Sorption, transformation and transport of sulfadiazine in a loess and a sandy soil

Veterinary antibiotics are unintentionally introduced into the environment and therefore found in ground and surface water, soil and sediments, air, plants etc. They enter these compartments mainly via application of manure or sewage sludge to soils for fertilizing purposes or after application in aquaculture, in form of the parent compound or a transformation product. Generally, sorption, transformation and transport determines the fate of these organic contaminants in soil. Their wide-spread distribution bears several risks, i. e. spreading of resistance genes or occurrence in the food chain. Long-term (60 days) batch studies were conducted applying radiolabelled sulfadiazine to samples from two agricultural soils to investigate the sorption and sequestration behavior in the plow layers. Sequential extractions at several time-steps served to analyze the dynamics of both processes. A numerical evaluation served to describe instantaneous sorption, the dynamics of sorption and sequestration, and the formation of non-extractable residues. Multiple extractions with the harsh method questioned the concept of non-extractable residues, since with each consecutive extraction step, further sulfadiazine could be extracted. Analyzing the liquid phase and the extracts from these batch experiments with Radio-HPLC served to improve the understanding of the transformation behavior in soils in different degrees of (bio- )availability. Apart from the deduction of rate-parameters for a compartment model, the resemblance of the compositions in the liquid phases and the harsh extracts was demonstrated. The formation of the up to six transformation products showed distinct dynamics, either spontaneous or with a time-lag.