Livestock and fish farm waste carries antibiotic resistance genes, microplastics and hormones into ecosystems

Agricultural waste was once primarily a nutrient management problem: excess nitrogen and phosphorus from manure running into waterways, triggering algal blooms and dead zones. That picture remains accurate, but incomplete. A scientific review published in 2026 documents a second, less-visible layer of contamination accumulating in waste from livestock and aquaculture operations worldwide - one that includes antibiotic residues, resistance genes, hormones, and microplastics with properties that make them considerably harder to manage than conventional organic pollution.

What is in modern farm waste

The review synthesizes recent global research on four categories of emerging contaminants found in animal agriculture waste streams.

Antibiotic residues and resistance genes are the most studied. A substantial fraction of veterinary antibiotics - estimates typically range from 30 to 90 percent depending on the drug and species - passes through animals without being fully metabolized and enters the environment through manure. Once in soil or water, these residues can select for resistant bacteria. More concerning still, antibiotic resistance genes can transfer between bacteria through horizontal gene transfer, meaning resistance developed in a farm environment can spread to bacteria that never encountered the original drug. "Antimicrobial resistance is no longer only a hospital issue," the authors note. "Agricultural systems have become an important environmental reservoir where resistance can develop, persist, and spread."

Endocrine-disrupting chemicals include synthetic hormones used to accelerate animal growth and natural hormones excreted by animals receiving those treatments. Even at low concentrations - sometimes parts per trillion - these compounds interfere with the hormonal signaling systems of wildlife and, potentially, humans. Effects documented in aquatic animals include reproductive abnormalities, feminization of male fish, and developmental disruptions. Long-term exposure to mixtures of endocrine disruptors has been linked to cancer risk, immune suppression, and developmental disorders in mammals.

Microplastics enter the system through the plastic equipment used throughout modern livestock and aquaculture operations: feed bags, water pipes, tank liners, fishing nets, and packaging. Once in manure or effluent, plastic particles spread widely. Their ecological impact extends beyond physical presence: microplastics can adsorb other contaminants - including antibiotics and heavy metals - onto their surfaces and release them when ingested by organisms, effectively concentrating and delivering toxic payloads deeper into food chains. The authors describe this as a "Trojan horse" effect.

How contaminants move through ecosystems

The review tracks contamination pathways from source to ecosystem. Manure applied as fertilizer carries antibiotic residues and resistance genes directly into soil, where they can persist for weeks to months and leach into groundwater. Aquaculture effluent enters waterways directly, introducing hormones and microplastics into aquatic systems. Air carries volatile antibiotic compounds and fine plastic particles from land-applied manure across distances of hundreds of kilometers.

Bioaccumulation adds a further dimension. Some contaminants concentrate as they move up food chains: an organism that ingests contaminated sediment carries a higher burden than the sediment itself; a predator that eats many contaminated prey accumulates more still. This biomagnification means that organisms - including humans - at the top of food chains can be exposed to concentrations far exceeding those in the original waste.

What can be done

The review does not present only problems. The authors identify strategies operating at multiple levels. At the source, reducing antibiotic use through improved animal husbandry, vaccinations, and alternatives such as bacteriophage therapy or probiotics would directly reduce resistance gene loadings in waste. Better manure treatment - composting at temperatures that degrade antibiotic residues, anaerobic digestion, constructed wetlands for effluent - can substantially reduce contaminant concentrations before waste reaches soil or water.

Detection and monitoring are significant gaps. Many of these contaminants lack regulatory thresholds and are not routinely measured in agricultural waste, soil surveys, or water quality monitoring. Establishing baseline data on their distribution and concentrations is a precondition for managing them effectively.

The review covers literature from multiple countries and farming systems, which introduces variability in methodology and exposure levels. Many studies focus on specific contaminants or specific farm types, making system-wide conclusions approximate. The field is also moving quickly: some contaminant categories identified here as emerging may have much larger bodies of evidence within a few years.