Geology Reference
In-Depth Information
218
III. Introduction to Water Resources and Contamination
TABLE 14.1 Common Trace Elements and Their Maximum Limit (MCL or SMCL) in Drinking Water in the United States
MCL
1
(mg/L)
SMCL
2
(mg/L)
Trace Element
Trace Element
Arsenic
0.01
Copper
1.0
Barium
2.0
Fluoride
2.0
Cadmium
0.005
Manganese
0.05
Chromium
0.1
Silver
0.1
Copper
1.3
3
Fluoride
4.0
Zinc
5.0
Lead
0.015
3
Selenium
0.05
Mercury (inorganic)
0.002
1.
MCL: Maximum contaminant level, National Primary Drinking Water Standards. These are maximum permissible levels set for contaminants that have
an adverse effect on human health.
2.
SMCL: Secondary maximum contaminant level, National Secondary Drinking Water standards. These are federally nonenforceable limits for contaminants
that affect aesthetic qualities such as taste and odor.
3.
Action level for treatment
other animals, and plants of some trace elements that
are present in commonly used or consumed products.
Humans require many trace elements, but in some
cases there is only a small range between requirement
and toxicity. For example, the lack of minute amounts
of copper in the diet causes nutritional anemia in
infants, but large concentrations may cause liver dam-
age. Another complicating factor is the chemical form
of the element. In one chemical state a trace element
may pass through the body with little or no harm, but
in another it may be absorbed to the point of toxicity.
An example of this phenomenon is mercury; metallic
mercury is generally harmless but methyl mercury is
highly toxic.
In the past three decades there have been numer-
ous trace element studies. In general, these show that
although most of the trace elements occur in barely
detectable concentrations in water, they may appear in
streamside or riverbed deposits in concentrations that
are two or three orders of magnitude (100 to 1,000
times) greater. Plants receiving their nutrients from the
sediment may contain trace element concentrations
that are several hundred or even several thousand
parts per million (ppm) more than the sediment.
Apparently, many trace elements are barely detectable
in water because they become attached to fine-grained
sediments, which are subsequently deposited. These
elements may then be removed and concentrated by
plants and mud- or bottom-feeding organisms.
Anomalous concentrations of trace elements may
be due to many natural or artificial causes. Contaminated
sediments may arise from industrial and municipal
point sources, run-off from farming and construction,
dumping on shore or at sea, accidental spills onshore
or at sea, leaching from waste disposal sites, and
atmospheric loading.
Arsenic
poisoning leading to
sickness and death among cattle in New Zealand was
attributed to drmking arsenic-rich water of natural ori-
gin. The Kansas River once contained local arsenic
concentrations that approached the recommended
limit set by the U.S. Public Health Service. The source
of arsenic in this case was municipal treatment plant
and septic tank effluent, which contained arsenic orig-
inating as an impurity in presoaks and household
detergents.
Near major highways in British Columbia, south-
ern England, Finland, and the United States, cereals
and vegetables once contained 4 to 20 times the nor-
mal amount of
lead.
These high concentrations were
mainly the result of air and soil pollution by the emis-
sion of lead-containing automobile exhaust. Lead was
added to gasoline to improve the octane rating but its
use for this purpose is now generally prohibited.
Mining and metal-producing activities are also
major causes of trace-element contamination. Along
the upper reaches of the Jintsu River Basin in Japan,
milling wastes from a mine producing lead, zinc, and
cadmium
were dumped untreated into the river. Down-
stream the contaminated water was used by farmers
for cooking, drinking, and irrigation of rice fields.
Eventually, many people in the basin began to suffer
from an unknown but very painful, sometimes fatal,
disease. Some years later, samples of river water, soil,
and rice were examined; water generally contained
less than 1 ppm of cadmium and less than 50 ppm of
zinc.
Soil samples from the irrigated rice fields con-
tained as much as 620 ppm of cadmium and 62,000
ppm of zinc. These metals accumulated to even higher
concentrations in the contaminated rice. Apparently,
ingestion of the cadmium-contaminated rice by the
local farmers had caused this debilitating bone disease
known as itai-itai or osteomalacia.
