Biosorption of heavy metals by microalgae: hazardous side effects for marine organisms

Biosorption is nowadays recommended as an ecological and environmentally friendly alternative to remove metals from contaminated regions. Even in situ incubations of algae on the seabed are conducted to investigate potential future ways of reducing metal contamination. Our study investigated the negative effects on microorganisms when metal-enriched algae are released into the marine environment. We cultured the microalgae Nannochloropsis oceanica strain CCMP1779 with ¹³C/¹⁵N amended f/2 medium enriched with four different metals (cadmium, copper, zinc, lead) and fed the resulting metal-enriched microalgal biomass to Ammonia confertitesta (Rhizaria, Foraminifera) for two and six days. Our study is the first study dealing with the interaction of biosorbed metals and the metabolism of microorganisms. The effects of the uptake of these metal-enriched algae were recorded by evaluating carbon and nitrogen uptake. Examinations using transmission electron microscopy (TEM) were also carried out to better assess the condition of the foraminifera. Foraminifera fed with metal-enriched microalgae show reduced carbon uptake and increased nitrogen storage, indicating stress conditions. These observations suggest that trace metals can induce stress which damages cellular metabolism. Interestingly, no cytological changes in TEM analyses could be observed, which might be attributed to the relatively short incubation time.