An ecological risk assessment method for species exposed to contaminant mixtures

Abstract

The method developed here provides a quantitative, objective measure of ecological risk for natural populations exposed to mixtures of chemical contaminants. It is founded on generally accepted risk assessment concepts: use of toxic units to assess the joint toxic effects of mixtures and expression of ecological risk as a relationship between toxicological end points and estimated environmental concentrations. Toxicologicai end points may be regulatory levels with zero variance and species‐dependent concentrations with estimates of variance. Risk is the probability that a linear combination of toxic units exceeds 1, which expresses the probability that a measurement end point (e.g., 50% mortality in 96 h) will occur. Computations have three variations. One addresses concentration addition, in which chemicals act independently to produce similar biological effects. For noninteractive joint action with no addition, in which the biological response to the mixture is not significantly different from the response to the most toxic component, the method reduces to an analysis of extrapolation error. For other noninteractive joint action — antagonism, partial addition, and supra‐addition — a correction factor similar to Konemann's mixture toxicity index is applied. An initial validation using published data indicated that increased in situ striped bass mortality was generally associated with elevated risk estimates. The method is applicable to many organisms and toxicant mixtures.

Environmental Risk Assessment of Agrochemicals — A Critical Appraisal of Current Approaches

“…In such cases, a toxic equivalent (TE) with reference to a standard compound in the same group of chemicals is estimated [57]. TEs are then used for assessing the total toxicity of such mixtures in tissues, sediments or another matrix [58].…”

The Toxicology of Chemical Mixtures Risk Assessment for Human and Ecological Receptors

“…The variance of this distribution is predicted using the variance values from individual chemical exposure concentrations and the variance from component toxicity values. Risk is then calculated by the normal probability function (Logan and Wilson, 1995).…”

“…Dose addition of mixtures containing up to 50 nonspecific toxicants has been confirmed in multiple aquatic species, providing mode of action additive concentrations were below thresholds for specific effects (Escher and Hermens, 2002). It is estimated that the majority of chemicals on the Toxic Substances Control Act inventory and most industrial chemicals (e.g., alcohols, ketones, ethers, aromatic and aliphatic hydrocarbons) have narcotic effects to aquatic life (Logan and Wilson, 1995;Van Leeuwen et a!, 1996).…”

“…Concentrations can be as low as 0.25% of an EC50 (effective concentration for 50% of the exposed organisms) (Escher and Hermens, 2002;Niederlehner et a!, 1998;Vighi and Calamari, 1996). Additivity was used to explain cumulative metals toxicity to striped bass in Chesapeake Bay; Al, Cd, Cr, Cu and Zn were present in the Bay below regulatory levels but dose additive predictions of toxicity correlated well with observed effects (Logan and Wilson, 1995).…”

Prediction of the Toxicity of Dimethylformamide, Methyl Ethyl Ketone, and Toluene Mixtures by QSAR Modeling

“…4 For this reason, researchers have addressed the issue of toxicity of mixtures. [5][6][7][8] However, testing mixtures requires far more experiments than does the testing of single compounds, and thus more requires time and expense. For these reasons, studies of mixtures have not been published at a high rate.…”