Ecotoxicological risk assessment due to the presence of bisphenol A and caffeine in surface waters in the Sinos River Basin - Rio Grande do Sul - Brazil. 
Bisphenol A (BPA) is an emerging contaminant, regularly detected in aquatic ecosystems, considered as an endocrine disrupting compound (EDC).  Caffeine is another chemical related to human activity, often found in surface waters.  The objective of this study was to evaluate the ecotoxicological risk due to BPA and caffeine in water samples from the Sinos River basin, Rio Grande do Sul, Brazil.  Water samples were collected at three sites monthly from May 9 th, 2016 to April 11th, 2017 (n = 36).  BPA concentrations in water samples collected were in the range of not detected to 517 ng L-1 and caffeine concentrations in the range of 41.7 to 28,439.6 ng L-1.  The concentration of BPA in the analyzed samples had a moderate correlation with caffeine (rs = 0.402).  High ecotoxicological risk for BPA was characterized in 77.77% of samples, with 11.11% presenting medium and 11.1% presenting low risk.  For caffeine 13.9%, 50% and 36.11% of the samples presented high, medium and low risk, respectively.  Caffeine concentrations in water can be used as predictors of BPA concentrations above 10 ng L-1, the lower concentration of ecotoxicological risk, with specificity of 66.7% and sensitivity of 70.4%.  The assessment of aquatic risks has shown that both investigated compounds pose risks to organisms in the studied surface waters, mouth of the Pampa stream, mouth of the Luiz Rau stream and catchment point for public supply in Lomba Grande.