Chemicals with increasingly complex modes of action result in greater variation in sensitivity between earthworm species

The scale of variation in species sensitivity to toxicants has been theoretically linked mode action. Specifically, it proposed there will be greater variations for chemicals with a putative specific biological target than non-specific narcotic mechanism. Here we test the hypothesis that action is related specifically designed experiment from single ecologically important terrestrial taxa, namely earthworms. Earthworm toxicity tests were conducted five four chemicals, providing series increasingly complex modes action: polycyclic aromatic hydrocarbon (fluoranthene), and three insecticides (chlorpyrifos, cypermethrin, imidacloprid) known neuronal receptor targets. Across all standard epigeic Eisenia fetida Lumbricus rubellus, generally among two least sensitive, while endogenic Aporrectodea caliginosa Megascolecidae Amynthas gracilis more sensitive (never being species). This indicates potential bias earthworm ecotoxicology literature, which dominated by studies Lumbricidae, but contains few endogeic or data. Results confirmed lowest range sensitivities effects on reproduction was fluoranthene (2.5 fold). All showed (cypermethrin: 7.5 fold, chlorpyrifos: 10.3 imidacloprid: 31.5 fold) consistent mechanisms pesticides. Difference toxicodynamics, based specificity complexity reflected magnitude variation. However, measurements tissue concentrations also indicated importance toxicokinetics explaining chlorpyrifos cypermethrin.