Pollution of crops and pastures by a smelter The study area. The South Australian town of Port Pirie is dominated by a metal-refining complex, incorporating the world's largest lead smelter. The complex almost holds another record: its 205-m- high chimney, completed last August, is the second- tallest man-made structure in Australia, surpassed only by a stack at Mt Isa. The smelters refine lead and zinc from ore mined at Broken Hill. The smoke climbing the chimney contains traces of these heavy metals — and of other elements, such as cadmium, that occur in smaller amounts in the ore. Nowadays these traces are very small, but from 1889, when the first smelter began operating, until 1925, when emissions were greatly reduced following a Royal Commission report, an enormous quantity — perhaps 40 000 tonnes — of Smelter 'fall-out' landing on the leaves and stems of wheat plants did not apparently contribute to contamination, even in crops grown nearby. Washing wheat plants made no difference to their metal content; this was not surprising, as the concentrations of heavy metals in the fumes from the smelters have been kept very low for years. Wind-blown soil dust could in theory contaminate plants, but wheat grain is well protected within the head as it develops, and the scientists found no evidence that dust had contributed to the higher levels of heavy metals found in grain grown near the smelters. All this may come as a relief to local farmers, but what of the pastures that form an essential part of crop rotations? Around Port Pirie the main pasture species are annual medic and various annual grasses, with native chenopods (species of goose- foot) and introduced weeds. In places stock graze over former wheatlands that have reverted to saltbush and bluebush, or on samphire growing on salty soils. Mr Merry and Dr Tiller, who carried out the study of pasture contamination, found that different plant species took up widely differing quantities of metal pollutants, and in different ways. Cadmium and zinc, it appears, are absorbed by the roots, but most of the lead is deposited on shoots, from dust and chimney fall-out. The scientists believe that soil dust plays little part in pasture pollution except within about 5—10 km of the smelters. Ward's weed recorded the highest cadmium and zinc concentrations, and potato weed topped the list for lead, with Ward's weed not far behind. At the other end of the scale, the least- 27 potentially toxic metals belched out of the smelter's chimney. What goes up must come down, and the metals eventually fell to earth, where they persist. At least 3400 sq km of land are contaminated by lead, and in 270 sq km the soil contains 10 or more times the general 'background' level of 10 parts per million (p.p.m.). Cadmium and zinc pollute similar areas. We know the concentrations of the contaminants in soil and vegetables (see Ecos 7). T o what extent are cereals and pastures affected, and is the health of humans and livestock at risk? A team of researchers from the CSIRO With increasing distance from the smelter, pollution falls to a 'background' level. Zinc is shown here; lead and cadmium curves are similar. Copper is a negligible component of smelter smoke. Division of Soils has been tackling these questions. Mr Richard Merry, Dr Kevin Tiller, Mr Paul de Vries, and Dr Brian Cartwright took samples of wheat and pasture plants from sites at various distances from Port Pirie, including points on a line stretching more than 30 km south from the smelters. The scientists collected both grain and whole tops of wheat plants, as well as specimens of some 30 pasture species and samples of the soils in which all these plants grew. They then analysed the plants and soils to find out Heavy metal uptake is illustrated here by cadmium: the more there is in the soil, the more will contaminate a plant. Most pasture species take up less cadmium than Ward's weed but more than bluebush. Soil metal values were obtained by extraction with a standard reagent, EDTA. how much lead, zinc, and cadmium these contained. As a check, they also measured the concentrations of metals that are very minor components of the smelter smoke, such as copper. They found a good correlation between the degree of contamination of most plants and the contamination of the soils they grew in. The more cadmium that pollutes the ground, for example, the more there will be in a wheat stalk or a paddy melon leaf. The farther the scientists travelled along their south- bound transect, the less contamination they found, until, about 35 km from the smelter, the pollutant concentrations had dropped to 'background' levels similar to those found elsewhere in the State. The levels of heavy metals in wheat came well within the limits set by State health authorities. What's more, the pollutant metals become diluted during bulk handling and milling, when contaminated grain is blended with wheat from unpolluted areas. The researchers believe that human health is unlikely to be endangered by the heavy metals in wheat grain harvested near the smelters.
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Pollution of crops and pastures by a smelter
T h e study area.
T h e Sou th Austra l ian t o w n
o f Port Pir ie is domina ted by
a metal-ref ining c o m p l e x ,
incorpora t ing the wor ld ' s
largest lead smelter.
T h e c o m p l e x a lmost ho lds
another record : its 205 -m-
h i g h c h i m n e y , c o m p l e t e d
last A u g u s t , is the s econd-
tallest man -made structure
in Austral ia, surpassed on ly
by a stack at M t Isa.
T h e smelters refine lead
and z inc f rom ore m i n e d at
Broken Hi l l . T h e s m o k e
c l i m b i n g the c h i m n e y
conta ins traces o f these
heavy metals — and o f other
e lements , such as c a d m i u m ,
that o c c u r in smaller
amounts in the ore .
N o w a d a y s these traces are
very small , but f rom 1889,
w h e n the first smelter began
operat ing, until 1925, w h e n
emis s ions were greatly
r educed f o l l o w i n g a R o y a l
C o m m i s s i o n report, an
e n o r m o u s quantity —
perhaps 4 0 000 tonnes — o f
Smel ter 'fall-out' l and ing
o n the leaves and stems o f
whea t plants d id no t
apparently cont r ibute to
con tamina t ion , even in crops
g r o w n nearby. W a s h i n g
wheat plants m a d e n o
difference to their metal
con ten t ; this was no t
surprising, as the
concen t ra t ions o f heavy
metals in the fumes f rom the
smelters have b e e n kept very
l o w for years.
W i n d - b l o w n soi l dust
c o u l d in theory con tamina te
plants, but wheat grain is
we l l protected wi th in the
head as it deve lops , and the
scientists found n o ev idence
that dust had cont r ibuted to
the h igher levels o f heavy
metals found in grain g r o w n
near the smelters.
A l l this may c o m e as a
rel ief to l oca l farmers, but
what o f the pastures that
fo rm an essential part o f c r o p
rotat ions? A r o u n d Port Pirie
the m a i n pasture spec ies are
annual m e d i c and various
annual grasses, w i th native
c h e n o p o d s ( spec ies o f g o o s e -
foot) and in t roduced w e e d s .
In p laces s tock graze over
former wheat lands that have
reverted to saltbush and
b luebush , or o n samphire
g r o w i n g o n salty so i l s .
M r Mer ry and D r T i l l e r ,
w h o carried out the study o f
pasture con tamina t ion ,
found that different plant
spec ies t ook u p w i d e l y
differing quantit ies o f metal
pol lutants , and in different
ways . C a d m i u m and z inc , it
appears, are absorbed by the
roots , but mos t o f the lead is
depos i ted o n shoo t s , f rom
dust and c h i m n e y fall-out.
T h e scientists be l i eve that
soi l dust plays little part in
pasture po l lu t ion excep t
wi th in about 5—10 k m o f the
smelters.
Ward ' s w e e d recorded the
h ighes t c a d m i u m and z inc
concen t ra t ions , and potato
w e e d topped the list for lead,
w i th Ward ' s w e e d no t far
beh ind . A t the other end o f
the scale , the least-
27
potential ly tox ic metals
b e l c h e d out o f the smelter 's
c h i m n e y . Wha t g o e s u p mus t
c o m e d o w n , and the metals
eventual ly fell to earth,
where they persist.
A t least 3 4 0 0 sq k m o f
land are con tamina ted by
lead, and in 2 7 0 sq k m the
soi l con ta ins 10 or m o r e
t imes the general
' background ' level o f 10
parts per m i l l i o n (p .p .m.) .
C a d m i u m and z inc pol lu te
s imilar areas. W e k n o w the
concen t ra t ions o f the
contaminants in soi l and
vegetables (see Ecos 7 ) . T o
what extent are cereals and
pastures affected, and is the
heal th o f h u m a n s and
l ives tock at risk? A team o f
researchers f rom the CSIRO
With increasing distance from the smelter, pollution falls to a 'background ' level. Z inc is shown here; lead and cadmium curves are similar. C o p p e r is a negligible c o m p o n e n t o f smelter smoke .
D i v i s i o n o f So i l s has been
tackl ing these ques t ions .
M r R i c h a r d Merry , D r
K e v i n T i l l e r , M r Paul de
Vr i e s , and D r Brian
Cartwright t ook samples o f
whea t and pasture plants
f rom sites at var ious
dis tances f rom Port Pirie,
i n c l u d i n g poin ts o n a l ine
stretching m o r e than 30 k m
south f rom the smelters. T h e
scientists c o l l e c t e d bo th
grain and w h o l e tops o f
whea t plants, as we l l as
spec imens o f s o m e 30
pasture species and samples
o f the soi ls in w h i c h all
these plants g rew.
T h e y then analysed the
plants and soi ls to find out
Heavy metal uptake is illustrated here by cadmium: the more there is in the soil , the more will contaminate a plant. M o s t pasture species take up less cadmium than Ward ' s weed but more than bluebush. Soil metal values were obtained by extraction with a standard reagent, EDTA.
h o w m u c h lead, z inc , and
c a d m i u m these con ta ined .
A s a c h e c k , they also
measured the concen t ra t ions
o f metals that are very m i n o r
c o m p o n e n t s o f the smelter
s m o k e , s u c h as coppe r .
T h e y found a g o o d
corre la t ion be tween the
degree o f con tamina t ion o f
m o s t plants and the
con tamina t ion o f the soi ls
they grew in. T h e m o r e
c a d m i u m that pol lu tes the
g round , for example , the
m o r e there wi l l be in a whea t
stalk or a paddy m e l o n leaf.
T h e farther the scientists
travelled a long their south
b o u n d transect, the less
con tamina t ion they found ,
unti l , about 35 k m f rom the
smelter , the pol lutant
concen t ra t ions had d ropped
to ' background ' levels
similar to those f o u n d
e l sewhere in the State.
T h e levels o f heavy metals
in whea t c a m e we l l wi th in
the l imits set by State health
authorit ies. What ' s m o r e , the
pol lutant metals b e c o m e
di luted dur ing bu lk hand l ing
and mi l l i ng , w h e n
con tamina ted grain is
b l ended wi th wheat f rom
unpo l lu ted areas. T h e
researchers be l ieve that
h u m a n heal th is un l ike ly to
be endangered by the heavy
metals in whea t grain
harvested near the smelters .
con tamina ted plants were the spec ies o f b luebush . T h e scientists c o l l e c t e d their samples at three t imes o f year, and i n c l u d e d plants at var ious stages o f their life c y c l e s , and this m a y at least partly a c c o u n t for the variations b e t w e e n spec ies .
S h e e p and cattle graze o n these pastures; are they b e i n g ha rmed by their Saltbush is grazed o n s o m e former wheatlands.
c h e m i c a l diet? T h i s is a t o u g h ques t ion . It seems that the risk depends to s o m e extent o n w h i c h spec ies they eat. B y c h o i c e , the s tock take the m a i n pasture plants, but w h e n these are in short supply the animals turn to saltbush and b luebush , and finally the burrs (fruits) o f m e d i c .
In the semi-arid c l imate o f Port Pir ie , the g r o w i n g season lasts for o n l y 5 m o n t h s and d rough t c o n d i t i o n s o c c u r frequently. T h i s m e a n s that sheep are often dr iven to r u m m a g i n g for m e d i c burrs, inevi tably garnished wi th a s ignif icant quanti ty o f so i l , w h i c h con ta ins h ighe r metal levels than d o the plants. T h e animals ' intake o f lead, in particular, w i l l r ise, s ince lead is abou t 10 t imes as concen t ra ted in so i l as in pasture.
Scient is ts d o n o t k n o w all the ways in w h i c h heavy metals may affect an imals . Cer ta inly t o o m u c h o f any o n e metal w i l l be t ox i c . Wha t ' s m o r e , s o m e pol lutant meta ls antagonize essential e l emen t s : for e x a m p l e , an an imal that s w a l l o w s s o m e c a d m i u m wi l l absorb less o f the c o p p e r in its f o o d than i f its mea l had been unpo l lu ted .
Ward ' s w e e d , w h i c h was in t roduced f rom the Medi te r ranean r e g i o n , con ta ins relatively large amoun t s n o t o n l y o f c a d m i u m but a l so o f sulfur, another e l em en t that antagonizes coppe r .
T h e risk is particularly hard to assess because several metals are invo lved , and they interact.
Z i n c , for e x a m p l e , aggravates lead toxic i ty . O n the other hand, c a l c i u m and p h o s p h o r u s he lp to offset the t o x i c effects o f bo th lead and z inc . T h e Por t Pir ie r e g i o n has ca lca reous so i l s , w h i c h perhaps offer s tock s o m e measure o f pro tec t ion .
Bluebush is less contaminated than most plants examined, but stock turn to it only when the main pasture species are in short supply.
A n i m a l s vary in their p h y s i o l o g i c a l r e sponses , t o o . S h e e p and cattle tolerate lead in their diets at concen t ra t ions u p to 3 0 0 p .p .m . w i thou t s h o w i n g any i l l effects, a l t hough they d o accumula t e the metal . ( T h i s concen t ra t ion is m a n y t imes h igher than any the scientists found in plants near Por t Pir ie .) Other n o n -ruminants c a n n o t pu t u p wi th lead levels nearly as h i g h as this: horses , for e x a m p l e , c a n tolerate o n l y about 80 p .p .m.
T h e scientists f o u n d lead concen t ra t ions o f 2 0 0 0 p .p .m . o r e v e n m o r e in soi ls in the t o w n , and wheat and pasture soi ls near Por t Pir ie often con t a ined 3 0 0 - 5 0 0 p .p .m. Because the m o s t con tamina ted soi ls g r o w the m o s t con tamina ted
vegeta t ion, the researchers be l i eve that the animals at greatest risk are those wi th in about 5 k m o f the smelter c o m p l e x .
M r Mer ry and D r T i l l e r feel that this ques t ion o f animal health needs further invest igat ion. A study be ing carr ied out at the Institute o f M e d i c a l and Veterinary S c i e n c e in A d e l a i d e is p rov id ing valuable informat ion . T h e r e , M r T e e -S iaw K o h and D r G e o f f Judson are test ing the idea that the c o p p e r de f i c i ency observed in sheep grazing near the smelters c o u l d b e caused by the levels o f heavy metals i n the diet.
T h e scientists se lec ted s ix propert ies f rom 6 to 4 0 k m sou th o f the smelters , and o n t o e a c h farm m o v e d 14 sheep f rom the State's unpo l lu t ed south-east. Ass is ted by M r W a r w i c k H a c k o f the S o u t h Austra l ian Depar tmen t o f Agr icu l tu re , they t ook samples o f b l o o d and faeces every 3 m o n t h s , and every 6 m o n t h s they k i l led three sheep o n e a c h property and r e m o v e d liver, k idney , m u s c l e , and b o n e samples .
T h e analyses s h o w h o w m u c h o f the heavy metals the sheep are s w a l l o w i n g and absorb ing into their t issues, and enab le the researchers to k e e p an eye o n the animals ' levels o f c o p p e r and other essential e lements .
T h e faecal samples to ld a
\t
Ward's weed, an introduced annual, takes up relatively large amounts of cadmium and zinc in polluted areas.
clear story o f increased heavy metal intake near the smelters. F a e c e s f rom the sheep nearest Port Pir ie con ta ined 4 0 t imes as m u c h lead as faeces f rom the sheep o n the m o s t distant property, w h e r e the animals were e x p o s e d on ly to ' background ' levels o f heavy metals . T h e co r r e spond in g ratio for c a d m i u m was 30 , and for z inc 4 .
W e mus t e x p e c t s o m e o f these addit ional heavy metals to f ind their way in to the sheep 's o rgans . M r K o h and D r Judson have found three to five t imes as m u c h lead and c a d m i u m i n the b l o o d and tissues o f the sheep near the smelters as in the ' background ' sheep .
T h e sheep c o n s u m i n g the largest quantit ies o f heavy metals also had the l o w e s t concen t ra t ions o f c o p p e r in their livers — on ly o n e -twent ie th the ' no rmal ' value.
T h e scientists c o m m e n t that the exper imenta l sheep near the smelters m i g h t have approached or even reached a state o f c o p p e r de f i c iency . T h e faecal analyses s h o w that o n all proper t ies the sheep inges ted the same amoun t s o f c o p p e r , so it s eems l ikely that the absorpt ion o f copper - f rom the gut into the b l o o d is impaired, p robab ly by h i g h leve ls o f o n e or m o r e o f the heavy metals .
Clear ly a ques t ion that wi l l n e e d answer ing is whe ther the metals accumula t i ng in l ives tock raised near Port Pir ie may , w h e n the meat reaches the d inner table, present a hazard t o h u m a n health.
Con tamina t ion o f whea t c r o p s a round a l e a d - z i n c smelter. R . H . Mer ry , K . G . T i l l e r , M . P . C . d e Vr i e s , and B . Cartwright . Environmental Pollution (Series B), 1981 , 2 , 3 7 - 4 8 .
T o x i c metals a round Por t Pir ie . Ecos N o . 7, 1976 , 2 7 - 3 1 .