Phosphate dosing of drinking water supplies, coupled with leakage from distribution networks, represents a significant input of phosphorus to the environment. The oxygen isotope composition of phosphate (δ18OPO4), a novel stable isotope tracer for phosphorus, offers new opportunities to understand the importance of phosphorus derived from sources such as drinking water. We report the first assessment of δ18OPO4 within drinking water supplies. Forty samples from phosphate-dosed distribution networks were analysed from across England and Wales. In addition, samples of the source orthophosphoric acid used for dosing were also analysed. Two distinct isotopic signatures for drinking water were identified (average = +13.2‰ or +19.7‰), primarily determined by δ18OPO4 of the source acid (average = +12.4‰ or +19.7‰). Depending on the source acid used, drinking water δ18OPO4 appears isotopically distinct from a number of other phosphorus sources. Isotopic offsets from the source acid ranging from -0.9‰ to +2.8‰ were observed. There was little evidence that equilibrium isotope fractionation dominated within the networks, with offsets from temperature-dependent equilibrium ranging from -4.8‰ to +4.2‰. Whilst partial equilibrium fractionation may have occurred, kinetic effects associated with microbial uptake of phosphorus or abiotic sorption and dissolution reactions may also contribute to δ18OPO4 within drinking water supplies.
This document is the Accepted Manuscript version of a Published Work that appeared in final form in Environmental Science and Technology, copyright © American Chemical Society after peer review and technical editing by the publisher.
To access the final edited and published work see http://pubs.acs.org/doi/abs/10.1021/acs.est.5b01137
Date of acceptance 04/06/2015
