Mechanisms of heavy metal accumulation and toxicity in fish

Abstract

INTRODUCTIONAs a result of mining, forestry, waste disposal and fuel combustion, our environment is becoming increasingly contaminated with heavy metals. The aquatic environment receives waste products from such activities and may be the final depository for these anthropogenic ally remobilized heavy metals. In order to understand the impact of heavy metals on aquatic biota it is important to characterize the mechanisms available for aquatic life to transport, immobilize and excrete heavy metals.Relatively little is known about the specific mechanisms of uptake of metals in cells of non-mammalian vertebrates. This chapter attempts to assemble available information on fish. In general, metals absorbed across the gills or the intestinal wall are distributed via the circulation, bound to transport proteins, to different tissues of the body. Within the tissues metals can participate in the essential life functions, but can also exert toxic actions, or be detoxified by binding to the protein, metallothionein (MT). The intracellular levels of essential metal are regulated by transporters (which translocate metals across the plasma membrane) as well as by MT and other metal-binding proteins. Metals themselves cannot be metabolized (using the strict definition of the term) and can only be eliminated from the body by excretion.Metals that enter the body will react with different components of the cell (Chapter 1). The heavy metals are soft donors and will therefore readily bind to soft acceptors, such as sulfhydryl-groups. MT is a low molecular weight cytosolic, cysteine-rich protein that binds group lB and 2B heavy metals (Olsson and Raux, 1985). Within the cells of the body, MT is the major heavy metal-binding protein (Dunn et ai., 1987). Environmental exposure of fish to heavy metals has been shown to result in primarily renal and hepatic accu-

Determination of Heavy Metals in Freshwater Fishes of the Tigris River in Baghdad

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Localization of Inorganic and Organic Mercury in the Liver and Kidney of Cyprinus carpio by Autometallography

“…According to Alvarado et al (2005), lysosomal metal sequestering is considered a general strategy for reducing metal toxicity. Then, methyl mercury deposits in the cytoplasm of liver and kidney cells of C. carpio corroborate data of others authors (Olsson et al, 1998;Baatrup & Danscher 1987). …”

Trace element concentrations in the apex predator swordfish (Xiphias gladius) from a Mediterranean fishery and risk assessment for consumers

“…Trace elements accumulation in fish is dependent on numerous factors, and the accumulation pattern is the result of physiological uptake and elimination rates (Guven et al, 1999). Absorption of these elements may occur directly from the water, through the gills, but the main route seems to be the gastrointestinal absorption of those elements present in food (Olsson et al, 1998). Furthermore, because these species are apex predators, they carry out very intense metabolic activities that require a continuous supply of energy (Kojadinovic et al, 2007).…”