Biological assessment methods sediments

Ecotoxicity can only be measured by the application of biological methods, whereas chemical analysis determines concentrations of defined chemicals that may be used to deduce toxic effects. All concentration levels such as screening values, guideline values, threshold concentrations, benchmark concentrations and trigger values used for the assessment of contaminated media (water, soil, sediments, etc.) should ideally be derived from the observation of biological effects. Comparing pollutant concentrations with these usually conservative standard values is a common practice in the preliminary assessment of contaminated sites. The integration of further information, such as ecotoxicity data from the site, can improve the risk assessment process and enable a more reliable prediction of environmental threats. 

Not aU the available methods extract the mercury species from solid samples (soil, sediment or biological material) with acceptable efficiency. The procedure giving the best recovery for methyl mercury from soil (95 4%) is the distillation method, and from fish tissue it is alkaline digestion using tetramethylammonium hydroxide with focused microwave power (95 to 105%). There is no standardized method to assess the extraction efficiency of a particular method, but several options are described in the subchapter on extraction efficiencies. 

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