Agricultural pollution refers to waste and chemicals from farming that harm the environment, ecosystems, and people. This pollution can come from specific places, like a single source of water pollution, or from widespread causes, such as runoff from fields or air pollution. Once in the environment, these pollutants can directly harm wildlife or contaminate drinking water. They can also cause long-term problems, like "dead zones" in large water bodies, where water is too polluted to support life.

How farms are managed greatly affects how much pollution is created and its impact. Practices include managing animals, using fertilizers and pesticides, and farming methods like plowing or overgrazing. Poor management, such as improper handling of animal waste or overuse of chemicals, increases pollution.

Agricultural pollution harms water quality in lakes, rivers, wetlands, estuaries, and groundwater. Common pollutants include soil, nutrients, harmful bacteria, pesticides, metals, and salts. Animal farming contributes heavily to pollution, especially when manure is not stored or used properly, allowing bacteria to enter water sources. Farming and land use changes also release air pollution, which affects climate change. These issues were discussed in the IPCC Special Report on Climate Change and Land and the 2024 UNEP Actions on Air Quality report. Reducing agricultural pollution is essential for creating a sustainable food system.

Abiotic sources

Without pest control, crops can lose about 40% of their yield before harvest. However, pesticides can stay in the environment for a long time. For example, 2,4-D and atrazine can remain for up to 20 years. Other pesticides like DDT, aldrin, dieldrin, endrin, heptachlor, and toxaphene also last a long time. How long pesticides stay in the environment depends on their chemical makeup. Pesticides can build up in animals that eat pests or soil organisms. The biggest risk from using pesticides is harm to animals and plants that are not the target of the pesticide.

Biopesticides, which come from natural sources, could help reduce pollution in farming. However, their use is limited. Sometimes, biopesticides cause the same problems as synthetic pesticides. In the United States, biopesticides face fewer environmental rules. Many are allowed under the National Organic Program, which sets standards for organic farming.

Pesticide leaching happens when water carries pesticides away from where they were applied. This is a major cause of groundwater pollution. Leaching depends on soil type, the pesticide used, and how much rain or irrigation occurs. Leaching is worse with water-soluble pesticides, sandy soils, heavy watering after application, and pesticides that do not stick well to soil. Leaching can also occur in areas where pesticides are mixed, cleaned, or disposed of.

Fertilizers help crops grow but can harm humans and the environment. A common problem is eutrophication, which happens when too much nitrogen enters water. Nitrogen fertilizers are often made of nitrate (NO₃) and ammonium (NH₄). These have greatly increased food production. However, nitrogen fertilizers can pollute groundwater, surface water, and the air. Not all fertilizer is used by crops, and the rest can build up in soil or run off into water. Nitrate is more likely to move into water because it dissolves easily and repels soil particles. High nitrate levels in groundwater can harm infants, cause thyroid issues, and increase cancer risk.

Nitrogen moves between the atmosphere and living things through processes like nitrogen fixation and denitrification. Other processes, such as nitrification and ammonification, help balance nitrogen levels in ecosystems. Too much nitrogen from farming can disrupt these balances, leading to eutrophication. This causes low-oxygen conditions in water, harming aquatic life. Nitrite (NO₂) from nitrogen pollution can also change river ecosystems by replacing sensitive species with more tolerant ones. Nitrogen fertilizers can release ammonia (NH₃) and nitrous oxide (N₂O) into the air. These gases can damage the environment and human health. Excess nitrogen can also harm soil by reducing organic matter and disrupting plant-microbe relationships.

Phosphorus fertilizers, like phosphate (PO₄), are used in farming and come from synthetic salts, manure, and compost. While phosphorus is needed for life, crops usually need only small amounts. Too much phosphorus enters water, causing eutrophication. This leads to algae blooms that reduce oxygen and release toxins harmful to humans and animals.

Phosphorus fertilizers can also contain high levels of cadmium, which can pollute soil and plants. Some phosphate rock has up to 188 mg/kg of cadmium. Using high-cadmium fertilizers can harm soil and livestock that eat contaminated soil. Fluoride from phosphate rock can also increase soil fluoride levels, which may harm soil microbes.

Fertilizer-related contamination is rare in food, but livestock may be affected by fluoride in soil. Farm equipment can also cause pollution through gas emissions, oil spills, hydraulic fluid leaks, and tire particles. Other farming tools and materials may add to environmental harm.

Biotic sources

Manures and biosolids, although useful as fertilizers, can also contain harmful substances, including medicines and personal care products (PPCPs). Many different types and large amounts of these products are used by animals.

The United Nations Food and Agriculture Organization (FAO) estimated that 18% of greenhouse gases caused by humans come directly or indirectly from raising animals worldwide. This report also said that emissions from raising animals are greater than those from transportation. While raising animals does contribute to greenhouse gas emissions, some argue these estimates may not be accurate. The FAO used a method called life-cycle assessment, which considers all aspects of animal farming, such as growing crops for feed and transporting animals. However, they did not use the same method for the transportation sector.

Other sources claim the FAO’s estimate is too low, saying the global livestock industry might be responsible for up to 51% of greenhouse gas emissions. Critics say the difference in estimates comes from the FAO using outdated data. Even if the FAO’s 18% estimate is correct, livestock would still be the second-largest source of greenhouse gas emissions.

A study by the Proceedings of the National Academy of Sciences (PNAS) showed that removing all animals from U.S. agriculture and diets would reduce U.S. greenhouse gas emissions by only 2.6% (or 28% of agricultural emissions). This is because replacing animal manure with fertilizers and other animal byproducts would still be needed. Also, livestock currently use parts of human food and fiber production that people cannot eat. Removing animals might also lead to more nutrient deficiencies in people, even though they might consume more energy, possibly increasing obesity.

The global expansion of agriculture has led to the accidental spread of pests, weeds, and diseases to new areas. If these organisms survive, they can become invasive species, harming native species and threatening farming. For example, bumblebees raised in Europe and brought to the United States or Canada for pollination introduced a parasite from Europe to North America. This may have contributed to declines in native bumblebee populations. Introduced species can also mix with native species, reducing genetic diversity and harming farming.

Farming practices that disturb natural habitats can help invasive species establish themselves. Contaminated machinery, animals, feed, and seeds can also spread weeds.

Quarantines are one way to prevent the spread of invasive species through policy. A quarantine is a rule that stops the movement of materials carrying invasive species from areas where they exist to areas where they do not. The World Trade Organization has international rules about quarantines under the Agreement on Sanitary and Phytosanitary Measures. Countries often have their own quarantine rules. In the United States, the USDA/APHIS manages quarantines for both domestic and imported materials. Inspectors at borders and ports enforce these rules.

Using biological pest control, such as predators, parasites, or diseases to manage pests, can reduce pollution from pesticides. However, introducing non-native pest control agents is debated because their effects are hard to predict. Once released, these agents can spread to natural areas or harm native species. For example, a parasitoid introduced to control moths in North America harmed native silk moth species.

Organizations like the European Biological Control Laboratory and the USDA/ARS help find potential pest control agents globally. Before introducing these agents, quarantines and research on their safety and effectiveness are required. If approved, they are tested in agricultural settings, and their performance is regularly checked.

Genetically modified (GMO) crops can mix with native plants through hybridization, potentially making native plants more weedy or causing their extinction. Also, GMO plants might become weeds if their traits improve their survival in the environment.

There are concerns that non-target organisms, like pollinators, might be harmed by eating parts of GMO plants. A study found that Bt corn pollen had little effect on monarch butterfly larvae feeding on milkweed.

GMO crops designed to resist herbicides can increase herbicide use, indirectly harming the environment. For example, more herbicide use in resistant corn fields in the U.S. has reduced milkweed, which is important for monarch butterflies.

Rules for releasing GMOs depend on the organism and the country.

While there are concerns about GM products, they might help reduce pollution from animal farming. One major source of pollution is the waste of vitamins and minerals in soil, caused by poor digestion in animals. Improving digestion can reduce waste and environmental harm. An example is the Enviropig, a genetically modified pig that produces an enzyme called phytase in its saliva.

Grains like corn and wheat contain phosphorus in a form that pigs cannot digest, called phytic acid. Without phytase, pigs waste most of the phosphorus in their feces, polluting soil. The Enviropig’s phytase breaks down phytic acid, allowing pigs to use the phosphorus. This reduces phosphorus waste by 20-60% and removes the need to add phosphorus to their feed.