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Environmental fate & pathways

Bioaccumulation: aquatic / sediment

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Description of key information

Key value for chemical safety assessment

BCF (aquatic species):
27 dimensionless

Additional information

The BCF of a commercial naphthenic acids sample was measured in rainbow trout by Young et al. (2008). The BCF of 2 L/kg wet-wt based, was measured for one C-13 component of the naphthenic acids. The Japanese METI-NITI database reports a measured range of BCF values between 1.6 and 27 (wet-wt based) for sodium naphthenate, with one, two and three cycles. The available data suggest low or no bioaccumulation potential. A range of 3.162 to 56.23 L/kg wet-wt for the BCF was obtained using the EPISuite modelling tool.

For further details, see IUCLID section 5.3.1.

Bioaccumulation is not considered relevant for essential elements such as Zn 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). 

In experimental work, high BCF factors are observed at the lowest zinc exposure levels, due to the fact that organisms will concentrate zinc to satisfy internal physiological needs for the essential element. For the same reason of homeostasis, the BCF will strongly decrease when exposure concentrations increase. This results in a general negative relationship between BCF and exposure (McGeer et al 2003).

On bioaccumulation, the EU risk assessment report (ECB 2008) concludes that “it is concluded that secondary poisoning is considered to be not relevant in the effect assessment of zinc. Major decision points for this conclusion are the following. The accumulation of zinc, an essential element, is regulated in animals of several taxonomic groups, for example in molluscs, crustaceans, fish and mammals. In mammals, one of the two target species for secondary poisoning, both the absorption of zinc from the diet and the excretion of zinc, are regulated. This allows mammals, within certain limits, to maintain their total body zinc level (whole body homeostasis) and to maintain physiologically required levels of zinc in their various tissues, both at low and high dietary zinc intakes. The results of field studies, in which relatively small differences were found in the zinc levels of small mammals from control and polluted sites, are in accordance with the homeostatic mechanism. These data indicate that the bioaccumulation potential of zinc in both herbivorous and carnivorous mammals will be low.”