Seasonal variability and risk evaluation of emerging organic contaminants in European river: linking in silico and in vitro approaches to prioritize hazardous EOCs.

Emerging organic contaminants (EOCs) are a growing concern for aquatic ecosystems, underscoring the need for advanced risk assessment methodologies. This study employed an integrated approach to evaluate the risks associated with 563 EOCs across 13 monitoring sites along the Sava River in Croatia. Sampling was conducted during the winter and spring months, spanning February to May. The detected substances, totaling 551 compounds, included pharmaceuticals, illicit drugs, pesticides, industrial chemicals, hormones, artificial sweetener, and sunscreen chemical. We hypothesized that combining high-resolution chemical monitoring with bio-effect assessment tools could enhance the prioritization of high-risk EOCs and their mixtures. Persistent, bioaccumulative, and toxic (PBT) profiling and risk quotient (RQ) evaluations identified pesticides and industrial chemicals as key contributors to biological impacts, peaking in April due to agricultural activities. In vitro prioritization using exposure-activity ratios (EARs) derived from the ToxCast database revealed exacerbated biological effects during colder months (February and March), driven by elevated levels of pharmaceuticals, particularly synthetic glucocorticoids used for treatments of respiratory infections. By integrating PBT, RQ, and EAR assessments, eight EOCs, including methylprednisolone (a synthetic glucocorticoid), bisphenol A (an industrial chemical), nicotine (a stimulant), and five pesticides (temephos, disulfoton, pyridaben, bifenthrin, and chlorpyrifos-methyl), were prioritized for monitoring and regulatory attention. This multi-method framework advances next-generation risk assessment, offering critical insights for managing EOC pollution and safeguarding aquatic ecosystems and public health.