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Environmental fate & pathways

Bioaccumulation: aquatic / sediment

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bioconcentration/bioaccumulation is not considered relevant.

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Bioaccumulation is not considered relevant for essential elements because of the general presence of homeostatic control mechanisms.

McGeer et al (2003) recently extensively the reviewed evidence on bioconcentration and bioaccumulation of zinc as a function of exposure concentration in a number of taxonomic groups (algae, molluscs, arthropods, annelids, salmonid fish, cyprinid fish, and other fish). The data clearly illustrated that internal zinc content is well regulated. All eight species taxonomic groups investigated exhibited very slight increases in whole body concentration over a dramatic increase in exposure concentration. In fact, most species did not show significant increases in zinc accumulation when exposure levels increased, even when exposure concentrations reached those that would be predicted to cause chronic effects. This suggests that adverse effects related to Zn exposure are independent of whole body accumulation. Due to the general lack of increased whole body and tissue concentrations at higher exposure levels, the zinc BCF data showed an inverse relationship to exposure concentrations. In all cases, the relationship of BCF to exposure was significant and negative. The slopes of the BCF/BAF – exposure relations were: algae: -1.0, insects: -0.79, arthropods: -0.73, molluscs: -0.83, salmonids: -0.92, Centrarchids: -0.80, Killifish: -0.84, other fish: -0.87. Overall, species mean slope was -0.85 +/- 0.03 (McGeer et al 2003).

The physiological basis for the inverse relationship of BCF to zinc exposure concentration arises from Zn uptake and control mechanisms. At low environmental zinc levels, organisms are able to sequester and retain Zn in tissues for essential functions. When Zn exposure is more elevated, aquatic organisms are able to control uptake. There is clear evidence that many species actively regulate their body Zn concentrations, including crustaceae, oligochaetes, mussels, gastropods, fish, amphipods, chironomids by different mechanisms (McGeer et al 2003), which is the same case for copper.