Diffusion of a dechlorinated metabolite of terbuthylazine in Northern Italian groundwaters

During a screening campaign on groundwaters used as a source of drinking waters in the area North of Milano, an anxiolytic drug, called Mebikar, has been found in some wells. The origin of this molecules has not been yet identified, but during the tests carried out by high resolution mass spectrometry (HRMS) for confirmation purpose an isobaric compound (MW 198.222360 g/mol and molecular formula C 8 H 14 N 4 O 2 )has been determined in many groundwater samples. The interpretation of the mass spectrum allowed to identify the compound as 4-(tert-butylamino)-6-hydroxy-1-methyl-1,3,5-triazin-2(1H)-one, which is a described dechlorinated metabolite of the erbicide terbuthylazine, also known as LM6. Other structurally related metabolites were tentatively identified by retrospective analysis via HRMS. These metabolites have been described in the registration document from Syngenta and in the ECHA dossier, but they are neither described in the scientific literature neither registered in CAS. Because ECHA underlined the need for reliable analytical methods for these polar terbuthylazine metabolites, we developed an HPLC-HRMS method based on an Orbitrap system which allowed to determine these compounds in groundwaters and treated drinking waters. In order to characterise the compounds and their diffusion in Northern Italian groundwater we carried out a wide monitoring campaign which highlighted the large diffusion of these compounds. The diffusion has been related to specific soil uses, with special regards to maize cultivation. The results of the occurrence study with literature toxicological data allowed to draft a preliminary risk assessment for these metabolites which should contribute to the derivation of threshold limits for groundwater.