Veterinary antibiotics in soils: Environmental processes, ecotoxicity, and risk mitigation

Abstract

Concentrated animal feeding operations have long extensively used antibiotics to prevent and treat infectious animal diseases and promote the growth of farmed animals, which have resulted in discharges of large quantities of un-metabolized veterinary antibiotics into agricultural soils along with the land application of animal manure. These veterinary antibiotics in soils could exert a range of ecotoxicological effects and even induce the emergence and development of antimicrobial-resistant microbes and genes, which pose a potential threat to human health. This review provides a systematic overview of the transport and fate processes of antibiotics in the soil environment and the corresponding mechanism, their ecotoxicological effects on crops, soil fauna, and soil microorganisms, and the strategies that can be used to mitigate the risk of antimicrobial pollution and the related mechanism. The major environmental processes of antibiotics in soil, including adsorption/desorption, biodegradation, and abiotic degradation, all strongly depend on the soil's physical and chemical properties (e.g., pH and organic matter content) and the chemical structures and properties of antibiotics (e.g., functional group and hydrophobicity). The ecotoxicological effects of veterinary antibiotics on crops, soil fauna, and soil microorganisms are mainly determined by their types and concentrations and the soil's physical and chemical properties. Antibiotic degradation during manure composting and anaerobic digestion primarily occurs through biodegradation and hydrolysis. The antibiotics in manure can be effectively degraded by high-temperature pyrolysis. In addition, biochar and graphene-based composite materials can stabilize the antibiotics in soils through hydrogen bonding, surface complexation, electrostatic interaction, and ion exchange. Important questions that must be addressed and recommendations for future research are proposed herein based on the summary of the recent research progresses on soil pollution by antibiotics.