**4. Conclusion**

The aim of this study was using zooplankton, *Moina micrura* Kurz. which is an important species in aquatic ecosystem of Thailand to evaluated ecotoxicity of main pesticide used in paddy field (malathion, chlorpyrifos, carbofuran, neem extract (azadirachtin) and glyphosate). The acute toxicity (48-h LC50 ) of malathion, chlorpyrifos, carbofuran, neem extract and glyphosate on *M. micrura* were 10.44, 0.08, 6.96, 196.3 and 3043 µg/L, respectively. Chlorpyrifos had highest toxicity followed by carbofuran, malathion, neem extract and glyphosate, respectively. Chronic toxicity test, the effect of pesticides to *M. micrura* on reproduction was studies by observing the number of offspring per female. Reproduction have significant reduced (P<0.05), with concentration of malathion at 0.50 µg/L, chlorpyrifos greater than 0.0025 µg/L, carbofuran at 2.50 µg/L and the concentration of glyphosate at 325 µg/L affected on reducing the number of offspring per female significantly (P<0.05). The neem extract had no significantly (P>0.05) effect on the number of offspring per female. The maximum acceptable - toxicant concentration (MATCs) of malathion, chlorpyrifos, carbofuran, neem extract and glyphosate were 0.36, 0.0001, 2.41, 172 and 281.9 µg/L, respectively. The result would be useful as an input to developing a biomonitoring tool for evaluation pesticide contamination in Thailand aquatic ecosystem.

Effect of experimental condition including duration test organism and end point on observed toxicity of pesticide to *M. micrura* were evaluated. Relative sensitivities of test varies with pesticide type. Among five pesticides toxicity test, chlorpyrifos had highest acute toxicity on *M. micrura* followed by carbofuran, malathion, neem extract and gyphosate, respectively. The significant reducing effect on number of offspring per female of *M. micrura* were observed in the present of malathion, chlorpyrifos carbofuran and glyphosate. For neem extract had no effect on the number of offspring per female. The results indicate that reproductivity parameters are very important interm of pesticide impact on aqutic population such as *M. micrura*. However, in the natural environment aquatic organism are often exposure to multiple pesticides simultaneously. Therefore under natural condition, there is the potential of pesticides may act in additive or synergistic manner, although the sensitivity of aquatic biota to multiple pesticides cannot be predicted by the individual pesticide sensitivities generate in this study.

The results showed *M. micrura* to be sensitive test organism, Thus its a good bioindicator and useful to developing a biomonitoring tool for evaluation pesticide contamination in Thailand aquatic ecosystem. However, in order to obtain more precise and conclusive toxicology data on application of these pesticide in paddy field and evaluation toxicity of pesticides on organism, similar study using another local freshwater in Thailand.
