Antibiotic residues and antibiotic-resistant bacteria in pig slurry used to fertilize agricultural fields

Pig manure may contain antibiotic residues, antibiotic-resistant bacteria or pathogens, which may reach the environment upon fertilization. During this study, 69 antibiotic residues belonging to 12 classes were quantified in 89 pig slurry samples. These samples were also studied for the presence of Salmonella and for E. coli resistant to meropenem, colistin, ciprofloxacin, or cefotaxim. The obtained isolates were further tested for antibacterial susceptibility. No antibiotic residues were detected in four samples, whereas in the other samples, up to 12 antibiotics were found. The most frequently detected antibiotic residues were doxycycline, sulfadiazine, and lincomycin. Doxycycline was found in the highest concentration with a mean of 1476 mu g/kg manure (range: 18-13632 mu g/kg). Tylosin and oxytetracycline were found with mean concentrations of 784 mu g/kg (range: 17-5599 mu g/kg) and 482 mu g/kg (range: 11-3865 mu g/kg), respectively. Lincomycin, had a mean concentration of 177 mu g/kg manure (range: 9-3154 mu g/kg). All other 18 antibiotic residues were found with mean concentrations of less than 100 mu g/kg manure. Fifty-one slurry samples harbored Salmonella; 35% of the Salmonella isolates were sensitive to a panel of 14 antibiotics, whereas the other 65% were resistant up to five antibiotics. For E. coli, 52 manure samples contained E. coli isolates which were resistant to ciprofloxacin and 22 resistant to cefotaxime. All ciprofloxacin and cefotaxime-resistant isolates were multi-resistant, with resistance up to nine and eight antibiotics, respectively. This research indicates that pig slurry used for fertilization often contains antibiotic residues and antibiotic-resistant bacteria, including pathogens

Simplifying dynamic river water quality modelling: A case study of inorganic nitrogen dynamics

Increasing water scarcity in many countries provides a strong impetus for investments in water quality remediation at the basin or sub-basin scale as a means to increase water availability. The application of mathematical river water quality modelling, as a support tool to evaluate remediation options, is often limited by the availability of reliable data. Current proposals to use the River Water Quality Model number 1 (RWQM1) are hampered by its relative complexity and large data requirements, with the result that use of such model is often not economically feasible, especially in developing countries. However, by simplifying this model to suit specific applications, the general water quality situation of a river can still be predicted with limited data. The ultimate goal of this study is to develop a simple dynamic river water quality model that is compatible with activated sludge models and which can be used for integrated water quality modelling studies in the future. During the present study, a simplified river water quality model was derived from the available RWQM1 model and used to investigate the daily dynamics of nitrate and ammonia nitrogen concentrations in the Crocodile River in South Africa. Using a modelling concept based on continuously stirred tanks in series, the simulation results for two years agree well with the measured seasonal dynamics of nitrate and ammonia concentrations in the river system. The model is most sensitive to the concentration of nitrifiers and to hydraulic parameters