Fate of persistent and mobile chemicals in the water cycle: From municipal wastewater discharges to river bank filtrate

Persistent and mobile (PM) chemicals are considered detrimental for drinking water resources as they may pass through all barriers protecting these resources against pollution. However, knowledge on the occurrence of PM chemicals in the water cycle, that make their way into drinking water resources, is still limited. The effluents of six municipal wastewater treatment plants (WWTPs, n = 38), surface water of two rivers (n = 32) and bank filtrate of one site (n = 15) were analyzed for 127 suspected PM chemicals. In the rivers, median concentrations of 92 detected analytes ranged from 0.3 ng/L to 2.6 µg/L (tetrafluoroborate, BF4). Lower than average dilution from WWTP effluent to surface water of 43 PM chemicals suggests significant discharge from other sources. Many of these compounds were industrial chemicals, including cyanoguanidine, trifluoromethanesulfonic acid and BF4. River bank filtration (RBF) reduced the total concentration of 40 quantified compounds by 60 % from 19.5 µg/L in surface water to 8.4 µg/L in bank filtrate, on average. Of these, 20 compounds showed good removal (> 80 %), 14 intermediate (80 - 20 %) and 6 no removal (≤ 20 %), among them carbamazepine, hexafluorophosphate, and 2-pyrrolidone. 13 substances occurred at concentrations ≥ 0.1 µg/L in bank filtrate; for six of them toxicological data were insufficient for a health-based risk assessment. The regulatory definition of P and M chemicals, if used together with existing data on environmental half-lives (P) and K_oc (M), showed little power to discriminate between chemicals well removed in RBF and those that were hardly removed. This comprehensive field study shows that RBF is a useful but incomplete barrier to retain PM chemicals from surface water. Thus, PM chemicals are, indeed, a challenge for a sustainable water supply.