| Summary: | There is growing concern about the need for unified criteria on bioindicators used to evaluate the impacts
of mine effluents or accidental spills. Toxicological tests based on lethal concentrations (e.g. LC50) have
been extensively used to assess effluents, although the biological impact of mining activities cannot
always be attributed to acute lethality alone. Geochemical methods, such as sequential or selective
chemical extraction, have also been widely used to provide indirect evidence of the availability of metals
to organisms. However, the relationship between geochemical parameters, metal uptake, and biological
effects is frequently not clear due to complicating interactions between variables. In order to
comprehensively characterize risks from mining related discharges, concerns with existing, commonly
employed methodologies must be resolved and protocols to assess the effects of sub-lethal or chronic
exposure must be established.
This paper reviews current understanding of bioaccumulation and bioavailability of heavy metals
associated with mining effluents and it explores the concept of the bioaccumulation factor (BAF) and its
applicability to mining impacted sites. Existing protocols for assessment of mining related discharges are
also compared and a simple, low-cost methodology using earthworms for the evaluation of metal
bioavailability in tailings and effluents is proposed. Earthworms are particularly suitable for the
assessment of contaminant bioavailability as they are proven metal accumulators and are in full contact
with the substrate they consume. As well, they are well studied, easily bred and participate in many food
chains and, unlike fish, can be used to assess a variety of media.
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