OECDテストガイドラインにおける給餌量が二クロム酸カリウムのミジンコ繁殖毒性に及ぼす影響

抄録

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.