Sorption characteristics of cyromazine and its metabolite melamine in typical agricultural soils of China

A myriad of physical, chemical, and biological processes controls the fate of organic contaminants in soils. The knowledge of bioavailability of a contaminant in soil can be useful to conduct environmental risk assessment. We conducted batch equilibrium experiments to investigate the sorption of cyromazine (CA) and its metabolite melamine (MA) onto five typical soils of China belonging to suborders Ali-Perudic Ferrosols, Udic Argosols, Gleyic-Stagnic Anthrosols, Ustic Cambosols, and Udic Isohumosols. Results showed that sorption of CA and MA onto soils was linear, as indicated by the Freundlich and Langmuir models. Different sorption behaviors of CA and MA were observed on the five agricultural soils, with lgK (f) values (Freundlich model) of 1.6505-2.6557 and 1.632-2.549, respectively. Moreover, the K (f) values for CA and MA were positively correlated with soil organic matter (r = 0.989, r = 0.976) and significantly negatively correlated with pH (r = -0.938, r = -0.964). The free energy of sorption of CA and MA ranged from -20.8 to -23.0 kJ mol(-1) and -20.8 to -22.8 kJ mol(-1), respectively, suggesting that the sorption of CA and MA onto the soils is primarily a physical process.