This study aims at investigating the abiotic degradation pathway of ethylenediaminetetra(methylenephosphonic acid) (EDTMP) simulated applying UV irradiation. The degradation of EDTMP and formation of degradation products was determined using LC‐MS and 31P‐NMR. In the laboratory scale experiments, EDTMP was degraded within 30 min and the degradation products, iminodi(methylenephosphonic acid) (IDMP), ethylaminobis(methylenephosphonic acid) (EABMP), and amino(methylenephosphonic acid) (AMPA), were simultaneously released. IDMP was the main degradation product of EDTMP. Therefore, we conclude that the initial cleavage of EDTMP is a heterolytically driven process, which starts the degradation process at the intramolecular CN bond. In contrast, the main product of a possible homolytic CC cleavage of methylaminobis(methylenephosphonic acid) could not be confirmed with either LC‐MS or 31P‐NMR. Additionally, there was no evidence for a primary attack on the CP bond. All identified degradation products of EDTMP have been mineralized to carbon dioxide (CO2). Three additional degradation products (M1, M2, and M3) have been found using the 31P‐NMR analysis but have not yet been quantified using LC‐MS. We assume that the unidentified degradation product M1 is related to m/z 312, M2 to m/z 341, and M3 to m/z 409. Thus we concluded that EDTMP undergoes photochemical conversion to IDMP, the main degradation product. EABMP and AMPA also accumulate, but in smaller amounts. All intermediates are further mineralized to CO2.

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