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OCR for page 16
Distribution of
Arsenic in the Environment
NATURAL SOURCES
Earth's Crust
Arsenic ranks twentieth among the elements in abundance in the
earth's crust. The abundance of arsenic in the continental crust of the
earth is generally given as 1.5-2 ppm. Thus, it is relatively scarce.
Nevertheless, it is a major constituent of no fewer than 245 mineral
species. Arsenic is found in high concentration in sulfide deposits,
where it is present as the native element or alloys (four minerals),
arsenides (27 minerals), sulfides (13 minerals), sulfosalts (sulfides of
arsenic with metals, such as lead, copper, silver, and thallium, 65
minerals), and the oxidation products of the foregoing (two oxides, 11
arsenites, 116 arsenates, and seven silicates). Of these minerals, arse-
nopyrite is by far the most common. In addition, many sulfides contain
appreciable amounts of arsenic in solid solution; the most important of
these is pyrite, which has a maximal arsenic content of about 5%
(common range, 0.02-0.5%~. The arsenic-bearing sulfides and sul-
fosalts oxidize readily; under surface conditions, oxidation proceeds to
arsenic trioxide and to the arsenate stage.
16
OCR for page 17
Distribution of Arsenic in the Environment
TABLE 3-1 Arsenic in Igneous Rocksa
17
Arsenic Concentration, ppm
No. Range Usually
Rocks Analyses Reported Average
Ultrabasic 37 0.3-16 3.0
Basalts, gabbros 146 0.06-113 2.0
Andesites, dacites 41 0.5-5.8 2.0
Granitic 73 0.2-13.8 1.5
Silicic volcanic 52 0.2-12.2 3.0
aEstimated on the basis of data of On~shi602 and Boyle and Jonasson.94
Igneous and Sedimentary Rock
Concentrations of arsenic in igneous rocks are listed in Table 3-1. No
trend of concentration is apparent with respect to content of silica or
other major elements. The limited data available indicate rather uni-
form distribution of arsenic among the major constituent minerals,
except for slight enrichment in the sulfide minerals of igneous rocks.
Data on the concentration of arsenic in sedimentary rocks are
summarized in Table 3-2. Shales, clays, phosphate rocks, and sedimen
TABLE 3-2 Arsenic in Sedimentary Rocksa
Arsenic Concentration, ppm
No. Range Usually
Rocks Analyses Reported Average
Limestones 37 0.1-20 1.7
Sandstones 1 1 0.6-120 2.0
Shales and clays 324 0.3-490 14.5b
Phosphorites 282 0.4-188 22.6
Sedimentary iron ores 110 1-2,900 400?
Sedimentary manganese ores (up to 1.5%)
Coal 1,150 0-2,000 13c
aEstimated on the basis of data of Onishi602 and Boyle and Jonasson.94
Excluding one sample with arsenic at 490 ppm.
CBoyle and Jonasson94 gave 4 ppm.
OCR for page 18
18
ARSENIC
tary iron and manganese oxides are notably enriched in arsenic. The
data of Tourtelot794 indicate that most of the arsenic in nonmarine clays
and shales is associated with the clay minerals, whereas a considerable
proportion of the arsenic in offshore marine samples is present as
pyrite. Tourtelot, Schultz, and Gill795 found a correlation between the
arsenic and organic carbon concentrations. A similar correlation was
observed by Ruch, Kennedy, and Shimp689 for unconsolidated sedi-
ments of Lake Michigan; they attributed this arsenic to manes
activities- the arsenic content in surface sediments (0-6 cm) averaged
more than twice that at depths greater than 20 cm (12.4 vs. 5.3 ppm).
It should be noted that a higher than average content of arsenic is
commonly found in sandstones, shales, and coals associated with
uranium mineralization in Utah, Colorado, Wyoming, and South
Dakota; this suggests considerable mobility of arsenic.
High concentrations of arsenic (maximum, 2,100 ppm; average, 1 15
ppm; median, 60 ppm) have also been noted in sediments from the area
of hot brines in the Red Sea.345 408
Most of the analyses for phosphorites3~6 797 are related to samples
from the United States (Table 3-31. There is considerable variation in
arsenic content, even from a single area, and no correlations with
concentrations of phosphorus pentoxide, organic matter, or other
major constituents are proved. Gulbrandsen3~6 suggested a correlation
of arsenic with organic matter for the phosphorites of the Phosphoria
Formation (Montana, Wyoming, and Idaho); Stow764 found no such
correlation for Florida land-pebble phosphate, but found a positive
correlation with iron content. The available analyses have been made
on whole rock; consequently, correlations of arsenic with other con-
stituents can be made with confidence only if the purified phosphate
mineral and associated clay material are determined. It would be
especially desirable to conduct such studies on samples of high arsenic
content.
Soil
Arsenic is present in all soils, and the geologic history of a particular
soil determines its arsenic content.308 The natural arsenic content in
virgin soils varies from 0.1 to 40 ppm. The average is about 5-6 ppm,
but it varies considerably among geographic regions. 159 Soils overlying
sulfide ore desposits commonly contain arsenic at several hundred
parts per million; the reported maximum is 8,000 ppm. This arsenic
may be present in unweathered sulfide minerals or in an inorganic
anion state. The most common sulfide is arsenopyrite, although arse
!
OCR for page 19
Distribution of Arsenic in the Environment
TABLE 3-3 Arsenic in Phosphoritesa
19
Arsenic Concentration, ppm
No.
Locality and Type of Rock Analyses Range Average Median
Soup Carolina, river rock 4 56.8-88.1 68.4 64.3
South Carolina, land rock 4 9.2-27.5 17.4 15.9
Florida, hard rock 8 1.4-9.6 5.4 5.7
Florida, land pebble 31 3.6-21.2 11.9 11.6
Florida, soft rock 6 0.4-18.6 7.5 5.7
Tennessee, blue rock 7 8.4-37.7 20.4 19.8
Tennessee, brown rock 25 5.1-56.1 14.6 12.5
Tennessee, white rock 3 4.8-21.7 10.6 5.2
Kentucky 3 6.7-12.7 9.9 10.3
Arkansas 8 14.6-188.2 61.0 43.8
Oklahoma 3 15.6-19.3 17.6 17.9
Montana 25 < 10-106 40.0 30
Idaho 27 8.4-60 18.5 15
Wyoming 17 < 10-150 26.4 17
Utah 14 8.4-43.2 16.0 14
British Columbia 1 28.3 28.3
Europe 10 7.6-54.8 25.1 20.8
North AfIica 13 7.0-36.7 17.4 16.3
Israel ? 20-40 ? ?
Insular (West Indies, Pacific) 21 5.1-76.2 16.3 12.0
Southern Australia 2 20.3-24.3 22.3 22.3
Summarized mainly from Tremearne and Jacob797 and Gulbrandsen.3l6
nosulf~des of almost any metal cation can be found. Inorganic arsenate
may be bound to iron and aluminum cations or oxides or to any other
cation present (such as calcium, magnesium, lead, and zinc).
Arsenic may also be bound to the organic matter in soils, in which
case it is released into the soil solution as the organic matter is oxidized
and is then available for plant uptake or fixation by soil cations.675
Some arsenic from other inorganic forms is also available for plant
uptake, inasmuch as the slightly soluble iron and aluminum arsenates
and the soil solution are in equilibrium. The amount released for plant
uptake is a function of the particular chemical and physical forms of
individual arsenic compounds. The amount of available arsenic (ex-
tracted with 0.05 N hydrochloric acid and 0.025 N sulfuric acid) is
small in virgin soils and averages about one-tenth of the total arsenic
present in most cultivated soils. t59330833~i
OCR for page 20
20
Water
ARSENIC
The cycle of arsenic in natural waters has recently been reviewed by
Ferguson and Gavis.249 Data on the arsenic content of waters and
sediments are summarized in Tables 3-4 and 3-5. Sugawara and
Kanamori768 showed that the ratio of As(V) to total arsenic was close to
0.8: 1 in ocean water. Braman97 reported ratios of 0.56 :1 and 0.81:1
for a tidal flat and saline bay water, respectively. He also found that
As(III), methanearsonic acid, and cacodylic acid were present. The
ratio of As(V) to As(III), based on thermodynamic calculations, should
be 1026: 1 for oxygenated seawater at a pH of 8.1. In reality, it is 0.1: 1
to 10 :1. This unexpectedly high As(III) content is caused, at least in
part, by biologic reduction in seawater.393 The content of arsenic in
seawater is a small fraction (perhaps 0.1%) of the amount calculated to
have been carried into the sea. Nearly all the arsenic has been precipi-
tated or adsorbed on marine clays (probably most important), phos-
phorite, and hydrous oxides of iron and manganese. The scavenging of
arsenic from solution by coprecipitation with hydrous oxides of iron
and manganese in laboratory experiments is well known, but its
occurrence in natural waters has not been studied in detail. Moenke55
noted that spring waters (pH, 5.1) of high arsenic content precipitated
about 80~o of their arsenic in iron-rich sediments within 160 m of the
source of entry.
The high content of arsenic in hot springs is notable; fumarolic gases
have been reported to contain arsenic at up to 0.7 ppm. Extremely high
arsenic concentrations have been reported in some groundwaters from
areas of thermal activity,3~2448 from areas of rocks with high arsenic
content,86 294~83 and in some waters of high dissolved-salt content.478 85~
Most of the other high values reported in rivers and lakes and in
sediments (Tables 3-4 and 3-5) are probably due to industrial contami-
nation. Angino and others have shown that household detergents
(mostly of the high-phosphate type) widely used in the United States
contained arsenic at 1-73 ppm; their use probably contributes signifi-
cant amounts of arsenic to surface waters. Sollins,75~ however, felt
that, after dilution during use, the concentration would be well below
the recommended maximum and constitute no particular hazard. It has
been generally assumed that surface waters, like the ocean, are "self-
purifying" with respect to arsenic-i.e., that the arsenic is removed
from solution by deposition with sediments; but quantitative studies
are lacking. Sediments are always higher in arsenic than the waters
with which they are associated.
The data on ground waters are inadequate. About 3% of the analyses
show arsenic at more than 50 ppb, the 1962 maximal permissible
OCR for page 21
Distribution of Arsenic in the Environment
TABLE 3-4 Arsenic in Fresh Waters
21
Arsenic Concentration,
Water ,ug/liter (ppb) Reference
United States, lakes:
New York, Chautauqua 3.5-35.6 474
Michigan 0.5-2.4 720
Superior 0.1-1.6 720
Wisconsin 4.0-117 141
California, Searles 198,000-243,000 851
California 0.0-100a 478
0.0-2,000b 478
Florida, Echols 3.58 99
Florida, Magdelene 1.75 99
United States, rivers:
Hillsborough 0.25 99
Withlacoochee 0.42 99
Fox (polluted watershed) 100-6,000 107
Yellowstone 4.5 231
Narrow 0.90 659
Providence 0.75-0.90 659
Seekonk 2.48-3.45 659
Sugar Creek (contaminated) <10-1,100 224, 859
Columbia 1.6 602
Schuylkill 30-180 436
United States, canals:
Florida <10-20 305
United States, well water:
California ~10-<2,000 296
Florida 0.68 99
Minnesota (contaminated) 11,800-21,000 244
Washington 5.0-6.0 241
Oregon 0.00-1,700 294
United States, Puget Sound 1.5-1,200 186, 187
United States, rainwater:
Rhode Island 0.82 659
Washington, Seattle 17 186
Argentina, Cordoba, drinking water 480-1,490
traces-300
315
42
Bosnia, Shebrenica, spring 4,607 385
Canada, well water 0.5-15 302
<2.3-7.500 883
Chile 800 86
OCR for page 22
22
TABLE 3-4 (Continued)
ARSENIC
Arsenic Concentration,
Water ,ug/liter (ppb) Reference
1
Italy, Modena Province:
Groundwater 3.0-5.0 824
Subsurface <0.4-2.1 155
Japan:
Rain 0.01-13.9 405
Rivers (40) 0.25-7.7 405
Aomori Prefecture 30-3,950 588
Lakes 0.16-1.9 602
Germany:
Elbe River 20-25 602
Rhine River 3.1 432
Greece, lakes 1.1-54.5 602
Formosa, well water 800 242
New Zealand, rivers:
Waikato Rived 5-100 448
Waiotapu Valley trace-276,000 312
Yagnob, Daiyee River,
suspended 100 300 445
Sweden:
Rivers 0.2-0.4 602
Glacial ice 2.0-3.8 847
Antarctica 0.60-0.75 405
Spring waters, California,
Kamchatka, U.S.S.R., New Zealand 130-1,000 851
Oil- and gas-field waters, California,
Louisiana, Hungary 0.0-5,800 851
Thermal waters, Wyoming, Nevada,
California, Alaska, Iceland 20-3,800 851
Spring waters, e U.S.S.R., Wyoming,
Algeria, Iceland 30-500 851
Dissolved solids, <2,000 ppm.
Dissolved solids, >2,000 ppm.
CHigh in bicarbonate; of geothermal origin.
dHigh in bicarbonate and boron.
eDeposit traverUne.
OCR for page 23
Distribution of Arsenic in the Environment
TABLE 3-5 Arsenic in Sediments
23
Arsenic Concentration,
Locality ppm Reference
United States:
New York, Chautauqua 0.5-306.0 694
Texas 3.C' 3
0.8-8.0 654
Winyah Bay 8.0-12.0 394
Lake Michigan 5.0-30.0 689
7.2-28.8 720
Lake Superior 2.8-5.4 720
Lalces, Wisconsin 0.1-45.0 727
Sugar Creek (conta'Tunated) 4,470-66,700 859
Puget Sound 2.9-10,000 186
Washington, rivers
Skagit 15-34 186,187
Stillaguamish 17-48 186,187
Snohom~sh 22-74 186,187
Duwam~sh 15-40 186,187
Puyallup 2.6-7.5 186,187
Nisqually 4.5-12 186,187
Dosewallips 7.4 186,187
Duckabush 6.8 186,187
Japan 0.0-93.4 405
Minamata area 4.7-60 319
Netherlands, Rhine Delta ND-3 10 197
New Zealand:
Wa~otapu Valley muds 51-14,250 312
Manne 6.6 652
Pelagic 40 819
England <2-5,000 38,456,789
ND = Not detected.
concentration in drinking water.8088~3 In view of recent reports of
chronic arsenic poisoning attributed to the use of such waters in Chile86
and in Oregon,294 further study is imperative. The volcanic rocks from
which the arsenic-rich waters come in Oregon are of a type that is
common in the western United States.262
OCR for page 24
24
Plants
ARSENIC
Arsenic is ubiquitous in the plant kingdom. Its concentration varies
from less than 0.01 to about 5 ppm (dry-weight basis). Appendix A lists
the arsenic concentrations of some plants and plant products. Differ-
ences in arsenic content probably reflect species differences in plants
and, in a larger sense, environmental and edaphic factors in a particular
geographic region. Plants growing in arsenic-contaminated soils gen-
erally have higher residues than plants grown in normal soils. Arsenic
concentrations are less than S.O ppm (dry wt) or O.S ppm (fresh wt) for
untreated vegetation, whereas treated plants may have much higher
concentrations. However, values for some nontreated plants are as
high as or higher than those for plants that were treated with arsenic or
grown in arsenic-contaminated soil. Natural variations among plants,
plant species, available soil arsenic, and growing conditions are all
responsible in part for these discrepancies. There appears to be little
chance that animals would be poisoned by consuming plants that
contain arsenic residues from contaminated soils, because plant injury
occurs before toxic concentrations could appear.
Marine plants, particularly algae and seaweed, may have extremely
high arsenic contents. In 11 varieties of British seaweed examined, a
range of 5.2 ppm (in Chondrus crispus) to 94 ppm (in Laminaria
digitata) was recorded.398 In green algae, the amount of arsenic varied
inversely with the apparent chlorophyll content, from O.OS to S.O ppm
on a dry-weight basis.5~9 For brown algae, values of around 30 ppm
have been reported.
Animals and Humans
Arsenic is present in all living organisms (Appendix B). Marine fish
may contain up to 10 ppm; coelenterates, some mollusks, and crusta-
ceans may contain higher arsenic concentrations. Freshwater fish
contain up to about 3 ppm, although most values are less than 1 ppm.
Domestic animals and man generally contain less than 0.3 ppm on a
wet-weight basis; The total human body content varies between 3 and 4
mg and tends to increase with age. With the exception of hair, nails,
and teeth, analyses have revealed that most body tissues contain less
than 0.3 ppm.
The median arsenic content in 1,000 samples of human hair was O.S I
ppm, as determined by neutron-activation analysis.743 The median
concentrations for males and females were 0.62 and 0.37 ppm, respec
OCR for page 25
Distribution of Arsenic in the Environment
25
lively. Arsenic content of hair has served as an indicator in incidents of
suspected poisoning. Values greater than about 2-3 ppm indicate
possible poisoning, although higher concentrations have been recorded
in occupational surveys. For example, a survey of workers in a copper
processing plant in Czechoslovakia showed mean arsenic contents of
178 ppm in 21 persons exposed to air containing arsenic tr~ox~ae at
1 01-5.07 m~/m3 and 56.6 prim in 18 persons exposed to air containing
. · . .
, 7 ,
0.08-0.18 mg/m3; a control (nonexposeu) group naa mu. Pam.-
such occupational surveys, it is important to distinguish between
exogenous arsenic from atmospheric pollution and cosmetics and that
from ingestion. Nail clippings from a patient with acute polyneuritis
from arsenic poisoning contained arsenic at 20-130 Pam. The normal
~r~.nic content of nails is 0.43-1.08 ppm.380
w_
The arsenic content ot urine can vary normally from 0.1 to 1.0 ppm.
Great daily variations exist and depend on the amount of arsenic in
various foodstuffs. It is generally high after consumption of seafood.
When arsenic is ingested, the amount excreted increases over several
days to a maximum and then declines to normal.
Some of the highest concentrations of arsenic in biota are encoun-
tered in marine organisms. The average arsenic content of freshwater
fish including shad, gar, carp, bullhead, pickerel, bluegill, black bass,
white bass, buffalo, and horned dace varied up to 2.1 ppm.233 The
average oil content of these fish was only 2.49%, but the oil carried
22.8% of the total arsenic present. The arsenic in the liver oil of the
large-mouthed black bass averaged 30 ppm. These values are generally
lower than those reported for marine fish, which range up to 32.4
ppm for cod. Shrimp contain arsenic at 3.8-128 ppm on a dry-weight
basis.~72 A survey of canned seafood showed the following arsenic
concentrations: clams, 15.9 ppm; oysters, 16.0 ppm; smoked oysters,
45.8 ppm; lobsters, 22.1 ppm; and shrimp, 19.9 ppm.203
Air
Trace amounts of arsenic may be present in air. Although no 24-h
maximal atmospheric concentration has been set in the United States,
3 ,ug/m3 has been recommended in the U.S.S.R. and Czechoslo-
vakia.676 The threshold limit recommended for industrial workers is 500
,ug/m3 for arsenic and its compounds and 200 ,ug/m3 for arsine.425
Exposure standards for inorganic arsenic have recently been proposed
by the Occupational Safety and Health Administration.809 They limit
OCR for page 26
26
ARSENIC
air concentration to ''4 ,ug As/m3 of air averaged over an eight hour
period." A ceiling limit of 10 ,ug/m3 is proposed for any 15-min period
during a work shift.
Data on emission of arsenic to the atmosphere have been sum-
marized by Sullivan770 and by Davis and Associates and are dis-
cussed at the end of this chapter. Arsenic content in air and dust is
summarized in Table 3-6. In areas remote from industrial contamina-
tion, air concentrations of arsenic generally are less than 0.02 ,ug/m3,
whereas in urban areas they vary from less than 0.01 to 0.16 ,ug/m3.
Two of the air values reported as ''United States, Miscellaneous" were
2.50 ,ug/m3 in Anaconda, Montana, in 1961-1962 (the maximum) and
1.40 ,ug/m3 in E1 Paso, Texas, in 1964.77°
MAN-MADE SOURCES
Production
Data on domestic and world production, imports, and domestic con-
sumption of arsenic from 1964 to 1973, as shown in Table 3-7, were
obtained from the Bureau of Mines, Minerals in the U.S. Economy.
Much of the arsenic processed in the United States is imported in
copper ore and concentrates. An equal amount is imported as arsenic
compounds. Agriculture is the largest user of arsenic, accounting for
about 80~o of the demand. Figure 3- 1 indicates sources of arsenicals by
country and type of material in 1973. Tables 3-8, 3-9, and 3-10 show
U.S. imports for consumption of white arsenic (arsenic trioxides, U.S.
imports of arsenicals by class, and world production of white arse-
nic.812
In the United States, arsenic is produced entirely as a by-product of
the smelting of nonferrous-metal ores. Domestic production of arsenic
has been adversely affected since the 1920's, when very large quan-
tities of imported by-product arsenic became available from a copper
mine in Sweden whose ore contained a high proportion of arsenic. The
demand for arsenic was reduced after World War II by the advent of
organic substances developed during and after the war that were used
as pesticides and for other purposes for which arsenic had previously
been used. The resulting surplus of by-product arsenic kept the price of
white arsenic (77% arsenic metal) at 6.25-6.75 cents/Ib (13.8-14.9
cents/kg) from July 1968 through 1973. However, in early 1974, the
price increased to 13 cents/lb (28.7 cents/kg).
Arsenic is a troublesome contaminant in ores. Some arsenic com
OCR for page 69
Distribution of Arsenic in the Environment
69
transfers to and from a field for the organoarsenical herbicides. They
concluded that transfers involving reduction to methylarsines, soil
erosion, and crop uptake were the primary redistribution mechanisms
in this model. Treatment with cacodylic acid resulted in a theoretical
buildup of arsenic of 2.6-3.3 ppm/ha pet year, whereas MSMA accumu-
lated at only 1.5-1.9 ppm/ha per year. They concluded that ''arsenic is
mobile and nonaccumulative in the air, plant and water phases of the
agronomic ecosystem. Arsenicals do accumulate in soil, but redistribu-
tion mechanisms preclude hazardous accumulations at a given site.''701
This model does not include the application of arsenic trioxide to
desiccate cotton before harvest.
Inputs into the environment and a redistribution of arsenic in the
terrestrial ecosystem are presented in Figure ~-4. Natural inputs are
from volcanic action, decay of plant matter, and weathering of minerals
within the soil, whereas man-made sources of arsenic are combustion
of coal and oil, smelting of ores, and use of fertilizers and pesticides.
The largest sink for man-made arsenic in the environment is the soil.
Onishi and Sandell calculated a balance between igneous rocks
(arsenic content, 2 ppm) and sedimentary deposits (shale and sedi-
ments, 10 ppm; sandstone and limestone, 1.5 ppm).603 They observed
that, if the amounts of sediments equaled that of weathered rocks, then
much of the arsenic in sediments must come from volcanism. At
present, this input is small, and weathering of continental rocks is in
approximate balance with oceanic sediment deposition. Using esti-
mates of arsenic weathering (45,000 tons/year, or 41,000 tonnes/year)
and deposition rates, Ferguson and Gavis concluded that "there is no
substantial imbalance between natural weathering and deposition of
arsenic at present."249 The amount of arsenic from weathering trans-
ported to the oceans as part of the dissolved load of the rivers is 33,000
tons/year (30,000 tonnes/year). Arsenic from man-made sources is
redistributed either through industrial processes, such as the burning of
coal, or by the refining of oil for gasoline and fuel oil. Man's activity
does cause high environmental concentrations at some locations.
Estimates are available for an arsenic balance at a coal-fired steam
plant in Memphis, Tennessee.85 The balance for most trace elements is
satisfactory. Elements that can be present in a gaseous form (e.g.,
arsenic and mercury) are not completely recovered. Most arsenic
recovered was in the precipitation inlet fly ash, but 52-64% of the
arsenic in coal could not be found. It may have been lost in the gas
stream. Coutant et al.~72a found that "only a small percentage of
arsenic is emitted from the stacks" and that it did not pose an
important problem from an air-pollution standpoint. "Arsenic tended
OCR for page 70
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OCR for page 71
Distribution of Arsenic in the Environment
71
to be distributed continuously through the system as a function of
temperature," and ''there is a definite tendency for concentration of
arsenic in the lower temperature deposits in the combustion system."
As coal utilization increases, the amount of arsenic escaping to the
environment will increase, unless proper control measures are used.
Smelter activities have traditionally introduced large amounts of
arsenic into the environment. The copper smelter at Tacoma, Washing-
ton, has been examined for arsenic emission into the environment.
Crecelius et al. reported that input amounts to 200,000 kg of arsenic
trioxide per year into the air via stack dust, 20,000-70,000 kg of arsenic
per year into Puget Sound through dissolved arsenicals in its liquid
effluent discharge, and 1,500,000 kg of arsenic per year in crystalline
slag dumped into the Sound. The installation of more pollution-
control equipment at this smelter is planned, so the amount of arsenic
released into the air and water will decrease significantly.
Information has been collected, to the extent available, to develop a
pattern of arsenic emission into the environment. It included informa-
tion on the arsenic associated with mineral raw materials and fuels, on
the arsenic content of salable mineral products, on solid waste dis-
carded by mineral processors, and on effluent from mineral plants.
Complete material-balance reports were obtainable for only a few
plants. However, considerable incomplete evidence was accumulated.
These data were used to trace the disposition of arsenic through
mineral processing steps and consumption in commodities containing
significant quantities of arsenic. They were also used to determine the
distribution of arsenic throughout commercial production and the
disposition of arsenic used in agriculture and industry. Arsenic emis-
sion to the atmosphere was calculated with the factors listed in Table
3-19.
TABLE 3-19 Arsenic Emission Factorsa
Arsenic Source
Arsenic Concentration
Mining and milling 0.45 tonne/million tonnes of copper, lead. zinc. silver. gold.
Or uranium ore
Smelting and refining 955 tonnes/million tonnes of copper produced
591 tonnes/million tonnes of zinc produced
364 tonnes/million tonnes of lead produced
Coal 1.4 tonnes/million tonnes of coal burned
Petroleum 5.2 kg/million barrels of petroleum
aCalculated on the basis of Davis and Associates' and Minerals Yearbook 1968.~2
OCR for page 72
72
ARSENIC
The principal source of atmospheric arsenic from manufacturing is
the processing of nonferrous metals. Gualtieri classified loo of copper
and copper-lead-zinc ores as being arsenical and stated that they have
an average arsenic: copper ratio of 1: 50.3~4 Analyses of nonferrous
ores considered nonarsenical are not available. However, reference to
mineralogic descriptions of other principal nonferrous mining districts
indicates that arsenic minerals usually occur in trace quantities, are
seldom visible in ore specimens picked at random, and have not caused
serious pollution. It is apparent that the arsenic content of nonarsenical
ores is less than one-tenth that of arsenical ores. Arsenic concentra-
tions would be equivalent to 160 ppm in arsenical ore containing 0.8%
copper and 12 ppm in nonarsenical ore containing 0.6% copper. The
arsenic concentrations of rocks in the earth's crust are shown in Tables
3-1 and 3-2 as: granite, 1.5 ppm; other igneous, 2.0-3.0 ppm; lime-
stone, 1.7 ppm; sandstone, 2.0 ppm; and shales and clays, 14.5 ppm
We may assume rock distribution in nonferrous-metal deposits as:
granite, 25%; other igneous, 25%; limestone, 25%; sandstone, 15%;
and shale, logo. The average arsenic content of unmineralized rock in
mining districts would then be over 3 ppm. The average arsenic con-
tent of waste moved in mining is estimated as the average of the values
for ore and unmineralized material, or 81 ppm for arsenical districts
and 7 ppm for nonarsenical districts.
An estimated 40~o of the arsenic in copper or copper-lead-zinc ore
is left in the concentrator tailings. Much of the arsenic can be allowed
to enter the tailing or can be depressed into an iron sulfide tailing,
provided that the arsenic mineral does not contain valuable metals. The
tailing is deposited on the surface, and some will be blown away by the
wind; however, this quantity should not exceed 1% of the annual
output. Arsenic in gold and uranium mill tailings is subject to similar
wind losses. Arsenic minerals in tailing dunes may eventually weather
to water-soluble compounds that will probably be transported over
short distances before reacting with iron, aluminum, calcium, and
magnesium in the soil to form largely insoluble substances.
Most of the arsenic emitted to the atmosphere during nonferrous-
metal production results from smelting. At the primary smelter, arsenic
contained in the ores and concentrates becomes distributed among the
metal product, slag, speiss (a heavy metallic mixture of iron and
nonferrous arsenides), flue dust, and atmospheric emission. Arsenic in
metal is removed by pyrometallurgic or electrolytic refining methods;
the arsenic-containing residues are recirculated to the smelting fur-
naces. After recovery of by-products, primary furnace slag is discarded.
Speiss is sent to smelters with facilities for processing high-arsenic ma
OCR for page 73
Distribution of Arsenic in the Environment
73
serial. Flue dust contains much of the volatile arsenic that is expelled
from the furnace melt and collected in the stack-gas cleaning system.
Some finely divided arsenic escapes ordinary dust-precipitating units,
but additional cooling and cleaning of the furnace gases, as is done be-
fore sulfuric acid recovery, should capture most of the finely divided
material. Flue dust is ordinarily recirculated to the furnaces, some of it
being removed, if necessary, to keep excessive arsenic from ac-
cumulating in the system. The high-arsenic flue dust usually contains
considerable metal value and, like the speiss, is shipped to the smelter
equipped for processing it. At this smelter, the flue dust and speiss are
roasted with fluxes to remove as much arsenic as possible. The arsenic
is refined to commercial-grade material, and the calcine is smelted for
its metal content.
Atmospheric arsenic emission during smelting was estimated for
1968 conditions by Davis and Associates on the basis of material
balances and sampling data obtained from industrial sources. i96 Aver-
age arsenic emission was estimated at 4.9 lb/ton (2.5 kg/tonne) of
copper produced, 1.3 lb/ton (0.65 kg/tonne) of zinc, and 0.8 lb/ton (0.4
kg/tonne) of lead.
Information obtained in February 1974 showed that arsenic emission
at smelters processing arsenical copper ores was much reduced from
the 1968 emission and that the average arsenic emission from copper
smelting was 2.1 lb/ton (1.05 kg/tonne) of metal. No new data on
emission from zinc and lead smelters are available. However, some
information was obtained on the arsenic content of ores and concen-
trates. On the basis of the indicated smelter inputs of arsenical and
nonarsenical concentrates and estimated percentage stack losses for
smelters treating various types of ore, the recovery factors were
estimated. These estimates are similar to those determined by the
Davis study for lead and zinc smelters.~96
Arsenic is in all coal and may be associated with metal sulfides, clay
minerals, or organic material in the coalbed. Using data developed by
Abernethy,2 Davison estimated that U.S. coal contains arsenic at an
average of 10 ppm in eastern fields, 5 ppm in midwestern fields, and
l ppm in western fields. A small fraction of the arsenic in coal escapes
dust-collecting equipment and reaches the atmosphere. Cuffe and
Gerstle estimated the average arsenic discharge to the atmosphere
from power plants at 0.000064 grains (0.004 ma) per standard cubic
foot, with l lb (0.4536 kg) of coal being burned for each 160 scf of flue
gas.~90 This is equivalent to 1.4 ppm of the coal burned. This factor
should be applicable to industry-wide coal use, inasmuch as nearly all
coal consumed is burned in plants with fly-ash control equipment.
OCR for page 74
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OCR for page 75
Distribution of Arsenic in the Environment
75
Assuming 600 million tons (544 million tonnes) of coal burned per year
in the United States' this would correspond to the emission of 840 tons
(762 tonnes) of arsenic.
The arsenic content of petroleum was investigated by Davis and
Associates' who obtained analyses of 110 oils.~96 The average content
was 0.042 ppm' or about 5.2 kg/million barrels. A future problem may
arise from producing oil from shale. Oil from Colorado shale contained
arsenic at 82 ppm. This arsenic, however' could be removed by contact
with a mixture of nickel sulfide and molybdenum sulfide on alumina
under reducing conditions.572 All arsenic present was removed until
there was 7.2% arsenic on the alumina; thereafter, arsenic was found in
the effluent gases.
Inconsequential arsenic emission results from mining and processing
of phosphate rock. The average arsenic content of mine run rock is
estimated at 5.7 ppm; of washed rock' 12.0 ppm; and of discarded
material, 2.6 ppm, on the basis of an analysis by Tremearne and
Jacob797 and production data shown in Bureau of Mines Mineral
Yearbc)oks.~2 Total arsenic placed in waste impoundments would be
about 200 tons (181 tonnes) annually. of which perhaps 1 ton (0.9
tonne) would be expected to enter the atmosphere through weathering.
About 17~ of phosphate rock is used for electric-furnace manufacture
of elemental phosphorus. The total arsenic in the furnace feed is about
60 tons (54 tonnes)' of which only a small proportion would reach the
atmosphere.
Iron ore contains arsenic, but only insignificant quantities of it are
emitted during iron and steel production. Boyle and Jonasson showed
arsenic contents of hematite up to 160 ppm and of magnetite up to
3 ppm.94 Arsenic occurs in part in the form of scorodite, a very stable
arsenate of iron. In the blast furnace, the arsenic compounds are
reduced to elemental arsenic, which combines with iron to form iron
arsenide and dissolves in the metal; very little of the contained arsenic
reaches the atmosphere. Table 3-20 shows an industrial balance for
arsenic emission into the environment based on the estimated emission
factors, the rate of consumption of mineral fuels, and the rate of
production of nonferrous metals, including arsenic.
Cartons surveyed arsenic input and movement in the United States.
He estimated a total movement of about 119,000 tons (108,000 tonnes)
of arsenic per year (Table 3-211. He distinguished between arsenic that
is found in end products and arsenic that is dissipated onto land'
emitted in air and water, or destined for landfills. Of the 108~000
tonnes, most is fixed in products in which the arsenic is immobile or is
OCR for page 76
76
TABLE 3-21 Summary of U.S. Arsenic Flow, Dissipation, and
Emission, 1974a
ARSENIC
Location of Arsenic
Arsenic Flow, Ready Environ
tonsb mental Transport
End products:
Steel
Cast iron
Other
Dissipation to land:
Steel slag
Pesticides
Copper leach liquor
Other
Airborne emission:
Waterborne effluent:
Phosphate detergents
Other
Landfill wastes:
26,438
17,089
3,638
5,711
63,030
39,690
11,565
9,702
2,073
9,757
Losses from copper-smelting 5,292
Pesticides 2,536
Coal 717
Other 1,212
165
121
44
19,691
10,584
3,748
1,984
3,375
Copper flue dusts
Copper-smelting slag
Coal fly ash
Other
No
No
No
Unknown
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
No
No
No
No
Derived from Carton.
bTo convert to tonnes, multiply values in table by 0.9072.
deposited in landfills as waste material. The remainder is in a form that
can move readily within the environment.
About half the mobile arsenic comes from the use of pesticides. That
which is applied to land becomes predominantly fixed in insoluble
compounds and is only minimally available for transport. Arsenic that
is emitted into air or water is most mobile and of greatest concern to the
general population surrounding the points of emission. It is the air-
borne arsenic trioxide residues that have been implicated in the
arsenic-cancer question. This topic is discussed in Chapter 6.
Arsenic from man-made sources eventually reaches the soil. Pro-
cessed arsenic is applied by way of pesticides and through natural
contamination of fertilizer materials. Arsenic that is gaseous or is
adsorbed onto particulate matter is removed from the atmosphere
through fallout or in rain. It is-deposited on vegetation, on soil, or in
OCR for page 77
Distribution of Arsenic in the Environment
77
water. Once in the water, arsenic can be accumulated to some extent
by various forms of aquatic life. Arsenate in solution is adsorbed or
incorporated into phytoplankton and algae, and an organic compound
is synthesized. Fish, when they consume the algae, incorporate this
organic arsenic compound. In some cases, the arsenical is further
metabolized to yield high-molecular-weight lipid materials, proteins,
or easily soluble low-molecular-weight compounds. The arsenical from
aquatic life, when consumed, is generally eliminated with very little
accumulation. i7~
Pesticidal arsenic that is deposited on the land may have several
fates. A portion of methanearsonic acid and cacodylic acid may be
reduced to volatile arsines (under both aerobic and anaerobic condi-
tions), but the predominant degradation product is arsenate.879 Under
anaerobic conditions, these two compounds are reduced to volatile
arsines. Arsenate and arsenite are also reduced or methylated to
volatile arsines under some conditions. ~75 499 Braman detected di-
methylarsine and trimethylarsine or their oxidation products above
grass that had been treated with sodium arsenite, methanearsonic acid,
cacodylic acid, and phenylarsonic acid. 97 Volatile arsenicals were
detected from soils treated with sodium arsenate, MSMA, and cacodylic
acid. Volatilization occurred under both aerobic and anaerobic condi-
tions. Amounts volatilized were 0.64, 8.22, and 14.10% of the applied
arsenate, MSMA, and cacodylic acid, respectively, in 150 days under
aerobic conditions. Under anaerobic conditions, the amounts produced
from arsenate, MSMA, and cacodylic acid were 1.60, 0.84, and 4.485S,
respectively. Regardless of initial form or oxidative condition, only
dimethylarsine was detected.875
Arsenate, from pesticide or from fallout and runoff, is fixed in the
soil as slightly soluble salts of iron, aluminum, calcium, and mag-
nesium. These may be true compounds or surface-adsorbed reaction
products. In addition, some arsenic is bound in organic forms in the
soil. The arsenic that is not in an insoluble form is available for leaching
into ground water, is available for uptake by plants and trees, and
appears in spring water. As indicated earlier, all vegetation contains
arsenic. Burning of agricultural wastes and forest and grass fires
redistribute arsenic into the atmosphere, from which it is redeposited
on the earth through particulate fallout or rain. Fungi and bacteria in
the soil metabolize arsenic and the methylated derivatives to methylar-
sines. The methylarsines are unstable and are oxidized to As(V). Some
of the reactions are shown in Table 3-22. These processes are mediated
by microorganisms, as well as by chemical action. The faster reactions
are the more environmentally important ones. The stable forms of
OCR for page 78
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OCR for page 79
Distribution of Arsenic in the Environment
79
man-made arsenic in the environment are o-arsenic acid and its
salts. All other forms of methylated arsenic compounds yield o-arsenic
acid in soil as a major sink. This form, however, can be methyl-
ated and put back into the cycle in nature. Braman detected arsenic in
the III, V, methanearsonic, and cacodylic forms in Florida water. 99 His
samples could not have been contaminated by pesticide application, so
these forms appear to be part of the natural cycle.
The most important concept with respect to arsenic cycling in the
environment is constant change. Arsenic appears everywhere in every
living tissue and is constantly being oxidized, reduced, or otherwise
metabolized. In the soil environment, insoluble or slightly soluble
compounds are constantly being resolubilized and the arsenic pre-
sented for plant uptake or reduction by organisms and chemical pro-
cesses. Man has modified the arsenic cycle only by causing localized
high concentrations.
Representative terms from entire chapter:
arsenic trioxide
