Molluscs, bioconcentration factors

In aquatic environments, waterborne lead was the most toxic form. Adverse effects were noted on daphnid reproduction at 1.0 pg Pb+2/L, on rainbow trout survival at 3.5 pg tetraethyllead/L, and on growth of marine algae at 5.1 pg Pb+2/L. High bioconcentration factors were recorded for filter-feeding bivalve molluscs and freshwater algae at 5.0 pg Pb+2/L. 

Bioconcentration of DEHP has been observed in invertebrates, fish, and terrestrial organisms. Mean bioconcentration factors (BCFs) have been reported for algae (3,173 3,149, two species), molluscs (1,469 949, five species), Crustacea (1,164 1,182, four species), insects (1,058 772, three species), polychaetes (422, one species), fish (280 230, five species), and amphibians (605, one species) have been compiled by Staples et al. (1997). Residues of DEHP have been found in the organs of terrestrial animals such as rats, rabbits, dogs, cows, and humans (EPA 1979). However, accumulation of DEHP will be minimized by metabolism, and biomagnification of DEHP in the food chain is not expected to occur (EPA 1979 Johnson et al. 1977 Staples et al. 1997 Wofford et al. 1981). Several metabolites of DEHP might be detected in animal tissues (Johnson et al. 1977). Uptake of DEHP from soil by plants has also been reported (EPA 1986 O Connor 1996). 

The bioconcentration factor (BCF) of copper in fish obtained in field studies is 10-100, indicating a low potential for bioconcentration. The BCF is higher in molluscs (i.e., oysters), where it may reach 30 000, possibly because they are filter feeders. There is a good deal of evidence that there is no biomagnification of copper in the food chain. 

If released into the soil, isodrin may undergo microbial oxidation to endrin. The behavior of isodrin in soil may range from moderately mobile to immobile and isodrin is not expected to hydrolyze since it contains no hydrolysable functional groups. The soil half-life of isodrin has been estimated to be 0.5-1 year. It is absorbed by the roots of plants and is likely to be translocated to above ground parts of plants. If released into water, isodrin may bioconcentrate in aquatic organisms, adsorb onto suspended soils and sediments and undergo very slow microbial transformation. The bioconcentration factor of isodrin was found to be 4500 in molluscs. 

Analogous relationships between BCF and other descriptors, generally collinear with log have been derived such as water solubility (Metcalf et ai, 1973, 1975 Chiou et aL, 1977 Kenaga and Goring, 1980). The bioconcentration factors for Daphnia, molluscs, mussels, algae and microorganisms have also been related to log P or water solubility (Table 4.14). 

---