Because pesticides are chemical compounds with physiological activity, differences in species sensitivities to them are extremely large compared with those in species sensitivities to industrial chemicals, and the prediction of ecotoxicities from chemical structures is difficult. Here, to investigate the relationship between the ecotoxicities and mode of action toward providing useful information for pesticide safety research, 112 active ingredients of insecticides and acaricides were analyzed following parameters for each mode of action: [1] differences in sensitivities of aquatic organisms, [2] correlations among test species’ sensitivities, [3] acute-chronic ratio（ACR: EC50 for acute immobilization test / NOEC for reproduction test）in daphnids, [4] correlations of log Pow and toxicity on fish and daphnids, and [5] correlation of bioconcentration factor（BCF） and ACR（LC50 for acute toxicity test / NOEC for long-term toxicity test）in fish. Our results demonstrated e.g., high sensitivities of arthropods, correlation of sensitivities between some taxonomic groups, and larger daphnid ACRs observed for insect growth regulators. However, for most ecotoxicological data analyzed, particularly for long-term toxicity data, clear trends or relationships were not obtained. These analytical results can be expected to facilitate pesticide safety research, particularly prioritization of various ecotoxicological studies, and to set nominal concentrations for such studies.

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We examined the cytotoxicity evaluation of the plastic marine debris collected in the coasts of Southwest Japan using in vitro tests, primarily the colony-forming assay （CFA） with V79 cells; the test system was based on Annex B of ISO10993-5. In approximately 30% of samples（9 of 29 samples） , the cytotoxicities were detected by the CFA, with IC50 values in the range of 18–74%. In 5 samples in which cytotoxicities were detected by the CFA, cell viability assays with TK6 cells also showed cytotoxicities. Among the samples tested, “moderate” level of cytotoxicity is the level indicating the mucosal tissue inflammation potential, which might negatively influence the physiological condition of marine based organisms via uptake into the body. In addition, we showed that floating microplastics can be evaluated using the CFA. This is the first study to determine the in vitro cytotoxicities of plastic marine debris using an international standard test method and quantitatively determine the cytotoxicities of plastic marine debris.

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Relationship between herbicide mode of action and difference in species sensitivity of 6 species primary producers（Pseudokirchneriella, Desmodesmus, Navicula, Anabaena, Synechococcus, and Lemna） was investigated. Toxicity data of 6 species for 120 herbicides was organized. The toxicity data was converted to standardize the difference in toxicity among herbicides as species sensitivity index（SSI）. The SSI indicates the relative difference in species sensitivity, and higher SSI means higher sensitivity. Pseudokirchneriella was not the significantly most sensitive species to herbicides of each mode of action. On the other hand, Lemna was the significantly most sensitive to herbicides of 2 mode of action groups（inhibitors of acetolactate synthase and 4-hydroxyphenyl-pyruvate-dioxygenase） . Desmodesmus was the significantly most sensitive to herbicides of a mode of action group（inhibitors of protoporphyrinogen oxidase）. These results suggest that difference in species sensitivity is specific to the mode of action, and a single species cannot always represent the sensitivity of primary producers to herbicides.

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This study focused on the toxic effects of low pH on Daphnia magna embryos, young, and adults in a soft and a hard water. Four- to six-hour-old embryos after egg laying were obtained from the female’s brood chamber and immediately exposed to four or five level of different low-pH solutions for 120 hours. Embryonic toxicity was determined by evaluating inhibition of hatching and immobilization of the embryos following 72, 96, and 120 hours of exposure to low-pH solutions. Young（<24 hours following release from the female）and adults were also exposed to four or five level of different low-pH solutions for 48 hours. Low pH resulted in significant toxicity during embryonic development, as was indicated by inhibition of hatching and/or immobilization in embryos following exposure to pH 6.6 in soft water and to pH 6.0 in hard water. Immobilization was observed in young when subjected to solutions at/below pH 6.5 in soft water and at/below pH 5.2 in hard water. Adults were more tolerant to low pH in soft water than young or embryos, with the pH causing 50% immobilization in adults following 48-hour exposure 1.4 points lower than that which resulted in young or embryos 50% immobilization. The hardness of the water in low-pH solutions can influence the immobilization ratio of young. These observations suggest that the embryonic developmental test in early life stages allows for rapid and sensitive determination of low-pH toxicity.

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