The toxicities of a polyunsaturated fatty acid and a microcystin to Daphnia magna.

Polyunsaturated fatty acids (PUFAs) are essential components of zooplankton diets. However, studies with PUFAs from cyanobacteria indicate toxic properties. We investigated the toxicity of the PUFA gamma-linolenic acid and the cyanobacterial peptide toxin microcystin-LR to Daphnia. The PUFA was acutely toxic at a concentration of 9 micrograms ml-1. The effect of microcystin-LR was not statistically significant at the concentration used (3 micrograms ml-1), but an additive effect with the PUFA was observed. Relative to LC50-values of well-known pollutants, the PUFA was intermediately toxic. The activity equaled that of microcystin-LR, which is commonly treated as one of the most potent cyanobacterial toxins. Our results suggest that the toxic properties of PUFAs deserve more attention.