Agricultural Activities: Water Pollution's Unseen Culprit

Agriculture is the single largest user of freshwater on a global basis and is a major cause of degradation of surface and groundwater resources through erosion and chemical runoff. The associated agro-food processing industry is also a significant source of organic pollution in most countries. In recent decades, there has been a rapid increase in the area equipped for irrigation, which has contributed to the transfer of agricultural pollution to water bodies. This, coupled with the increased demand for meat, dairy, and eggs, has led to unsustainable agricultural intensification and water-quality degradation.

Use of untreated wastewater

With a rising demand for agricultural commodities, farmers are increasingly turning to unconventional water sources of marginal quality, such as domestic and municipal wastewater. Wastewater is an attractive option due to its high nutrient content, especially when conventional water resources are scarce. However, the unsafe use of wastewater in agriculture can lead to severe consequences.

Wastewater contains a range of microbiological and chemical pollutants, including antibiotics, vaccines, growth promoters, pesticides, and fertilisers. When untreated wastewater is used in agriculture, these pollutants can accumulate in crops, livestock products, soil, and water resources. This not only poses risks to the environment but also to human health, with exposed food consumers and farm workers vulnerable to the health impacts of these pollutants. Additionally, the use of untreated wastewater can exacerbate antimicrobial resistance, further complicating the issue.

In the United States, livestock and poultry produce nearly 1.4 billion tons of manure annually, contributing significantly to agricultural pollution. Unlike human waste, which is treated at wastewater plants, animal waste is often spread untreated on land. When excess manure is applied beyond the ground's absorption rate, it can lead to runoff into water sources, causing pollution. The manure also emits ammonia, which combines with other air pollutants to form harmful solid particles that can cause heart and lung diseases, contributing to deaths globally.

To address the issue of untreated wastewater in agriculture, proper treatment and safe application are crucial. If wastewater is adequately treated, it can become a valuable source of both water and nutrients, contributing to food security and livelihood improvement. Additionally, implementing conservation practices, such as nutrient management, efficient irrigation schemes, and establishing protection zones, can help reduce the migration of pollutants into water bodies. By adopting these measures, agriculture can play a role in mitigating water pollution and protecting both the environment and human health.

Industrial farming

Industrial agriculture is one of the leading causes of water pollution, especially in the United States. The Environmental Protection Agency's (EPA) 2017 National Water Quality Inventory found that 46% of the nation's rivers and streams are in "poor biological condition", and 21% of lakes are "hypereutrophic", meaning high levels of nutrients and algae are degrading water quality.

Factory Farming

Factory farming, or Confined Animal Feeding Operations (CAFOs), is a major contributor to water pollution. The primary issue is the vast amount of animal waste produced, which is often stored in pits or open ponds, known as lagoons. These waste containment areas frequently leak and can rupture during storms, releasing billions of gallons of untreated waste into nearby water sources. This waste contains high levels of nutrients such as phosphorus and nitrogen, which are components of synthetic fertilizer and byproducts of animal waste. When released into waterways, these nutrients can cause eutrophication, leading to a loss of aquatic life and their habitats, shellfish contamination, and seasonal dead zones.

Contaminants in Animal Waste

Animal waste also contains harmful contaminants, including pharmaceutical residues, heavy metals such as copper, zinc, cadmium, lead, mercury, and arsenic, and bacteria. When sprayed onto fields as fertiliser, these contaminants can accumulate in the soil and leach into water supplies. Copper toxicity, for example, can cause gastrointestinal and liver disorders in humans, as well as negatively impact the environment, affecting soil microbial activity and plant growth. Zinc pollution can cause fish kills and damage to algae, crustaceans, and salmon.

Antibiotic Use

The widespread use of antibiotics in meat production is another concern. Nearly two-thirds of antibiotics important to human medicine in the US are sold for use in livestock. The overuse of these drugs contributes to the rise of antibiotic-resistant bacteria, which public health officials warn is one of the gravest health threats we face today. These bacteria can spread via air and water, including water used to irrigate crops, and can end up in animal waste used to fertilise crops, spreading into our communities.

Fertilizer and Pesticide Runoff

Pollution via runoff, or agricultural nonpoint source pollution, is the leading source of harm to water quality for rivers and streams, and the third-largest for lakes. Farmers can reduce nutrient runoff by following fertilizer best practices and adopting regenerative agriculture strategies, such as improving soil health through planting cover crops and streamside buffer crops. However, the use of pesticides (herbicides, insecticides, rodenticides, and fungicides) also contributes to water pollution, as these toxic chemicals have serious side effects when they enter water sources.

Soil erosion and salinization

Soil erosion occurs when the top layer of soil is washed away by wind or water, a process that is often accelerated by poor agricultural practices. These practices can include overgrazing by livestock, improper cultivation techniques, and the removal of natural vegetation cover. The eroded soil, along with any chemicals or fertilizers present, is then carried by wind or water into nearby water bodies, leading to the pollution of these sources. This not only degrades water quality but also affects the health of aquatic ecosystems and the safety of drinking water.

Agricultural activities that contribute to soil erosion include excessive or improper use of fertilizers and pesticides, as well as the overapplication of manure and other organic matter. The excessive use of fertilizers, for example, can lead to increased nutrient loading in water bodies, causing eutrophication and harmful algal blooms. This process not only reduces oxygen levels in the water, harming aquatic life, but also poses risks to human health and recreational activities.

Soil salinization, on the other hand, occurs when salts accumulate in the soil to levels that negatively affect plant growth. This often happens due to improper irrigation practices, where water containing dissolved salts rises to the surface through capillary action and evaporates, leaving the salts behind. Over time, these salts can accumulate and impact soil fertility, making it difficult for plants to absorb water and nutrients. Salinization is particularly common in arid and semi-arid regions with limited rainfall, where irrigation is necessary for agriculture.

To address these issues, farmers can implement a range of soil conservation practices. These include contour plowing, terracing, and the use of cover crops to reduce soil erosion. Additionally, adopting efficient irrigation schemes can reduce water return flows and decrease the migration of fertilizers and pesticides into water bodies. By implementing these practices, farmers can not only improve soil health and fertility but also reduce their impact on water sources, contributing to the overall sustainability of their agricultural operations.

Furthermore, the use of untreated wastewater in agriculture, driven by increasing water scarcity, has led to the accumulation of microbiological and chemical pollutants in crops, livestock, and soil and water resources. This practice can have severe health impacts on exposed food consumers and farm workers and may exacerbate antimicrobial resistance. However, if adequately treated and safely applied, wastewater can be a valuable source of both water and nutrients, contributing to food security and livelihood improvement.

Pesticides and fertilizers

Pesticides are chemicals used globally to control pests, weeds, and diseases in crops and for human and animal healthcare. They are also used to increase crop yield and reduce vector-borne diseases. However, the excessive and uncontrolled use of pesticides has serious negative impacts on the environment, ecosystems, and human health.

Pesticides are one of the main contributors to water pollution, with over 4,000,000 tons of pesticides used annually worldwide. The toxic chemicals in pesticides can contaminate water systems through runoff, erosion, or leaching, causing toxic effects on aquatic life, wildlife, and humans. Pesticides can also increase the concentration of heavy metals in the soil, which can negatively impact plants and find their way into water resources.

Fertilizers are another major contributor to water pollution in agriculture. Fertilizers have a high concentration of nutrients, specifically nitrogen and phosphorus, which are necessary for crop growth. However, when excess nitrogen and phosphorus from fertilizers and manure are not fully utilized by the plants, they can be washed off the soil during irrigation, rainfall, or snowmelt, polluting water resources. High levels of nitrogen and phosphorus can cause eutrophication of water bodies, leading to hypoxic "dead zones" that kill fish and decrease aquatic life. Additionally, excess nutrients can stimulate harmful algal blooms, disrupting wildlife and producing toxins harmful to humans.

To mitigate water pollution from pesticides and fertilizers, proper nutrient management practices are essential. Farmers can adopt techniques such as soil testing, crop-specific calibration, and timing applications to maximize nutrient uptake and minimize runoff. Implementing conservation practices, such as cover crops, field buffers, and conservation tillage, can also help reduce erosion and nutrient loss into waterways. Additionally, efficient irrigation schemes and establishing protection zones around water bodies can reduce the migration of pesticides and fertilizers into water resources.

Livestock and antibiotics

Livestock production accounts for 70% of all agricultural land and 30% of the planet's land surface. The use of antibiotics in livestock farming is an emerging environmental and human health concern. Antibiotics are used in agriculture as additives in animal food for growth stimulation or the treatment of infectious diseases. The intensive and excessive use of antibiotics, coupled with their presence in solid and liquid farming waste, has led to environmental risks and antibiotic resistance.

Antibiotics are released into the environment through various pathways, including human and animal waste streams. The antibiotics administered to animals are not fully metabolized and are discharged unchanged into water bodies, manure, or soils. This release of antibiotics into the environment contributes to antibiotic pollution, which has been linked to the emergence of antibiotic-resistant bacteria.

The presence of pathogenic bacteria and antibiotic-resistant bacteria in untreated or treated animal manure is a significant concern. When manure from livestock farming is applied to nearby agricultural fields, it can be flushed by heavy rainfall or runoff into water bodies used for human activities. This transfer of manure-borne antibiotics and bacteria into water sources poses risks to human health and the environment.

The use of antibiotics in livestock farming has been associated with the pollution of animal manures and agricultural soils by antibiotic residues. This pollution can lead to the multiplication of antibiotic-resistant pathogens, resulting in the rapid spread of infectious diseases in animals, plants, and humans. The impact of antibiotic resistance is a critical issue that requires attention and effective solutions.

To address the issue of antibiotic pollution and resistance in livestock farming, various methods for antibiotic removal have been studied. These include physicochemical and biological approaches, such as the use of ligninolytic microorganisms and their enzymes. Additionally, the implementation of efficient manure management practices for individual livestock species in sub-basins can help reduce multiple pollutants, including antibiotics, entering river systems.

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