Persistence or degradation of synthetic antibiotics in soil is crucial in assessing their environmental risks. Microbial catabolic activity in a sandy loamy soil with pig manure using 12C- and 14C-labelled sulfamethazine (SMZ) respirometry showed that SMZ was not readily degradable. But after 100 days, degradation in sulfadiazine-exposed manure was 9.2%, far greater than soil and organic manure (0.5% and 0.11%, respectively, p < 0.05). Abiotic degradation was not detected suggesting microbial catabolism as main degradation mechanism. Terminal restriction fragment length polymorphism showed biodiversity increases within 1 day of SMZ spiking and especially after 200 days, although some species plummeted. A clone library from the treatment with highest degradation showed that most bacteria belonged to α, β and γ classes of Proteobacteria, Firmicutes, Bacteroidetes and Acidobacteria. Proteobacteria (α, β and γ), Firmicutes and Bacteroidetes which were the most abundant classes on day 1 also decreased most following prolonged exposure. From the matrix showing the highest degradation rate, 17 SMZ-resistant isolates biodegraded low levels of 14C-labelled SMZ when each species was incubated separately (0.2-1.5%) but biodegradation was enhanced when the four isolates with the highest biodegradation were incubated in a consortium (Bacillus licheniformis, Pseudomonas putida, Alcaligenes sp. and Aquamicrobium defluvium as per 16S rRNA gene sequencing), removing up to 7.8% of SMZ after 20 days. One of these species (B. licheniformis) was a known livestock and occasional human pathogen. Despite an environmental role of these species in sulfonamide bioremediation, the possibility of horizontal transfer of pathogenicity and resistance genes should caution against an indiscriminate use of these species as sulfonamide degraders.

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Wastewater biosolids are large potential sources of macronutrients for agriculture, conservation and restoration of soils; there are, however, few studies on phosphorus (P) release in soils amended with biosolids. Biosolids and vermicomposted biosolids were tested in concentrations (5-30 g amendment kg-1 soil) equivalent to 18-100 Mg ha-1. Desorption of P was determined by successive extractions for 65 days. Soil P was low, and biosolid and vermicompost addition released 8 and 6 times more P, respectively, than soil alone. To describe the release of P, zero-, first-and second-order equations, simple Elovich and power functions and the parabolic diffusion law were compared based on their coefficient of determination (r 2) and standard error (SE). In all treatments, the power function and especially the parabolic diffusion law were the best fit, with 0.898-0.996 r 2 and 0.022-0.732 SE. The general behavior of the kinetic parameters mostly depended on the amendment doses. Eutrophication posited to start beyond 16 mg P kg-1 soil was more likely allayed by a maximum vermicompost dose of 50 Mg ha-1 , higher than the 36 Mg ha-1 maximum biosolid dose. The higher vermicompost P addition and lower P release could favor gradual and longer-term P absorption by plants and may reduce leaching or runoff P losses.

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