Single- and two-species tests to study effects of the anthelmintics ivermectin and morantel and the coccidiostatic monensin on soil invertebrates.

Soil invertebrates in arable land are potentially exposed to veterinary medicines excreted by husbandry. The toxicity of three widely used pharmaceuticals was therefore investigated with the use of common soil invertebrates exposed in the laboratory in single- or two-species test system. The anthelmintic morantel did not cause significant mortality to either Folsomia fimetaria or Enchytraeus crypticus even at the highest tested concentration of 900 mg kg(-1) dry soil. The coccidiostatic monensin affected the reproduction of F. fimetaria and E. crypticus with soil concentrations estimated to cause a 10% effect at values of approximately 109 and 71.8 mg kg(-1) dry soil, respectively, but caused no mortality to adult. The anthelmintic ivermectin did not affect the survival of adult Hypoaspis aculeifer. Reproduction of H. aculeifer declined approximately 45% in response to ivermectin exposure of 5 mg kg(-1) dry soil. Ivermectin was highly toxic to F. fimetaria and affected the survival of adults with soil concentrations estimated to cause a 50% mortality at values of 5.3 mg kg(-1) dry soil in the single-species test system and 0.14 mg kg(-1) dry soil in the two-species test system. Reproduction of F. fimetaria was reduced by ivermectin with 10% effective concentration at 0.19 mg kg(-1) dry soil in the single-species test system and 0.02 mg kg(-1) dry soil in two-species test system. It was shown that species interactions may influence the response of test organisms to toxic substances. The data from this study and previously published data showed that, whereas ivermectin is likely to pose a risk to soil-dwelling invertebrates, adverse effects of morantel and monensin are unlikely to occur as a result of residue excretion from treated farm animals.