PARENT SESSION
5A Assessing and predicting toxicant effects in an ecologically complex world
9:00 AM to 7:00 PM, Monday, 07 May 2001

(M/MF191) IQ-Tox: A Computerized Model for Assessing the Direct Ecotoxic Risks of Environmental Cocktails of Contaminants.

Mulder, Christian¹, Zwart, Dick¹, Aldenberg, Tom¹, Posthuma, Leo¹, ¹

ABSTRACT- "IQ-Tox" stands for "Instrument for the Quantification of Toxic stress". This contribution will show the conceptual design and the type of output as generated on the basis of an operational protoype. The program is meant for use in the daily practice of toxic-compound risk assessment, to rank hazards among contaminated sites, to identify the taxonomic groups experiencing the largest hazards, and to rank the relative contribution of different chemicals to those hazards. As input for the combined ecotoxic stress calculation, IQ-Tox will accept total concentrations of a large variety of environmental contaminants in environmental compartments (surface-, groundwater, soil and sediments). It will approximate the bioavailable concentration in water and soil by applying compound-specific rules. Log-logistic Species Sensitivity Distributions (SSDs) for individual contaminants of species within taxonomic groups (e.g. algae, plants, crustaceans, fishes) are used to calculate Potentially Affected Fractions (PAF). PAF is defined as the fraction of the group of species locally exposed to bioavailable concentrations that exceed the test endpoint (like NOEC, EC₅₀). In the calculation of combined toxic stress (multi-substance PAF) per taxonomic group, a recently developed aggregation protocol will be used, addressing both concentration and response additivity as well as the correlation of sensitivities. As the last step in the ms-PAF calculation, the overall ecotoxic risk can be calculated as an aggregated value of ms-PAF over taxonomic groups. An outlook on further developments of the program will be presented, focusing on the basic concepts that can be addressed, and the extent to which these concepts are necessary elements to use in practice, e.g. ecology-based evaluations of remediation urgency.

Key words: quantification of toxic stress, ecotoxic risks, aggregation protocol, remediation urgency