Accurate predictions of toxicity due to soil contamination can only be made if information is available on the biological effects of contaminants. This information may come from a variety of sources, including data from toxicity tests or bioassays. Because plants and animals are constantly exposed to the effects of various stressors, these communities reflect not only current conditions, but also stresses and changes in conditions over time and their cumulative impacts. Biological tests detect the potential for harmful effects on organisms before those effects occur. By identifying specific molecular, biochemical, physiological and behavioural changes in populations of animals and plants following contaminant exposure, biological tests may provide and early warning of impending ecological change. The use of a suite of biological techniques increases the chances of identifying the presence of a potential (contaminant) stress and in then diagnosing the significance of that stress for soil organisms living in the affected patch.
The use of biological techniques offers a number of potential advantages that complement chemical analysis. These include:
Taken together these advantages present an overwhelming case for the inclusion of biological tools within any soil quality risk assessment (Spurgeon et al., 2002).
Biological tests should be used selectively to exploit their strengths and to complement conventional chemical-specific techniques. Biological tests may include the use of ecotoxicity tests or biosensors in the laboratory or in situ. Biological assessment can be undertaken at varying levels of biological organisation, including ecological function or structure, where effects may be assessed at the sub-cellular level, through effects on individual species, up to effects at the population, community or ecosystem levels.
The use of biological tests in Ecological Risk Assessment is attracting research interest. The outputs of a series of recent European and UK research programmes have now made it possible to envisage the use of a suite of biological assessment tools in temporal and spatial surveys of chemical effects on soil quality.
Selection of test species should take into consideration the possible routes of exposure, and it is preferable to stimulate, as far as possible, the route of exposure that is actually encountered in the field. A range of trophic levels from the soil biota should be included in any testing programme: higher plants, herbivores, predators, parasites and decomposers (including micro- and mesofauna and microflora) (Løkke and Van Gestel, 1998).
Author Danielle Ashton, Environment Agency UK
Handbook of Soil Invertebrate Toxicity Tests Eds Hand Løkke and Cornelis A.M. Van Gestel. John Wiley & Sons (1998).
Spurgeon, D., Svendsen, C., Hankard, P., Weeks, J., Kille, P., & Fishwick, S. Review of sublethal ecotoxicological tests for measuring harm in terrestrial ecosystems. R&D Technical Report P5-063/TR1, Environment Agency, Bristol, 2002.