Metal Toxicity across Different Thallus Sections of the Green Macroalga, Ulva australis

We aimed to identify functional differences between different sections of the thallus of Ulva australis and develop tissue-endpoint combinations to assess the toxicity of six metals (i.e., Ag, As, Cd, Cr, Cu, and Ni). EC50 values for these metals in three sections of the thallus of Ulva were obtained for multiple endpoints: relative growth rate (RGR), chlorophyll a fluorescence, pigment contents, and the expression of the photosynthesis-related gene, rbcL. The responses of the endpoints varied across the respective thallus sections; overall, the most toxic metals were Ag and Cu. These endpoints were the best for evaluating metal toxicity: ETRmax of the middle thallus sections for Ag toxicity; RGR of the middle thallus section for As and Cd; ETRmax of the marginal thallus section for Cr; Chl b contents of the marginal thallus section for Cu; RGR of the basal thallus section for Ni. The EC50 values for the inhibition of ETRmax in middle (0.06 mg & BULL;L-1) and Chl b in the marginal thallus sections (0.06 mg & BULL;L-1) were all lower than those of the quality standard for wastewater discharge values of Ag and Cu in Republic of Korea and the US, pointing to the suitability of U. australis-based endpoints for risk assessment.

Automated summary

The study aimed to identify functional differences between different sections of the thallus of Ulva australis and develop tissue-endpoint combinations for assessing metal toxicity. EC50 values for six metals (Ag, As, Cd, Cr, Cu, and Ni) were obtained in three sections of the thallus using multiple endpoints. The responses of the endpoints varied across the thallus sections, with Ag and Cu being the most toxic metals. The EC50 values for some endpoints were lower than the quality standard for wastewater discharge values, indicating the suitability of U. australis-based endpoints for risk assessment.