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The predictability of mixture toxicity of demethylase inhibiting fungicides to Daphnia magna depends on life-cycle parameters

Journal article
Authors E. Hassold
Thomas Backhaus
Published in Aquatic Toxicology
Volume 152
Pages 205-214
ISSN 0166-445X
Publication year 2014
Published at Department of Biological and Environmental Sciences
Pages 205-214
Language en
Links dx.doi.org/10.1016/j.aquatox.2014.0...
Keywords Mixture toxicity, DMI fungicides, Daphnia magna, Concentration Addition, Independent Action, Anti-, JOINT ALGAL TOXICITY, ENDOCRINE-DISRUPTING CHEMICALS, DISSIMILARLY, ACTING CHEMICALS, HONEYBEE APIS-MELLIFERA, VIBRIO-FISCHERI, DMI, FUNGICIDES, INDEPENDENT ACTION, AZOLE FUNGICIDES, AQUATIC TOXICITY, RISK-ASSESSMENT, Marine & Freshwater Biology, Toxicology
Subject categories Toxicology, Marine ecology

Abstract

A variety of different fungicides are found simultaneously in surface waters, among which demethylase inhibitors (DMIs) are a major group. The joint toxicity of four DMIs from different chemical classes (Fenarimol, Prochloraz, Triadimefon and Pyrifenox) was investigated in the reproduction test with Daphnia magna, following an extended protocol according to ISO 10706. We assessed the toxicity of the DMI mixtures across different endpoints and effect levels and evaluated the predictability of their joint action using Concentration Addition (CA) and Independent Action (IA). The mixture reduced fecundity, delayed molting and caused characteristic malformations in offspring in a concentration-dependent manner which is possibly due to an anti-ecdysteroid action, as previously described for individual DMIs. However, also mixture-specific effects were observed: exposed daphnids reached sexual maturity already after the third juvenile molt, and thus significantly earlier than unexposed daphnids, which needed four juvenile molts to reach maturity. This effect is not caused by any of the DMIs alone. Additionally, the percentage of aborted broods was synergistically higher than expected by either CA or IA. IA underestimates the mixture toxicity for all parameters. The predictive quality of CA differed between life history responses, but was always within a factor of two to the observed toxicity. The parameter "fecundity reduction, counting only normally developed offspring", was the most sensitive endpoint, while the parameter "fecundity reduction, counting all living offspring", was slightly less sensitive. The mixture caused a 90% reduction in fecundity at individual concentratioris that only provoke 7% effect or less, which calls for a mixture-specific toxicity assessment of DMI fungicides. (C) 2014 Elsevier B.V. All rights reserved.

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