Lifecycle-dependent toxicity and removal of micropollutants in algal cultures of the green seaweed Ulva (Chlorophyta)

Abstract The green marine seaweed Ulva (Chlorophyta) is widely suggested as a biofilter for cost-effective bioremediation in integrated multitrophic aquaculture and wastewater management. Micropollutants (MPs), including antibiotics, endocrine disruptors, and herbicides, can severely affect humans and the environment. As these compounds may be accumulated or transformed by Ulva, its simultaneous function as an efficient biofilter and as a food and feed source might be affected. Therefore, we investigated the removal of ten MPs often found in wastewater effluents by Ulva and its associated bacteria, and characterized the effects of these MPs on the alga during two crucial lifecycle phases (germination and vegetative growth) using dose dependent tests. We monitored MP detoxification at elevated concentrations in a reductionistic tripartite Ulva mutabilis - Roseovarius - Maribacter model system to reduce interference from the fluctuating algal microbiome. Our results showed that the tripartite community was resistant to the MPs tested, although the gametes were between 2 to 140 times more susceptible based on the half-effective concentrations (EC 50 ) than the growing vegetative alga. The herbicide atrazine and the endocrine disruptor bisphenol A proved the most toxic MPs for germinating gametes. U. mutabilis and its associated bacteria could not eliminate the tested antibiotics and herbicides but efficiently reduced the concentration of endocrine disruptors, including bisphenol A, estradiol, and ethinylestradiol, by over 98% to below the detection limit. We also confirmed that Ulva is not likely to become contaminated under the studied exposure conditions because no biotic processes are used to remove the other MPs, which emphasizes yet another benefit of its use in aquaculture. Compared to green microalgae, U. mutabilis appears to be more resistant to micropollutants.