The concentrations of 56 active pharmaceutical ingredients (APIs) and seven metabolites, including 50 prioritized APIs were measured, in 24-hour composite effluent samples collected from 50 very large municipal wastewater treatment plants across the US. Hydrochlorothiazide was found in every sample analyzed. In addition, metoprolol, atenolol, and carbamazepine were found in over 90% of the samples. The highest concentration measured was 5300 ng/L for valsartan, which also had the highest average concentration (1600 ng/L) across all 50 samples. The six highest ratios of measured concentration to therapeutic dose rate were all for anti-hypertensive APIs (lisinopril, hydrochlorothiazide, valsartan, atenolol, enalaprilat, and metoprolol), but the ratio was below 0.003 in every case. These ratios suggest risks to healthy human adults from exposure to ambient water and drinking water are low. The ratio of measured concentration to therapeutic plasma concentration was between 0.1 and 1 for four analytes (sertraline, propranolol, desmethylsertraline, and valsartan), suggesting the need for further study of the potential impact of environmental exposure to aquatic life for a handful analytes. The rationale is presented for extending these conclusions to aquatic exposure of any prescription pharmaceutical, including those that have never been surveyed.You may need Adobe Reader to view files on this page. See EPA’s About PDF page to learn more.