Arch. Environ. Contam. Toxicol. 29, 366-372 (1995) ARCHIVES OF Environmental Contamination a n d Toxicology © 1995 Sprh~ger.Vexlag New York Inc. Influence of Salinity on Copper and Azide Toxicity to Larval Topsmelt Atherinops affinis (A yres) B. S. Anderson*, J. W. Hunt, W. J. Piekarski, B. M. Phillips, M. A. Englund, R. S. Tjeerdema, J. D. Goetzl** Institute of Marine Sciences and Departmentof Chemistry and Biochemistry,Universityof California, Santa Cruz, California95064, USA Received: 17 September1994/Revised:6 March 1995 Abstract. Performance of a 7-d growth and survival toxicity test protocol using larval topsmelt, Atherinops affinis (Ayres), was evaluated for copper chloride and sodium azide at repre- sentative estuarine salinities. Results showed that topsmelt are amenable to toxicity testing at estuarine salinities ranging from 5 to 34%0 since control survival was 100% in all toxicity tests. Sensitivity to both toxicants increased at lower salinities, with the LC50s for copper ranging from 205 Ixg/L at 34?00 to 44 p,g/L at 10%o, and those for sodium azide ranging from 54 mg/L at 34%0 to 7 mg/L at 5?00. Larval tissue osmolality de- creased with increasing copper concentration relative to control fish. Copper uptake was not affected by changes in salinity. This suggests that increased sensitivity to copper was due, in part, to the increasing physiological challenge of osmoregula- tion. It is also possible that cupric ion concentration increased at lower salinities, resulting in reduced larval survival. It is hypothesized that increased sensitivity to azide at lower salinity was due to the interaction between azide toxicity and increasing osmotic challenge. A second experiment with azide showed that larval acclimation time did not affect the interaction be- tween salinity and azide toxicity. A 7-day growth and survival toxicity test protocol for the tops- melt, Atherinops affinis, is being evaluated by the California State Water Resources Control Board as part of an effort to develop protocols to estimate chronic toxicity to species indig- enous to the west coast of the United States (Hunt et al. 1991, Anderson et al. 1994). The topsmelt is particularly appropriate for use in toxicity testing because of its ecological importance, relative sensitivity to a variety of toxicants, amenability to * Present address: Marine Pollution Studies Laboratory, 34500 Coast Route 1---GraniteCanyon, Monterey, CA 93940 ** Present address: California Department of Fish and Game, Moss Landing, California, USA Correspondence to: B. Anderson laboratory culture, and similarity to other Atherinid species already used widely in toxicity testing (e.g., Menidia spp.; Weber et al. 1988). There have been a number of recent toxico- logical studies with this species (Anderson et al. 1991; Hemmer et al. 1992; Goodman et al. 1992; Anderson et al. 1994; Mc- Nulty et al. 1994; for review, see Middaugh and Anderson 1994). Topsmelt are able to tolerate a wide range of salinities. Car- pelan (1955) found that topsmelt may survive and reproduce at salinities up to 72%o. Middaugh and Shenker (1988) reported that topsmelt larvae survive salinities from 2 to 60%0. Because pollutants are discharged into estuarine and coastal receiving waters ranging from brackish to marine salinities, and because changes in salinity may influence toxicity, the use of euryhaline species allows for a more relevant assessment of toxicity in receiving waters. Therefore, there is a need for toxicity test protocols using euryhaline species. A number of studies have investigated the relationship be- tween salinity and toxicity using heavy metals (Cd, Zn, Ni, Pb, Cr, Cu, Hg). Most have focused on the interaction between thermal and osmotic stress and exposure to sublethal concentra- tions of heavy metals, particularly cadmium. Studies include those with fish embryos and larvae (Lorz and McPherson 1976; Alderdiee et al. 1979, Voyer et al. 1979, Voyer et al. 1982) and those conducted with other phyla, primarily crustaceans (Thurberg et al. 1973; Jones 1975; McLusky and Hagerman 1987; DeLisle and Roberts 1988, 1994). This paper evaluates the performance of a 7-d growth and survival protocol for larval topsmelt at representative estuarine salinities, and describes the relationship between salinity and the toxicity of two compounds. The influence of salinity on copper chloride (cupric chloride; CuC12) toxicity was investi- gated because copper is a commonly used reference toxicant and ubiquitous contaminant (Weber et al. 1988; Anderson et al. 1991, 1994), and because cupric ion complexation and bio- availability are affected by organic ligand concentrations which may vary with salinity. There have been few studies on the influence of salinity on copper toxicity to larval fish. Salinity dependent toxicity of sodium azide (NAN3) was investigated because the bioavailability of azide is salinity independent (at pH 8.0). Sodium azide has been used previously as a reference toxicant (Cherr et al. 1990). Although azide is considered an