Leptodora kindtii is a major predator of small zooplankton in eutrophic and fish-abundant lakes. However, as it is very difficult to culture in the laboratory, information about its sensitivity to pollutants is lacking. We have successfully established a laboratory clonal culture of Leptodora. In this study, acute toxicities of an insecticide and three heavy metals to Leptodora were estimated by using laboratory-cultured individuals. Our results suggest that Leptodora is more susceptible to contamination with those chemicals than the standard test organism, Daphnia.
Diaphanosoma brachyurum (Cladocera: Sididae) is a common limnetic species in summer-temperate and tropical water bodies. Few studies have investigated the sensitivity of D. brachyurum to toxic chemicals despite this species often being dominant in natural lakes and ponds. We performed acute toxicity tests of three heavy metals, copper (Cu), zinc (Zn), and cadmium (Cd), to D. brachyurum. For D. brachyurum, the lethal concentration (LC) 50 values of Cu (24-h LC 50 = 16.4 lg/L, 48-h LC 50 = 10.4 lg/L) and Zn (24-h LC 50 = 253.4 lg/L, 48-h LC 50 = 174.1 lg/L) were lower than those for D. magna, one of the most used test organisms for toxic chemicals. On the other hand, for D. brachyurum the 24-h LC 50 of Cd (166.4 lg/L) was much greater than that for D. magna, and the 48-h LC 50 of Cd (69.8 lg/L) was comparable.Our results indicate that D. brachyurum may be more strongly influenced by Zn and Cu than is D. magna. It is likely that the summer plankton community in which Diaphanosoma species is dominant is more sensitive to heavy metals than a community in which Daphnia species are dominant.
Summar y Dichlorvos and fenitrothion were detected frequently in rainwater collected at Yokohama Environmental Science Research Institute located in the Isogo ward of Yokohama in 2001 and 2002. Further, some rainwater samples in 2003 had a lethal effect on Daphnia magna after adding minerals. Thus, toxic potency of insecticide in rainwater (wet deposition) was considered to be an important problem for environmental protection. However, there were few studies on the atmospheric dry deposition of organophosphorous insecticides in Japan. Therefore, atmospheric deposition of dichlorvos and fenitrothion were determined by gas chromatograph mass spectrometer (GC/MS). Average atmospheric deposition amount of dichlorvos was 7.0 ng/m 2 /hr and that of fenitrothion was 6.3 ng/m 2 /hr. The highest concentration of insecticides in the aqueous solution exposed to air overnight was less than 0.05 μg/L, although the concentraions of dichlorvos and fenitrothion in rainwater sampled on October 1 st , 2014 were more than 0.10. μg/L. The toxic potency of insecticides in aqueous solution exposed to air overnight might be less than that in rainwater sampled on October 1 st , 2014. However, the concentrations of dichlorvos and fenitrothion in the solution exposed to air overnight were not less than PNEC (predicted no-effect of concentration). Therefore the atmospheric deposition of insecticides was considered to be one of important ecological problems for environmental protection as well as wet deposition of them.
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