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.

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.

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.

Lead (Pb) is extensively used in industries and often inadvertently discharged into the environment. Despite some studies examining the effects of Pb pollution on raptors and waterfowl, its effects on other avian species have not been investigated. This study investigated the feeding selectivity of a black-headed gull (Chroicocephalus ridibundus) population using stable isotope ratios to determine the source of Pb pollution. Gulls in Tokyo and Mikawa Bay were captured from December 2016 to February 2017 and from December 2020 to March 2021, respectively. These gulls were measured 13C/12C carbon ratio (δ13C), and 15N/14N nitrogen ratio (δ15N). Blood Pb level (BLL) was measured gulls in Mikawa Bay. Based on the measurement values of δ15N, gulls were classified into two groups: primary and higher predator groups. No differences in stable isotope ratios were found between the two groups. The secondary consumers showed significantly high BLLs (P=0.002). BLLs during the wintering period were significantly higher in the primary consumer group. Our findings suggest that reducing Pb emissions, along with biological and chemical remediation of water sediment is required to prevent further Pb pollution and bioaccumulation in wild animals.

The cumulative ecological risks from multiple herbicides in Japanese rivers were evaluated using species sensitivity distribution and were compared with natural periphytic diatom communities. Region-specific predicted environmental concentrations were estimated at 9 rivers considering the region-specific parameters of environmental conditions. Then the multi-substance potentially affected fraction (msPAF) was calculated as a risk index of multiple herbicides using the computation tool NIAES-CERAP. On the other hand, river ecological survey focusing on diatom community were conducted in these 9 rivers and several biological metrics for species composition were calculated such as genus number, Shannon’s diversity, DAIpo, and SPEAR_herbicides which is an indicator of the herbicide effect on the diatom community. DAIpo and SPEAR_herbicides (but the population number of each genus was not log-transformed) significantly correlated with msPAF, indicating the applicability of these metrics for assessing the effect of herbicide mixture. Moreover, the percentage of abundance for genus Planothidium and Nitzschia were significantly correlated with msPAF negatively and positively, respectively.