Author(s): PS R ainbow
In assessing the distributions of trace metals in aquatic environments as a prerequisite to any study of the variation of local toxic metal contamination over space and time, it is tempting to measure dissolved and/or sediment concentrations. A third and preferred alternative, however, is the measurement of accumulated trace metal concentrations in selected organisms, termed biomonitors. Such concentrations are high enough to be easily measured without significant risk of contamination. Most significantly, the accumulated concentrations are time-integrated relative measures of the amounts of metal that have been taken up into the organism via all uptake routes, by definition the bioavailable metal - the ecologically significant ambient metal in a habitat given its potential for ecotoxicological effects. To be selected as a biomonitor, an aquatic organism must fulfil several characteristics, and importantly we need an understanding of its accumulation kinetics for a particular metal, as might be described for example by biodynamic modelling. It is preferable to use a suite of biomonitors to investigate the several possible metal sources (solution, suspended material, newly deposited or older sedimented material, etc.) in an aquatic habitat. The choice of this suite should ideally include cosmopolitan biomonitors for which a database of accumulated metal concentrations has been compiled, therefore allowing the identification of trace metal availabilities considered high on an international scale. A major caveat is the need to avoid interspecific comparisons of accumulated metal concentrations, given the wide variation in accumulation patterns between even relatively closely related taxa. Case studies are used to illustrate the principles of the biomonitoring of trace metals in estuarine and marine environments. Threshold accumulated trace metal concentrations in key biomonitors have the potential to be used as simple measures identifying the presence of ecotoxicologically significant trace metal pollution in a coastal habitat.