Mercury

Endpoint summary

Additional information

The bioaccumulation of inorganic mercury in biota is generally regarded to be of low relevance compared to that of organic forms of mercury and particularly methylmercury (SCHER, 2007). Therefore, in line with the recommendation of the CSTEE, it was suggested in the WFD to base the assessment for secondary poisoning of top predators on methyl mercury. (The WFD “Mercury and his compounds” 2005) Although there are several models describing the bioaccumulation and biomagnification potential of mercury in different ecosystems, the variability – in terms of both the methylation potential and the overall biomagnification – is so high that no sound generic estimations can be done with the current level of knowledge.

Indeed, considerable uncertainty exists with regard to the bioconcentration and biomagnification of mercury. Whereas the reported BCFs measured in laboratory studies for inorganic and organic mercury are highly variable, there is no quantitative information on biomagnification along the food chain available (e.g. BMFs). BAF values span around 4 orders of magnitude – from a geometric mean of 21,700 used by RIVM to calculate MPAs for the Netherlands up to 79,000,000 reported by Horvat et al. (2003) for sharks as top predators in the marine environment. The US-EPA stresses that within an individual trophic level BAFs generally ranged up to two orders of magnitude due to various site specific biotic and abiotic factors. In fact, the conclusion presented by the European Commission within the process of setting EQSs for mercury under the WFD was that “Due to the different site specific factors driving bioaccumulation of mercury in aquatic food webs, it seems on the basis of the current knowledge not appropriate to derive a general QSsecpois, water. For the time being the QS for methylmercury has been set for the concentration in biota only: QS_{biota, sec.pois.}= 22 µg/kg. An in depth assessment of the uncertainties associated with the bioaccumulation potential of (inorganic and organic) mercury and its toxicity to predators is required in order to derive more reliable quality standards depending on site specific factors.” Recently, the existing environmental quality standard for mercury and its compounds has been re-evaluated.  “The revision of environmental quality standard for mercury: status and critical points” report published in 2010 reiterates the issues associated with assessing secondary poisoning for mercury and suggests some possible ways forward but no decision has been taken yet by the member states.

 

In light of the remaining uncertainty and the ongoing scientific discussions at the WFD level it is currently deemed inappropriate to proceed with this assessment based on the current knowledge.