Sensitivity of two Mesocyclops (Crustacea, Copepoda, Cyclopidae), from tropical and temperate origins, to the herbicides, diuron and paraquat, and the insecticides, temephos and fenitrothion.

Ecotoxicological assessment in the tropics is based mainly on knowledge gained from temperate organisms, although many studies have shown the need for models that are more appropriate to tropical regions. The toxicity of two herbicides and two insecticides to nauplii of two freshwater zooplankton species, Mesocyclops aspericornis (von Daday in Inseln Zool Jb Syst 24:175-206, 1906) from a tropical reservoir and a Mesocyclops sp. from a temperate pond, were compared. Both strains were sensitive to paraquat, temephos and fenitrothion, tropical M. aspericornis being generally more tolerant (EC50s of 207, 1,450 and 1,840 μg L(-1) for paraquat, temephos and fenitrothion, respectively) than the temperate Mesocyclops sp. (EC50s of 152, 45 and 1,017 μg L(-1) for paraquat, temephos and fenitrothion, respectively) whereas diuron was only slightly toxic (LOEC = 446 μg L(-1) for both strains). The nauplii mortality increased with the exposure time for both species during each experiment. Further isolation of model organisms from tropical ecosystems is needed, to meet the requirements for a tropical risk assessment scheme.