Toxic Mixtures in Time-The Sequence Makes the Poison.
"The dose makes the poison". This principle assumes that once a chemical is cleared out of the organism (toxicokinetic recovery), it no longer has any effect. However, it overlooks the other process of re-establishing homeostasis, toxicodynamic recovery, which can be fast or slow depending on the chemical. Therefore, when organisms are exposed to two toxicants in sequence, the toxicity can differ if their order is reversed. We test this hypothesis with the freshwater crustacean Gammarus pulex and four toxicants that act on different targets (diazinon, propiconazole, 4,6-dinitro-o-cresol, 4-nitrobenzyl chloride). We found clearly different toxicity when the exposure order of two toxicants was reversed, while maintaining the same dose. Slow toxicodynamic recovery caused carry-over toxicity in subsequent exposures, thereby resulting in a sequence effect-but only when toxicodynamic recovery was slow relative to the interval between exposures. This suggests that carry-over toxicity is a useful proxy for organism fitness and that risk assessment methods should be revised as they currently could underestimate risk. We provide the first evidence that carry-over toxicity occurs among chemicals acting on different targets and when exposure is several days apart. It is therefore not only the dose that makes the poison but also the exposure sequence.
Department of Environmental Toxicology, Eawag - Swiss Federal Institute of Aquatic Science and Technology , 8600 Dübendorf, Switzerland.|Environment Department, University of York , Heslington, York YO10 5DD, United Kingdom.
Roman
0000-0002-9579-8793
R
Ashauer
Department of Environmental Toxicology, Eawag - Swiss Federal Institute of Aquatic Science and Technology , 8600 Dübendorf, Switzerland.
Isabel
I
O'Connor
Department of Environmental Toxicology, Eawag - Swiss Federal Institute of Aquatic Science and Technology , 8600 Dübendorf, Switzerland.|Cell Toxicology, Helmholtz Centre for Environmental Research - UFZ, Leipzig, Germany.|Environmental Toxicology, Center for Applied Geosciences, Eberhard Karls University , Tübingen, Germany.
Beate I
BI
Escher
D033304:Amphipoda / Q000187:drug effects*; D000818:Animals; D003976:Diazinon / Q000633:toxicity*; D015386:Hazardous Substances; D011042:Poisons; D018570:Risk Assessment
D015386:Hazardous Substances; D011042:Poisons; D003976:Diazinon