Assessment of bioavailability of metals in natural waters with the Lemna gibba toxicity test.

SOBRERO, MARIA CECILIA; RIMOLDI, FEDERICO; MUGNI, HERNAN DIEGO; RONCO, ALICIA

Vilnius, Lithuania

Simposio; 11th International Symposium on Toxicity Assessment.; 2003

11th International Symposium on Toxicity Assessment, Vilnius, Lituania, 2003 Assessment of bioavailability of metals in natural waters with the Lemna gibba toxicity test. C Sobrero, F Rimoldi, H Mugni and A Ronco -CIMA, Faculty of Sciences, National University of La Plata and CONICET, La Plata, Argentina. cima@quimica.unlp.edu.ar The sensitivity of Lemna gibba to salts of Cu(II), Cd(II) and Cr(VI) in two different hydrochemical environments (Vitel and Juan Blanco streams) of the Pampean plain of the Buenos Aires province, Argentina, is reported here. L. gibba is a widely distributed macrophyta in ponds and streams of the region and it is at present being considered as a potential reference organism by local Environmental Control Offices. Since water composition defines metal speciation and, eventually, its different bioavailability and toxicity to biota, the response of Lemnaceae by means of toxicity tests on spiked natural surface waters provides valuable information for risk assessment evaluations within a specific area. Laboratory assays were performed with standard growth medium and with natural surface waters added of metal solutions by separate. Phytotoxic effects on multiplication rate and chlorophyll content were assessed by the 14 days IC50s. Water-effect ratios (WER: IC50stream/IC50growth medium) for each metal were calculated to express the metal toxicity variation in natural waters respect to culture media. Water physicochemical characterisation indicates slight differences between both streams, being the Juan Blanco of a hard water richer in some of the nutrients respect to Vitel stream, of very hard water. Results show lower metal toxicity in natural waters than in growth media, except for Cu(II) in Vitel water. For the last case no significant differences were observed between treatments. Although chemical composition of water was slightly different, Cr(VI) toxicity was very similar in both streams. Cd(II) WER values indicates that metal toxicity in the tested natural waters is reduced from 3.8 to 7.3 times for Cd(II) and from 2.2 to 3.9 for Cr(VI), for the studied end points.