Agricultural Soil Pollution: Causes, Impacts, And Solutions

Soil pollution, or land contamination, is a serious issue that endangers human health and well-being, particularly through the food we eat. It is caused by the presence of harmful chemical substances, often produced by human activity, that infiltrate the soil and disturb its natural composition and structure. Agricultural soil pollution is mostly caused by the use of agrochemicals, such as pesticides and fertilisers, as well as industrial and mining activities, waste management, and stock breeding. These activities release toxic substances that accumulate in the soil, leading to a decline in soil quality and fertility, and ultimately impacting the growth of plants, animals, and humans. The effects of agricultural soil pollution are far-reaching, with consequences for food security, biodiversity, and the overall health of the ecosystem.

Pesticides and fertilisers: the rampant use of these can be devastating for soil quality

Pesticides and fertilisers are often used rampantly in agriculture to increase crop production and combat certain circumstances. While they serve a purpose, their overuse and misuse can be devastating for soil quality and the health of the wider ecosystem.

The use of pesticides and fertilisers has been identified as a major cause of soil pollution. Soil is a complex and biodiverse ecosystem, containing nearly a quarter of all species. A single handful of soil contains about 10 to 100 million organisms. These organisms, particularly invertebrates like earthworms, ants, beetles and bees, provide essential ecosystem services such as cycling nutrients that plants need to grow, decomposing dead organic matter and regulating pests and diseases.

The overuse of pesticides and fertilisers can contaminate the soil, air and water, and have significant impacts on the ecosystem. Pesticides are designed to kill, and while they are often targeted at specific pests or weeds, they can also be toxic to other organisms. In fact, research has shown that in 71% of cases, pesticides kill or harm soil invertebrates. They can also persist in the soil for years or decades after they are applied, continuing to harm soil health. The type of soil and the type of pesticide can affect how long it persists. For example, pesticides applied to sandy or coarse-grained soils are more likely to leach through the soil and contaminate groundwater.

Similarly, fertilisers can have unintended consequences for the environment. While they are essential for replenishing nutrients in the soil, their overuse or misuse can lead to contaminated air, water and soil, degraded land, increased greenhouse gas emissions and reduced biodiversity. Nitrogen fertilisers, in particular, can end up in neighbouring water bodies or in the air, where they contribute to the eutrophication and acidification of fragile ecosystems. This, in turn, has a negative impact on landscape quality and biodiversity.

The use of pesticides and fertilisers is regulated by national governments and organisations like the Food and Agriculture Organization of the United Nations (FAO), which has developed a Code of Conduct for Sustainable Use and Management of Fertilizers. However, it is important for everyone to realise the detrimental effects of these substances and take steps to minimise their usage by substituting them with more sustainable alternatives.

Plastic pollution: plastic products used in agriculture can cause soil pollution

Plastic products are integral to modern agricultural production, with applications including mulch films, nets, storage bins, seed and fertiliser bags, pesticide containers, seedling trays, and pots. However, their widespread use has led to the accumulation of macro-, micro-, and nanoplastics in soils, causing plastic pollution in agricultural areas. This issue has attracted the attention of the scientific community and authorities, who recognise it as a significant source of soil pollution.

Plastic mulch films, in particular, cover over 25 million acres of farmland globally, resulting in a direct annual flux of approximately 6.7 million tons of non-biodegradable material into terrestrial systems. While single-use plastic mulch is a valuable tool for weed management, temperature and moisture modulation, and cost-effective crop production, it gives rise to concerns from both an environmental and human health perspective. The rise of plastic-dependent agriculture, or "plasticulture", has been linked to soil plastic contamination, which threatens environmental health and food security.

The presence of microplastics as pollutants in agricultural soils has detrimental effects on soil, surface, and underground water resources. Climatic variables such as high temperatures, solar radiation, precipitation, and wind contribute to the physical weathering, aging, and quality deterioration of plastic films, leading to increased degradation and soil pollution. Additionally, the application of agrochemicals containing sulfur, halogen, iron, or chlorine has been confirmed to cause early aging of plastic films, further exacerbating the problem.

To address plastic pollution in agriculture, it is crucial to promote the rational use, reduction, collection, reuse, and innovative recycling of plastic products. Encouraging the use of biodegradable plastics and phasing out toxic additives are also essential steps towards more sustainable agricultural practices. The United Nations has recognised the urgency of this issue, with 175 countries agreeing to negotiate a legally binding Plastics Treaty to end plastic pollution by 2024.

Soil acidification: this can reduce the availability of plant nutrients in the soil

Soil pollution is a risk to human health and food security. It can reduce crop yields and make crops unsafe for consumption. Soil acidification is one of the major causes of soil pollution. It is an environmental condition that can reduce the availability of many plant nutrients in the soil, cause direct toxic effects from soil elements, increase the risk of soil-borne plant diseases, and limit the capacity of plants to fight pathogens.

Soil acidification occurs in agricultural soils due to several factors. The pH of the soil is a measure of its acidity or alkalinity, with a pH of 7 being neutral, above 7 being alkaline, and below 7 acidic. A pH of 6 is ten times more acidic than a pH of 7. The ideal pH range for most plants is between 5 and 6. Once the soil pH falls below 5, it starts to negatively impact plant productivity. At a low pH, many plant nutrients become less available, while others like iron, aluminium, and manganese become toxic.

The availability of nutrients like nitrogen, phosphorus, potassium, sulfur, calcium, and magnesium is reduced in acidic soils. This insufficiency of nutrients can hinder optimal plant growth. Additionally, the poor root growth associated with acidic soils further limits the plant's ability to access nutrients and water. Phosphorus, an essential nutrient for plant growth, can become less available to plants due to its combination with aluminium in acidic conditions.

Soil acidification can also lead to an increase in the availability of certain toxic elements, particularly aluminium and manganese. At a pH of 4.5, aluminium becomes soluble in toxic quantities, and manganese can also reach toxic levels in some soils, depending on temperature and moisture conditions. This toxicity can be harmful to plants, inhibiting their growth and survival.

To mitigate the effects of soil acidification, liming is often used to raise the pH of acidic soils and increase the availability of nutrients. This process can help reduce the toxicity of aluminium and make essential nutrients more accessible to plants, promoting healthier growth.

Animal waste: waste from factory farms can contain harmful microbes and antibiotics

Animal waste from factory farms can have detrimental effects on agricultural soil. The waste can contain harmful microbes and antibiotics, which can then be released into the soil. This waste often includes animal urine and faeces, which may contain antibiotic residues, antibiotic-resistant bacteria, and resistance genes. These can enter the soil when raw manure is used to fertilize fields, and the antibiotics can persist in the soil, leading to the emergence of new pests and diseases.

The overuse and misuse of antibiotics in farm animals have contributed to the rising threat of antibiotic resistance. This occurs when bacteria develop the ability to resist the effects of antibiotics, rendering them ineffective in treating infections. Antibiotic-resistant bacteria can be transmitted to humans through food chains, as well as through the environment, via animal waste.

Factory farms often administer antibiotics to their livestock to prevent disease and promote growth. While this practice may initially be successful in keeping the animals healthy, it can also create an ideal environment for the development of drug-resistant microbes. These microbes can then be transmitted to humans, either through direct contact with farmworkers or by ingesting contaminated meat.

The transmission of antibiotic-resistant bacteria from farm animals to humans can have severe health consequences. For example, in a 2012 study, the FDA found that a large percentage of raw retail meats, including chicken, turkey, beef, and pork, were contaminated with antibiotic-resistant bacteria. Improper handling or insufficient cooking of contaminated meat can lead to food poisoning and other severe health issues.

To address this issue, the World Health Organization (WHO) has recommended that farmers and the food industry stop using antibiotics routinely in healthy animals. By reducing the unnecessary use of antibiotics, we can help preserve their effectiveness and mitigate the risk of antibiotic resistance. Additionally, implementing improved soil management practices and regulations can help limit agricultural pollution and its adverse impacts on human health and food security.

Soil erosion: caused by over-tilling, excessive irrigation and heavy precipitation

Soil erosion is a significant issue in agriculture, causing economic losses and environmental damage. It is caused by various factors, including over-tilling, excessive irrigation, and heavy precipitation.

Over-tilling is the excessive turning of the soil, often with machinery, which can break up the soil structure, making it more susceptible to erosion. This practice is common in conventional agriculture to aerate the soil, mix in fertilisers and pesticides, and prepare seedbeds. However, it can lead to soil compaction and a loss of soil structure, making it more challenging for water to penetrate and plants to grow.

Excessive irrigation, especially on hillsides, can also cause soil erosion. When soil is over-irrigated, it can become waterlogged, reducing its ability to absorb and retain water. This leads to increased runoff, as water flows over the surface of the soil, carrying it away and leaving the land vulnerable to erosion by wind and water.

Heavy precipitation, such as intense rainfall, can also cause soil erosion, particularly when the land has been degraded by other factors, such as over-tilling or overgrazing. Intense rainfall can lead to soil crusting, where raindrops impact and compact the soil, sealing the surface and making it difficult for water to infiltrate. This increases surface runoff, which carries away the soil, a process known as sheet erosion. In areas with sloping land, heavy rainfall can also cause gully erosion, where water cuts deep channels into the soil, washing away the topsoil and leaving the land unable to support plant growth.

Soil erosion has far-reaching consequences. It degrades the land, reducing its ability to support plant growth and decreasing biodiversity. As soil is washed away, the land loses its fertility, leading to reduced crop yields and negatively impacting agricultural productivity. Soil erosion also sends large amounts of sediment downstream, clogging rivers and waterways, disrupting aquatic ecosystems, and increasing the risk of flooding.

To mitigate the impacts of soil erosion, sustainable land management practices must be implemented. These include adopting techniques such as terraced farming on hillsides, intercropping, and agroforestry, which can help to prevent erosion and improve soil health. By conserving soil, we not only protect our agricultural productivity but also contribute to climate change mitigation by preserving the land's ability to sequester carbon and reduce greenhouse gas emissions.

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