Agricultural Pollution: Causes And Impacts Explained

Agriculture is a significant contributor to pollution, and it affects not just the air but also the water and soil. The major agricultural air pollutants are carbon dioxide, methane, and nitrous oxide, all of which contribute to the greenhouse effect and climate change. In addition, ammonia emissions from livestock manure and chemicals comprise 95% of ammonia emissions, which account for 58% of the particulate matter air pollution in European cities.

Agricultural water pollution is caused by animal manure and the excessive use of agrochemicals, which are washed away with runoff and accumulate to unnatural levels. This leads to eutrophication, where algal blooms block out sunlight and consume oxygen, making it harder for other flora and fauna to survive.

Soil pollution caused by agriculture can negatively impact biodiversity, reduce fertility, and cause erosion due to over-tilling and excessive irrigation.

Overall, the effects of agricultural pollution are far-reaching and have negative consequences for human health, the environment, and the planet itself.

Animal waste and ammonia emissions

Animal waste is a major source of ammonia emissions, which have a significant impact on both the environment and human health. Ammonia (NH3) is a colourless gas with a sharp, pungent odour. It is produced by the biological and chemical breakdown of manure protein, uric acid, and urea during the storage and decomposition of animal waste. The inefficient conversion of feed to animal products results in 50-80% of the nitrogen in the feed being excreted as waste. As microbes begin to break down this waste, ammonia is released, making manure and urine a primary source of ammonia emissions.

Agricultural activities, particularly livestock and poultry farming, are the largest contributors to ammonia emissions, according to the USEPA national emission inventory. Dairy and beef cattle production contribute about 54% of total ammonia emissions, poultry production contributes 33%, and swine production contributes 12%. Ammonia emissions from animal feeding operations can have both environmental and health impacts.

Environmental Impact of Ammonia Emissions

Ammonia emissions from agriculture can have several environmental impacts:

• Acidity of the Natural Environment: Ammonia emissions can lead to increased acidity in the natural environment, including soil and water systems. This can be harmful to crops and aquatic ecosystems.
• Algae Growth in Lakes: High levels of ammonia in water bodies can promote the growth of algae, leading to issues such as eutrophication and reduced water quality.
• Formation of Small Particles in the Air: Ammonia can react with other atmospheric pollutants, such as sulfuric and nitric acid, to form small ammonium aerosol particles. These particles can contribute to haze and reduced visibility in the atmosphere.

Health Impact of Ammonia Emissions

Ammonia emissions from animal waste can also have significant health impacts:

• High Ammonia Levels in Animal Production Buildings: Ammonia emissions can cause high ammonia levels inside animal production buildings, especially during winter months when ventilation rates are low. Prolonged exposure to high concentrations of ammonia can irritate the eyes, nose, and throat, and cause respiratory issues.
• Respiratory Issues: Ammonia is a strong irritant and can inflame the eyes and lungs, even at low concentrations. Higher concentrations can lead to severe eye irritation, coughing, and respiratory distress.
• Asthma in Children: Recent studies suggest that exposure to agricultural ammonia emissions may contribute to the early onset of asthma in young children.

Strategies to Reduce Ammonia Emissions

To mitigate the environmental and health impacts of ammonia emissions, several strategies can be implemented:

• Separation of Urine and Faeces: Separating urine and faeces can help reduce ammonia emissions by minimising the contact between them, thus decreasing the formation of ammonia.
• Manure Storage and pH Control: Controlling the temperature, moisture content, and pH of stored manure can influence ammonia formation and emissions. Keeping the pH low (<7) can help retain ammonia in its liquid form (ammonium) and reduce gaseous ammonia emissions.
• Improved Manure Management: Implementing improved manure management practices, such as deep placement of manure or using enhanced-efficiency fertilisers, can significantly reduce ammonia emissions from animal waste.
• Dietary Adjustments: Reducing the overuse of nitrogen-based fertilisers and adjusting dietary patterns, such as reducing beef consumption, can also contribute to lowering ammonia emissions.

Pesticides and herbicides

The use of pesticides and herbicides has increased rapidly since World War II, and three billion kilograms are used worldwide every year. However, only 1% of total pesticides are used effectively to control insect pests on target plants. The large amounts of remaining pesticides penetrate or reach non-target plants and environmental media, causing environmental pollution and negative impacts on human health.

Climate change-related factors, such as increased temperature, precipitation, and carbon dioxide levels, can also impact the use of pesticides and herbicides. For example, higher temperatures can enhance the potential for soil erosion and increase the size and frequency of crack formation in soils, leading to changes in pesticide application. Changes in temperature and precipitation can also affect the geographical distribution of pests, hosts, and bio-control agents, as well as the abundance of pests and the number of pest outbreaks.

To minimize the negative impacts of pesticide and herbicide contamination, measures such as integrated pest management, laws that forbid pesticides with high risks, and the development of a national implementation plan should be implemented.

Greenhouse gases

Agriculture is a significant contributor to greenhouse gas emissions, which are essential heat-trapping gases that maintain life on Earth. However, human activities, such as burning fossil fuels, have led to an excess of these gases in our atmosphere.

Agricultural practices can release greenhouse gases, which contribute to air pollution. The major agricultural pollutants associated with air pollution are carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). Each of these pollutants is created through different processes in agriculture.

CO2 is primarily released from two agricultural practices: land-use change and tilling. Deforestation, which often occurs when land is cleared for agricultural use, is the leading agricultural cause of CO2 pollution. Similarly, tilling or breaking up the soil before planting exposes buried organic matter to the air, where it decomposes and is released as CO2.

CH4, or methane, traps about 25 times more heat than a CO2 molecule in the atmosphere. There are two principal ways methane is released in agriculture: rice production and livestock digestion and waste from ruminant animals. Ruminant animals, such as cattle, sheep, and goats, have a special system of digestion where consumed grasses undergo fermentation by gut microbes, releasing CH4. Their excrement continues to release CH4 as it decomposes. Additionally, flooded rice paddies create anaerobic conditions for soil microbes, causing them to release CH4 as a byproduct of respiration.

N2O is a highly potent greenhouse gas with over 250 times the warming potential of a molecule of CO2. It is a major agricultural pollutant that comes from the application of nitrogen-containing agrochemical fertilizers and the decomposition of animal waste. When excess nitrogen-containing fertilizers are applied to fields, microbes break down the nitrogen, resulting in the release of N2O in much greater quantities than what occurs naturally. Similarly, animal waste contains high levels of nitrogen, and when it decomposes, microbes release N2O into the atmosphere.

In the United States, agriculture accounted for an estimated 10-11% of greenhouse gas emissions in 2021-2022. This includes emissions from livestock, agricultural soils, rice production, and the electricity used in the agricultural sector.

Soil pollution

Agriculture can cause soil pollution through two primary processes: the accumulation of contaminants in the soil and the loss of soil through erosion.

Accumulation of Contaminants

Soil acts as a filter and buffer for contaminants, but its potential to cope is finite. If the capacity of the soil to mitigate the effects of pollutants is exceeded, the contaminants can pollute other compartments of the environment. Unsustainable agricultural practices that reduce soil organic matter can facilitate the release of pollutants into groundwater or make them available for plant uptake and entry into the food chain.

Pollutants accumulate in plant tissues, passing to grazing animals, birds that eat fruits and seeds, or to humans that consume them. Many pollutants become more concentrated as they rise up the food chain, increasing the potential for harm to human health. Soil-dwelling organisms such as earthworms can also absorb pollutants.

The nitrification process that occurs after excessive nitrogen-based fertilizers are applied to soils can produce significant and rapid acidification, which only occurs over hundreds to millions of years under natural conditions. Acidification affects the bioavailability of contaminants and can lead to metal toxicities in plants. Nitrates can also accumulate and easily leach into groundwater. Nitrous oxide (N2O), a major greenhouse gas, is released from excessively fertilized soils and contributes to climate change.

Soil contamination can also occur through the use of agrochemicals and irrigation. Soil salinization can happen when the water used in irrigation is high in dissolved salts, which are left behind to accumulate when the water evaporates. Heavy metals can enter the soil through the application of agrochemicals. As metals and salts accumulate to toxic levels, soil microbes and plant growth can be negatively affected.

Loss of Soil Through Erosion

Erosion or loss of soil is initiated by agricultural practices that physically disturb the soil structure, such as tilling. Breaking apart soil aggregates makes soil particles more susceptible to being lost to wind or water erosion. Some forms of contamination from agrochemicals can also contribute to weakening soil aggregates. Soil transported by water runoff can accumulate around water sources and contribute to water pollution. Excess sediment becomes suspended in water and can block out sunlight, constricting aquatic plant growth.

Economic Impacts of Soil Pollution

Water pollution

Agriculture is the single largest user of freshwater resources, accounting for 70% of all surface water supplies worldwide. It is also a major cause of water pollution, both as a polluter and as a user of marginal quality water.

Agriculture as a Water Polluter

Agriculture intensification is often accompanied by increased soil erosion, salinity, and sediment loads in water, as well as the excessive use (or misuse) of agricultural inputs such as fertilizers to increase productivity. The pollution caused by agriculture can contaminate water, food, fodder, farms, the natural environment, and the atmosphere.

Pesticides and Fertilizers

Pesticides and fertilizers used in agriculture can contaminate both groundwater and surface water. Excessive use of nitrogen-based fertilizers has been a major factor in the industrialization of agriculture, allowing high yields even on overtaxed land. However, when excess nitrogen makes its way into the atmosphere, it can become nitrous oxide, a potent greenhouse gas, or nitrogen oxide, which contributes to ground-level smog. Nitrogen and phosphorus from fertilizers and manure can also cause eutrophication in water bodies, leading to the destructive overgrowth of algae, which then die off and are decomposed by aerobic bacteria. This process consumes oxygen, starving other marine life and creating "dead zones".

Livestock Waste

Livestock and poultry grown in the United States produce nearly 1.4 billion tons of manure annually, which is often disposed of by spreading it untreated on land. This waste can contain antibiotics residue, chemicals, and bacteria, and when applied beyond the ground's natural absorption rate, it leads to runoff into water sources. Manure is often stored in vast, unlined manure lagoons that are prone to overflows, leaks, and spills, causing the contents to leach into the soil and groundwater.

Antibiotics

The widespread use of antibiotics in meat production contributes to the public health crisis of antibiotic resistance. Nearly two-thirds of antibiotics important to human medicine in the United States are sold for use in livestock. The regular use of these drugs in the food and water of farm animals contributes to the rise and proliferation of antibiotic-resistant bacteria, which can then spread via air and water, including water used to irrigate crops, and can end up in animal waste used to fertilize crops.

Pesticides

Farmers routinely use pesticides such as herbicides, insecticides, rodenticides, and fungicides to keep away any unwanted weeds, insects, rodents, and fungi. These toxic chemicals have serious side effects and can cause many chronic diseases such as endocrine (hormone) and neurological disorders and cancer. Children are especially vulnerable to exposure and face the worst health impacts.

Agriculture as a User of Marginal Quality Water

With increasing demand for agricultural commodities, farmers are increasingly turning to non-conventional water sources of marginal quality, including wastewater, due to its high nutrient content and the scarcity of conventional water resources. The unsafe use of wastewater in agriculture can lead to the accumulation of microbiological and chemical pollutants in crops, livestock products, and soil and water resources. This can ultimately have severe health impacts on exposed food consumers and farm workers, and it may also exacerbate antimicrobial resistance.

Mitigation Strategies

To minimize water quality impacts, farmers can adopt soil and water conservation practices, such as nutrient management practices, targeted fertilizer and manure application, drip irrigation, and storing livestock manure in protected areas to minimize runoff risks.

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