Bioaccumulation and toxicity of metals is influenced by physical and chemical factors and is dependent on the speciation of the metal. Bioavailability of metals can be affected by sediment characteristics such aspH, redoxpotential, organic content and the presence of acid volatile sulfides (Di Toro, 1992). In many cases, it is the free ion that is responsible for accumulation (Zamuda and Sunda, 1982). The salinity of the water is a critical factor, and generally uptake is inversely proportional to salinity. This may also relate to the amount of free ion available (Sunda, Engel, and Thuotte, 1978). Dissolved organic matter may bind metals and make them less bioavailable (Zamuda and Sunda, 1982). Organisms in areas with higher dissolved organic matter will have relatively less bioaccumulation. Organisms also derive their metal body burden from food, and organisms at higher trophic levels derive a greater amount of their body burden from food than from water.
Despite elevated levels of some metals in sediments, bioaccumulation does not always occur in fish from even the most contaminated areas in the estuary. Fish from Berry's Creek (a Hg Superfund site) and the nearby Passaic River had mean body burdens of Hg that were well below 1 |g g -1, the U.S. Food and Drug Administration (FDA) action level (Santoro andKoepp, 1986). However, the mean level alone does not demonstrate that individual specimens of striped bass Morone saxatilis, American eel Anguilla rostrata and sun-fish Lepomis sp. from these sites had 1-2 |g g-1 Hg. Bioavailability of Hg in Berry's Creek was low, probably in part because Hg in the Creek is not methylated perhaps due to the high sulfur levels in the sediments that inhibit methylation by bacteria (Bermanand Bartha, 1986).
In contrast, organisms in Foundry Cove, a Superfund site off the main stem HR with Cd levels in the sediments of up to 10,000 |g g-1 did bioaccumulate Cd. Analysis of Cd in the mac-robenthos in Foundry Cove indicated that Cd was bioavailable and accumulated in striped killifish
Fundulus diaphanus and cattails Typha angus-tifolia (Hazenand Kneip, 1980). Consumption of contaminated blue crabs Callinectes sapidus, appeared to be a potential source of Cd exposure to humans (Kneip and Hazen, 1979).
Many have noted, however, that populations from contaminated sites tend to accumulate proportionately lower amounts of metals in relation to sediment levels than populations from cleaner sites (Khan, Weis, and D'Andrea, 1989; Khan and Weis, 1993a). This may be due to enhanced excretion or reduced uptake, either of which can result in enhanced tolerance in organisms from polluted environments (Foster, 1977).
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