Intensive farming and environmental health

Pollution by manure, slurry and animal carcases

In traditional farming, animals such as pigs, chickens and cows live in much smaller groups than they do on factory farms. They have space to move around, and their manure does not become an environmental hazard; on the contrary, it is often used as a valuable fertiliser and source of fuel.

However, when farm animals are kept together in unnaturally large numbers, their manure can pose environmental problems, being difficult to dispose of safely in such large quantities. Much of the nitrogen, phosphorus and any heavy metals that are in the animals’ feed are excreted and are potential pollutants. A dairy cow can produce 20 tonnes of solid manure, 108 kg of nitrogen and 54 kg of phosphorus a year. A US Senate Committee estimated that 200 dairy cows can produce as much nitrogen in their manure as a town of 10,000 people.

In industrial pig farms, the slurry (a mixture of urine and faeces) is stored in huge tanks or lagoons and is disposed of onto land, where it can cause pollution of soil and water. Slurry has a very high ‘biological oxygen demand’ when it is broken down by bacteria. As much as 30% of the total nitrogen in animal slurry may escape into the environment as ammonia gas. High nitrate levels in water near animal feedlots have been linked to the risk of miscarriage in pregnant women.

One damaging effect of slurry on the environment is eutrophication (excessive growth of algae due to nutrient enrichment). This can affect rivers and other waterways, sometimes resulting in blooms of toxic algae and the death of fish. Many pig slurry lagoons flooded when Hurricane Floyd hit North Carolina in 1999, causing massive fish deaths and millions of dollars in clean-up costs.

The European Union has become so concerned by the environmental damage caused by nitrogen from overcrowded factory farms that it has introduced legal limits to the amount of nitrogen a farm can produce per hectare of land.

Another source of pollution is the organic waste of dead animals (blood, flesh, bones, skin, brains, intestines, etc) that has to be disposed of. This organic waste comes both from the large numbers of animals that die on the farms from a variety of illnesses and injuries and also from slaughterhouses.

Animal waste pollution in China

In China, intensive farming has increased rapidly in recent years, bringing manure disposal problems and pollution. The China State Environment Protection Administration reports that farms have become a major source of pollution, with unprocessed manure being dumped into rivers that are used as water supplies. The waste from pig and chicken farms in central China contaminated the Yangtze river, producing 40 times as much nitrogen as all the region’s factories. Large concentrations of heavy metals such as copper, zinc, chromium, lead and cadmium were found in the manure, according to Chinese scientists. These water pollutants can potentially affect embryonic development.

Diarrhoeal disease from manure

In both developing and developed countries, disease-causing micro-organisms can enter both soil and drinking water supplies from the waste products of animal farms. In developing countries, contaminated drinking water is one of the main causes of diarrhoeal disease among both vulnerable children and adults. Waterborne illnesses can be due to bacteria such as E. coli, Yersinia entercolitica, Salmonella, Listeria, parasites such as Toxoplasma gondii and Cryptosporidium, and viruses such as Hepatitis E.

In Michigan (USA), samples of water downstream from a cattle feedlot have been found to contain 1,900 times the maximum allowed concentration of E. coli, and in Canada over 1,000 residents near a cattle farm were affected by E. coli poisoning.

Hormones and antibiotics in manure

A large amount of the antibiotics put in feed in factory farms is excreted and distributed into the environment, encouraging the spread of antibiotic-resistant bacteria. Hormones fed to animals to make them grow faster also contaminate groundwater and soil. The water runoff from fields spread with manure has been found to contain significant levels of hormones. Some of these can disrupt the hormonal systems of animals that come into contact with them, including humans. This can lead to an increased risk of breast and ovarian cancer in women and reduced sperm count in men. Researchers have found that male fish exposed to the runoff from animal feedlots had gender disruption such as reduced size of testes.

Air quality

Air quality near factory farms or feedlots can be a serious problem for local residents and farm workers, ranging from unpleasant smells to potentially dangerous emissions. In a typical poultry factory farm, decomposing manure releases up to 400 compounds including phenols and sulphides. Hydrogen sulphide, released from slurry, causes the well-known ‘rotten egg’ odour and is also associated with respiratory problems, headaches and potentially permanent respiratory damage. Studies have shown that residents near pig farms report more tension, depression, fatigue, confusion and physical symptoms such as nausea and irritation in the eyes, nose and throat.

Soil erosion and informal settlements

The growth of industrialised animal farming and animal feed plantations, such as soya, have resulted in the displacement of many small farmers in developing countries. These displaced families often move to marginal land that is unsuitable for farming or settlement. Many informal settlements are in areas where it is potentially dangerous to farm, such as hillsides, made worse by soil erosion that is caused by cutting down trees. Such people are put at greater risk of natural disasters such as floods, landslides and earthquakes.