Sequestration of Manure-Applied Sulfadiazine Residues in Soils

Abstract

It is not the total but the (bio)accessible concentration of veterinary medicines that determines their toxicity in the environment. We elucidate the changes in (bio)accessibility of manure-applied sulfadiazine (SDZ) with increasing contact time in soil. Fattening pigs were medicated with 14C-labeled SDZ, and the contaminated manure (fresh and aged) was amended to 2 soil types (Cambisol, Luvisol) and incubated for 218 days at 10 degrees C in the dark. Antibiotic residues of different bioaccessibility were approached by sequential extractions with 0.01 M CaCl2 (CaCl2 fraction), methanol (MeOH fraction), and finally acetonitrile/water (residual fraction, microwave extraction at 150 degrees C). In each fraction, total radioactivity, SDZ, and its major metabolites were quantified. The results showed that both SDZ and,to a lesser extent 4-hydroxysulfadiazine (4-OH-SDZ) were rapidly reformed from N-acetylsulfadiazine (N-ac-SDZ) during the first 2-4 weeks after fresh manure application, i.e., the N-acetylated metabolite does not sequester in soil to a significant extent Yet, the water and methanol extractable SDZ and 4-OH-SDZ also dissipated rapidly (DT50 = 6.0-32 days) for the fresh manure treatment with similar rate constants for both soil types. In the residual fractions, however, the concentrations of both compounds increased with time. We conclude that the residual fraction comprises the sequestered pool of SDZ and its hydroxylated metabolite. There they are entrapped and may persist in soil for several years. Including the residual fraction into fate studies thus yields dissipation half-lives of SDZ which exceed those previously reported for sulfonamides by a factor of about 100.

Accumulation of Sulfonamide Resistance Genes in Arable Soils Due to Repeated Application of Manure Containing Sulfadiazine

“…This might indicate the development of microbial SDZ degraders in this treatment. The contribution of reversibly sequestered residues to the bioavailable fraction is not yet clear, but they might well serve as a long-term reservoir for SDZ in soils treated with SDZ-containing manure (11). The results obtained from the soil microcosm experiment supported the hypothesis that repeated applications of manure increase the abundance of sulfonamide resistance genes in soil.…”

Increased Abundance and Transferability of Resistance Genes after Field Application of Manure from Sulfadiazine-Treated Pigs

“…The field trial with grassland and maize plots (3 by 6 m; n ϭ 4) arranged in a randomized block design was performed as described in reference 6 from May 2009 until June 2010 near Jülich (Germany) on a Luvisol described earlier (7). Air temperature and precipitation were recorded by a meteorological station and are reported elsewhere (6).…”

“…Through field fertilization by manuring, SDZ and its metabolites enter arable soils in bioactive amounts (4,5). Although the concentration of readily extractable SDZ in soil was reported to decrease rapidly (6,7), SDZ might still select resistant populations and stimulate horizontal spread of antibiotic resistance genes, leading to an increased abundance of bacterial populations carrying resistance genes (reviewed in reference 8). In bacteria, SDZ inhibits the dihydropteroate synthase (DHPS), a crucial enzyme in the folic acid biosynthesis pathway, by competing with the natural substrate p-amino-benzoic acid (9).…”

Excretion masses and environmental occurrence of antibiotics in typical swine and dairy cattle farms in China

“…These antibiotics (e.g. tetracyclines, fluoroquinolones and sulfonamides) could persist in the soils for a long time (Forster et al, 2009;Golet et al, 2003;Hamscher et al, 2002). Antibiotic residues in soil could be taken up by vegetables Hu et al, 2010), and affect soil microbial and enzyme activities (Liu et al, 2009;Underwood et al, 2011), thus resulting in negative impacts on the soil environment and human health.…”