Wastewater-impacted streams within an agricultural catchment: Occurrence, attenuation, and risks of organic micropollutants

• Pharmaceuticals, pesticides, and bisphenols were investigated in a rural catchment. • Small streams were the most polluted watercourses due to low in-stream attenuation. • Wastewater-derived stressors can be relevant even in an agricultural area. • Pharmaceuticals, not pesticides, posed the greatest risk in streams investigated. The occurrence, attenuation factors, and risks of 31 organic micropollutants (OMPs), including pharmaceutically active compounds (PhACs), pesticides, and bisphenols were investigated in the transboundary catchment of the lower River Mur. Water samples were collected monthly for one year from the river and its small, wastewater-impacted tributaries in two Central European countries, Croatia and Hungary. The analysis showed that the most polluted streams for PhACs, as well as the herbicides and neonicotinoids studied, were the smallest tributaries on the Hungarian side. However, the concentrations of persistent pollutants detected in almost all River Mur samples (e.g., bezafibrate, carbamazepine, diclofenac (DIC), atrazine) were not affected by the polluted water of the sampled tributaries. This, in turn, highlighted the importance of long-distance pollution of the river. Principal component analysis showed that photo- and biodegradation may be considered the most important attenuation factors in the river, resulting in lower OMP concentrations in warmer seasons. This, however, could not be confirmed in the case of the tributaries, in which there is not enough space and time for in-stream attenuation. The risk assessment showed that DIC and estrone were the pollutants of greatest risk in all watercourses investigated, including small streams. The key findings of the study are that even in small streams in rural settings, some wastewater-derived PhACs pose serious environmental risks throughout the year, compared to pesticides with stronger seasonality. This is exacerbated by low attenuation and increased detection of some non-persistent OMPs due to relatively low dilution and short retention time.