Sand_Metagenome_Baltic_Sea_2022_23

Background: The water quality in recreational beaches is constantly monitored. However, given that beachgoers often spend more time in contact with sand than with seawater, it is essential to regularly assess also beach sand quality. Results: In this study, 34 beach sand samples were collected in seven locations along the south shore of the Baltic Sea (Europe) between 2022 and 2023. The samples were obtained from recreational beaches with significant anthropogenic pressure. Since the use of new chemicals is widespread, it is imperative to not only monitor known contaminants but also to actively seek the presence of new ones in the environment. In order to establish the connection between the bacterial biodiversity and their possible resilience in the contaminated marine environment, the bacterial abundances in the beach sand were compared based on 16S rDNA sequencing with chemical contamination examined with non-targeted GC-MS. 149 distinct chemicals were detected, many of which are of human health concern. The presence of polycystic aromatic hydrocarbons, plasticisers and benzothiazoles in the sand samples was observed, and these contaminants were found to be associated with alterations in the microbial structure, characterised by a decrease or increase in certain taxonomic classes. Notably, the bacterial communities exhibited specificity to each location and demonstrated stability throughout the seasons. Furthermore, the presence of DNA from 31 potential human pathogens was detected in the sand. Conclusions: These findings emphasise the necessity for regular monitoring of beach sand for the presence of toxic chemicals and pathogens to safeguard public health and the environment.