Local anesthetics such as lidocaine and dibucaine are widely used in surgical and therapeutic applications and are subsequently released into aquatic environments through human excretion and household wastewater. Lidocaine has been detected in rivers and in both influent and effluent of wastewater treatment plants at concentrations ranging from 7 ng/L to 9.133 µg/L, raising concerns about its potential effects on aquatic organisms. In this study, we used goldfish scales as a model system to investigate the effects of lidocaine and dibucaine on bone cells, as they contain osteoblasts (bone-forming cells) and osteoclasts (bone-resorbing cells), which are sensitive to environmental pollutants. Alkaline phosphatase (ALP) and tartrate-resistant acid phosphatase (TRAP) activities, markers of osteoblast and osteoclast activity, respectively, were measured in goldfish scales after 6 h of incubation with lidocaine or dibucaine. The results showed that neither lidocaine nor dibucaine affected osteoblast or osteoclast activity in goldfish scales at environmentally relevant concentrations (10⁻¹¹ to 10⁻⁷ M; lidocaine: 2.34 ng/L–23.4 µg/L; dibucaine: 3.43 ng/L–34.3 µg/L). To evaluate the ratio of Measured Environmental Concentration (MEC) to Predicted No Effect Concentration (PNEC), additional experiments were conducted using higher concentrations of lidocaine (10⁻⁶ to 10⁻² M). TRAP activity significantly decreased following treatment with lidocaine at 10⁻² M. The MEC/PNEC ratio was 0.0038, which is below 1, suggesting that the environmental risk of lidocaine to fish bone metabolism is very low.

Cationic surfactants such as hexadecyltrimethylammonium salts (HTAC) are known to exhibit high toxicity to aquatic organisms; however, the extent to which water quality conditions influence their apparent toxicity has not been sufficiently clarified. In this study, we investigated the effects of selected water quality factors on algal growth inhibition by HTAC using the freshwater green alga Raphidocelis subcapitata. Algal growth inhibition tests were conducted using standard OECD medium and modified OECD media in which dissolved organic carbon (DOC), pH, hardness (Ca²⁺/Mg²⁺), or sodium concentration was independently adjusted. The results showed that algal growth inhibition by HTAC was significantly reduced under high-DOC conditions achieved by the addition of humic acid, compared with the standard OECD medium. In contrast, no significant effects of pH, water hardness, or sodium concentration on HTAC-induced growth inhibition were detected under the tested conditions. These findings suggest that the algal toxicity of HTAC is highly dependent on DOC concentration in the test medium, likely due to reduced bioavailability through sorption to organic matter. Consideration of DOC is therefore essential for reliable algal toxicity testing of HTAC.

Chronic toxicity tests (OECD TG 210 and 211) are now required for pesticide registration under the Agricultural Chemicals Regulation law in Japan. While Daphnia magna is typically sensitive to chemicals under limited food, the impact of differential feeding conditions in the TG 211 on EC_x values remains unclear. Therefore, we investigated whether the food amounts would affect the chronic toxicity (EC_x) of the reference substance (potassium dichromate). The D. magna reproduction test (OECD TG 211) specifies algal food (Chlorella vulgaris) levels at 0.1–0.2 mg C/daphnia/day. We performed the 21-day chronic reproduction tests under four groups separated by differential food amounts: 1) Overfeeding group (0.4 mg C/Daphnia/day); 2) Normal feeding group (0.2 mg C/Daphnia/day); 3) Changing amounts group (0.1 mg C/Daphnia/day for 1 week from the birth, then, 0.2 mg C/Daphnia/day for 2 weeks); 4) Minimum-feeding group (0.1 mg C/Daphnia/day). In group 4, the EC₁₀ and EC₂₀ values (based on the total reproduction of offsprings) were four to seven times lower than those in the other groups. Moreover, the total number of neonates did not met the criteria (≥60 neonates) in the control of group 4. At least 0.14 mg C/Daphnia/day of C. vulgaris is needed to produce 60 neonates. Although the feeding amount was within the recommended range, our study found that lower feeding amounts could cause unreliable EC_x value estimates. When interpreting chronic toxicity tests, we need to verify both guideline compliance and whether the conditions for EC_x calculations are met.

In the European Union, a revised version of the “Guideline on Environmental Risk Assessment of Medicinal Products for Human Use” (EMEA/CHMP/SWP/4447/00) came into effect in September, 2024. This review explains the revised contents of the Guideline, summarizes points to note when conducting an environmental risk assessment, and proposes a useful project model for the pharmaceutical industry.