs). However, recognizing that
there aremany other high-volume production chemicalspotentially
falling into the POP category (40),
Diffuse sources:widespread activities,with no discretesource,
that causepollution
these conventions allow addition of new com-pounds to the list.
Recent examples of suchemerging POPs that are under considerationto
be added are the polybrominated diphenylethers (PBDEs) widely used
as ame retardants(41, 42), and a variety of peruoroalkyl chem-icals
(PFCs) that, because of their very spe-cial properties (43), are
used in numerous in-dustrial applications (44). It should be
pointedout that many emerging pollutants, includ-ing some POPs, may
have already been presentin the environment for decades but werenot
detected because of analytical limitations(32, 33). From a
toxicological point of view,POPs may threaten the health of both
humansand wildlife because of their various adverse ef-fects,
including disruption of the endocrine, thereproductive, and the
immune systems, as wellas their ability to cause behavioral
problems,cancer, diabetes, and thyroid problems.
In the context of global water pollution,POPs pose a severe
problem primarily becauseof their particularly large
bioaccumulation andbiomagnication potential in aquatic foodwebs(45,
46). A series of monitoring studies have re-vealed critical
concentrations of POPs in fresh-water and marine sh and in marine
mammalsand, as a consequence, in human milk and hu-man tissues of
peoplewho depend on these foodsources (47, 48). Owing to various
long-rangetransport mechanisms, accumulation of POPsis particularly
pronounced in the worlds coldregions (e.g., in the Arctic) (46,
49). Even legacyPOPs, such as DDT or PCBs that have beenbanned or
are restricted in their use, remainof great concern because they
continue to bereleased from various old deposits, includingwaste
sites and contaminated sediments.
For emerging POPs, such as, for example,the PBDEs in the past 30
years, there hasbeen an exponential increase by a factor ofabout
100 in concentration in human tissueswith a doubling time of about
5 years, whichcan be observed in various parts of the world(Europe,
Japan, North America). This is, ofcourse, the result of several
different exposureroutes, including primarily terrestrial ones(47).
However, very similar trends can also be
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Point source: a singleidentiable localizedsource of
pollution
seen in marine mammals in North Americaand northern Europe
(47).
As is evident from the still ubiquitous globalpresence of many
legacy POPs in the environ-ment, global control strategies aimed
only atreducing production and use of POPs do notnecessarily lead
to an immediate reduction ofemissions because of the presence of
various oldsources. To identify and design optimal mitiga-tion
strategies, further development of emissioninventories, as
attempted for PCBs (50), and ofmore renedmodels for assessment and
predic-tionof (a) the (global) transport anddistributionbehavior
(51) and (b) the effects on humans andwildlife (52) of legacy and
emerging POPs isstill important on the research agenda. There-fore,
the inuence of climate change on thedistribution and the effects of
POPs in theenvironment needs to be addressed (53). Froman
environmental policy point of view, themost urgent actions to be
taken by the inter-national community are to phase out POPsthat are
still in use, to improve source controlswherever possible, and to
make sure that nonew chemicals with POP characteristics appearon
the market (22).
Agriculture and Water Quality
Several million tons of chemicals are consumedannually for
agricultural production to main-tain and increase crop yields by
controlling
GLOBAL PESTICIDE CONSUMPTION
Three to seven million tons of pesticides are produced
annually(60). Estimates of pesticide use vary between approximately
0.2and 2 kg of active substance per hectare (ha) of arable land
indeveloping versus developed countries, respectively (54).
Suchestimates are imprecise by nature. The amount of active
chem-icals required to control pests depends on the crop treated,
thetype of pesticide used, the application technique, as well as
geo-graphic and climatic boundary conditions. More recently
devel-oped agrochemicals generally operate at lower doses compared
toestablished products, but toxic loads per dose of active
ingredientvary widely among different agrochemicals.
fungi, weeds, insects, and other pests (seethe sidebar Global
Pesticide Consumption;54). Pesticides and related agrochemicals
areavailable on the market as tens of thousandsof different
commercial products that containapproximately hundreds of different
activechemical ingredients (55, 56). Owing to thetoxicity of these
chemicals for biota andhumans and their intentional release into
theenvironment, the use of new and establishedagrochemical products
is regulated in detail:Country-specic registration and risk
assess-ment procedures aim at protecting not onlysoil and water
resources/ecosystems but alsofarmers and consumers (5659).
Contamination of water resources in catch-ment areas of
agricultural land and continuousexposure of humans and biota to
biologicallyactive chemicals are of great concern. Peak
con-centrations of pesticides and their transforma-tion products,
such as the frequently detectedtriazines or chloroacetanilides in
U.S. rivers(61), can exceed ecotoxic levels for nontargetorganisms
in soils and aquatic systems and com-promise the use of surface and
groundwater fordrinking water supplies (61). Quantifying theshare
of used pesticides that reach surface andgroundwater (62) and
designing effective miti-gation measures (63, 64) beyond a
case-by-casebasis are challenging because of the substantialspatial
and temporal variability of pesticidelosses (65). Typical
agricultural point sourcesinclude pesticide runoff from hard
surfaces,mostly from farmyards or storage facilitiesduring the
handling of agrochemical productsor accidental spills. Depending on
connectionsto sewer systems, pesticides can either inltrateinto the
nearby soil or enter aquatic systemsvia sewage treatment plants.
Point sources cancause high-concentration peaks in the outlet ofa
catchment area, but they do not necessarilyconstitute a major share
of the mass input (66).Instead, diffuse losses, including eld
runoff,drainage/leaching into the subsurface, or spraydrift, are of
much greater concern, and abroad variety of mitigation measures
have beenevaluated to minimize their impact on waterresources (67).
The occurrence of pesticide
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losses from runoff is determined largely by thesoil hydraulic
properties (permeability, waterow patterns), topography, and
meteorolog-ical conditions, whereas compound-specicproperties
(e.g., sorption behavior to the solidmatrix) are less relevant
(68). Restricted ap-plication of pesticides to such hot spots
proneto increased runoff would be a more effectivemitigation
measure than replacing pesticideproducts and/or alternative
application timing(6668).
Water contamination also arises in drainageand sewer systems
from pesticide applica-tions in nonagricultural/urban areas
throughincreased runoff of pesticide-containing rain-water over
sealed surfaces, such as roofs androads (69). From the perspective
of the overallenvironmental impacts of extensive agriculture,a
reduction of soil and water pollution by pes-ticide emissions is
considered a key element inagricultural management practices to
minimizeecological changes and to maintain biodiversity(60, 70).
Finally, acute poisoning from directpesticide exposure is a
considerable risk for agri-cultural workers. Although the impact of
thisexposure pathway is debated in North Americaand Europe (71,
72), accidental exposure anddeliberate misuse of agrochemicals seem
morefrequent in developing countries (7375), re-sulting in an
estimated poisoning of 3 millionpeople with as many as 20,000
unintentionaldeaths per year (76).
Apart from distinct climatic/ecological con-ditions and grown
crops, agricultural practice inmost developing countries is driven
by the needto achieve or maintain food security for grow-ing
populations and the economic/politicalimplications of this
overarching goal (60).Together with trends toward urbanizationand
industrialization, these agricultural de-velopments are causing
water quality issues(77). Pesticide use per hectare of cropland
(seethe sidebar Global Pesticide Consumption)increased over the
recent years, even if, asdocumented for China, contributions to
cropyield were marginal (78). In developing coun-tries, resources
and capabilities for monitoringpesticide concentration in aquatic
systems
and assessing the risk for humans and theenvironment are often
limited (79), and atti-tudes toward enforcement of regulations
arescant (80). Monitoring programs of pesticideoccurrence and
distribution illustrates that thespectrum of active ingredients can
still differfrom those used in the developed countries.Especially,
the persistent organochlorinepesticides [DDT,
hexachlorocyclohexanes(HCHs)] are applied extensively for
agricultureand sanitation purposes because they are
stillcomparatively cheap and effective (74, 81)
Geogenic Contamination Sources:The Problem with Arsenic
inGroundwater
The geological composition of aquifers in someareas of the world
is the main cause of leachingof toxic elements into drinking water
supplies.The main elements of concern are arsenic,uoride, selenium,
and a few others, such aschromium and uranium. Among all these
ge-ogenic contaminants, arsenic has so far causedthe greatest
negative health effects as well asglobal concern. For this reason,
arsenic is dis-cussed as an illustrative example. In
Bangladeshalone, arsenic-contaminated groundwateraffects between 35
and 75 million people (82).About 6 million people are at risk
inWest Ben-gal in India (83), and other regions of concerninclude
the highly populated river deltas inCambodia and Vietnam (84). In
these regions,arsenic poisoning developed over the pastdecade as a
result of efforts to provide safedrinking water. Until the 1970s,
most peoplein these rural areas depended on untreateddrinking water
from rivers and ponds, whichare often a source of infectious
diseases. Thehigh mortality of up to 250,000 children peryear in
Bangladesh alone triggered large-scaleprograms to install
groundwater wells to pro-vide safe drinking water. More than 95% of
thepopulation now uses groundwater from about10 million tube wells.
About 60% of these wellsalong the Ganges-Brahmaputra River systemin
Bangladesh are affected by arsenic levelsexceeding the World Health
Organization
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WHO: World HealthOrganization
(WHO) limit (85). Arsenic pollution is also ofconcern in other
parts of the world, such as theUnited States (86, 87) and Eastern
Europe (H.Rowland, E. Omoregie, R. Millot, C. Jiminez,J. Mertens
& M. Berg, submitted).
Factors responsible for the arsenic con-tamination are the high
weathering rates ofarsenic-rich source rocks in mountain
ranges,deposition of organic-rich deposits in riveroodplains, and a
at and humid terrain withlong residence times of water in the
aquifer,leading to anoxic conditions whereby adsorbedarsenic is
released into the water (88). A secondpathway of arsenic
mobilization is occurring inarid areas, such as in the U.S.
Midwest, easternAustralia, and central Asiawhere high-pHconditions
mobilize arsenic in oxygen-richgroundwater. Because the chemical
factorsgoverning arsenic mobilization are well un-derstood, the
risk of arsenic contaminationin groundwater has been modeled at a
globalscale (Figure 2; see color insert) (89).
Chronic arsenic poisoning leads to an ac-cumulation of the
element in the skin, hair,and nails; this accumulation results in
symp-toms such as strong pigmentation of hands andfeet (keratosis),
high blood pressure, and neuro-logical dysfunctions (82). Another
health prob-lem is the carcinogenic effect of arsenic [i.e,an
increased risk of cancers of the skin, lung,and other internal
organs (90)], which has beenknown for a long time. The estimated
risk ofarsenic-induced cancer could be as high as 1 in100
individuals, who consume drinking waterat the former maximum
contaminant level of50 g As/L (91). In 1993, WHO reduced
thestandard for safe drinking water to 10 g As/L,which still
results in a smaller margin of safetycompared to typical organic
pollutantswith car-cinogenic properties. Thus, arsenic
illustratesthe dilemma between public health concernsand economic
feasibility. High safety marginswould result in widespread
requirements forvery costly drinking water treatment.
For industrialized countries, a broad rangeof technologies is
available for the adsorptionof arsenic to achieve or improve on the
WHOlimit (92). In critical areas, switching to bottled
water may be more economical than large-scale treatment of the
whole water supply. Forrural areas in developing countries,
however,simple but effective household-level treatmenttechnologies
need to be implemented (93, 94).Alternative drinking water sources,
such asdeep aquifers or rainwater harvesting, provideanother
potential solution (95). Although ar-senic in drinking water
remains a technologicalchallenge for water supplies, there is
recentevidence that enrichment of arsenic along thefood chain is
not of primary concern (96).Furthermore, themechanisms that produce
thearsenic problems in groundwater work as a self-purication system
at the soil surface: Seasonalooding during the monsoon season leads
toreducing conditions in the soil matrix, whichfavors arsenic
mobilization and ushing of thistoxic element into river systems and
the sea (25).
Surface Water Contaminationfrom Mining Operations
Mining activities worldwide mobilize morethan 50 109 metric tons
of geological mate-rial per year, which is similar to the ux of
par-ticles transported by rivers from the continentsto the sea
(97). Most mining operations trig-ger signicant environmental and
social prob-lems as they result in largewaste deposits, whichare
exposed to oxidation by air and weather-ing by precipitation, and
subsequent pollutionof water resources (98). Mining for coal,
lig-nite, building materials, and iron involves thelargest mass
movements with a signicant yieldof end products (Table 2). The
extraction ofraremetals, such as copper, nickel or gold, how-ever,
produces up to 1,000 tons of waste mate-rials per kilogram of pure
metal. These massivewaste streams are accompanied by
problematicgeochemical weathering reactions and specicpollutant
loads, which are introduced as miningchemicals. Ores, such as coal,
iron, and copper,typically contain large fractions of
suldemate-rial; this material is oxidized in contact with airand
water and releases sulfuric acid in the formof acid mine drainage
(99). Because the sul-fur concentrations can reach high
proportions
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(120 wt% pyrite in the case of coal), a conser-vative worldwide
estimate assumes that about20,000 river kilometers and 70,000 ha of
lakeand reservoir area are seriously damaged byacidic mine efuent
(100).
In addition, mining and extraction of pre-cious metals are
associated with intense useof chemicals, energy, and water that
posesgreater pollution hazards and environmentalrisks. Gold
production serves as an illustrativeexample. As the average ore
grade decreasedover the past two centuries, chemical extrac-tion
either by mercury amalgamation in arti-sanal gold mining or via the
industrial cyanideextraction process became increasingly
impor-tant. Both reagents are extremely toxic to hu-mans and the
environment. Artisanal gold min-ing with mercury is increasingly
practiced byabout 13 million miners in 55 countries, suchas Brazil,
Tanzania, Indonesia, and Vietnam(101). Traces of gold are dissolved
in liquidmercury, which is then removed by heating andevaporation
to the atmosphere. Mine workersare thereby directly exposed to
hazardous lev-els of the neurotoxic metal, and the local
en-vironmental contamination of water resourcescan be severe. A
review based on detailed casestudies in Brazil (102) estimates that
more than100 tons of mercury are discharged into the en-vironment
every year, and about 50% of thisis mobilized into surface water,
where mercurybiomagnies up to 106-fold in predatory shand then
represents a health risk to indigenouspopulations.
At lower gold concentrations and largervolumes, the cyanide
extraction facilitates ox-idative leaching of gold as a complex
intoaqueous solution. Dissolved gold is then ad-sorbed, and the
cyanide solution is recycled.Typically, 700 tons of water and 140
kg ofcyanide are required to extract 1 kg of gold(103). Cyanide
blocks the function of iron- andcopper-containing enzymes in the
respiratorychain of higher organisms (104). It is acutelytoxic to
humans at a level of a few 100 mg foran adult person. Fish react at
about 1,000 timeslower levels and are killed in water containingas
little as 50 g/L of cyanide. Gold mining
Table 2 Estimated global mass movements by mining activities
inmillion metric tons per yeara
Mining activity Total Refined product WasteCoal 18,444 3,787
14,657Building stone 14,186 10,430 3,756Lignite 9,024 930
8,094Copper 4,190 9.3 4,181Petroleum 3,489 3,065 424Iron 3,138 604
2,534Gold 2,138 0.002 2,138Phosphate 477 119 358Nickel 403 0.72
402Aluminum 302 101 201
aSources (97, 106).
operations are therefore often associated withspectacular sh
kills. Most aquatic organismswere killed along the main stem of the
TiszaRiver inHungary, andmostwater supplies wereclosed when a dam
failure at a tailing pond inRomania triggered the release of
about100,000 m3 of cyanide-containing waste inJanuary 2000
(105).
More sustainable mining practices requiremitigation measures for
existing tailings andimproved processes and safety procedures
forongoing activities (106). Highly toxic chemi-cals, such as
cyanide or mercury, should be re-placed by less harmful extraction
agents, suchas halogens or thiourea, or a zero-emission pol-icy
should be enforced (107). Such technicalmeasures should be
supplemented by clear in-ternational regulations (108) and
corporate so-cial responsibility in themining industry, whichis
based on open information policies (109).Although international
agreements and prac-tice codes cannot substitute for stronger
en-forcement of environmental regulations bydeveloping countries,
they represent helpfulbenchmarks for protecting water quality.
Groundwater Contamination by Spillsand Hazardous Waste Sites
Contamination of groundwater from munici-pal solid waste
landlls, hazardous waste sites,accidental spills, and abandoned
production
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facilities is a prominent cause of water pollu-tion. Several
hundred thousands of sites can befound throughout the world, where
100milliontons of wastes have been and still are discarded.Many of
them contain large amounts of haz-ardous or radioactivematerial
(110112).How-ever, estimates point to an even higher numberof
unknown, groundwater-contaminating land-lls (111). Even
thoughmanyof the ofcial con-taminated sites are under control, the
large ma-jority of them are expected to release chemicalsinto the
environment. In addition, thousandsof oil, gasoline, and other
chemical spills occureach year on land and in water from a
variety
REDOX PROCESSES CHANGECONTAMINANT BEHAVIOR
Many physical and chemical properties of organic and
inorganiccontaminants are determined by their redox state.
Therefore, re-dox conditions in subsurface environments directly
impact con-taminant fate, and the control of redox conditions is
essential forthe design of successful mitigation processes.
Metal contaminants from radioactive waste repositories or
re-processing sites, such as uranium (U)or assionproduct like
tech-netium (Tc), are generally present in their oxidized state
[U(VI),Tc(VII)] in contaminated soils and groundwater. The same
istrue for chromium [Cr(VI)] waste from tannery operations.
Al-though these metal anions are very mobile and thus a threat
tohumans and the environment, they are sparingly soluble in
theirreduced forms [U(IV), Tc(IV), Cr(III)]. Consequently,
creatingor maintaining reducing conditions in the subsurface, for
exam-ple, through in situ stimulation of microbial activity with
organicsubstrates (134), is seen as a key process for the metal
immobi-lization and containment of hazardous materials.
Different approaches apply to organic contaminants becausethey
can, in principle, be mineralized to carbon dioxide and
othernonproblematic compounds. However, organic water
contami-nants, such as the explosives di- and trinitrotoluene or
the sol-vents tetra- and trichloroethene, are persistent because
they arehighly oxidized. Complete transformation is possible only
aftertransient reduction by metal catalysts or microbes. These
pro-cesses partially lead to reduced products, like aromatic amines
orvinyl chloride (23, 121), which are of even greater toxicity
thanthe parent contaminant. These electron-rich products,
however,are much more susceptible to complete oxidation by
microbes.
of types of incidents, including transportationand facility
releases.
Estimating the number and uxes of toxicchemicals from such
contaminated sites to thegroundwater is difcult (113, 114). In
manycases of spills, waste disposal sites, and aban-doned
facilities, their primary contaminantsare known: fuel hydrocarbons
(115), chlori-nated ethenes (116), PCBs and
polychlorinateddibenzo-p-dioxines (PCDDs) from wastes ofpesticide
manufacturing (117), methylmercuryfrom contaminated soils and
wastewater (118),radionuclides from former nuclearweapons testsites
(119) and radioactive waste repositories(120), and nitroaromatic
explosives from am-munition plants (121), to name just a few.
Dis-carded materials are, however, often not wellcharacterized and
heterogeneous (114). Apartfrom some predominant contaminant
species,the leachate composition from the landll ma-terials cannot
be predicted in detail (122).Because the hydrogeology of such sites
is in-herently complex, the dynamics of pollutantrelease can only
be quantied reliably on acase-by-case basis through combined
continu-ous on-site monitoring and adequate ground-water models
(see the sidebar Redox ProcessesChange Contaminant Behavior;
123).
Owing to the widespread use of ground-water as a drinking water
resource and thepersistence of contaminations for decades ifnot
centuries, assessment of human healthrisks of exposure to mixtures
of chemicals andimplementation of appropriate,
cost-effectiveremediation strategies are essential (112,
124).Typical approaches for the active mitigationof groundwater
contaminants from spills andwaste sites are site excavation,
pump-and-treatprocedures, permeable reactive barriers,
andphytoremediation (125, 126). The mitigationconcepts either aim
at removing the contam-ination source or intend to catalyze
reactionsthat lead to an immobilization (metals) ortransformation
to benign and biodegradableproducts (organic contaminants).
However,many remediation approaches are often eithertoo expensive
or inefcient in that they requiretreatment for years to decades
(125). To this
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end, strategies focusing on microbial or abioticdegradation in
situ (natural attenuation) areincreasingly being considered as
viable long-term treatment options (116, 127). Bioavailablecarbon
loads and microbial activity at contam-inated sites and in leachate
plumes can oftenlead to anoxic conditions. Such reducing
envi-ronments not only alter some properties of thesolid matrix for
contaminant retention but alsogenerate conditions that promote the
growth ofalternative microbial communities, for examplefor
dehalorespiring bacteria that are capableof initiating the
reductive dehalogenation ofpolychlorinated organic compounds (116,
128).Anoxic environments, especially iron-reducingconditions, can
also lead to the formationof abiotic reactants through the activity
ofmetal-reducing microorganisms (129). Suchiron-bearingminerals are
capable of transform-ing organic and inorganic pollutants
(130132).Thus, a comprehensive assessment of con-taminant exposure,
and thus water pollution,requires a sound understanding of the
dynamicsof biogeochemical processes in the subsurfaceand their
interplay with contaminant mobilityand reactivity. One of the major
scienticchallenges and prerequisites for a thoroughassessment of
groundwater pollution by spillsand hazardous waste sites is thus to
quantify thesite-specic, relevant processes that determinethe
transport and transformation behaviorof a given pollutant and its
transformationproducts. One promising analytical tool toobtain such
information is compound-specicstable-isotope analysis (133).
Pharmaceuticals in Wastewaterand Drinking Water
Municipal wastewater contributes signicantlyto the
micropollutant load into the aquatic en-vironment (135). The main
concerns are phar-maceutical compounds and personal care prod-ucts.
Approximately 3,000 pharmaceuticals areused in Europe and the
United States today,including painkillers, antibiotics, beta
block-ers, contraceptives, lipid regulators, antidepres-sants, and
others (136). In Germany, 30 new
pharmaceuticals are launched on themarket ev-ery year with 8% of
the worldwide researchand development (R&D) expenditure
(137).Onthe basis of the worldwide R&D expenditure ofabout
US$83 billion in 2007 (137), it can be ex-trapolated that on
average more than 300 newpharmaceutical compounds are launched
everyyear.Theworldwidemarket of pharmaceuticals[100,000 tons per
year (138)] was US$773 bil-lion, with the highest per capita sales
ofUS$676in the United States (137). In most Europeancountries, per
capita sales vary between aboutUS$200 (in the United Kingdom) and
US$400(in France) (137).
Pharmaceutical compounds are highlybioactive, and therefore,
undesired effectsin organisms cannot be excluded after
theirdischarge into the aquatic environment, where,owing to their
polarity, they tend to be quitemobile (Figure 1) (139). Even though
thepresence of pharmaceuticals in wastewaterand natural water could
be expected fromtheir large production and widespread use,only
developments in analytical chemistry(LC-MS/MS) allowed the analysis
of thesecompounds in the nanogram to microgramper liter range,
which is typical for wastewaterand aquatic systems (135, 140). The
observedconcentrations of human pharmaceuticals inraw sewage of up
to several micrograms perliter conrm that municipal wastewater
isthe main pathway for their discharge to thereceiving water bodies
(141).
Currently, in wastewater systems, pharma-ceuticals are removed
unintentionally by sorp-tion to sludge and by biodegradation
(142).Biodegradation of pharmaceuticals in wastewa-ter often does
not lead to their full mineraliza-tion but to the formation of
metabolites. In thecase of iopromide, an iodinated X-ray
contrastmedium, 12 metabolites were identied (143).Therefore, in
terms of the (eco)toxicological ef-fects of the discharged
wastewater, not only theparent compounds but also their
wastewater-borne metabolites have to be considered. For-tunately,
the more hydrophilic metabolites areexpected to have a smaller
(eco)toxicologicalpotential than their more hydrophobic parent
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compounds, unless another specicmode of ac-tion becomes
important (38). It was shown re-cently by a mode-of-action test
battery withve in vitro bioassays that nonspecic effects,such as
bioluminescence and growth rate inhi-bition, and specic effects,
such as acetylcholineesterase activity, estrogenicity, and
genotoxic-ity, decreased dramatically from primary waste-water to
the efuent despite the fact that manydifferent pharmaceuticals and
their metabo-lites were detected in the wastewater efu-ent (144).
However, an assessment of the dis-charge of 742 wastewater
treatment plants inSwitzerland showed that for diclofenac, an
anti-inammatory agent and its metabolites, thewater quality
criterion of 0.1 g/L (a sum ofthe parent compound and metabolites)
was ex-pected to be exceeded in 224 river sections(145).
Although the main issues related to phar-maceutical in
wastewater efuents are con-nected to their ecotoxicological
effects, thereis a growing concern about human health be-cause of
the presence of some of these com-pounds in drinking water derived
from indirector direct potable reuse. In indirect reuse sys-tems,
wastewater-derived pharmaceuticals andtheir metabolites can
inltrate into the aquifersthrough the riverbank. Luckily, the
riverbankappears to be a good barrier for many of thesecompounds.
In a study where 19 antibioticswere found in a surface water in
concentrationsbetween 5 and 151 ng/L, only sulfamethox-azole could
be detected in the bank ltrate(146). However, even in the worst
case of sul-famethoxazole, a removal of 98% from 151ng/L to 2 ng/L
was observed. Nevertheless, arecent reviewon residues of
humanpharmaceu-ticals in aqueous environments presented evi-dence
that a complete removal of all potentialpharmaceutical residues by
riverbank ltrationcannot be guaranteed (147). A comparison
ofdrinking water concentrations of pharmaceu-ticals, such as the
antibiotic sulfamethoxazole,shows a difference of >6 orders of
magnitudecompared to the therapeutic dose of this com-pound. For
other compounds, the safety mar-gin might be in the range of 4 to 6
orders of
magnitude. These factors are still signicantlyhigher than the
safety factor of 1,000, which isapplied to potentially carcinogenic
compoundssuch as the herbicide atrazine (148). Further-more, from a
human toxicological point ofview, pharmaceuticals are probably the
mostrigorously tested synthetic organic chemicals.Authorization of
a new pharmaceutical com-pound requires detailed information on
phar-macology, pharmacokinetics, toxicology (e.g.,carcinogenicity,
genotoxicity, reproductive anddevelopment toxicity), and clinical
tests (149).On the basis of this assessment, the risk for
con-sumers fromexposure to individual pharmaceu-ticals in drinking
water seems rather low. How-ever, more information is needed for
long-termexposure to small concentrations and mixturesof
pharmaceuticals.
Because wastewater is a major point sourcefor pharmaceuticals,
several options for pol-ishing treatment, such as activated carbon
andozonation, are discussed as mitigation strate-gies (150).
Recently, full-scale studies haveshown the feasibility of ozonation
with accept-able operation costs (141). Polishing treatmentof
wastewater efuent has the advantage thatthe aquatic environment,
including the waterresources, is protected from human
pharma-ceuticals and endocrine-disrupting compounds(see the sidebar
Endocrine Disruption in theAquatic Environment and Its Inuence
onEnvironmental Sciences). Alternatively, if thepresence of these
compounds in drinking wa-ter is the major concern, various drinking
watertreatment processes, such as granular or pow-dered activated
carbon, oxidation, and nanol-tration/reverse osmosis, can be used
for the re-moval of these compounds (151).
VIRUSES AND MICROBIALPATHOGENS: THE CHALLENGESCONCERNING
WATERBORNEDISEASES
Global Health Problems Related toSanitation and Drinking
Water
The problems related to sanitation, hy-giene, and drinking water
differ fundamentally
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between industrialized and developing coun-tries. In high-income
countries, maintenanceand replacement of the installed sanitation
andwater supply infrastructure are the predomi-nant tasks during
the next 2030 years. In de-veloping countries, where most of the
sewageis discharged without treatment, the improve-ment of
sanitation and access to safe drinkingwater are of primary
importance (1). However,becausemost of the population increase will
oc-cur in urban areas of developing countries, cur-rent estimates
predict that 67% of the worldspopulation will still not be
connected to publicsewerage systems in 2030 (1).
Currently, 1.1 billion people lack accessto safe water, and 2.6
billion people do nothave proper sanitation, primarily in
developingcountries, and an imbalance exists between ru-ral and
urban areas in access to both improvedsanitation and safe drinking
water supply. Fourout of ve of the worlds inhabitants with noaccess
to safe sources of drinking water live ina rural environment (155).
On a global scale,the restricted access to safe water and to
im-proved sanitation causes 1.6 million deaths peryear (156); more
than 99% thereof occur in thedeveloping world. Nine out of ten
incidentsaffect children, and 50% of childhood deathshappen in
sub-Saharan Africa (157). The easilypreventable diarrheal diseases
caused by unsafewater and lack of sanitation and hygiene
con-tribute to 6.1% of all health-related deaths; onereport
estimates that unsafe water is responsi-ble for 15% to 30% of
gastrointestinal diseases(158).
The main acute disease risk associatedwith drinking water in
developing and transi-tion countries is due towell-knownviruses,
bac-teria, and protozoa, which spread via the fecal-oral route
(158). According to WHO recordsof infectious disease outbreaks in
132 coun-tries (from 1998 to 2001), outbreaks of water-borne
diseases are at the top of the list, withcholera as the next most
frequent disease, fol-lowed by acute diarrhea, legionellosis, and
ty-phoid fever (159). It is alarming that, after anabsence of
almost 100 years, cholera reappearedin Africa and accounted for
94%of the reported
ENDOCRINE DISRUPTION IN THE AQUATICENVIRONMENT AND ITS INFLUENCE
ONENVIRONMENTAL SCIENCES
One of the main triggers in the eld of pharmaceuticals and
en-docrine disruptors was the discovery of intersex sh in
Englishrivers downstream of municipal wastewater discharge in
1978(152). Later, this observation was attributed to the presence
ofestrogenic compounds in wastewater efuents (153). The
activeingredient of the contraceptive pill [17-ethinylestradiol
(EE2)]and to a lesser extent industrial chemicals, such as
alkylphenolsor bisphenol A, were recognized to be able to cause
feminiza-tion of shes in exposed populations. In a more recent
study,it was shown that the sh population (fathead minnow) in
anexperimental lake in northwestern Ontario, Canada, was
nearlyextinct after a seven-year exposure to 56 ng/L EE2 (154).
Theearly observations of intersex sh and 30 years of research ledto
(a) development of analytical methods to determine polarcompounds
in municipal wastewater efuent in the ng/L range;(b) novel highly
sensitive biological in vitro test systems, whichcan detect various
toxicological end points; (c) recognition of mu-nicipal wastewater
as a source for micropollutants; and (d ) devel-opment of
mitigation strategies to reduce their discharge into thereceiving
water bodies.
global cholera cases in this period. In additionto cholera, the
most proliferate waterborne dis-ease outbreaks were due to
(para)typhoid fever(caused by Salmonella typhi and S.
paratyphi,respectively). Also hepatitis A and E
viruses,rotaviruses, and the parasitic protozoa Giar-dia lamblia
are often found associated with in-adequate water supply and
hygiene (158). Astudy in Bangladesh reported that 75% of di-arrheal
and 44% of the control children wereinfected with either
Cryptosporidium parvum,Campylobacter jejuni, enterotoxigenic and
en-teropathogenic Escherichia coli, Shigella spp.,or Vibrio
cholerae (160). In high-income coun-tries, outbreaks caused by
pathogenic E. coliand cryptosporidiosis are often reported,
andLegionella pneumophila is increasingly dis-tributed in warm
water supplies and air-conditioning systems of large buildings,
such ashospitals.Outbreaks of typhoid fever occur
onlysporadically.
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MDG: millenniumdevelopment goal
Even though health problems associatedwith wastewater and
drinking water supply areintimately linked, issues related to
sanitationare treated politically with lower prioritythan water
supply problems, and more fundsare allocated to the latter.
Throughout theOrganization for Economic Co-operationand Development
(OECD) projects relatedto drinking water and sanitation, 82% ofthe
funding was directed toward drinkingwater projects (161). This
preference contrastswith strong epidemiological evidence,
whichsuggests that improved sanitation would dras-tically reduce
the burden of infectious diseasesand, linked to this, also
malnutrition. In Africaalone, owing to the lack of access by a part
ofthe population to sanitation and safe drinkingwater, the overall
economic loss is estimatedto be 5% of the gross domestic product
(1).
To reduce the human health burden due topoorwater quality and
the lack of improved san-itation and hygiene,WHO and the
UnitedNa-tions Childrens Fund have launched as a mil-lennium
development goal (MDG) to halve thepopulation without access to
safe drinking wa-ter and basic sanitation by 2015 (157). In
2006,87% of the worlds population used safe drink-ing water sources
compared to 77% in 1990(155). With respect to sanitation, however,
thenumbers are less encouraging; the total popula-tion without
access to improved sanitation hasdecreased only slightly since 1990
from approx-imately 2.5 to 2.4 billion (1).
Wastewater Treatmentand Water Reuse
Mitigation of wastewater streams from house-holds and industry
is one of the key compo-nents for improving sanitation and
maintain-ing public and ecosystem health. Treatmentof municipal
wastewater aims at eliminatingnutrients (carbon, nitrogen,
phosphorous) andpathogenic microbes. Nutrient removal leadsto a
reduction of the biological oxygen de-mand (BOD) of efuent water
and thus a de-crease in eutrophication of inland water bodiesand
coastal areas. In industrialized countries,
connectivity tomunicipal wastewater treatmentplants is in the
range of 50% to 95%, whereasmore than 80% of the municipal
wastewater inlow-income countries is dischargedwithout
anytreatment, polluting rivers, lakes, and coastalareas of the seas
(1). Industrial wastewater is,however, not only a source of BOD but
alsoa point source of chemical pollution of heavymetals and
synthetic organic compounds. Inindustrialized countries, these
pollutants havebeen reduced signicantly through implemen-tation of
internal water recycling and recoverysystems and end-of-pipe
treatment using ad-vanced technologies, such as activated
carbon,advanced oxidation, or membrane processes.The water efciency
of industrial wastewatertreatment (i.e., the product revenues per
treatedvolume of process water) is highly variable,ranging from
approximately US$140 per m3 inDenmark to only US$10 per m3 in the
UnitedStates (1) and even less in low-incomecountries.These numbers
depend on the type of industrialactivity. To date, a substantial
potential existsfor water reuse, which would strongly reducethe
discharge of potentially polluted water.
Water recycling and reuse for agricultureand for drinking water
through surface andgroundwater bodies are common and
long-established practices (162, 163). Today, aframework of
integrating aspects of risk assess-ment and risk management is
recommendedby WHO to ensure water safety for agricul-tural reuse.
This includes water safety plansthat rely on hazard analysis of
critical con-trol points (HACCP) and the multibarrierprinciple
(163). Furthermore, with increasingwater scarcity, wastewater reuse
for drinkingand industrial water becomesmore widespread.For
example, in Windhoek, Namibia, wastew-ater has been recycled since
1973, using a se-ries of advanced processes to obtain drinkingwater
(164). In many other urban areas thatare under water stress
(California, Australia,Singapore), direct or indirect potable or
indus-trial reuse is practiced on large scales. Thesesystems mostly
rely on membrane technolo-gies (microltration followed by reverse
osmo-sis) to treat secondary wastewater efuent and
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remove micropollutants and pathogens ef-ciently (164).
Detecting Pathogensand Waterborne Diseases
Enteric diseases spread mostly via water con-taminated with
feces from ill persons and ani-mals. Hence, assessing treatment
schemes, in-cluding the potential for water recycling, withregard
to the transfer of waterborne pathogens,requires reliable hygienic
drinking water qual-ity parameters. Despite the urgent need
forso-called pathogen indicators, fast, cheap, andeasy-to-use
methods for a worldwide applica-tion are still lacking. Todays
hygiene conceptrelies on the detection of such indicators as
ahygienic drinking water quality parameter, andthe enteric
bacterium E. coli is used worldwideas an indicator of possible
fecal contamination(163). In addition, the general
microbiologicalstate of water is assessed by counting the
totalnumber of colony-forming microbes growingon a nutrient agar
plate (the heterotrophic platecount, HPC). As the HPC method
largely un-derestimates the number of heterotrophic mi-crobial
cells present in a water sample (165),the HPC was omitted from the
recent lists ofhygiene parameters of WHO, the EuropeanUnion, and
the United States (163, 166). Asa consequence, it is becoming
current practiceto rely exclusively on the presence/absence ofE.
coli to judge the hygienic quality of drinkingwater. However, this
approach is not suited formonitoring the hygienic quality of water
treat-ment and distribution (discussed in depth inReference 167).
The vulnerability of this con-cept was demonstrated painfully in
Milwaukeein 1993 when chlorine-resistant Cryptosporid-ium oocysts
from an upstream cattle farm con-taminated the drinking water.
Despite chlori-nation and absence of E. coli, more than 50people
died after consumption of contaminatedwater and 400,000 persons
suffered from cryp-tosporidial diarrhea (168).
Although the detection of E. coli willremain the hygiene
parameter for the nextdecades, a wealth of
cultivation-dependent
HPC: heterotrophicplate count
and -independent microbiological methodsis currently being
proposed for the detectionand quantication of pathogens and
indicators(169). For practical testing of treated watersamples, ow
cytometry (FCM) is one of themost promising approaches. FCM
enableson-site and online enumeration of microbialcells independent
of their cultivability, allowsfast screening for specic pathogens
(170, 171),and permits detection ofmicrobial activity
afterdisinfection (172). A total microbial cell countcan be
obtained within 15 min (173). However,FCM-based methods require a
paradigmchange regarding the number of microbes thatare expected in
raw and disinfected water: in-stead of a tolerableHPC count of less
than 300500 bacterial cells per milliliter, FCM countsamount to
100,000200,000 cells per milliliterin high-quality (nondisinfected)
drinking water(174).
Complementary approaches are currentlybeing tested to address
the spreading ofinfectious diseases on an epidemiological
scale.Increasing water temperatures as well as severerainfall and
ooding events as a consequenceof climate change are likely to
impact thespreading patterns and frequency of infectiousdisease
outbreaks (175). To this end, satellitesurveillance data for
weather and climate fore-casting may become an essential early
warningsystem for water-related diseases because theirspread can be
correlated with heavy rainfallsand/or increased water temperatures
(176).The potential of this approach is illustratedby the
successful prediction of outbreaks ofinfectious diseases, such as
dengue, West Nilefever, yellow fever, and malaria (177, 178).
The Multibarrier Concept forImproved Sanitation and SafeDrinking
Water Supply
Because many waterborne pathogens spreadprimarily via
feces-contaminated water, a clearseparation between wastewater and
drinkingwater systems is key to successful water man-agement. To
reduce the load of pathogenicmicrobes and viruses into surface
water from
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wastewater, amultiplicity of conventional treat-ment methods are
available, and feasible op-tions for low-income countries have
recentlybeen comprehensively summarized (162).Mostof thesemethods
rely on physical elimination ofthe pathogens by coagulation,
sedimentation,and ltration, typically eliminating pathogensby 13
log units (162). Today, disinfectionof treated wastewater by UVC
irradiation orchemicals (UVC, chlorination, ozone) is per-formed in
some countries. Even disinfection ofthe raw wastewater is practiced
occasionally.
One of the main ways of producing safedrinking water is by the
removal and/or inac-tivation of pathogenic microbes through
mul-tiple barriers. These barriers include ltrationby soil aquifer
treatment, riverbank ltration,sand ltration, or membrane systems
and alsodisinfection steps, such as boiling, chemicaldisinfection,
or UV light. Chlorination is stillthe most widely used technique
for disinfectingdrinking water because it is effective and
eco-nomical, and it maintains a disinfectant residualconcentration
during distribution as additionalsecuritymeasure. The formation of
chlorinateddisinfection by-products is today consideredinsignicant
when compared to the healthbenets from the inactivation of
pathogens(162). During the past decade, membrane-based processes
became cost-effective for theirapplication in municipal water
treatment andare increasingly used as polishing steps toremove
microbes and viruses from pretreatedwater (179). Recent work
suggests that gravity-driven low-ow ultraltration may becomea valid
option for producing drinking waterdirectly from low-quality source
water evenfor low-income countries (180).
The efcacy of the above disinfectionprocesses strongly depends
on their imple-mentation as centralized versus
decentralizedsolutions. In densely populated urban
areas,centralized drinking water production anddistribution systems
are economically favorableand, therefore, the usual case in
industrializedcountries. However, experiences from largecities in
low-income countries also show thatcentralized systems often fail
to supply safe
drinking water to their customers (179). Thereasons are manifold
and include insufcientmaintenance owing to lack of nances
orexpertise, as well as to pressure failure, illegaltapping, etc.
Hence, in low-income countries,treatment at the household level is
requirednot only in rural areas (for example, by solardisinfection)
but also in cities with existingcentralized systems. The impact of
household-based methods in low-income countries fordrinking water
treatment on human health iscurrently debated (181). The
reliability of suchmethods, however, is of primary
importancebecause even occasional consumption of unsafewater
results in an increased health risks,particularly for children
(182).
CONCLUSION
Tackling global water pollution requires an ef-fective set of
policies, technologies, and sci-entic advances on very different
scales. Thelegacy of persistent priority pollutants, such asPCBs,
calls for a general phase-out and a regu-latory effort on the
global scale. Volatile chem-icals, such as halogenated compounds or
mer-cury, which are not subject to biodegradationbut accumulate in
the food chain, should be re-stricted in their use to applications
in strictlyclosed systems. Human food production sys-tems require
rigorous protection against com-pounds with a potential for
bioaccumulation;thus water as the key commodity for agricul-ture
needs the same attention. In addition, theprecautionary principle
has to be applied in de-signing potential substitutes for such
prioritypollutants to make sure that todays solutionwill not become
tomorrows problem.
Global agriculture faces the challenge to in-crease production
yields and at the same timesafeguard the environment and protect
the foodchain against contamination. Improving waterquality in
agricultural areas requires more inte-grated approaches to farming.
Precision agri-culture is based on local characteristics such
assoil type, topography, irrigation and drainagesystems, and makes
sure that the optimal cropmanagement practices are implemented in
the
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right place at the right time, thereby reducingthe risk of
emitting nutrients and pesticides intosurface water (183).
Geogenic contaminants act as diffusesources of toxic elements at
regional scales, in-icting chronic diseases on large populationson
all continents. As the main geochemicaldrivers are known,
geochemicalmodelingbasedon hydrogeochemical data and spatial
analysishelps identify the populations at risk and imple-ment
advanced treatment technologies for cen-tral water distribution
systems. In many partsof the developing world, however, rural
pop-ulations depend on contaminated groundwaterwells. For these
settings, identifying alternativewater resources or implementing
simple, reli-able household-centered water treatment tech-nologies
requires special effort.
Cleaning up large-scale water pollutionfrom mining activities
and groundwater con-tamination from waste sites requires
science-based decisions that take into account the spe-cic
hydrological conditions, the microbial and
geochemical transformationpathways, andpos-sible remediation
technologies to choose themost effective strategies. Such waste
manage-ment strategies need to be superseded in thelong run by
proactive strategies based on life-cycle assessments and
cradle-to-grave steward-ship for toxic compounds. Global water
cyclesshould no longer be used as transport pathwaysfor pollutants;
it is the responsibility of eco-nomic actors to keep toxic
compounds withincontrolled, closed loops.
Finally, the many point sources of waterpollution from urban
water systems need in-creased attention and investments over the
nextdecades. To reach the MDGs to provide im-proved sanitation and
safe drinking water forabout 2 billion people, concerted efforts to
de-velop and implement cost-effective sanitationsystems in the
growing megacities in areas withwater stress are of highest
priority. Developingthe techniques and social networks to
improvehousehold-centered sanitation in rural areas re-quires an
effort of similar magnitude.
SUMMARY POINTS
1. The increasing global chemical pollution of natural water
with largely unknown short-and long-term effects on aquatic life
and on human health is one of the key problemsfacing humanity.
2. The point and diffuse sources of chemical pollution are
manifold, and their temporaland spatial impacts on water quality
range from short-term local to long-term global.Agriculture, mining
activities, landlls, industrial and urbanwastewater, as well as
naturalgeogenic releases are the most relevant pollutant
sources.
3. Owing to the enormous variability of micropollutants,
mitigating a given chemical wa-ter pollution problem is commonly a
quite challenging task. Each case requires its owninterdisciplinary
scientic knowledge and methods, and each has its own technical,
eco-nomical, and societal dimensions.
4. Reliable wastewater collection and treatment systems are
critical for sanitation and forhuman and ecosystem health.
Centralized municipal wastewater systems provide reliablesolutions
to many of these problems but lead to estimated global annual
infrastructurecosts of US$100 billion over the next 20 years. Such
a nancial outlay may be prohibitivefor low-income countries.
5. Access to improved sanitation for one-third of the worlds
population is an urgent issue,and lack of proper sanitation systems
is responsible for the spreading of waterborneinfections and for
unsafe drinking water. Despite this fact, 80% of the nancial aid
forwater-related projects is spent on drinking water instead of
sanitation issues.
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6. At present, cheap production in emerging economies is too
often accompanied withunacceptable pollution of natural water.
International chemical regulation, consumerinformation, and good
practice codes should therefore work synergistically to
preventlarge-scale emission of chemicals into the hydrosphere in
all parts of the world.
FUTURE ISSUES
1. Despite the anticipated advances in water treatment
technologies, efforts to reduce intro-duction of problematic
chemicals into the (aquatic) environment should be given
highestpriority. This requires the improvement of the scientic
tools to identify those existingchemicals that need to be
substituted and phased out and the political will to enforcesuch
action.
2. In the chemical industry, the green chemistry approach should
be more strongly im-plemented, including efciency engineering of
chemical processes to minimize materialows into the environment and
emphasizing the design of new chemicals that are com-pletely
biodegradable and therefore of less environmental concern. In
addition, improvedtreatment and removal technologies will allow
coping with the legacy of existing waterpollutants.
3. Surface- and groundwater pollution from mining activities,
known and unknown land-lls, and spill sites will continue to
threaten our water supplies. Mitigation of thesecontaminant sources
will require enormous nancial resources over the next decades
andresearch on effective removal technologies.
4. The high costs of centralized wastewater systems and their
low water efciency requirethe development of alternative solutions,
possibly decentralized systems. They will allowreusing the water
and nutrients locally and lead to low discharge systems.
5. The goal of cheap, fast, and reliable detection of a broad
variety of micropollutants andpathogens in natural water calls for
innovative developments in analytical technologiesand
internationally compatible protocols for water quality
assessment.
6. T