Relative sensitivity of life-cycle and biomarker responses in four earthworm species exposed to zinc

Abstract Life-cycle (survival, weight change, and cocoon production rate) and biomarker (neutral-red retentionby coelomocytes lysosomes) responses to zinc in four earthworm species were measured in laboratory tests. In all species, dose-dependent effects on survival, cocoon production, and neutral-red retention times were found (one-way ANOVA p < 0.05). However, for weight change, only Aporrectodea caliginosa showed a clear response. Comparisons of the effects of zinc on these parameters in the different earthworm species indicated similar order of sensitivity. Thus, Lumbricus rubellus and Aporrectodea caliginosa were more sensitive to zinc than Lumbricus terrestris and Eisenia fetida in all cases. To compare the relative sensitivities of life-cycle and biomarker responses, a sublethal sensitivity index (SSI) was applied. For cocoon production, SSIs indicated that the EC10s were below LC50s by a factor of between 8.3 and 16.5. These values are toward the high end of the range found previously for soil invertebrates, indicating an emphasis on maximizing survival. For neutral red, SSIs ranged from 4.5 to 41.2. Thus, the biomarker was predictive of life-cycle effects in some (Lumbricus rubellus and Aporrectodea caliginosa), although not the other two species tested.