7088

• UCREFRP Catalog Number: 7088
• Author: Eisler, R.
• Title: Mercury Hazards to Fish, Wildlife, and Invertebrates
• USFW Year: 1987.
• USFW - Doc Type: A Synoptic Review.
• Copyright Material: NO

(dietary) for birds; and from 100 to 500 ug/kg body weight (daily dose) and
1,000 to 5,000 ug/kg diet for mammals. Organomercury compounds, especially
methylmercury, are always more toxic than inorganic Hg compounds. Numerous
biological and abiotic factors modify the toxicity of Hg compounds--sometimes
by an order of magnitude or more--but the mechanisms of action are not clear.
Significant adverse sublethal effects were observed among selected aquatic
species at water concentrations of 0.03 to 0.1 ug Hg/1. For some birds,
adverse effects--predominantly on reproduction--have been associated with
total Hg concentrations (in ug/kg fresh weight) of 5,000 in feather, 900 in
egg, and 50 to 100 in diet; and with daily intakes of 640 ug/kg body weight.
Sensitive nonhuman mammals showed significant adverse effects of Hg when daily
intakes were 250 ug/kg body weight, when dietary levels were 1,100 ug/kg, or
when tissue concentrations exceeded 1,100 ug/kg.
The most recent mercury criteria proposed by the U.S. Environmental
Protection Agency for protection of freshwater aquatic life are 0.012 ug/l
medium (4-day average), not to exceed 2.4 ug/l on an hourly average; however,
these criteria offer only limited protection to freshwater ecosystems. The
saltwater criteria of 0.025 ug Hg/l medium (4-day average), not to exceed 2.1
ug/1 hourly, are unsatisfactory for the protection of marine life. For the
protection of sensitive species of mammals and birds that regularly consume
fish and other aquatic organisms, total Hg concentrations in these prey items
should probably not exceed 100 ug/kg fresh weight for birds, and 1,100 ug/kg
for small mammals. The significance of elevated Hg levels in tissues of fish
and wildlife is not fully understood; some species of marine pinnipeds, for
example, normally contain high concentrations of Hg in various tissues without
apparent adverse effects. Usually, however, concentrations in excess of 1,100
ug/kg fresh weight of tissue (liver, kidney, blood, brain, hair) should be
considered as presumptive evidence of an environmental mercury problem.
Four courses of action now seem warranted. First, toxic mercurials in
agriculture and industry should be replaced by less toxic substitutes.
Second, controls should be applied at the point of origin to prevent the
discharge of potentially harmful Hg wastes. Third, continued periodic
monitoring of Hg in fish and wildlife is needed for identification of
potential problem areas, and for evaluation of ongoing mercury curtailment
programs. And fourth, additional research is merited on mechanisms of mercury
accumulation and detoxication in comparatively pristine ecosystems.
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