A test for determining the toxicity of contaminants in the environment is described, with a proposal that this test can be used to determine assimilative capacity for some contaminants. This test is based upon the observation that organisms have a measurable capacity to internally detoxify, and thereby safely assimilate, metal and organic contaminants. Toxic effects of contaminants appear to coincide with saturation of in vivo detoxification systems with metal or organic contaminants and appearance of these contaminants at intracellular sites of toxic action. A simple gel chromatography procedure has been devised to determine the intracellular partitioning of contaminants between an enzyme-containing (ENZ) pool which is a site of toxic action for both metals and organic compounds, a metallothionein-containing (MT) pool which is a site of detoxification for metals, and a glutathione-containing (GSH) pool which is a site of detoxification for organic compounds.

Several marine species including sea urchins, scorpion fish, croakers, and Dover sole were sampled from populations living near and away from a major California municipal wastewater outfall, and the partitioning of contaminants between intracellular pools was determined. Cadmium, copper, and zinc appeared to be successfully detoxified by the MT pool in all field-exposed organisms. Laboratory exposures were used to measure cadmium-detoxification capacity in tissues of scorpion fish; the relative sensitivity to cadmium was in the order: kidney > gills > intestine > liver. Oxygenated metabolites appeared to have exceeded the capacity of the GSH pool in field-exposed croakers and Dover sole, with fatty livers and fin erosion, respectively.

Therefore, at present levels of contamination of southern California coastal waters, the detoxification (assimilative) capacity of some marine organisms for certain trace metals does not appear to have been exceeded, whereas that for organic contaminants has.

Sediments and their associated microorganisms were also suggested to have a measurable capacity to detoxify contaminants by binding them so that they are not bioavailable or by degrading them to nontoxic forms.