Development of marine sediment reworker tests with Western Australian species for toxicity assessment of drilling mud

Two burrowing species, the estuarine euryhaline amphipod Grandidierella sp. and the marine mollusc Paphies elongata, were used for the development of marine sediment re-worker toxicity tests. Acute static toxicity tests were performed on these species at 25 degreesC with reference toxicants in a wat er phase or drilling fluids in a sediment phase. The 96-h 50% lethal concen tration (LC50) of cadmium for Grandidierella sp, was 0.95 mg/L. The mean 10 -d LC50 of hexavalent chromium for Grandidierella sp, in six independent te sts was 1.40 mg/L with a coefficient of variation of 24%. The average 96-h LC50 value for P. elongata was 32.1 mg Cr(VI)/L. The 10-d LC50 values for G randidierella sp. exposed to drilling muds based on synthetic paraffin, iso -olefin, and ester fluids were in the range of 200-1500 mg/kg. The 5-d LC50 values of the same paraffin and iso-olefin drilling muds for P. elongata w ere greater than 20,000 mg/kg. The high sensitivity and response reproducib ility of Grandidierella sp. in toxicity bioassays, under tropical condition s, demonstrated the suitability of this local sediment re-worker species fo r drilling mud toxicity testing in Western Australia. (C) 2000 by John Wile y & Sons, Inc.