Persistence of gabapentin, 1H-benzotriazole diglyme, DTPA, 1,4-dioxane, melamine, and urotropin in surface water

For seven test compounds the biodegradability in surface water was measured according to the OECD 309 guideline. The goal of this study was to measure the biodegradation of a series of test substances that occur in surface water that is used as a source for drinking water, and pose a subsequent challenge for drinking water production.
The water used in the study was taken from the location “Schalterberg”, selected since it is known to contain hardly any anthropogenic compounds. Based on the results on both aniline and ATP measurements it can be concluded that the surface water showed sufficient microbial activity for biodegradation and that the test compounds weren’t toxic to the microorganisms present in the surface water.
The test compounds were spiked to bottles containing the water, and these bottles were gently shaken during the test period. At different time intervals bottles were taken and the test compound concentrations were analysed. Following the OECD 309 test requirements, all selected test compounds showed no (gabapentin, 1H-benzotriazole, diglyme, 1,4-dioxane and melamine) or only slow (DTPA, urotropin) decrease in test compound concentrations analytically determined. Therefore, abiotic and biotic degradation of the all selected test compounds is evaluated to be slow or negligible in surface water. Calculated half-lives were as follows: gabapentin >10.000 days; 1H- benzotriazole: >10.000 days; diglyme: >10.000 days; DTPA: 67.6 days; 1,4-dioxane: >10.000 days; melamine: >10.000 days; urotropin: 128 days.
According to the REACH legislation, a compound is considered persistent (P) if half-lives (DT50) are larger than 40 days, and it is deemed to be very persistent (vP) if the DT50 in surface water exceeds 60 days. Comparing the obtained half-lives for the selected compounds in this study with vP/P-criteria, gabapentin, 1H-benzotriazole, diglyme, DTPA, 1,4-dioxane, melamine and urotropin seem to be very persistent in surface water.