Proportion data obtained from binary responses in ecotoxicity tests (e.g., survival, mortality, and hatchability) are conventionally analyzed using statistical analyses based on the assumption of normality (e.g., analysis of variance), often by applying arcsine square root transformation. However, proportion data are rarely normally distributed and use of proportion loses the sample size information. In this review, we sum up several issues of the conventional statistical analyses and introduce generalized linear model (GLM) with a binomial distribution to overcome them. To demonstrate the benefits of using GLM in an easy-to-understand manner, we simulate simplified toxicity data and compare the statistical power of three different methods (i.e., t-test without transformation, t-test with arcsine square root transformation, and GLM) for detecting a treatment effect in the simulated data. Simulations indicate that the GLM provides as high or higher statistical power than other methods. We recommend that proportion data such as survival be analyzed using the binomial GLMs.

Nonylphenol (NP) is widely used in the manufacture of nonyphenol ethoxylates, and highly toxic to aquatic organisms. However, limited information is available on the toxic effects of NP isomers to crustaceans. In this study, we investigated the acute and subchronic effects of NP isomers on the mysid, Americamysis bahia (Crustacea: Mysidacea). In the acute toxicity test, the median lethal concentration (96 h-LC50) values of 4-NP, NP-C’, NP-I, NP-N, NP-O and NP-Q in mysids were estimated to be 78, 131, 91, 72, 144 and 89 μg/L, respectively. In order to further evaluate the subchronic effects of NP isomers on survival, growth (body and carapace length and body weight), sexual development and molting, 7-day-old mysids were exposed to NP-N and NP-Q (0.5, 5 and 50 μg/L) for 14 days. The adverse effects of NP-N and NP-Q on the body and/or carapace length were the most prominent, and the lowest observed effect concentrations (LOECs) of these NPs were 50 and < 0.5 μg/L, respectively. Furthermore, the total number of molting was significantly decreased in mysids exposed to NP-N (the LOEC value: < 0.5 μg/L) and NP-Q (5 μg/L) for 14 days. These results suggest that subchronic exposure to environmentally relevant concentrations of NP isomers affect growth and molting of the mysids. In addition, it was suggested that the toxicity may be different for each isomer.

In the present study, we examined copper accumulation and distribution in the gills of Japanese freshwater crabs Geothelphusa dehaani exposed to copper chloride, using microbeam scanning particle induced X-ray emission (micro-PIXE) analysis to clarify the potential of this decapod crustacean as an indicator organism for copper pollution. After exposure of the crabs to copper chloride (1mg/L) for 3 days, the copper concentration in the gills was 161±48μg/g of tissue wet weight, which was four times higher than the control value. Copper was found not only on the surface, but also inside the gills, and especially localized at the gill axis. In the morphological examination, severe damage of the gills was not observed in the exposure group, while hemagglutination was detected at the gill axis. The results suggest that the Japanese freshwater crab would be useful as a model organism for understanding mechanisms of toxicity, and that crab gills may be an effective indicator of copper pollution.