The role of bioassays in soil testing

Depending on the type and extent of data available from historical investigations or chemical analysis, different information may be obtained from bioassay applications (Fig. 10.3). 

Pollution unknown or information limited. If no data are accessible on the presence of pollution, bioassays may be used for toxicity screening in order to identify polluted samples. Moreover, if only insufficient data from chemical analysis are available, bioassays may identify samples that require further analysis (presence of undetected or unknown toxicants). Although bioassays respond to a wide range of toxicants, success in identification of contaminated samples may be reduced if false negative results are achieved (see below). 

Complete information on pollution available. If all contaminants present in the sample have been analysed using conventional physical or chemical methods, the application of bioassays provides further information e.g. on toxicity interactions and bioavailability. It has to be emphasised that for multiple contamination, bioassays reveal an overall combined toxicity response to the bioavailable part of each contaminant present in the mixture. The identification of the bioavailable fraction of a particular substance by relating the measured effect to the measured concentration of the chemical is only possible for a single substance contamination (only one toxic chemical present). Although it may be tempting for risk assessors, the response of multiple pollution cannot be used to calculate the bioavailable fraction (percentage of the total concentration of a compound) of a particular chemical from the mixture, unless toxicant 

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