Degradation Of Chlortetracycline And Sulfadiazine In Soil And Their Effects On Soil Microorganisms

Antibiotics have been widely used in livestock industries as feed additive, but most antibiotics could be excreted as the parent compound and their metabolites by animals via feces or urine, and the animal excrements containing antibiotics were repeatedly applied into soil as organic manure and then led to soil pollution. Sulfadiazine (SDZ) is a sulfonamide widely used as veterinary antibiotic to prevent and treat diarrhea and other infectious diseases, and chlortetracycline (CTC) is a tetracycline antibiotic with a broad spectrum of activity including both Gram-positive and Gram-negative bacteria widely used as a feed additive to promote growth in calves, pigs and poultry. To assess the impacts of repeated antibiotics treatments on soil quality and health, SDZ and CTC alone and in combination were repeated applied into soil together with pig manure. The degradation of SDZ and CTC, the changes of soil respiration activity and microbial functional diversity, and development of antibiotics resistance were studied. The main results were summarized as follows:During five repeated applications, the initial rapid degradation of SDZ and CTC alone and in combination in soil during the first0to7days was followed by a slower second phase decline. After treatment for7days, the degradation rate of SDZ in soil was obviously higher than that of CTC, and the degradation rate of SDZ and CTC in combined treatment was slightly higher than that in single treatment. The degradation rate of SDZ and CTC in single and combined treatments initially decreased and then increased, furthermore, a faster resilience trend on the degradation rate of CTC was observed in all treatments.Soil CO2flux was determined by substrate-induced respiration method. After7h of incubation, soil CO2flux in all treatments with SDZ and CTC was somewhat lower than that in the manure treatment during the first and second applications, but the corresponding CO2flux gradually recovered to or exceeded the similar leve in the manure treatment during the third, fourth and fifth applications. After24h of incubation, an obvious trend on CO2flux was observed. In addition, in the present study, soil respiration activity in all manure-amended treatments was significantly much higher than that in unamended control with antibiotics and manure.The functional diversity of soil microbial communities was assessed using BIOLOG ECO microplates. After60days of the first treatment, the AWCD value, Simpson, Shannon and McIntosh indices of soil microorganisms in all treatments with SDZ and CTC were lower than those in the manure treatment, and soil microbial functional diversity was inhibited, but this inhibitory effect gradually disappeared with application frequency. Up to60days after the third treatment soil microbial functional diversity was similar or higher than that in the manure treatment..Pollution-induced community tolerance (PICT) of SDZ and CTC was dertermined by BIOLOG method. During the five successive treatments, no obvious change of bacterial community resistance and cross-resistance to SDZ and CTC was observed in the manure treatment, but antibiotics resistance and cross-resistance of soil microbial community in all treatments with SDZ and CTC were much higher than those in the manure treatment, and this induced resistance significantly increased with application frequency of antibiotics.