Effects of anthropogenic pollution on aquatic environment have been concerned because some of pollutants have toxicities to aquatic organisms including immunotoxicity. Because immune system is responsible for biological defense and maintenance of good health, toxic effects of chemicals on immune system would decline health condition of organisms. Aquatic organisms which live in polluted areas were reported to be occurred immunotoxic symptoms such as histological changes of lymphoid tissue, changed immune functions and immune cell populations, and changed host resistance to infection pathogens. In addition, aquatic organisms are always thought exposed to pathogen (bacteria, virus, fungi, etc.) via water. Therefore, suppressed immune system by contaminants should increase infection risk. Furthermore, it poses ecological risks such as extinction. In this review, we introduced immunotoxic effects of pollutant contaminants on aquatic organisms including aquatic invertebrates, fish, amphibian and marine mammals, and discussed posed-effects on aquatic population and ecosystem.

We examined the acute-to-chronic toxicity ratio (ACR) with use in the risk assessment of aquatic combined toxicity. The deterministic method using fixed values and the probabilistic method using distributions are applied to ACR. 1000 sets of virtual mixture each consisting of 2, 5, 10 or 20 components were created. And simulation was conducted to derive the predicted no effect concentration of mixture (PNECmix) of those mixtures. First, PNECmixs derived using fixed ACR and true PNECmixs derived from NOEC without using ACR were compared. It was shown that the PNECmixs derived using the fixed ACR became smaller than the true PNECmixs when the number of chemicals in the mixture increased. Next, PNECmixs derived using probability distribution of ACR and true PNECmixs were compared. It was shown that the differences between the PNECmixs derived using the probability distribution of ACR and the true PNECmixs got smaller when the number of chemicals in the mixture increased. As a result, it was suggested that in the risk assessment of complex toxicity, fixed ACR derives conservatively biased PNECmixs and probabilistic ACR derives realistic PNECmixs.

This study was performed to investigate the toxicological effects of seven neonicotinoid insecticides and their two metabolites on juvenile (approximate total length of 10-15 mm) kuruma prawn Marsupenaeus japonicas, settled in estuary areas for nursery establishment. Following neonicotinoid insecticide treatment for 96 h under semi-static exposure, the effective concentration (mean 96 h-EC₅₀ with 95% credible intervals in parenthesis) was 31 (25-37) μg/L, 14 (9.0-18) μg/L, 530 (410-660) μg/L, 50 (36-63) μg/L, 490 (270-720) μg/L, 20 (11-29) μg/L, and 940 (420-1500) μg/L, for acetamiprid, clothianidin, dinotefuran, imidacloprid, nitenpyram, thiacloprid and thiamethoxam, respectively. IM-2-1, a metabolite of acetamiprid and IC-O, a metabolite of neonicotinoid insecticides with chloronicotinic group had 96 h-EC₅₀ of 1300 (1100-1500) μg/L and >12000 μg/L, respectively. These results indicate the substantial variation in the toxicity of the insecticides to the crustacean species and the correlation of their magnitude with the logarithm of the octanol water partition coefficient (Log K_ow). Furthermore, for some insecticides, molting frequency significantly decreased with increasing concentrations, implying that the insecticide delayed molting of the organism. In summary, the present study provides the first demonstration that neonicotinoid insecticides adversely affect kuruma prawn and that two metabolites were less toxic than the parent compounds. Future research will be necessary to investigate marine contamination of the insecticides, especially in estuaries.