STAGE-DEPENDENT SUSCEPTIBILITY OF COPPER ON CHAUNUS ARENARUM EMBRYOS.

CAROLINA ARONZON, MARÍA T. SANDOVAL, JORGE HERKOVITS AND CRISTINA S. PÉREZ-COLL.

Jackson, Mississippi, EEUU

Congreso; Fourth International Symposiumon recent advancesin environmental health research; 2007

Jackson State University

Copper is an essential element for many metabolic processes. However, concentrations slightly higher to the physiological ones can generate adverse effects on wildlife and human health. Its presence in the ecosystems is increasing due to agriculture and industrial activities. The main aim of this study was to evaluate the lethal and teratogenic effects of Cu2+ (CuCl2. 2H2O) on the embryonic development of Chaunus arenarum by employing the early life stage and the short term chronic toxicity bioassays of the standardized AMPHITOX test. Groups of 10 embryos, by triplicate, were  treated as follow: (1) continuous exposure to Cu2+  from the 2 blastomers stage (S.3) up to the end of the embryonic development (S.25); (2) exposure in ten selected stages during 24 hr: blastula (S.3), gastrula (S.10); neural folds (S.14), tail bud (S.17),  neuromuscular activity (S.18), heart beat (S.19) gill circulation (S.20), open mouth (S.21), opercular folds (S.23) and complete operculum (S.25); and (3) at the end of embryonic development (S.25) during 168 hr. Control embryos were simultaneously maintained in AMPHITOX Solution (AS). Lethal, teratogenic and behavioral effects of Cu on developing embryos were daily registered. The LCs 10, 50 and 90 were estimated by PROBITS and the Toxicity Profile (TOP) curves were obtained. (1) The LC50 decreased from 0.14 at 24 hr to 0.02 mg.L-1 Cu2+ at 168 hr, which represent 700% of increase in susceptibility. (2) By treating the embryos with Cu during 24 hr in different developmental stages as well as by the short-term chronic exposure at S.25, this remarkable change in susceptibility was confirmed with the neuromuscular stage as the most susceptible to Cu2+. From neuromuscular activity stage onwards there is a gradual recovery in the resistance of the embryos until the end of their development. In the case of 24hs treatments, a transient and limited cellular dissociation and alterations in the pigment arrangement was observed. The lowest NOEC value registered was 0.0075 mg.L-1 Cu2+. As teratogenic effects, underdeveloped body size, delayed development, underdeveloped/agenesis gills, axial flexures, microcephaly, edema were registered, and abnormal behavior such as erratic swim, lack of response to stimulus /hyper kinesis, and spasmodic movements were observed. Considering that the levels of this metal in Argentinean plain rivers are between 0.003 and 0.027 mg.L-1 Cu2+ that is in the range of the lowest NOEC value obtained in this study, this metal could represent a risk for Chaunus arenarum populations. This study confirms the relevance to evaluate the stage-dependent susceptibility as a tool to identify the most sensible stages to toxic agents in order to preserve the integrity of ecosystems   Key words: amphibian, copper, teratogenic effects, early life cycle studies   Acknowledgements: CONICET: PIP 2316, 2317; PICT 14375