Cadmium and zinc in mar chiquita coastal lagoon (Argentina):: Salinity effects on lethal toxicity in juveniles of the burrowing crab Chasmagnathus granulatus

The large Argentine marine littoral zone is characterized by great number of wetlands and includes only one coastal lagoon, Mar Chiquita, which has been declared as a Biosphere Reserve by the Man and Biosphere Reserve Program from UNESCO. Its margins present populations of Chasmagnathus granulatus, a semiterrestrial crab distributed along wide salinity gradients that plays an important role as a key species within the corresponding trophic web. Dissolved cadmium (Cd) and zinc (Zn) concentrations present in this ecosystem were determined. Cadmium concentrations ranged between n.d. and 0.82 mu g/L and zinc levels ranged between n.d. and 1224.38 mu g/L within the mentioned coastal lagoon. Cd and Zn acute semistatic toxicity bioassays were carried out for 96 h on juvenile crabs of C. granulatus. LC50 96-h values were 2.24 mg Cd2+/L and 7.07 mg Zn2+/L at 5 psu, and 15.42 mg Cd2+/L and 11.41 mg Zn2+/L at 25 psu. Higher salinities resulted in lower metal toxicity. This effect was stronger for Cd than for Zn. C. granulatus juveniles LC50 96-h values determined for Cd were three to four orders of magnitude higher than the corresponding dissolved metal concentrations in the Mar Chiquita coastal lagoon; nevertheless, those Zn values determined were similar to several ones corresponding to natural water samples.