E NVIRONMENTAL G EOCHEMISTRY AT T EXAS A&M U NIVERSITY Introduction Bruce Herbert Geology & Geophysics.

ENVIRONMENTAL GEOCHEMISTRY AT TEXAS A&M UNIVERSITY

http://environmentalgeochemistry.pbworks.com//

Introduction

Bruce HerbertGeology & Geophysics



What is Environmental Geochemistry?



Definition of Environmental Geology

■ Environmental geology applies geologic information to the solution, prediction and study of geologic problems such as:■ Natural hazards: Floods, volcanic eruptions, earthquakes and tsunamis,

and mass wasting events■ Landscape evaluation: Land-use planning & siting critical facilities■ Environmental quality and remediation: Risk assessment of contaminants

in the environment, waste disposal, and remediation■ Earth materials: Evaluation of mineral, petroleum, and water resources &

engineering aspects of Earth materials.



Access to Clean Drinking Water

■ Scientific American: http://www.sciam.com/1197issue/1197scicit5.html■ In developing countries, waterborne and sanitation-related diseases kill well over three million annually and disable hundreds of millions

more, most of them younger than five years of age. ■ The map shows the percent of urban populations with access to safe drinking water. Around the world a billion people lack access to safe

water, and 1.8 billion do not have adequate sanitary facilities.



Anthropogenic Compounds

Global Production of Synthetic

Organics

0

50

100

150

200

250

1930 1940 1950 1960 1970 1980 1990

Year

Production

(10^6 tr/yr)

Figure 1.1 Global increase in synthetic organic production since 1930 (taken from Schwarzenbach et al., 1993)



Anthropogenic Compounds

DDT Production in US and Accumulation in Lake

Ontario Sediments

0

10

20

30

40

50

60

70

80

1930 1940 1950 1960 1970 1980

Year

Production (x1000 t)

0

50

100

150

200

250

Accumulation

(ug/m^2/yr)

Production

Accumulation

Figure 1.2 Production and accumulation of DDT (taken from Schwarzenbach et al., 1993)



Tenets of Environmental Geology

■ Modified Concept of Uniformitarism: the same Earth processes that are operating today, also operated in the past. Geologic processes that occurred in the recent past are our best indications of geologic processes that will happen in the future.

■ "The recent past may be the key to the near future"■ An understanding of past geologic processes, scale of their effects, and

the rates of their occurrences, allows environmental geologists to predict future occurrence and potential effects.

Environmental geochemistry adapts the Concept of Uniformitarism to the prediction of important geologic processes that can affect living organisms and to the solution of environmental problems.



Environmental Issues and Human Society

■ Currently, the expanding world population requires more resources; faces increasing losses from natural hazards; and contributes to growing pollution of the air, water, and land.

■ The activities of humans and their consequences are now comparable in magnitudes and rates as perturbations of the Earth's environment to many natural processes.

■ Many of these human perturbations are not beneficial to life on the planet.

Committee on Status and Research Objectives in the Solid-Earth Sciences: A Critical Assessment (National Research Council). 1993. Solid-Earth Sciences & Society. National Academy Press. Washington, DC. 346 p.



Environmental Issues and Human Society

■ Human societies face momentous decisions concerning their control of many future activities that require understanding the Earth.

■ The rates of changes have become so rapid that these issues cannot be ignored any longer if the Earth is to be managed as a sustainable habitat.

■ To accomplish sustainability will require all of our scientific understanding of the natural materials and processes, particularly the material and energy transfers linking the geosphere, hydrosphere, atmosphere, and biosphere.

■ Life prospers or fails at the surface of the Earth where these environments intersect

Committee on Status and Research Objectives in the Solid-Earth Sciences: A Critical Assessment (National Research Council). 1993. Solid-Earth Sciences & Society. National Academy Press. Washington, DC. 346 p.



Scale of Environmental Problems

■ Given the size of the planet as well as its age (4.5 billion years), most geologic processes occur outside human experience

■ Scale denotes the resolution in the range of a measure quantity■ Geologic processes occur at very large ranges of spatial scale, from

planet-wide processes to chemical reactions on the surface of a mineral■ Likewise, geologic processes occur at very large ranges of temporal scale.

They can be very fast (occur over short time spans) such as earthquakes or they can occur over very long times, such as the erosion of mountains

An understanding of past geologic processes, scale of their effects, and the rates of their occurrences, allows Environmental geologists to predict future occurrence and potential effects.



Spatial & Temporal Scales of Geologic Processes



Observations and Scientific Investigations

■ Laboratory experiments ■ Point measurements over small areas such as aquifers■ Large number of point measurements and remote sensing provides

information over large spatial scales■ Study the geologic record, which is the vast amount of rock that makes up

the outermost layer of the Earth called the crust. Information on the processes that shaped the Earth is reflected in the properties of the rock layers that make up the geologic record

■ It is easier to measure over space than time

Geologic evidence for processes occurring at different time and space scales: How do we collect data?



Significant Scales of Time and Space

Human experience limits the geologic processes we can directly experience. Due to technological advances in the 20th century, we can directly experience

geologic events occurring all over Earth, as well as many nearby celestial bodies

The development of written history has extended our ability to experience geologic events from the lifetime of an individual (or several if oral histories are preserved, to several thousands of years. This, of course, is a very short time span compared to the great age of the Earth

Environmentally-significant geologic processes are mainly those that occurred over the last 100 thousand years BP or later



Perturbed Environments



Geochemical Perturbations of the Near-Surface Environment

■ The degree of localization of a source is described as point or nonpoint sources

■ The loading history describes the variation over time in the amount of the perturbation

■ Source of geochemical perturbation: contaminant type

■ Nature of geologic system

Four important characteristics distinguish geochemical perturbations of near-surface environments such as soils, aquifers, wetlands, and estuaries.



Geochemical Perturbations: Localization

■ Point source: a source characterized by the presence of an identifiable, small scale source

■Examples: leaking storage tank, disposal pond, or a sanitary landfill

■ Nonpoint source: a larger-scale, relatively diffuse contamination originating from many smaller sources, whose location is often poorly known

■Examples: agricultural pesticides and herbicides, nitrates from household disposal systems, salt from deicing highways, and acid rain

The degree of localization of a source is described as point or nonpoint sources.



■ Pulse loading: short-term loading at fixed concentrations. Example: a spill

■ Continuous source loading: fixed concentrations that remain constant over time

■ Variable source loading: concentrations vary over time. This is the most common case

■ Example: a storage pond where chemical wastes are sporadically added

The pollutant loading history describes how the concentration or rate of production of a chemical varies with time

Geochemical Perturbations: Loading History



■ Radioactive contaminants

■ Trace metals

■ Nutrients

■ Other inorganic species: Salts and natural metals like Al

■ Organic contaminants

■ Biological contaminants

Domenico and Schwartz (1990) grouped contaminants into six categoriesbased upon classes of reaction type and mode of occurrence.

Geochemical Perturbations: Contaminant Type



■ Radioactive contaminants■Produced by the nuclear industry■Includes radionuclides 239Pu, 233U, 235U, 238U, 230Th, 226Ra,

222Rn (gas), 90Sr, 137Cs.■Health hazards include ionizing radiation and metal toxicity

■ Trace metals■Several major sources■Includes Al, As, Ba, Be, B, Cd, Cr, Co, Cu, Pb, Li, Mn, Hg, Mo,

Ni, Se, Ag, Sr, Th, Sn, Ti, U, V, and Zn■Health hazards due to toxicity. May bioaccumulate.

Classes of Environmental Contaminants



■ Nutrients

■ Several major sources including agriculture and sewage

■ Includes inorganic and organic sources of nitrogen, phosphorus, and other elements that are nutrients

■ Health hazards of nitrogen include methemoglobinemia and carcinogenicity of organo-nitrogen compounds. Phosphorus has lower health hazards due to low solubility of inorganic P compounds. Nutrients are important in disrupting ecosystem processes.




■ Other inorganic species

■ These species are found in nontrace quantities and are major contributors to water salinity. Major ion salinity originates from saline brine contamination, agricultural and mining leachate, and industrial processes.

■ Includes the cations Ca2+, Mg2+, and Na+, and the anions Cl-, F, HS-, SO42-,

HCO3-, CO3

-, and H2CO3.

■ Health hazards of these species are not as serious. Contamination by saline waters can make fresh water supplies unfit for use.




■ Organic contaminants

■ Major sources include the industrial, agricultural, and energy industries

■ Includes over 70,000 organic chemicals in use by human society. The EPA priority pollutant list has 116 different organic compounds.

■ Health hazards of these compounds are varied. They can be carcinogens or have toxic effects on organisms. Because of the large number of compounds, there is incomplete toxicological data on this group of contaminants. There is even less known about the long term ecological damage cause by the persistence of these chemicals in the environment.




■ Biological contaminants

■ Major sources include animal waste from agricultural practices, sewage from centralized treatment facilities or septic tank systems, and sanitary landfills.

■ Includes pathogenic bacteria, viruses, or parasites.

■ Health hazards of these contaminants include disease and abdominal disorders.




25 Most Common Contaminants Detected in Groundwater at Hazardous

Waste SitesDomenico & Schwartz, 1990



Influence of Environmental Characteristics

Al, Fe

Ca, SO4, Si, CO3



Building Geochemical Conceptual Models: Soil



Building Geochemical Conceptual Models: Estuary



Processes that Affect the Fate and Transport of Contaminants



Geochemical Processes Affecting the Fate and Transport of Contaminants

■ Transport/Mixing Processes

■ Aqueous phase transport: the pollutant is dissolved in water

■ Nonaqueous phase transport: liquid organic pollutants that form their own phase

■ Gaseous phase transport: important for volatile inorganics (ex. methylated arsenic) and organics (ex. petroleum)

Much of the information required to understand the effects of contaminants released into the environment is centered on understanding and modeling the fate and transport of contaminants.

Quantifying the fate and transport is required to perform a risk assessment or predict remediation effectiveness.




■ Geochemical Processes

■ Hydrolysis and complexation reactions: reactions of the pollutant in solution

■ Precipitation/dissolution: reaction that transfers pollutant between the solid and liquid phase

■ Oxidation/reduction reactions: reaction where elements change oxidation state through electron transfer

■ Sorption and partitioning reactions: pollutant binding to a solid surface or moving into a 3-D material

■ Biochemical Processes

■ Microbial degradation of organics: enzyme catalyzed reactions

■ Microbial methylation of metals: enzyme catalyzed reactions which add a methyl group to a metal



Contaminant Bioavailability and Ecotoxicology

Environmental geochemistry is heavily involved in predicting the toxicity of contaminants in different environments. The toxicity of a contaminant is related to the contaminant's bioavailability.

Bioavailability is dependent on the relative amounts of each chemical form of the contaminant. Chemical speciation, based on thermodynamics, is used to describe the activity (concentration) of the contaminant in its different forms in any phase.




Basic Premise of Ecotoxicology: The uncomplexed or free metal/organic is typically the most toxic form.

Bioavailability: the degree to which a contaminant is free for uptake by an organism and then affects that organism.

Chemical speciation: a quantitative description of the activities (concentrations) of different forms or species of a compound. Example: species of copper in an aqueous solution:

Cu2+(aq), CuCl+(aq), CuSO4

˚(aq), CuOH+

(aq),




Conceptual model linking geochemical processes to the bioavailability and toxicity of metal and organic pollutants.

hydrolysiscomplexation

biodegradationand

toxicity

bioavailability

sorptionprecipitation-dissolution

redox reactions

solidphase

aqueousphase organism

A contaminant usually enters the aqueous phaseprior to uptake by an organism

Physiochemical processes determine bioavailabilitywhich in turn determines toxicity or biodegradation rate



Conceptual Models of Perturbed Geologic Environments



Molecular Scale

Local Macroscopic Systems

Environmental Systems

Quantification of environmental factors:T, P, pH, Eh, Ionic strength, major ions,organic matter, colloids, microbialpopulations, NAPL and solid phases

Element or Molecule(Contaminant)

Quantitative description of individual environmental processes:phase change, complexation, sorption, biodegradation,precipitation-dissolution, redox processes, microbial reactions

Quantitative description oftransport processes andgeologic system structure

Quantitative description of dynamic behavior of chemical inthe environmental system: modeling and field investigations

Description of interactions andimpacts of human activities,structures and/or policies

Quantitative description ofecosystem components,structure and functioning

Qualitative description of molecular-scalecontaminant chemistry: physiochemicalproperties, specific reactivities





Coupled solute transport, geochemical reactions, and biotic degradation in subsurface systems.



NABIR Conceptualization of Biodegradation

http://www.lbl.gov/NABIR/researchprogram/strategicplan/images/fig_1.gif






Risk Assessment and Risk Management



So how bad is it?



EPA National Water Quality Index: Rivers

EPA Index of Watershed Indicators

16%, better water quality 36%, some problems 21% , serious problems

The Index characterizes the condition and vulnerability of aquatic systems in each of the 2,111 watersheds in the continental U.S.



EPA National Water Quality Index: Rivers

■ 19% of all rivers were surveyed■ Data reports percentage of

impacted watersheds■ Agricultural runoff was the

dominant source of stressors



Sediment Contamination in the US

U.S. EPA Assessment of Sediment Contamination

20,000 sites but covers only 11% of the rivers, lakes and coastline High concern = watersheds with >20 Tier 1 sites (known adverse effects) and 75% of all sites are Tier 1 & 2

EPA characterized sediment chemistry, sediment toxicity, and fish tissue residue data from individual monitoring stations throughout the nation



The Estuarine Pollution Susceptibility Index

NOAA’s National Estuarine Inventory

Built on a watershed- based spatial framework Assessments exist for over 130 estuaries

Susceptibility to pollution is defined by the dissolved concentration potential (DCP), the particle retention efficiency (PRE), and by the estimated loadings and predicted concentrations of nitrogen (N) and phosphorus (P).



Sediment Delivery to Rivers and Streams from Cropland and Pastureland

Hydrologic Unit Modeling of the US (HUMUS) project

Erosion based on SWAT estimates Uses several national- level natural resource and land use databases

SWAT is a process model incorporating hydrology, weather, sedimentation, crop growth, and agricultural management.



Potential Pesticide Runoff from Farm Fields

Hydrologic Unit Modeling of the US (HUMUS) project

Loss based on process model estimates Total loss of pesticides was estimated by summing loss for all pesticides used

This indicator was developed to show which watersheds have the greatest potential for the movement of agricultural pesticides from farm fields through surface water runoff.



Society Interaction with the Natural Flow of Matter and Energy in Geologic Systems

Florida Everglades

Development has led to excessive nutrient and pesticide loading and disruption of natural hydrologic cycle through channelization in the 1960’s

E NVIRONMENTAL G EOCHEMISTRY AT T EXAS A&M U NIVERSITY Introduction Bruce Herbert Geology & Geophysics.

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