Effects of pharmaceuticals and other contaminants on the structure and health of diatom communities of urban streams.

Diatom communities respond to water pollution with changes in species and abundances. Some contaminants may cause teratologies in cell walls which may be caused by environmental stress. Among others, pharmaceuticals have become an emerging concern in urban streams, presenting risks to the health of ecosystems and humans. This study evaluates the use of diatom communities and their teratologies as indicators of water contamination, namely by pharmaceuticals. Fifteen urban streams in Coimbra, Portugal, were sampled and diatom communities analysed, alongside in situ parameters, nutrients, and 19 pharmaceuticals. Diatom communities were affected by nutrients and organic carbon, and teratologies were detected in over half of the sites, with deformities ranging from 1 % to more than 20 % of the counted diatoms. Tolerant taxa, including Nitzschia amphibia, Craticula subminuscula, Sellaphora nigri, and Sellaphora saugerresii, exhibited high incidences of deformities, even in sites with good biological quality. In the stream with the highest frequency of diatom teratologies, 18 pharmaceuticals were detected, with 14 reaching the highest concentrations observed among all sites. These compounds included stimulants, anti-inflammatories, antibiotics, anticonvulsants, antidepressants, among others. Findings suggest a link between biological health of aquatic organisms and emerging contaminants, especially in contributing to the segregation of sites between the boundaries of good/moderate from poor biological quality. In addition, the results highlight the importance of using diatom deformities as early warning indicators of environmental degradation and risks for One Health, as they were more sensitive indicators of environmental degradation of streams than biological indices' classifications and community structure analyses.