The herbicide glyphosate and aminomethyl phosphonic acid (AMPA), a transformation product of glyphosate and other aminopolyphosphonates 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