Effects of salinity and chemical speciation on cadmium accumulation and toxicity to two mysid species

The estuarine environment is characterized by frequent fluctuations in sali nity. Consequently, organisms used for environmental monitoring of estuarie s must be euryhaline so that their laboratory responses to chemical polluta nts are measured under the full range of salinity exposures experienced in the field. Neomysis integer and Praunus flexuosus are two potential candida tes for use in environmental monitoring of European estuaries. The present study assesses the effects of salinity on survival, trace metal accumulatio n, and toxicity to these two mysid species. Neomysis integer was more euryh aline, showing 100% survival at 1 to 40 parts per thousand compared with P. flexuosus, which showed 100% survival at salinities of 10 to 40 parts per thousand. Toxicity of the free cadmium ion to both species was unaffected b y salinity, and 96-h LC50s ranged from 4.8 to 15 mug Cd2+/L for N. integer and from 12.3 to 16 mug Cd2+/L for P. flexuosus. The 7-d LC50s ranged from 1.0 to 4.2 and 4.8 to 5.3 mug Cd2+/L for N. integer and P. flexuosus, respe ctively. No effect of exposure salinity was found on cadmium body burdens o f mysids exposed for 7 d to 0.5 and 1.0 mug Cd2+/L. The results are discuss ed in terms of possible effects of osmoregulatory mechanisms on trace metal uptake, accumulation, and toxicity.