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- Hassold, E., et al.
(författare)
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CHRONIC TOXICITY OF FIVE STRUCTURALLY DIVERSE DEMETHYLASE-INHIBITING FUNGICIDES TO THE CRUSTACEAN DAPHNIA MAGNA: A COMPARATIVE ASSESSMENT
- 2009
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Ingår i: Environmental Toxicology and Chemistry. - 0730-7268. ; 28:6, s. 1218-1226
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Tidskriftsartikel (refereegranskat)abstract
- Demethylase inhibitors (DMIs) are broad-spectrum fungicides that are ubiquitously used in agriculture and medicine. They comprise chemically heterogeneous substances that share a common biochemical target in fungi, the inhibition of a specific step in sterol biosynthesis. Several DMIs are suspected to disrupt endocrine-mediated processes in a range of organisms and to inhibit ecdysteroid biosynthesis in arthropods. It is unclear, however, whether and, if so, to what extent different DMI fungicides have a similar mode of action in nontarget organisms, which in turn would lead to a common chronic toxicity profile. Therefore, we selected a representative of each of the major DMI classes-the piperazine triforine, the pyrimidine fenarimol, the pyridine pyrifenox, the imidazole prochloraz, and the triazole triadimefon-and comparatively investigated their chronic toxicity to Daphnia magna. No toxicity was detectable up to the limit of solubility of triforine (61 mu mol/L). All other DMIs reduced reproductive success by delaying molting and development and by causing severe developmental abnormalities among offspring. Prochloraz was most toxic (median effective concentration [EC50] for fecundity reduction, 0.76 mu mol/L), followed by fenarimol (EC50, 1.14 mu mol/L), pyrifenox (EC50, 3.15 mu mol/L), and triadimefon (EC50, 5.13 mu mol/L). Mean effect concentrations for fecundity reduction were related to lipophilicity and followed baseline toxicity. However, triadimefon and fenarimol (but none of the other tested DMIs) caused severe eye malformations among exposed offspring. Affected neonates did survive, but a reduced ecological fitness can be assumed. Offspring exposed to fenarimol in mater matured earlier. The investigated different life-history parameters were affected in a substance-specific manner. These qualitatively different toxicity profiles suggest additional, substance-specific mechanisms of action in D. magna that probably are related to an antiecdysteroid action.
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| 2. |
- Hassold, E., et al.
(författare)
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The predictability of mixture toxicity of demethylase inhibiting fungicides to Daphnia magna depends on life-cycle parameters
- 2014
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Ingår i: Aquatic Toxicology. - : Elsevier BV. - 0166-445X. ; 152, s. 205-214
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Tidskriftsartikel (refereegranskat)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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