Comparing the effects and potencies of perchlorate and nitrate on amphibian metamorphosis using a modified amphibian metamorphosis assay (AMA)

Abstract

AbstractA modified amphibian metamorphosis assay was performed in which Nieuwkoop and Faber (NF) stage 47 Xenopus laevis larvae were exposed to different concentrations of either perchlorate (ClO4−) or nitrate (NO3−) for 32 days. Larvae were exposed to 0.0 (control), 5, 25, 125, 625, and 3125 μg/L ClO4−, or 0 (control), 23, 71, 217, 660, and 2000 mg/L NO3−. The primary endpoints were survival, hind limb length (HLL), forelimb emergence and development, developmental stage (including time to NF stage 62 [MT62]), thyroid histopathology, wet weight, and snout‐vent length (SVL). Developmental delay as evidenced by altered stage distribution and increased MT62, a higher degree of thyroid follicular cell hypertrophy, and an increase in the prevalence of follicular cell hyperplasia was observed at concentrations ≥125 μg/L ClO4−. The no observed effect concentration (NOEC) for developmental endpoints was 25.0 μg/L ClO4− and the NOEC for growth endpoints was 3125 μg/L ClO4−. Exposure to nitrate did not adversely affect MT62, but a decreasing trend in stage distribution and median developmental stage at ≥217 mg/L NO3− was observed. No histopathologic effects associated with nitrate exposure were observed. An increasing trend in SVL‐normalized HLL was observed at 2000 mg/L NO3−. Nitrate did not alter larval growth. The NOEC for developmental endpoints was 71 mg/L NO3−, and 2000 mg/L NO3− for growth endpoints. The present study provided additional evidence that the effects and potency of nitrate and perchlorate on metamorphosis and growth in X. laevis are considerably different.