Manure and livestock waste as fertilizer pose high risks: antibiotic contamination reaches deep into the soil

Antibiotics, as veterinary drugs and feed additives, are widely used in the livestock and poultry farming industries of countries around the world. According to statistics, China's annual use of veterinary antibiotics had already exceeded 6000 tons by 2000. However, about 60% to 90% of the antibiotics administered to farmed animals are excreted in their original form through manure, urine and other excreta, and are applied to farmland soil as organic fertilizer. The environmental exposure of veterinary antibiotics and their potential ecological and human health hazards have become a research hotspot in recent years. Developed countries and regions such as the European Union, the United States, Canada, Japan and Australia have already enacted legislation requiring environmental risk assessment for registration before veterinary drugs are placed on the market.

In recent years, reports on the contamination concentrations of veterinary drugs in environmental media such as animal manure, soil and surface water have been common in China, but research reports on ecological risk exposure assessment of veterinary drugs are rarely seen. In response to the current situation of a gap in China's veterinary drug environmental management and ecological risk exposure assessment, in 2014, Dr. Wang Na and others at the Nanjing Institute of Environmental Sciences of the Ministry of Environmental Protection published research on the environmental exposure of veterinary antibiotics. They selected three typical veterinary antibiotics commonly used in China's farming industry - sulfadimidine (SDM), oxytetracycline (OTC) and enrofloxacin (ENF) - and conducted research on their environmental exposure assessment.

Since manure fertilization is the most important pathway for environmental exposure of veterinary drugs, the European Federation of Animal Health (FEDESA) first established the u-ni·form method for predicting the soil PEC of veterinary drugs. This method has been cited by the VICH "Guideline on Environmental Risk Assessment for Veterinary Medicinal Products".

Wang Na and others' research found that the PEC (predicted environmental concentration in soil) of veterinary antibiotics in the manure of different farmed animals, from high to low, was pig manure, chicken manure and cattle manure; the PEC of the three veterinary antibiotics remaining in manure, from high to low, was SDM, OTC and ENF; the fertilization substrates for veterinary antibiotic PEC in soil, from large to small, were pig manure, chicken manure and cattle manure; for the three veterinary antibiotics, the soil PEC was largest under pig manure and cattle manure fertilization, from high to low being SDM, OTC and ENF, but the maximum soil PEC under chicken manure fertilization, from high to low, was ENF, SDM and OTC. The PEC of veterinary antibiotics in water bodies for different farmed animals, from high to low, was pig farms, chicken farms and cattle farms, and the water body PEC of SDM was significantly greater than that of OTC and ENF.

The study also pointed out that when analyzing the degree of influence of parameters on the final prediction results, it was found that the PEC results obtained using different animal types and dosing regimens differed greatly, and at the same time the half-life of the drug in manure or soil and the storage time of manure were also key factors affecting the prediction results.

The abuse of antibiotics in the farming industry urgently needs to be addressed

At present, the use of antibiotics in the farming industry is fairly common, and in some cases has far exceeded the scope of antibacterial use, causing bacteria to develop drug resistance, bringing new difficulties to the prevention and control of livestock and poultry diseases, and also posing a threat to the safety of livestock and poultry products. This urgently requires great attention and remediation.

It is understood that the main reasons leading to the abuse of antibiotic drugs in the farming industry are as follows: First, to prevent and control livestock and poultry diseases, farmers use large amounts of antibiotics during the farming process, and some farmers even give livestock and poultry medication in advance to prevent disease. The author learned in daily drug supervision work that antibiotic drugs sell in relatively large quantities in rural areas, and most are purchased by farmers, far exceeding the demand for treating animal diseases. Second, some feed production enterprises use antibiotics in order to highlight product efficacy, causing farmers to use them continuously without knowing it until the livestock and poultry are ready for market, resulting in antibiotic residues in animal-derived foods. Third, relevant laws, regulations and mandatory standards are incomplete, and supervision and punishment are weak. Although the "Measures for the Administration of Veterinary Prescription Drugs and Non-prescription Drugs", which took effect on March 1 last year, imposed certain restrictions on the use of antibiotics in the farming industry, the antibiotics used by farmers do not necessarily all come from veterinary drugs, and there are obvious blank areas in both regulations and supervision. Due to the lack of substantive punitive measures, the small intensity of punishment and the extremely low cost of violating the law, farmers and feed production enterprises feel no fear.

The abuse of antibiotics not only restricts the sustainable development of the farming industry, but the food safety problems it causes also cannot be underestimated, and great efforts are urgently needed to address it.

First, a sound monitoring system for antibiotic drug residues should be established and improved, and antibiotic drug monitoring should be brought onto the track of rule-of-law management. All antibiotics should be placed under prescription drug management (whether for human or veterinary use), and production and sales should have complete purchase and sales records to facilitate supervision. Only by controlling the production and sale of antibiotics at the source can the abuse of antibiotics truly be curbed. Second, industry standards should be formulated as soon as possible, and detection methods for antibiotic drug residues should be improved. Investment in technology should be increased, and rapid, accurate and simple detection methods should be developed as soon as possible. At the same time, punishment and crackdowns on farmers who abuse antibiotics should be intensified, raising the cost of violating the law. Third, support for science and technology in the poultry farming industry should be increased, support for research on antibiotic substitutes should be increased, and farmers should be actively guided to voluntarily give up feed antibiotics and adopt substitute products for green farming. Finally, publicity and guidance should be strengthened so that the public correctly understands the dangers of antibiotic abuse.