September 30, 2011 by Adam Peters
I recently contributed to a workshop organised by the OECD which was aimed at raising awareness of the various approaches that have been developed (mostly in Europe and North America) for performing hazard assessments for metals. The workshop covered a broad variety of issues such as how to deal with the very large datasets that are available for some metals, ensuring that data are both reliable and relevant to the assessment, combining data from multiple tests where appropriate, and normalising for bioavailability. The information presented was focused on the European assessments made under the Existing Substance Regulations (ESR) and, more recently, REACH. Although there were also presentations made on the approaches taken in both the US and Canada, and the development of the first EQS to be applied in Japan. The Metals Environmental Risk Assessment Guidance (MERAG) which was developed by the ICMM in collaboration with DEFRA also follows the same assessment principles.
Bioavailability was an important topic at the meeting, and issues such as whether or not a bioavailability correction should always be preferred, and if so how it should be implemented were discussed. Whilst there may have been the suggestion in the past that bioavailability is important for the assessment of all metals, a few examples were provided where bioavailability was either not important, was driven by factors other than those usually considered to be dominant, or where bioavailability correction was considered possible but not necessary due to low expected risks. The degree of complexity of different bioavailability models was discussed, as these may vary from simplistic corrections based on a single parameter to multiple models considering numerous parameters for different organisms. Ultimately, validation of which ever models are to be applied is likely to be the most important issue for the uptake of such methods by regulators
Bioaccumulation was another key area of discussion, although there was rather less consensus on how this should generally be addressed. Whilst metals can bioaccumulate in some cases this is due to biological requirements for them as micronutirents, although there are some cases where their accumulation can lead to problems. An important issue is the difference between the bioaccumulation of metals and organic compounds, and the use of bioaccumulation as an indicator of potential chronic toxicity in organic chemicals. It was also noted that whilst bioavailability is commonly considered to be critically important in assessing ecotoxicity it is rarely considered in assessments of bioaccumulation, although there is evidence to suggest that the bioavailability does affect bioaccumulation of metals.