Antibiotics and Heavy Metals Residues in Farm Animal Wastewater: Environmental Contamination, Co-selection Mechanisms, and Ecotoxicological Risks

The increasing use of antibiotics and heavy metals in livestock production has resulted in their widespread presence in farm animal wastewater, posing serious environmental and public health risks. This review examines the sources, occurrence, and environmental behavior of these contaminants, with emphasis on their interactions and contribution to antimicrobial resistance (AMR). These pollutants enter the environment through manure application, wastewater discharge, and agricultural runoff, where they undergo processes such as degradation, adsorption, and transport in soil and aquatic systems. Their co-occurrence enhances persistence and bioavailability, promoting co-selection mechanisms including cross-resistance, co-resistance, and horizontal gene transfer of antimicrobial resistance genes (ARGs). Consequently, ecosystems become contaminated, affecting soil microbial communities, aquatic organisms, and biodiversity. Human exposure through food chains, water, and environmental contact further increases AMR risks. The review also highlights analytical methods for detection and discusses mitigation strategies such as wastewater treatment, phytoremediation, and sustainable livestock practices. Despite these advances, gaps remain in understanding multi-pollutant interactions and integrated risk assessment. Addressing these challenges requires a multidisciplinary “ One Health ” approach to protect environmental and human health.