The co-existence of microplastics and hydrophobic organic chemicals is ubiquitous in the environment. Microplastics may act as vectors for the transmission of organic pollutants to organisms. In the present study, we co-exposed 33 adult medaka fish to a mixture of chlorobenzenes (CBs; trichlorobenzene, tetrachlorobenzene, pentachlorobenzene, and hexachlorobenzene—at 10, 10, 10, and 8 µg/L, respectively) and two different sizes of polystyrene microplastics (PS-MP)—10-µm PS-MP at 0.1 mg/L and 45-µm PS-MP at 0.45 mg/L. We exposed the fish to CBs, CB10MP (CBs+10-µm PS-MP), and CB45MP (CBs+45-µm PS-MP) for 7 days followed by 3 days for excretion. We measured the concentrations of CBs and PS-MP in the fish on days 7, 8, 9, and 10 and in the water on days 5, 6, and 7. Our results clearly indicated that there was no increase in the concentration of CBs in the medaka co-exposed to MPs and either size of PS-MP. This result might have been due to the sorption of Tri- and TetCBs to PS-MP and little or no desorption in the gut. Our study revealed the absence of a vector effect of PS-MP on the bioaccumulation of CBs in medaka.

Unicellular algae, Raphidocelis subcapitata and Desmodesmus subspicatus, belonging to class Chlorophyceae, order Sphaeropleale, are used for ecological risk assessment of pesticides such as herbicides. Pyrazosulfuron-ethyl (PE), a sulfonylurea herbicide, shows a lower impact on cell growth in Desmodesmus than in Raphidocelis. We investigated the cause of the difference in PE sensitivity between these two algae from the aspect of target-site resistance (TSR) and nontarget-site resistance (NTSR). The cells of two algae showed similar accumulation levels of PE with no detection of a presumed PE metabolite with cytochrome P450 (CYP), indicating no differences in its uptake or metabolism. The 72-hour ErC₅₀s for CYP inhibitors were >2.4 and <0.023 mg/L in R. subcapitata and D. subspicatus, respectively, for ketoconazole, whereas they were 60 and 160 mg/L in R. subcapitata and D. subspicatus, respectively, for 1-aminobenzotriazole (ABT). Co-exposure to ABT with PE showed no effect on the PE-dependent inhibition of cell growth in Raphidocelis, and rather mitigation of the inhibition in Desmodesmus, indicating no detoxification metabolism by CYP in either species. These data indicated no difference in terms of NTSR. As for acetolactate synthase, the target enzyme of sulfonylurea herbicides, PE-dose dependency of inhibition of its activity showed no great difference, and the amino acid residues important for sulfonylurea herbicides binding were conserved between the species. Therefore, no difference was shown in terms of TSR. In this study, the cause of the difference in PE sensitivity was not clarified, but different effects of CYP inhibitors were demonstrated in the two algal species.

We aimed to investigate the changes in water quality and benthic macroinvertebrates at two sites (N1 and N2) downstream and upstream of the inflow of treated mine discharge from a legacy mine (Yoshino mine located in Akita prefecture) in the Naruse river. Based on field surveys conducted in spring (May) and fall (October) 2022, detectable increases in dissolved concentrations of trace metals (Cu, Zn, Cd, and Pb) were observed at the downstream site (N2) but those concentrations were well below the U. S. water quality criteria. In addition, reductions of richness (number of taxa) and abundances (number of individuals) of metal-sensitive mayflies were not detected at the downstream site, and most of the richness and abundance metrics for macroinvertebrates showed no significant difference between the two sites.

A methodological investigation was conducted for analyzing the natural communities of aquatic insect and diatom using environmental DNA metabarcoding, followed by the application for ecological effect assessment of pesticides. Water samples were collected from two distinct sites: the Yamaguchi River, as an unpolluted environment, and the Kokai River, characterized by the widespread presence of paddy fields and potentially elevated pesticide concentrations. In consideration of the pesticide effect on riverine ecological communities, the analysis focused on aquatic insect, known to be vulnerable to insecticides, as well as attached diatoms with susceptibility to herbicides. The Yamaguchi River generally exhibited higher values of bioindicators compared to the Kokai River, supporting the promising role of the environmental DNA approach in assessing ecological effect within natural aquatic ecosystems. An advantage of this methodology lies in its capacity for concurrent use alongside environmental monitoring of chemical substances. Ideally, future monitoring should encompass the simultaneous analysis of chemical concentrations and biota.

The biochemical oxygen demand (BOD) is widely used as an indicator of organic pollution in river water. Comparisons with environmental quality standards at environmental reference points in public water were conducted across Japan. In this study, we conducted consecutive 5-day weekday BOD measurements at four locations over four seasons in three rivers in the southeastern part of the Gunma Prefecture, to evaluate the day-of-the-week and parts-of-the-day-specific BOD variations. Although not statistically significant, higher BOD values were observed in the order—Thursdays, Wednesdays, Tuesdays, Mondays, and Fridays. The observed BOD was significantly higher in the afternoon than in the forenoon. In the study area, most of the previous BOD measurements for comparison with the environmental quality standard were conducted on Wednesday forenoon. Our study highlights the importance of understanding sampling design bias in BOD measurements to avoid overlooking possible over- or under-evaluation of water quality status.

The ecotoxicity of copper (Cu) in the marine environment is of increasing concern. An understanding of benefits and risks in the use of Cu in Japanese coastal areas, particularly information of Cu effects on native copper-sensitive organisms is urgently required. In this study, we conducted ecotoxicity tests on the sensitive early life stages of local abalone (Haliotis discus hannai) using seawater collected from their natural habitat in Miyagi Prefecture, Japan. The no observed-effect concentration (NOEC), 10% effect concentration (EC10), and 50% effect concentration (EC₅₀) for Cu were determined to be 3.5, 5.8, and 8.6 µg/L, respectively. To account for bioavailability, we calculated the EC10 using the correction formula for dissolved organic carbon (DOC) provided in the Voluntary Risk Assessment Report of the European Chemical Agency, using literature values for DOC specific to the Japanese coastal area. As a result, the EC10 ranged from 3.2 to 11.7 µg/L. These results are important for policy makers to establish more realistic Cu water quality standards that take into account the effects on key species and the diverse characteristics of different regions within Japanese coastal areas.

Sediments accumulate contaminants and serve as sources of chemical pollution to ecosystems. Due to the complexity of fate, distribution, and exposure routes of chemicals in sediment environments, there are still many unresolved issues about sediment toxicity assessments. In this review, I provide an overview of sediment ecotoxicity research, with a focus on neutral hydrophobic organic chemicals. I discuss experimental methods of sediment toxicity tests, concentration metrics for sediment toxicity, and how to assess the risks of sediment contamination. I also summarize some important findings from our research team on this topic, which earned me the CERI award in 2022.

This is the report of CERI award in 2023. We evaluated the long-term effects of chemicals, i.e. carbamate pesticides on the aquatic organisms (cladocerans and chironomids), which contributes to receiving the award. Several chemicals, e.g. pesticides transiently discharge into the river or lake because the chemicals rapidly flow into river by heavy rainfall. Considering the realistic exposure to chemicals, we performed the several multigenerational studies on aquatic organisms under the two conditions; 1) transient exposure (48 h) of the test organisms to the model chemical (insecticides or a pharmaceutical); 2) continuous exposure to the model chemical. In both of cases, a part of species acquired chemical tolerance to the test substance. We then elucidated the several mechanisms of chemical tolerance and the fitness costs. Here, I summarize our findings in this review paper. Additionally, to obtain the information on the multigenerational alteration in chemical sensitivity, I made literature search of the research papers on the multigenerational studies for cladocerans and chironomids. To clarify further long-term effects of chemicals, we should connect each finding in several multigenerational study.