The clearwater consensus: the estimation of metal hazard in fresh water

Background, aim, and scope Task Force 3 of the UNEP/SETAC Life Cycle Initiative has been working towards developing scientifically sound methods for quantifying impacts of substances released into the environment. The Clearwater Consensus follows from the Lausanne (Jolliet et al. Int J Life Cycle Assess 11:209–212, 2006) and Apeldoorn (Apeldoorn Int J Life Cycle Assess 9(5):334, 2004) statements by recommending an approach to and identifying further research for quantifying comparative toxicity potentials (CTPs) for ecotoxicological impacts to freshwater receptors from nonferrous metals. The Clearwater Consensus describes stages and considerations for calculating CTPs that address inconsistencies in assumptions and approaches for organic substances and nonferrous metals by focusing on quantifying the bioavailable fraction of a substance. Methods A group of specialists in Life Cycle Assessment, Life Cycle Impact Assessment, metal chemistry, and ecotoxicology met to review advances in research on which to base a consensus on recommended methods to calculate CTPs for metals. Conclusions and recommendations Consensus was reached on introducing a bioavailability factor (BF) into calculating CTPs where the BF quantifies the fraction of total dissolved chemical that is truly dissolved, assuming that the latter is equivalent to the bioavailable fraction. This approach necessitates calculating the effects factor, based on a HC50EC50, according to the bioavailable fraction of chemical. The Consensus recommended deriving the BF using a geochemical model, specifically WHAM VI. Consensus was also reached on the need to incorporate into fate calculations the speciation, size fractions, and dissolution rates of metal complexes for the fate factor calculation. Consideration was given to the characteristics of the evaluative environment defined by the multimedia model, which is necessary because of the dependence of metal bioavailability on water chemistry.