PARENT SESSION

PW13 Metals in the Environment: Regulatory and Risk Concerns
Exhibit Hall
8:00 AM - Wednesday

(PW230) The toxicity of free cyanide to yellow rock crab (Cancer irroratus) first stage zoae.

Caldwell, R.¹, Gensemer, R.², Cardwell, R.², Stewart, M.³, ¹ Northwest Aquatic Sciences, Newport, OR, USA² Parametrix, Corvallis, OR, USA³ Water Environment Research Foundation, Alexandria, VA, USA

ABSTRACT- The U.S. Environmental Protection Agency (U.S. EPA) national water quality criterion for cyanide in salt water is driven by zoeal toxicity data for the yellow rock crab, Cancer irroratus. The reported LC50 for C. irroratus is six times lower than for any other marine species, and from 14 to 31 times lower than recent larval toxicity data for four other species of Cancer crab. This discrepancy prompted a reexamination of C. irroratus cyanide toxicity as part of a larger study that is re-evaluating the national Ambient Water Quality Criteria (AWQC) for cyanide. Flow-through cyanide acute toxicity tests were undertaken with first stage zoeae of C. irroratus. Free cyanide was measured daily by the microdiffusion method in all test concentrations. Median lethal concentrations based on free cyanide elicited a LC50 ranging from 44 - 72 g CN/L in 96-hr acute tests, which are approximately 10 times higher than previously reported for this species. Combined with acute toxicity data from other species of Cancer, the genus mean acute value appears to be 10 times higher than that presently used in the 1984 U.S. EPA water quality criteria. If further confirmed experimentally, use of these revised data suggest that the current AWQC for marine species may be overly protective of the acute toxicity of cyanide to marine organisms.

Key words: yellow rock crab, cyanide, Cancer irroratus, water quality criteria