In-situ formation of glyphosate and AMPA in activated sludge from phosphonates used as antiscalants and bleach stabilizers in households and industry
Lisa Engelbart, Sarah Bieger, Katharine J. Thompson, L. Fischer, Thomas K. Bader, M. M. Kramer, Stefan B. Haderlein, Anna M. Röhnelt, P.R. Martin, Daniel Büchner, Robert J. Bloch, Hermann Ruegner, Carolin Hühn
Abstract
• Glyphosate is a transformation product of a laundry additive in activated sludge. • De novo formation is unambiguously demonstrated using isotope labeled compounds. • The transformation also proceeds under abiotic conditions after azide treatment. • Extrapolation of formation rates reveals relevant effluent concentrations. • A possible pathway is deduced from known transformation reactions of glyphosate. The herbicide glyphosate and aminomethyl phosphonic acid (AMPA), a transformation product of glyphosate and other aminopholyphosphonates are widespread pollutants in European rivers. We recently showed that besides rain-driven input after agricultural or urban herbicide application, municipal wastewater significantly contributes to glyphosate contamination in European rivers. The rather constant mass fluxes over the year, made an explanation by herbicide applications difficult. In our search for a new source of glyphosate and AMPA, we here provide experimental evidence that a certain aminopolyphosphonate, used as antiscalant and bleach stabilizer in household detergents and numerous industrial processes, is a precursor of both glyphosate and AMPA. During incubation experiments with diethylenetriamine penta(methylene phosphonic acid) (DTPMP) in fresh activated sludge, we observed the formation of glyphosate with yields ranging from 0.017 to 0.040 mol% and formation of AMPA in the range of 0.402 to 1.72 mol% after 72 h. Both compounds are formed from DTPMP and possible intermediates, but they are also further transformed themselves in consecutive reactions. Glyphosate formation from DTPMP was further proven by incubating 13 C-labeled DTPMP, which transformed into 13 C-glyphosate and 13 C-AMPA. The addition of DTPMP to azide-treated activated sludge yielded similar or even higher glyphosate and AMPA concentrations indicating that abiotic processes dominate the transformation process. In order to judge the relevance of this in-situ formation of glyphosate and AMPA from the laundry additive DTPMP, we estimated the average concentrations in wastewater.