Ecotoxicology is more developed for aquatic ecosystems than for soil. Methods of testing aquatic invertebrates, fish, and algae were developed more than 30 years ago and large toxicity database is available for aquatic ecosystem. Recently, database for soil has also grown. A major complicating factor in soil ecotoxiclogy is that most of the polluting substances are bound to the soil particle; thus, bioavailable fraction of the free or unbound toxic substance is much smaller. In soil one has to deal with three compartments (soil, pore water, and organisms) compared to just two (water and organisms) in aquatic ecosystems. Additionally in soil ecotoxicology studies, factors such as soil chemistry (sorption to soil, partitioning, and specia-tion) have to be taken into consideration. Bioavailability and soil chemistry are the principal factors determining changes in toxicity and biodegradation rates.
In ecological risk assessment, acceptable risk of substances in the environment has to be defined first. This is done simply by exposing organisms to series of concentrations and effects are measured at each concentration. The concentration corresponding to the maximum acceptable effect is then estimated from the results. This may be expressed as, for example, EC10 (or 10% effect concentration). However, in soil assessment, due to many site-specific modifying factors the maximum risk standards may not be applicable. Thus, site-specific estimate of risk is needed in soil treatment decisions.
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