A Review of Mercury in the Aquatic Environment: Mercury in FIsh

Defense Date

1998

Document Type

Capstone

Degree Name

M.S. Coastal Zone Management

First Advisor

Curtis Burney

Second Advisor

Richard E. Spieler

Abstract

The behavior of mercury in aquatic ecosystems has undergone much study in the past thirty years. It is continually cycling through natural systems. Mercury performs no known beneficial function in human metabolic pathways (Eisler, 1987). Mercury's compounds are toxic to humans. It is a neurotoxin capable of causing fetal brain damage, birth defects, tremors, emotional disturbances, and death (Driscoll et al. 1994). Human exposure to mercury comes most often through fish and shell fish (Driscoll et al. 1994, Eisler, 1987).

In aquatic ecosystems mono-methyl mercury (MeHg) is the form of mercury that is of the most concern. This is the form that accumulates in aquatic organisms. MeHg is usually associated with protein sulfhydryl groups in fish muscle (Driscoll et al. 1994; Mason et al. 1995). MeHg is also more soluble in lipids than most other mercury species (Driscoll et al. 1994).

Recent investigations have focused on the mercury burden of relatively pristine northern lakes. It is now believed, that in the absence of a nearby anthropogenic source, mercury enters these lakes from atmospheric dryfall and precipitation.

Mercury is the seventh metal of antiquity. It has been in use for more than 3500 years. Applications have ranged from its early use in religious rites, cosmetics, uses in medicine and aphrodisiacs, and for decorative uses; to modern uses in thermometers and barometers, florescent lights, batteries, antifungal preparations for preserving seeds for agricultural use, and as a catalyst in the chlor-alkali industry (Nriagu, 1979).

The first recorded fatal case of mercury poisoning was from a chemical factory in England in 1865 (Eisler, 1987). Incidents of mercury poisoning have been reported from dermal applications and respiratory contact. There is little evidence that fillings in people's teeth release mercury vapor in sufficient quantity that may adversely affect health. However, pregnant women exposed to mercury in the work Place, such as dental workers, may be at risk. As are people who eat more than 30 pound of fish per year. The most famous incidents of mercury poisoning occurred in Japan, in Minamata Bay and the Niigata River where industrial effluent contaminated fish, the main component of the diet there (Harte et al. 1991). Bird poisonings or kills, of both terrestrial and aquatic birds have also occurred (Eisler, 1987).

Mercury ecotoxicologists agree on six points. 1) Mercury has no known beneficial biological function, and its presence in living organisms is potentially hazardous. 2) Forms of mercury that have a relatively low toxicity can be biologically or abiologically transformed into forms that are highly toxic. 3) MeHg can be accumulated and amplified in food chains. 4) Mercury is a mutagen, teratogen, and carcinogen, and can cause embryocidal, cytochemical, and histopathological effects. 5) The complexity of the mercury cycle is demonstrated by the high concentrations of mercury in fish and wildlife from remote locations. 6) Anthropogenic use of mercury must be reduced or curtailed, because the difference between natural background levels and the level of mercury in the environment at which harmful effects can occur is very slight (Eisler, 1987).

The understanding of the behavior of mercury in the environment has increased in recent years. This has lead to the development of environmental sampling techniques using specialized protocols. There is reduced confidence in aqueous sample results taken before 1985 (Driscoll et al. 1994).

A detailed study of mercury speciation in the aquatic environment is difficult, because of the number of combinations in which mercury is able to engage. This is based mainly on the stability of mercury’s three valence states, Hg0 (elemental), Hg( I) (mercurous), and Hg(II) (mercuric) (Nriagu, 1979). It is not the purpose of this paper to present a complete, in depth, discussion of the chemistry of mercury in the aquatic environment. However, a brief discussion is presented to provide the reader with a description of what may be important factors influencing the mobility of mercury in the aquatic environment that may ultimately impact mercury accumulation in fish.

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