The tissue residue dose concept has been used, although in a limited manner, in environmental toxicology for more than 100 y. This review outlines the history of this approach and the technical background for organic chemicals and metals. Although the toxicity of both can be explained in tissue residue terms, the relationship between external exposure concentration, body and/or tissues dose surrogates, and the effective internal dose at the sites of toxic action tends to be more complex for metals. Various issues and current limitations related to research and regulatory applications are also examined. It is clear that the tissue residue approach (TRA) should be an integral component in future efforts to enhance the generation, understanding, and utility of toxicity testing data, both in the laboratory and in the field. To accomplish these goals, several key areas need to be addressed: 1) development of a risk-based interpretive framework linking toxicology and ecology at multiple levels of biological organization and incorporating organism-based dose metrics; 2) a broadly applicable, generally accepted classification scheme for modes/mechanisms of toxic action with explicit consideration of residue information to improve both single chemical and mixture toxicity data interpretation and regulatory risk assessment; 3) toxicity testing protocols updated to ensure collection of adequate residue information, along with toxicokinetics and toxicodynamics information, based on explicitly defined toxicological models accompanied by toxicological model validation; 4) continued development of residue-effect databases is needed ensure their ongoing utility; and 5) regulatory guidance incorporating residue-based testing and interpretation approaches, essential in various jurisdictions.

A diverse array of environmental data from Ohio were placed into a geographical information system (GIS). This GIS allowed for the investigation of approaches and paradigms currently advocated for ecological risk assessment. The paradigm of chemical mixture additivity was investigated in this project. Toxic units (toxic unit ) concentration of a chemical in an organism/chemical concentration causing a specified effect) for 12 organic and 11 metal contaminants were calculated from 2878 fish samples collected at 1010 sites throughout the state of Ohio. Additive analysis of TUs for organic chemicals based on regulatory-based protective limits (toxicity reference value ) USEPA water quality criterion*bioconcentration factor) overpredicted adverse effects to individual fish and fish communities. However, addition of organic chemical molar units did not overpredict adverse effects, thus, supporting the concept of baseline toxicity. Molar units of organic chemicals with diverse modes of action may be added together, so long as they are at concentrations below levels deemed protective of most species (e.g., 95%, water quality criterion). Analysis of metal TUs benchmarked against regulatorybased limits overpredicted adverse effects, whereas benchmark concentrations from population response (survival, growth, reproduction) data from the literature and Ohio reference site fish community responses corresponded better to field observations. Of the factors analyzed, habitat quality is the best single predictor of fish community integrity in Ohio, not body burdens of metals or organic chemicals.

Distribution and forms of the metals cadmium (Cd) and zinc (Zn) in sediment and the possible significance of a die‐off of the aquatic macrophyte Potamogeton crispus in Cd cycling in a metal‐contaminated lake were studied. Metal levels in the upper 5 cm of lake sediment ranged from 2.54 ppm Cd and 115 ppm Zn in an uncontaminated area of the lake to 805 ppm Cd and 6,120 ppm Zn near the entrance of a metal‐bearing ditch to the lake. Evidence of metal contamination existed at a depth of 30 cm in sediments in contaminated areas of the system. Dominant forms present in the sediment were the carbonate for Cd and carbonate and organic for Zn. Analysis indicated Cd levels as high as 89.6 ppm in P. crispus in the lake with a maximum burden of 1.5 kg Cd held by the lake's P. crispus population. Release of the total amount could raise water concentrations by a maximum of 1 µg/liter.

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