title: Measuring and modelling mixture toxicity of imidacloprid and thiacloprid on Caenorhabditis elegans and Eisenia fetida.
abstract: While the standard models of concentration addition and independent action predict overall toxicity of multicomponent mixtures reasonably, interactions may limit the predictive capability when a few compounds dominate a mixture. This study was conducted to test if statistically significant systematic deviations from concentration addition (i.e. synergism/antagonism, dose ratio- or dose level-dependency) occur when two taxonomically unrelated species, the earthworm Eisenia fetida and the nematode Caenorhabditis elegans were exposed to a full range of mixtures of the similar acting neonicotinoid pesticides imidacloprid and thiacloprid. The effect of the mixtures on C. elegans was described significantly better (p<0.01) by a dose level-dependent deviation from the concentration addition model than by the reference model alone, while the reference model description of the effects on E. fetida could not be significantly improved. These results highlight that deviations from concentration addition are possible even with similar acting compounds, but that the nature of such deviations are species dependent. For improving ecological risk assessment of simple mixtures, this implies that the concentration addition model may need to be used in a probabilistic context, rather than in its traditional deterministic manner.
authors: Department of Soil Science, School of Human and Environmental Sciences, University of Reading, Reading RG6 6DW, Berkshire, UK.
authors: Jose L
authors: JL
authors: Gomez-Eyles
authors: Centre for Ecology and Hydrology, Monks Wood, Abbots Ripton, Huntingdon PE28 2LS, Cambridgeshire, UK. Electronic address: csv@ceh.ac.uk.
authors: Claus
authors: C
authors: Svendsen
authors: Centre for Ecology and Hydrology, Monks Wood, Abbots Ripton, Huntingdon PE28 2LS, Cambridgeshire, UK.
authors: Lindsay
authors: L
authors: Lister
authors: School of Biosciences, University of Birmingham, Birmingham B15 2TT, UK.
authors: Heather
authors: H
authors: Martin
authors: Department of Soil Science, School of Human and Environmental Sciences, University of Reading, Reading RG6 6DW, Berkshire, UK.
authors: Mark E
authors: ME
authors: Hodson
authors: Centre for Ecology and Hydrology, Monks Wood, Abbots Ripton, Huntingdon PE28 2LS, Cambridgeshire, UK.
authors: David J
authors: DJ
authors: Spurgeon
mesh_terms: D000818:Animals; D017173:Caenorhabditis elegans / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D004781:Environmental Exposure; D007093:Imidazoles / Q000633:toxicity*; D007306:Insecticides / Q000633:toxicity*; D008954:Models, Biological; D000073943:Neonicotinoids; D009574:Nitro Compounds / Q000633:toxicity*; D009835:Oligochaeta / Q000187:drug effects*; D010575:Pesticides / Q000633:toxicity*; D011725:Pyridines / Q000633:toxicity*; D011978:Receptors, Nicotinic / Q000187:drug effects; D013570:Synaptic Membranes / Q000187:drug effects; D013843:Thiazines / Q000633:toxicity*
chemical_list: D007093:Imidazoles; D007306:Insecticides; D000073943:Neonicotinoids; D009574:Nitro Compounds; D010575:Pesticides; D011725:Pyridines; D011978:Receptors, Nicotinic; D013843:Thiazines; C082359:imidacloprid; C417209:thiacloprid