AS arsenic
Transcript of AS arsenic
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*: .18,,
Arsenic , As . ""." Orpiment"
Orpiment
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Periodic Table of
the Elements
As is a Group V element (like N and P)
Replaces S in minerals and metabolic systems
replaces P in minerals and ATP energy cycle
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Sources of arsenicSoi l and Sediment
Arsenic concentrations in soils depend in part on the parent materials from
which the soils were derived, although they may be enriched by other
sources, including anthropogenic sources.
Typical natural concentration ranges are 0.1 to 40 mg/kg, with an average
concentration of 5-6 mg/kg (NAS, 1977).
The level of arsenic in soil derived from basalts tends to be higher than insoils of granitic origin, and concentrations of 20 to 30 mg/kg may be found
in soils derived from sedimentary rocks (Yan-Chu, 1994). In areas of
recent volcanism, soils average arsenic concentrations are approximately
20 mg/kg. Very high natural concentrations of arsenic (up to 8,000 mg/kg)
may occur in soils that overlay deposits of sulfuric ores (NAS, 1977).Arsenic can be found in soil in the inorganic state bound to cations, and it
can also be found bound to organic matter. Arsenic may be transferred to
surface water and ground water through
erosion and dissolution; plants may also uptake arsenic. Because arsenic
can be fixed in inorganic and organic compounds in soil, soil may also bea sink for arsenic
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Geothermal Waters
Geothermal water can be sources of arsenic insurface water and ground water. Welch et al., (1988)
identified 14 areas in the Western United States
where arsenic conditions in water exceed 50 g/L
because of known or suspected geothermalsources. In these areas, dissolved
arsenic concentrations ranged from 80 to 15,000
g/L. Welch et al.,found that mean dissolved arsenic
concentrations in geothermal ground waters arehigher than mean arsenic concentrations in non-
thermal ground waters in any of the physiographic
provinces in the United States.
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Other Sources
Natural emissions of arsenic associated with volcanic activity
and forest and grass fires are recognized to be significant.Indeed, volcanic activity appears to be the largest natural
source
of arsenic emissions to the atmosphere (ATSDR, 1998).
Estimates of natural releases (of which volcanic arsenic
emissions are the primary source).
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natural sources, arsenic is released from a variety of
anthropogenic sources (USEPA, 1998b), including:
Manufacturing of metals and alloys
Petroleum refining Pharmaceutical manufacturing
Pesticide manufacturing and application
Chemicals manufacturing
Burning of fossil fuels
Waste incineration
These anthropogenic releases of arsenic can elevate
environmental arsenic concentrations. Human exposure to
arsenic can result in a variety of chronic and acute effects. Inparticular, there is evidence that associates chronic arsenic
ingestion at low concentrations with
increased risk of skin cancer, and that arsenic may cause
cancers of the lung, liver, bladder, kidney, and colon (ATSDR,1998). Because of the human health risks associated with
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Mining and Smelt ing
Arsenic can be obtained from two of its ores, arsenopyrite and
lollingite, by smelting in the presence of air around 650700 C(Kirk-Othmer, 1992), or arsenic trioxide (As2O3) in flue dust
from the extraction of lead and copper can be captured
(Ferguson, 1990). Subsequently, arsenic trioxide can be used
to produce other arsenic compounds or purified to elemental
arsenic.
Arsenic trioxide was produced for commercial use in the United
State at the ASARCO smelter in Tacoma, Washington, until
1985, at which time the smelter ceased operations (ATSDR,
1998). The USEPA Office of Air Quality Planning and Standardsindicates that
primary and secondary6 lead smelters, primary copper
smelters
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E
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Exposure
Arsenic is continually cycled through all environmental
compartments. Arsenic can be elevated to high levels in water
and soil because of the underlying geology or geothermal
activity. In the aquatic environment arsenic concentrations canalso become elevated in some estuaries and in waters near
heavy industrial or mining and mineral-processing areas. The
highest concentrations of arsenic in soil tend to be associated
with mining waste.Mean total arsenic concentrations in air from remote and rural
areas range from 0.02 to 4 ng/m3. Mean total arsenic
concentrations in urban areas range from 3 to about 200 ng/m3;
much higher concentrations (> 1000 ng/m3) have been
measured in the vicinity of industrial sources.
Reported concentrations of arsenic in surface waters are
summarized in Fig. 6. Concentrations of arsenic in open ocean
seawater are typically 12 g/litre. Arsenic is widely distributed
in surface freshwaters, and background concentrations in rivers
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Mean arsenic concentrations of 500 g/litre and a
maximum of 25 mg/litre have been reported for geothermalwaters. Enhanced arsenic levels of < 10 mg/litre have
been reported near anthropogenic sources such as mining
and agrochemical manufacture. Mean sediment arsenic
concentrations range from 5 to 3000 mg/kg, with the
higher levels occurring in areas of contamination.Reported concentrations of arsenic in soils are
summarized in Fig. 7. Background concentrations in soil
tend to range from 1 to 40 mg/kg, with a mean value of 5
mg/kg. Naturally elevated levels of arsenic in soils may beassociated with geological substrata such as sulfide ores.
Anthropogenically contaminated soils can have
concentrations of arsenic up to several percent
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Terrestrial plants
Arsenic species can enter into edible tissues of food crops
through absorption (i.e. not just surface contamination)(Woolson, 1973; Helgesen & Larsen, 1998). Helgesen & Larsen
(1998) demonstrated that bioavailability of arsenic pentoxide to
carrots in soil from a wood preservative treatment plant (soil was
contaminated with CCA) was 0.47 0.06% of total soil arsenic
burden. This study showed that arsenite, arsenate, MMA and
DMA were present in carrot tissue, where only arsenite and
arsenate were present in soil. In soils dosed with arsenate (0
500 g/g) at the concentrations which inhibited growth of
vegetable crops (green bean, lima bean, spinach, cabbage,tomato and radish), high levels of accumulation when found in
the edible parts of radish (76 g/g) spinach (10 g/g) and green
bean (4.2 g/g). Arsenic accumulation in Lima bean, cabbage
and tomato ranged from 0.71.5 g/g. The studies of Woolson1973 and Hel esen & Larsen 1998 hi hli ht the otential of
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Environmental levels
Arsenic is a natural component of the earths crust, and found
in all environmental media. Concentrations in air in remote
locations range from < 1 to 3 ng/m3, but concentrations in
cities may range up to 100 ng/m3. Concentrations in water
are usually < 10 g/litre, although higher concentrations can
occur near natural mineral deposits or anthropogenicsources. Natural levels in soils usually range from 1 to 40
mg/kg, but pesticide application or waste disposal can
produce much higher values
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Levels of arsenic in ambient air are summarized in Examples
are given of mean total arsenic concentrations in remote and
rural areas ranging from 0.02 to 4 ng/m3. Levels of arsenic in
outdoor air near to urban and industrial sources are
summarized in . Examples are given of mean total arsenicconcentrations in urban areas ranging from 3 to 200 ng/m3;
much higher concentrations (> 1000 ng/m3) have been
measured in the vicinity of industrial sources. Arsenic in
ambient air is usually a mixture of arsenite and arsenate, withorganic species being of negligible importance except in areas
of substantial methylated arsenic pesticide application or biotic
activity. Schroeder et al. (1987) reviewed worldwide arsenic
concentrations associated with particulate matter.
1 -Air
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They identified arsenic levels ranging from 0.007 to 1.9
ng/m3for remote areas, 1 to 28 ng/m3for rural areas and 2 to
2320 ng/m3
in urban areas. The highest arsenic levelsdetected in the atmosphere were near non-ferrous-metal
smelters.
Typical background levels for arsenic are now 0.21.5 ng/m3
for rural areas, 0.53 ng/m3for urban areas and < 50 ng/m3
for industrial sites (DG Environment, 2000).
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Environmental effects of arsenic
The arsenic cycle has broadened as a consequence of human
interference and due to this, large amounts of arsenic end up inthe environment and in living organisms. Arsenic is mainly emitted
by the copper producing industries, but also during lead and zinc
production and in agriculture. It cannot be destroyed once it has
entered the environment, so that the amounts that we add can
spread and cause health effects to humans and animals on many
locations on earth.
Plants absorb arsenic fairly easily, so that high-ranking
concentrations may be present in food. The concentrations of thedangerous inorganic arsenics that are currently present in surface
waters enhance the chances of alteration of genetic materials of
fish. This is mainly caused by accumulation of arsenic in the
bodies of plant-eating freshwater organisms. Birds eat the fish thatalread contain eminent amounts of arsenic and will die as a
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Risk evaluation
Conventional, generic risk assessment would apply uncertainty factors to
the lowest reported chronic effects concentration. For arsenic in freshwaters,
this would be 5 g/litre for growth in algae. This concentration is similar to
the upper limit of the natural range of arsenic concentrations in most surface
freshwaters. It is almost four orders of magnitude lower than the highest
natural concentrations of arsenic in geothermal regions. Since communities
of organisms occur in surface waters across the whole natural range (0.05
25 000 g/litre), a single protective concentration target for arsenic isinappropriate. Although there is no direct evidence that populations of
organisms living at the higher end of the range for most surface waters
(around 2 g/litre) are less sensitive to arsenic than those at the bottom end
of the range (0.05 g/litre), this might be inferred from laboratory and field
evidence. There is clear laboratory and field evidence that populations livingat much higher concentrations have adapted to high inorganic arsenic
levels. may mitigate arsenic toxicity in the environment. Realistically, risk
assessment for inorganic arsenic can only be done on a site-by-site basis
taking into account background arsenic concentrations, local population
tolerance and other local mitigating factors
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For populations of organisms living in low inorganic arsenic
environments with little possible mitigation (e.g. low
phosphate levels), a concentration of around 5 g/litre would
be protective of all but the most sensitive algae. Adapted
populations at high natural inorganic arsenic concentrations
will be specialized communities, possibly of lower biodiversity
but probably of high conservation interest. Areas polluted by
anthropogenic activity, therefore, present the risk managerwith different options based on both practicability and
desirability of remediation; if adapted communities have
developed over time, these might be destroyed by
remediation. Clearly the contamination of pristine areas witharsenic to levels which cause adaptation and decreased
biodiversity is unacceptable.
What are the Potential Health Effects?
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What are the Potential Health Effects?
The primary health concern with
exposure to arsenic is cancer. Exposure
to arsenic over many years can increaseyour chances of getting certain types of
cancer, or other health effects, such as
diarrhea, poor blood production, and
abnormal heart beat. The healthoutcomes depend on the length of time
that you are exposed to arsenic from
any source, the amount of arsenic in
your water, the amount of water that youdrink, and your current level of health.
The risk of developing health effects are
the same for everyone, including
children re nant women and other
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Effects on human health
Cancer Melanosis
Hyperkeratosis
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Summary of Method
The ICPMS methods have been described previously in Faires
(1993) and Garbarino and Taylor (1994). The following sections
only provide additional information specific to the elements thatare
being added to the method.
Former methods and ICPMS method detection limits and
calibration limits for new elements determined in filtered,acidified natural water
[All concentrations are in micrograms per liter; MRL, minimum
reporting level; MDL, method detection limit; CC, catalyzed
colorimetry; DCPAES, direct current plasmaatomic emissionspectrometry; FAAS, flameatomic absorption
spectrophotometry; GFAAS, stabilized temperature graphite
furnaceatomic absorption
spectrophotometry; HGAAS, hydride generationatomic
absorption spectrophotometry; ICPAES, inductively coupled
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Accuracy of inductively coupled plasmamass
spectrometric arsenic determinations in the presenceof bromide using different correction equations. The
error bars correspond to one standard deviation based
on three instrumental measurements.
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Sample Preparation
Filtered, acidified natural-water samples analyzed by ICP
MS for dissolve arsenic, boron, lithium, selenium,
strontium, thallium, and zinc and other elements do not
require additionalprocessing.
.
Analytical Procedure
Refer to Perkin-Elmer (1997a, 1997b) and NWQL
Standard Operating Procedure IM0011.1 (T.M. Struzeski,
U.S. Geological
Survey, written commun., 1998) for details of
the analytical procedure. In addition, the accuracy of
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Statistical analysis of long-term ICPMS
results for U.S. Geological Survey Standard
Reference Water Sample T145 [ICPMS,inductively coupled plasmamass
spectrometry; elemental results are in
micrograms per liter; MPV, the most probablevalue; , the plus or minus symbol precedes
the F-pseudosigma in the MPV
column and the standard deviation in the
experimental mean column; n, number ofreplicates used to calculate the experimental
mean; p-value, level of significance;
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Short-term analytical variability as a function of elemental
concentration for ICPMS [ICPMS, inductively coupled
plasmamass spectrometry, the percent relative standarddeviations are based on three sequential determinations in
a 0.4-percent solution of concentrated nitric acid in
deionized water; g/L, micrograms per liter;
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Average percent spike recoveries in reagent-
water, surface-water and ground-water matrices
by inductively coupled plasmamassspectrometry [mg/L, micrograms per liter; number
following the plus or minus symbol () is the
standard deviation on the basis of sevendeterminations accrued on separate days; high
spike, 75 mg/L for all elements; na, not applicable
because the difference between the spike
concentration and ambient concentration wasgreater than a factor of 10;
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