Acute zinc toxicity to Cnesterodon decemmaculatus (Pisces: Poeciliidae) and application of the Biotic Ligand Model in Pilcomayo River water (South America)

CASARES, MV; DE CABO, LI; SEOANE, R; NATALE, O

Revista de Toxicología

Asociación Española de Toxicología

Año: 2012 vol. 29 p. 84 - 89

0212-7113

The Biotic Ligand Model (BLM) is a chemicalequilibrium-based model that incorporates the effect of physicalchemicalwater characteristics on the bioavailability and toxicity ofmetals to aquatic biota. It was developed for four metals (Cu, Zn, Agand Cd), two fish species and three daphnids. It is assumed that itspredictions can be extrapolated between similar species. In this study,a cross-fish-species extrapolation of the BLM developed for zinc(Zn-BLM) was assessed in Pilcomayo River water. An acute zinctoxicity test was performed to assess zinc toxicity to the local fishCnesterodon decemmaculatus. The dissolved zinc concentrationstested were: 3.74; 9.2; 21.6 and 26.4 mg Zn L-1. The median letalzinc concentration (96-h Zn LC50) calculated for C. decemmaculatuswas 22.6 mg Zn L-1 (17.5-27.6) and the predicted by Zn-BLM forPimephales promelas in the test water was 1.71 mg L- 1. Zincconcentrations measured exceeded zinc solubility causing metalprecipitation which derived in a 96-h LC50 that most probablyincluded both dissolved and precipitated zinc species. Nevertheless,speciation estimates showed that the more abundant zinc species ineach treatment was the free ion. This higher proportion of zinc in itsfree ionic form would explain the low protective effect exerted byelevated water hardness. The difference between the observed zinctoxicity to C. decemmaculatus and the predicted by BLM for P.promelas may be due to the combination of inaccuracy in zincdissolved measurements and a lower sensitivity of C.decemmaculatus to zinc exposure.