Acute Toxicity of Copper, Cadmium, and zinc to Larvae of the Crab Paragrapus quadridentatus (H. Milne Edwards), and Implications for Water Quality Criteria

Abstract

Acute toxicity tests were carried out on the larvae of P. quadridentatus and 96-h LC50 values of 0.17, 0.49, and 1.23 mg/l were determined for copper, cadmium, and zinc respectively. Potency ratios of the three metals were as follows: Cu/Cd 3.1, Cu/Zn 7.2, and Cd/Zn 2.4. Larvae were found to be nine times more sensitive to zinc and at least 29 times more sensitive to cadmium than were adults. The larval 96-h LC₅₀ values multiplied by an application factor of 0.01 (as recommended in Victorian water quality criteria) results in derived 'safe' concentrations, which in the case of copper and zinc are below the stated 'minimal risk concentrations' of 10 and 20 µg/I respectively. In view of the known greater sensitivity of larvae of many taxa to heavy metal toxicity, the validity of using the same application factor for both adult and larval stages is questioned.