Arsenic - Toxicology of Metals - page 361

ones. Andreae (1978) reported that arsenate is gen-
erally the dominant form in seawater. Clement and
Faust (1973) found that only approximately 8% of the
total arsenic in well-aerated stream water was in the
form of As(III), whereas all of the arsenic in anaero-
bic reservoirs seemed to be in the form of As(III). The
chemical form of arsenic in different ground waters is
largely unknown. Clement and Faust (1973) found that
25-50% of the total arsenic in a few groundwater
samples was in the form of As(III).
The average daily intake of arsenic through drink-
ing water can vary widely, depending on the source
of the water. McCabe et al . (1970) reported that less
than 1% of more than 18,000 community water sup-
plies in the United States had concentrations exceed-
ing 0.01 mg As/L. Engel and Smith (1994) investigated
the levels of arsenic in drinking water throughout the
United States between 1968 and 1984. They found
that 30 counties in 11 states had mean arsenic levels of
>5

in Hanoi, Vietnam, averaged 159 µ g/L, ranging from

1-3050 µ g/L (Berg et al ., 2001).

4.3 Soil
Arsenic is widely distributed in the earth's crust,
which contains about 3.4 ppm (Wedepohl, 1991). It is
mostly found in nature as minerals, and in its elemen-
tal form only to a small extent. Typical arsenic concen-
trations for uncontaminated soils range from 1-40 ppm
( g/g), with the lowest concentrations in sandy soils

and soils derived from granites. Higher arsenic con-
centrations are found in alluvial soils and soils with
high organic content (Mandal and Suzuki, 2002).
Soils in mining areas or near smelters may con-
tain high levels or arsenic. Arsenic concentrations up
to 27,000 mg/kg were reported in soils contaminated
with mine or smelter wastes (EPA, 1982). Soils at an
abandoned mining site in the Tamar Valley in south-
west England have arsenic concentrations that may
exceed 50,000 mg/kg (Erry et al ., 1999).
Soil on agricultural lands treated with arsenical pes-
ticides may retain substantial amounts or arsenic. A
study reported an arsenic concentration of 22 mg/kg in
treated soil compared with 2 ppm for nearby untreated
soil (EPA, 1982). Soil samples from 13 old fruit orchards
in New York state, where lead arsenate was used for
pest control for many years, had arsenic concentra-
tions from 1.6-141 mg/kg (Merwin et al ., 1994).
Natural concentrations of arsenic in sediments are
usually <10

µ

µ g/L, 15 counties had mean levels from 5-10 µ g/L;

10 counties had mean levels from 10-20 µ g/L; and 5

counties had levels >20 g/L. The highest levels were

found in Churchill County, Nevada, where 89% of the
population was exposed to a mean arsenic concentra-
tion of 100

µ

g/L. More
recently, investigators at the USGS (Focazio et al ., 2000)
have developed an extensive map of the occurrence
of arsenic in ground water in the United States on
the basis of 18,850 sample locations; 2262 of these were
identifi ed as public water supplies. The results of these
studies indicate a number of states in specifi c regional
areas (e.g., New England, the Midwest, Rocky Moun-
tain states, and the Pacifi c Coast with elevated concen-
trations (>10.0

µ g/L and 11% to a mean of 27 µ

g/g dry weight but can vary widely
around the world (Mandal and Suzuki, 2002). Contam-
ination by heavy metals is a serious problem in some
developing countries. Sepetiba Bay, a semi-enclosed
coastal lagoon in Brazil, had sediment arsenic concen-
trations up to 80,000

µ

g/L) in the ground water supplies, so
the issue of elevated arsenic concentrations in ground-
water is national in scope. In January 2001, the EPA
lowered the MCL for arsenic from 50-10

µ

g/g in an area adjacent to a plant
that produced zinc and cadmium (Moreira, 1996). The
literature regarding the cycling and effects of arsenic
in coastal marine environments has been reviewed by
Sanders et al . (1994).
It has recently been suggested that the wood preserv-
ative, chromated copper arsenate (CCA), commonly
used in dock pilings and bulkheads, can be toxic to estu-
arine organisms. Wendt et al . (1996) measured arsenic
in surface sediments from creeks with high densities of
docks and from nearby reference creeks with no docks.
The average concentrations in the sediments ranged
from 14-17

µ

g/L (EPA,
2001). With an assumed daily intake of 1.5 L drinking
water, a concentration of 0.01 mg/L will result in the
daily ingestion of 0.015 mg arsenic.
Some developing countries, such as Mexico,
Bangladesh, India, and Vietnam, have highly elevated
levels of arsenic in drinking water in some regions
(Bagla and Kaiser, 1996; Berg et al .. 2001; Tondel et al .,
1999; Wyatt et al ., 1998a; 1998b). In Bangladesh and West
Bengal, India, it is estimated that more than 1 million
people are drinking arsenic contaminated water and
tens of millions more could be at risk in areas that have
not been tested for contamination. Analysis of 20,000
tube-well waters indicated that 62% have arsenic levels
in drinking water above the WHO permissible expo-
sure limit of 10

µ

g/g throughout the study area, which is
within the range of natural background levels.

µ

4.4 Air
Arsenic naturally occurs in soil and is present in
the atmosphere as airborne dust. It is also emitted

g/L
(Bagla and Kaiser, 1996). Arsenic concentrations in
water samples from private small-scale tube-wells

µ g/L, with some as high as 3700 µ