THE CAPACITY OF AMPHIBIAN EMBRYOS TO NEUTRALIZE LOW pH CONDITIONS AND ITS ROLE ON ALUMINIUM TOXICITY

LUIS CASTAÑAGA, JOSE LUIS D´ERAMO AND JORGE HERKOVITS

Jackson, Mississippi, EEUU

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

Jackson State University

  Acidification of surface water, reported in a large number of environmental scenarios exerts deleterious effects by itself and enhancing the toxicity of different xenobiotics.  It is well known that low pH values increase the solubility, bioavailability and toxicity of aluminum. Moreover, the lethal effects of Al for amphibian embryos occur in a range of pH values which are toxic by themselves. The main purpose of this study is to report the capacity of amphibian embryos to modify the pH in the maintaining media towards less toxic conditions. At this end two experimental strategies were applied: 1) employing buffer solutions and 2) with Al. 1) 10 Chaunus arenarum embryos at stage 25 (complete operculum) by triplicate were maintained in glass Petri dishes for 96 hr containing 40 ml of citrate or acetate buffers prepared at 1% v/v  in AMPHITOX Solution (AS) which represented NOEC concentrations as obtained in preliminary studies In the case of citrate, the pH values were adjusted to   4  (4.12), 5 (4.85), 6 (5.97) and for acetate, they were 4 (4.06), 5 (5.00) and 6 (5.95)  nominal (and determined) pH values respectively. 2) Bioassays with Al in AMPHITOX Solution (AS) were conducted in 0.3, 0.5 and 1 mgAl/ ; their  pH values were 4.41, 4.10, 3.83 respectively. The control conditions were embryos maintained in AS and the two buffers employed. pH values were recorded each 24hr. with a Luftman portable pH meter up to the end of the test. The pH values in citrate buffer rose from 4.12 to 7.05 [Surviving embryos (Se) 50%]; 4.85 to 7.25 Se 95%; and 5.97 to 7.5 Se 95%, the values for acetate buffer changed from: 4.11 to 4.34 Se 0%; 5.00 to 6.11 Se 100% and 5.95 to 7.5 Se 95% respectively while the pH of the buffer solutions without embryos did not change (citrate buffer 5.97 to 5.99, acetate buffer 5.95 to 5.95) during the experimental period (96hr). The LC50/96hr. value for Al in AS was 0.534mgAl/l. The pH values in the three concentrations of Al solutions tested (with the presence of 10 embryos per exposure chamber) changed from: 4.41 to 6.35 Se 85%; 4.10 to 5.50 Se 60% and 3.83 to 4.1 Se 0% for 0.3, 0.5 and 1.0 mgAl/l respectively. The results points out that amphibian embryo were able to modify the pH in their maintaining media towards more physiological conditions a fact which also imply a decrease in the aluminum toxicity. Although the alkalinization of the solutions could be related to the fact that amphibians excrete ammonia in their aquatic stages, the perspective that these organisms can change to some extent their habitat toward less noxious conditions is relevant for a better understanding of the interactions of living forms and their environment.