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Joint algal toxicity of phenylurea herbicides is equally predictable by concentration addition and independent action
Author(s) -
Backhaus Thomas,
Faust Michael,
Scholze Martin,
Gramatica Paola,
Vighi Marco,
Grimme L. Horst
Publication year - 2004
Publication title -
environmental toxicology and chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.1
H-Index - 171
eISSN - 1552-8618
pISSN - 0730-7268
DOI - 10.1897/02-497
Subject(s) - toxicity , environmental chemistry , hazard , hazard analysis , aquatic toxicology , chemistry , action (physics) , pesticide , photosynthesis , toxicology , biological system , biology , ecology , biochemistry , organic chemistry , physics , quantum mechanics , engineering , aerospace engineering
Abstract Photosynthesis‐inhibiting phenylurea derivatives, such as diuron, are widely used as herbicides. Diuron concentrations clearly exceeding the predicted‐no‐effect concentration have been regularly measured in European freshwater systems. The frequently observed exposure to mixtures of phenylureas additionally increases the hazard to aquatic primary producers. Fluctuating numbers and concentrations of individual toxicants make experimental testing of every potential mixture unfeasible. Thus, predictive approaches to the mixture hazard assessment are needed. For this purpose, two concepts are at hand, both of which make use of known toxicities of the individual components but are based on opposite mechanistic suppositions: Concentration addition is based on the idea of similar mechanisms of action, whereas independent action assumes dissimilarly acting mixture components. On the basis of pharmacological reasoning, it was therefore anticipated that the joint algal toxicity of phenylurea mixtures would be predictable by concentration addition. Indeed, we could demonstrate a high predictive power of concentration addition for these combinations. Surprisingly, however, the opposite concept of independent action proved to be equally valid, because both concepts predicted virtually identical mixture toxicities. This exceptional case has previously been derived from theoretical considerations. Now, the tested phenylurea mixtures serve as an example for the practical relevance of this situation for multicomponent mixtures.