Effect of heavy metals on lipids from the freshwater alga Selenastrum capricornutum.

Algae are a common component of freshwater ecosystems. The presence and abundance of these organisms has often been used as an indicator of water quality. In addition, algae such as Enteromorpha are able to accumulate pollutants, and have been used to monitor toxic trace metal pollution in aquatic environments [l]. In marine algae, heavy metal pollution has been shown to affect acyl-lipid composihon with respect to fatty acid elongation and desaturation [2]. It is envisaged that similar changes in the lipid profile of Selenastnun capricornutwn will enable identification and quantification of heavy metal pollutants in freshwater environments. In metal toxicity tests, S. capricomutwn was grown in batch culture and treated with a range of copper, zinc and cadmium concentrations. Metal EC-50 values of 124 pM Cu, 20 pM Zn and 5.7 pM Cd were determined from these growth inhibition tests, according to OECD Guidelines for the Testing of Chemicals [3]. Subsequently, algal cells were exposed to these metal concentrations and grown into late stationary phase; then harvested and freeze dried. Lipids were extracted from freeze dried material, separated into polar and neutral lipid fractions by TLC, and fatty acid methyl esters prepared [4] and analysed by capillary GC. Analysis was performed using a 30m x 0.25mm ( 0 . 2 5 ~ film thickness) Omegawax fused silica capillary column. in a Unicam 610 gas chromatograph with cold oncolumn injection. The following temperature programme was used: the column was ramped from 55°C to 205°C min-1 with the detector at 255°C. Typical acyl lipid compositions of total lipids from control and metal treated algal cells are shown in Figure 1. These results indicate that metal exposure had significant effects on acyl-lipid metabolism, leading to increased levels of palmitate and oleate. A similar increase in oleate levels has been observed in brown marine algae with Cu exposure, although these authors found levels of palmitate to be significantly reduced [5].