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

(M/EH009) Lead toxicity bioassay in microalgae: influence of EDTA addition and seawater source.

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

ABSTRACT- Addition of EDTA and type of seawater are still a matter for discussion in performing metal toxicity bioassays with marine phytoplankton. Two experiments have been conducted in laboratory using the diatom Skeletonema costatum for assessing 1) use of artificial and natural seawater and 2) addition of the metal ligand EDTA in lead toxicity tests. Both enriched and non-enriched media were also tested. The S. costatum strain isolated from Cassino Beach, south Brazil, was maintained in batch cultures containing f/2 enrichment under controlled temperature and light conditions. Maximum chlorophyll-a, cell and chlorophyll growth rates were used as parameters for monitoring culture development. Results from the first experiment showed that cell growth rates were approximately 18% more inhibited by lead in cultures made with artificial seawater, compared to natural seawater. In the second experiment, where a higher Pb concentration was tested (500 g/l Pb), cells grown in non-enriched seawater showed a very low maximum chl-a (0,6 g/l) compared to the other treatments (over 300 g/l), but duplication rate was similarly inhibited to the one in enriched natural medium without EDTA (approx. 50% inhibition in relation to control). However, for f/2 enriched seawater, EDTA addition was shown to have a strong effect on lead toxicity to S. costatum. Both maximum chlorophyll-a and growth rates were highly inhibited in the absence of EDTA, especially in natural seawater (51% growth inhibition and 5% for medium without and with EDTA, respectively). It was concluded that enriched natural seawater without EDTA addition has a satisfactory response to lead toxicity and it has the advantage of being closer to environment composition, compared to artificial seawater.

Key words: Skeletonema costatum, EDTA, lead, toxicity tests