Investigations on the fate of sulfadiazine in manured soil: laboratory experiments and test plot studies.

The fate of 14C-labeled sulfadiazine (SDZ) in manured soil has been investigated in laboratory test systems. In the first approach, stability of 14C-SDZ in liquid bovine manure has been tested. Only 1% of the initially applied radiotracer was mineralized to 14C-carbon dioxide and 82% were transferred to nonextractable residues within a 102-d incubation period. Test slurries with defined aged residues were prepared and, supplementary to standard solutions, applied to silty-clay soil samples. These tests showed the high affinity of 14C-SDZ residues to the soil matrix. In the second approach, basic data on microbial, chemical, and photoinduced degradability in soil were gathered. The data indicated the formation of nonextractable residues as the predominant process in soil, which was accelerated by the test slurry application. In the third approach, laboratory lysimeter tests were conducted to investigate leaching and degradation as simultaneously occurring processes. The 14C-SDZ residues (64%) mainly were retained in the surface layer as nonextractable residues. Although a high mobility in soil was revealed by a soil/water distribution coefficient of 2 L kg(-1), percolate contamination amounted to only 3% of the initially applied 14C-SDZ. The tendencies of leaching and degradability in soil also were observed in test plot studies under field conditions.