Toxicity tests using the kelp Undaria pinnatifida for heavy metal risk assessment

Abstract

The toxicity of six metals (Cd, Cu, Hg, Ni, Pb and Zn) to the early life stages of the brown seaweed Undaria pinnatifida were tested using two endpoints: spore germination and germ tube elongation. The optimal test conditions determined for photon irradiance, pH, salinity and temperature were darkness, pH 8, 35‰ and 15°C, respectively. The EC50 values could be determined only for Hg and Cu and were 27 μg · L-1 and 186 μg · L-1, respectively, for germination and 16 μg · L-1 and 45 μg · L-1, respectively, for germ tube elongation. The variability of our U. pinnatifida test in response to the metal toxicants, as estimated from the coefficient of variation of the mean EC50 values, was less than 28%. When tested against two different wastewater samples (PCB manufacturer and TV & communication equipment manufacturer), U. pinnatifida exhibited an EC50 of 66.09-80.73% for germination and 24.98-62.62% for germ tube elongation with the CV (Coefficient of variation) range for both germination and germ tube elongation between 1.24 and 13.18%. The novel aspect of the present method is that the testing procedure requires no lighting or photoperiodic control. Additionally, the response of Undaria to the toxicity of Hg and Cu is very similar to that reported for other very sensitive macroalgal species. Because of its ecological and economic importance, the evaluation of toxicity using early stages of U. pinnatifida will provide useful scientific information, and we propose that this represents a valid bioassay within the battery of aquatic bioassays for the assessment of anthropogenic impacts on coastal ecosystems and commercial cultivation areas in nearshore environments.