Assessing Melamine Mobility in European Soils: Experimental Log K_oc Determination and Relative Mobility Mapping

Persistent, mobile and toxic (PMT) and very persistent, very mobile (vPvM) substances pose increasing risks to the quality of groundwater and drinking-water resources. Melamine, a high-production-volume chemical has recently been listed as a Substance of Very High Concern under EU REACH. Mobility assessments under the EU CLP regulation rely on log K_oc, with experimentally derived values preferably obtained in accordance with OECD Test Guideline 106. However, for melamine such data remain scarce and highly variable. In this study melamine sorption coefficients following OECD TG 106 using five European soils were determined. Experimentally derived log K_d values ranged from -0.25 to 1.84, corresponding to log K_oc values of 1.52 to 3.21. Sorption was influenced by soil properties, particularly pH and organic carbon, consistent with melamine's pH-dependent speciation. The lowest log K_oc value (1.52) meets the CLP criterion for "very mobile" substances (vM). By integrating these results with the 2018 LUCAS European soil dataset, regions exhibiting comparatively higher relative melamine mobility, were identified. These were predominantly in southern Europe, where alkaline soils with low organic carbon contents are more common. These findings highlight the need for monitoring and regulatory attention in areas characterized by melamine emissions alongside soil conditions that may enhance melamine mobility.