Acute Toxicity of Copper, Zinc, and Ammonia to Larvae (Glochidia) of a Native Freshwater Mussel Echyridella menziesii in New Zealand

Adult New Zealand freshwater mussel Echyridella menziesii were collected from three locations in the North Island of New Zealand. In a series of tests that followed standard test guidance, glochidia were exposed to either dissolved copper (Cu), zinc (Zn), or total ammonia nitrogen (TAN) for 6, 24, or 48 h (20 °C, pH 7.8, water hardness 30 mg L−1 as CaCO3, dissolved organic carbon [DOC] 2.0–2.9 mg L−1). Of the three contaminants and tests that met control survival criteria, mussel larvae (glochidia) were most sensitive to Cu exposure (48-h EC50 = 1.7–3.4 μg L−1, 48-h no observed effect concentrations (NOEC) of 1.3–2.6 μg L−1). The Zn 48-h EC50 concentrations were 229–337 μg L−1 and the 48-h NOEC values were 128–240 μg L−1. Compared with other native New Zealand species, glochidia were also relatively sensitive to TAN exposure (48-h EC50 12–15 mg TAN L−1 [pH 7.8], 48-h NOEC 8–10 mg TAN L−1). Comparison of our data with those of previous studies on North American freshwater mussels indicates that (1) E. menziesii are among those aquatic species most sensitive to acute Cu or TAN exposure; and (2) E. menziesii juveniles would not be adequately protected by current ANZECC water quality guidelines for TAN or Cu. Inclusion of North American juvenile mussel data in a revision of the current ANZECC water-quality guideline (95th percentile) for chronic ammonia exposure results in a decrease from 0.9 mg to 0.2 mg TAN L−1 (pH 8).