The ecological risk assessment has become incleaseingly an important issue of the conservation of biodiversity. Many countries including Japan have introduced the test guideline maintained by OECD, in which the ecological risk of each chemicals is assessed based on the acute toxicity test of the three water organism species, that is algae, water flea, and fish, in the laboratory. However, there is little in the studies regarding whether such toxicity data reflect the ecological impacts of each chemical in the actual field. We have promoted the paddy field masocosm test for assessing how insecticides influence the communities of organisms in paddy fields, which is difficult to predict by laboratory tests. We tested the ecological impacts caused by the 2 systemic insecticides, imidacroprid and fipronyl, widely used in the Japanese paddy fields by the paddy field masocosms sice 2010 to 2012. In each the year, we conventionarily applied the chemical into the experimental paddy fields and researched the occurrence of water organism species. As result, we could detect that the insecticides severely influenced the population dynamics of some species even under the standard concentration for the environmental safety provided by the OECD test guideline. And also it was discovered that the divergence of community components of the insecticide applied paddy fields from those of non-chemical paddy filelds increased as years go by because of accumulation of the insecticides residues. We aim to construct and spread a standard method for mesocosm test to each region in Japan for assessing the ecological impact of pesticide to each regional ecosystem.

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Although many ecological risk assessments of hazardous chemicals have been conducted with test organisms, such procedures may be insufficient for establishing reliable hazard assessments in wild organisms. The genetic variation within a species is rarely considered in such assessments. Here, the relationship between variability in susceptibility to fenvalerate, an agrochemical toxicant, and the degree of divergence in allele frequencies at six microsatellite loci were assessed in Daphnia galeata populations in Lake Kasumigaura and an adjacent local pond. The acute EC50, based on changes in neonate immobility, in isofemale lines from three populations in Lake Kasumigaura was 5–10 times that observed in lines from the local pond population; however, the degree of divergence in allele frequencies was much larger among the Lake Kasumigaura populations than between the lake and local pond populations. These results suggest that the level of resistance to the toxicant was determined primarily by the gradient of pollutants resulting from water flow and did not reflect the genetic divergence of local populations. I also discuss a possible causal link between susceptibility against toxicant and genetic variation for future perspectives of ecological risk assessments.

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Omics technologies clearly provide scientific advancement in ecotoxicology. On the other hand, it is still uncertain whether omics can provide actual advancement in ecological risk assessment and management. The key problem is the difficulty of &lquo;anchoring&rquo; the context of omics and ecological risk, due to the large difference in relevant biological levels of omics (e.g., DNA, transcriptome and metabolome) and of ecological risk management (e.g., population, community and ecological function). This article discussed approaches for anchoring omics and ecological risks.

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Pesticide inventory as information infrastructure consists of several databases for ecological effect assessment and exposure assessment. In ecological effect assessment, ecotoxicity database was constructed by collecting ecotoxicity data for aquatic organisms. Laboratory ecotoxicity data was extrapolated to effect on actual ecosystem using species sensitivity distribution. In exposure assessment, pesticide physicochemical database, pesticide usage ratio database in each year, region, and application way, database on pesticide environmental fate in paddy water, land use and river flow databases were constructed. Temporal-spatial variability in predicted environmental concentration in river water was analyzed using the constructed databases. Ecological risk can be quantified by combination of species sensitivity distribution and temporalspatial variability in predicted environmental concentration.

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Aquatic ecosystems have many real problems due to anthropogenic impacts. Chemical pollution is one contributing factor to these problems. Population dynamics of the organisms are controlled by complex combinations of biotic interaction and abiotic environmental factors. Vulnerability to the toxic chemicals differs between each species, so the chemicals should induce different community structures. Moreover, the chemicals not only affect the individual survival or the reproduction rate, but also disturb the prey-predator interactions at very low concentrations. Here, we will introduce the recent studies focusing on the impacts of anthropogenic chemicals on aquatic food webs.

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Metals are ubiquitous, and concentrations of them are at a level at which risks to aquatic biota cannot be ignored. There are a lot of toxicity data for metals, and those tests revealed that the toxicities of metals vary depending on water chemistry. Ecological risk assessment（ERA）of metals has long been obstructed due to the large uncertainty. After a powerful troubleshooter, a biotic ligand model（BLM）which predicts the varying toxicity, has been developed, there are much progresses in the ERA of metals. We first provide a brief review on the history of the ERA of metals. Then we introduce our recent results of the population level assessments and discuss their implications for future ERA. At the end, we argue what we need to develop more ecologically relevant ERAs.

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Sensitivity to several rice paddy pesticide formulations（4 nursery-box-applied insecticides and 7 herbicides）for the tadpoles of Japanese Tree Frog（Hyla japonica） was tested. LC₅₀ values of 4 insecticides and 4 paddy herbicides for the tadpoles were high（> 100mg/L）, however, those of 3 herbicides（Kirifuda one kilo granule, Boss one kilo granule and Sparkstar one kilo granule）were relatively low（10-30mg/L）. In the active ingredients of the 3 herbicides, which showed high toxicity, LC₅₀ values of indanofan, esprocarb, pretilachlor and dimethametryn were low（0.3-5mg/L）. Concentration changes of these active ingredients in paddy water was calculated by the simulation model（PADDY）, and the calculated maximum concentrations of indanofan, esprocarb, pretilachlor and dimethametryn were less than LC₅₀ values of these active ingredients for the tadpoles. These results suggest that the tested rice paddy pesticides are less likely to influence to the Japanese Tree Frog’s tadpoles.

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Marbled flounder Pleuronectes yokohamaewere fed with a formulated diet spiked with 7 nitrated polycyclic aromatic hydrocarbons（NPAHs）during a 7-day intake period after which they were fed with NPAHs-free diet during the next 7 days as elimination period. Results showed that NPAHs concentrations in fish body were increased but levels were lower than in the dietary concentrations and did not show signs of accumulation. Genotoxicity was manifested in the significantly higher frequencies of micronuclei（MN） and other nuclear abnormalities（NA）formation in erythrocytes with higher frequencies of ΣMN+NA at day 7 in lower and higher dietary exposure groups at 42.3 and 45.7 per 1000 erythrocytes, respectively and 5.66 per 1000 erythrocytes in the control.

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Studies on the accumulation of waterborne nitrated polycyclic aromatic hydrocarbons （NPAHs）, commonly known as nitroarenes, by fish are not well known. In this study, bioconcentration of NPAHs by marbled flounder, Pleuronectes yokohamae exposed to a mixture of six NPAHs was investigated in a continuous flow-through system for a period of seven days exposure followed immediately with seven days elimination. P. yokohamae is one of commercially important fish in Japan and is known to accumulate pollutants. Results show that NPAHs steady-state conditions were established from day 1 to 4 of exposure. Estimated bioconcentration factors（BCFs）ranged from 4 to 422 with 6-nitrochrysene and 2-nitrofluorene having the lowest and highest BCFs, respectively. Half-lives were from 0.96 to 5.59 days with 2-nitroflourene and 6-nitrochrysene being the shortest and the longest, respectively. The present study showed that waterborne NPAHs were accumulated by marbled flounder but the BCFs were lower than reported values of their parent PAHs. Furthermore, the difference in BCFs between NPAHs and PAHs could be attributed to the biotransformation processes and steric hindrance of these compounds.

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Butylparaben（BuP）is an alkyl hydroxyl benzoate preservative that can be present in aquatic environments, where it can adversely affect the development and reproduction of aquatic organisms due to its estrogenic properties. The BuP concentrations detected in aquatic environments are generally low（ng/L levels）, but few reports have addressed their effects on fish reproduction. Therefore, we exposed mature medaka（Oryzias latipes）to mean measured BuP concentrations of 102, 218, 482, and 979 μg/L for 14 d and assessed the effects on the egg number and fertility of paired medaka during the exposure period. We also assessed vitellogenin-1（VTG-1） gene expression levels in the liver of the exposed fish. The number of eggs produced and the fertility of the paired medaka exposed to 979 μg/L BuP were significantly reduced compared with those of the control fish. Hepatic VTG-1 levels were significantly increased in all BuP-treated males. The lowest observed effective concentrations （LOECs）of BuP for reproductive impairment（decreased fecundity and fertility）and eliciting estrogenic responses（VTG-1 expression）were 979 and < 102 μg/L, respectively. Since the environmental concentrations of BuP are at least three orders of magnitude lower than the LOEC for population-level effects, BuP alone may not affect the reproduction of wild fish populations.

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