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.

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.