PARENT SESSION
1C Ecologically relevant and cost-effective toxicity test designs
9:00 AM to 7:00 PM, Monday, 07 May 2001

(M/EH014) Lead toxicity and bioaccumulation in diatoms from South Brazil.

Devilla, Rosangela ^1,2, Garcia, Virginia¹, ^{1 2}

ABSTRACT- In the estuarine area of Patos Lagoon, South Brazil, where industries, ports and other anthropogenic activities take place, high levels of metal contamination, including lead, have been recorded. In order to assess the effect of lead on local microalgae, two diatoms species from plankton (Skeletonema costatum) and benthic (Cylindrotheca closterium) habitats were isolated from a pristine site and subjected to toxicity bioassays. In addition, cells ability to absorb and adsorb lead from the medium were estimated by 24h-bioaccumulation experiments using 500 g/l Pb. Bioassays were performed with f/10 enriched seawater medium, without EDTA. Growth rates in terms of chlorophyll-a and cell numbers were monitored during the experiments. Results of toxicity bioassays showed no algicidal effects at the concentrations tested, up to 3000 g/l Pb. However, relatively low values of EC50 were observed, especially for S. costatum. EC50 related to chlorophyll-a biomass after 96 h were 6.0 g/l for S. costatum (SK-PC2) and 27 g/l for C. closterium (CY-PC1). Bioaccumulation experiments showed that C. closterium (CY-PC1) retained more Pb (0.188 pg/cel), than S. costatum (SK-PC2), for which 0.065 pg/cel was observed. However, on a volume basis, S.costatum (SK-PC2) presented a higher accumulation value, which may have contributed to a higher sensitivity to Pb, observed for this strain. As much as 60% of Pb added to the medium was retained by C. closterium and for both species, a higher percentage of accumulated Pb was associated with the cell surface (adsorbed) rather than in the particulate fraction. It can be concluded that relatively low Pb concentrations (< 30 g/l) can cause considerable inhibition of physiological functions on the diatoms tested in this study. In addition, both diatoms show a considerable potential to remove dissolved Pb from water, by accumulating the metal outside and inside the cells.

Key words: diatoms, bioaccumulation, bioassays, lead toxicity