Semi-continuous pharmaceutical and human tracer monitoring by POCIS sampling at the watershed-scale in an agricultural rural headwater river

[Display omitted] •A headwater watershed was sampled at 3 stations semi-continuously by POCIS in 2016.•Three wastewater human tracers and 20 pharmaceuticals were quantified in headwaters.•Successive small WWTP and untreated effluent impacted pharmaceutical content.•Dilution of (un)treated wastewater discharges is crucial to consider.•Pharmaceutical in river depend on season, agricultural use and age of the population. Pharmaceutical monitoring (37 pharmaceuticals and 3 human tracers) was conducted in a headwater streams in southwest France, an area characterized by a low population density with an elderly population (30% > 60 years old) and extensive agriculture (cow cattle breeding). Polar Organic Chemical Integrative Sampler (POCIS) were exposed for 14-day consecutive periods in 2016 at three sampling points. Three human wastewater tracers and 20 pharmaceuticals commonly used for human and/or cattle were quantified in headwaters. Succession of small Wastewater Treatment Plant (WWTP), non-collective sanitation, discharges of untreated effluents as well as the river ability to dilute discharged wastewater, mainly explain the pharmaceuticals and human tracers concentrations. Pharmaceutical loads were time-dependent and were higher during cold season due to increase of pharmaceutical consumption. In contrast, better degradation and/or sorption onto river biofilms in warm season induced the decrease of headwater pharmaceutical content. The headwaters streams were contaminated by compounds found in other type of watershed, but β-blocker were the compounds quantified in higher concentration with frequencies of 100%, which was consistent with the elderly population living in the watershed. Specific compounds (sulfamerazine and sulfamethoxazole) used to cattle medical care were detected in waters, but at a low content.