Assessing Fe and Zn content in Egeria densa: Sample treatment influences significantly the quantification of metals in Egeria densa

Wetlands are fragile ecosystems that support diverse habitats and are under constant environmental pressure. The "Carlos Anwandter" Ramsar Site located in Valdivia, Chile, is home to many waterfowl species, and it is the main reproductive site for black-necked swan in the world. The main food source for these swans, Egeria densa, has been affected by sediment deposits with high iron (Fe) and zinc (Zn) concentrations, however the methodology for the evaluation of such concentrations has not been standardised. In fact, results obtained from commercial labs showed significant differences in metal concentrations highlighting the need to develop better assessment protocols for improved reproducibility and comparability of metal content in aquatic plants. The study aimed to understand the effects of different sample treatments and plant section subsampling on Fe and Zn concentrations in E. densa. To address this aim, samples were collected at the Ramsar site and a control site. Results indicated that washing the samples in the field and in the laboratory significantly reduced reported Fe and Zn concentrations. These findings highlighted the need for stablishing standard protocols for sampling and sample pre-treatment and their influence in interpreting metal pollution.