Chemical Fertilizers: Water Pollution's Hidden Poison

Fertilizers are used to enrich the soil with minerals like potassium, nitrogen, phosphorus, iron, and magnesium, which are essential for plant growth. However, the excessive use of fertilizers can lead to water pollution. This occurs through the process of eutrophication, where an overload of nutrients, particularly nitrogen and phosphorus, enter water bodies and cause uncontrolled algae growth, known as algal blooms. These algal blooms deplete the water of oxygen, creating dead zones where aquatic life cannot survive. The pollution of water by fertilizers also occurs through leaching and runoff, contaminating groundwater and surface water with nitrates and heavy metals, which can be harmful to both humans and animals.

Nitrogen and phosphorus runoff from agricultural fields

Nitrogen and phosphorus are essential nutrients for plants, and fertilizers are used to ensure that the soil contains enough of these nutrients to support plant growth. However, when nitrogen and phosphorus are not fully utilized by growing plants, they can be lost from farm fields and negatively impact water quality.

The runoff of nitrogen and phosphorus from agricultural fields can have significant environmental impacts. High levels of nitrogen and phosphorus in water bodies can cause eutrophication, a process that enriches the water surface with nutrients. Eutrophication can lead to hypoxia, or "dead zones," where aquatic life cannot survive due to a lack of oxygen. Additionally, excess nutrients can cause harmful algal blooms (HABs), which can produce toxins harmful to wildlife and humans.

To mitigate the negative impacts of nitrogen and phosphorus runoff, farmers can implement various strategies. Adopting nutrient management techniques involves applying the right amount of fertilizer at the right time of year, using the appropriate method and placement. Conservation tillage practices can also help by reducing the frequency and intensity of tilling, improving soil health, and reducing erosion and runoff. Implementing conservation drainage practices, such as subsurface tile drainage, is important for managing water movement and reducing nutrient loads while maintaining adequate drainage for crop production.

Eutrophication and algal blooms

Eutrophication is a type of pollution that occurs when excess nutrients, primarily nitrogen and phosphorus, enter a water body. This process enriches the water surface with nutrients, causing an abundance of algal blooms.

The algal blooms deplete the water of oxygen as they die, leading to low oxygen levels in the water, known as hypoxia. Aquatic life can become stressed in hypoxic conditions, and when there is no oxygen, the water becomes anoxic, and no aquatic life can survive. While hypoxia is a naturally occurring phenomenon, there has been a significant increase in hypoxic areas (dead zones) due to human impact.

Chemical fertilizers are a significant contributor to eutrophication. They contain compounds of nitrogen and phosphorus, which, when over-applied, can cause an excess of nutrients in the soil. This excess is then taken up by runoff water, which carries the nutrients into nearby water bodies. The excess nutrients in the water fuel the uncontrolled growth of algae, leading to algal blooms.

Algal blooms can create toxic conditions in lakes and oceans, as certain algae produce toxins to protect themselves from being eaten by small animals. While algae are crucial to the environment, providing a significant portion of the oxygen we breathe, their uncontrolled growth due to nutrient pollution from fertilizers can have detrimental effects on aquatic ecosystems and water quality.

Groundwater pollution

The use of chemical fertilizers in agriculture and gardening results in the release of nitrate, potassium, and phosphate into the environment. These chemicals are then absorbed by groundwater, leading to water quality deterioration. This process is known as leaching and runoff, where excess nutrients from fertilizers find their way into nearby water bodies through irrigation, rainfall, and snowfall. The increased nutrient concentration, particularly nitrogen and phosphorus, contributes to eutrophication, which enriches the water surface with nutrients, leading to an abundance of algal blooms. These algal blooms deplete the oxygen levels in the water, creating "dead zones" where aquatic life cannot survive.

The impact of groundwater pollution from chemical fertilizers extends beyond the environmental consequences. Groundwater is a crucial source of drinking water in many regions, and contamination poses significant risks to human health. Additionally, the economic implications of groundwater pollution cannot be overlooked, particularly in agricultural and fishing industries that rely on clean water sources.

To address the issue of groundwater pollution caused by chemical fertilizers, sustainable agricultural practices, and mitigation measures are necessary. Implementing environment-friendly fertilizers (EFFs), such as coated fertilizers that control the release of nutrients, can help reduce pollution. Additionally, natural alternatives like leaving lawn clippings to decompose and returning valuable nutrients to the soil can be considered.

Heavy metal concentration in water

Heavy metals are needed for several organs of both plants and humans, but they become toxic when their concentration exceeds the prescribed level. They can enter the water system through human activities such as industrial production, mining, agriculture, and transportation. Some methods by which they enter the water system include fossil fuel burning, smelting, waste from municipalities, fertilizers, pesticides, and sewage.

The presence of heavy metals in inorganic fertilizers is well-established. Analytical testing of a wide range of fertilizer products shows that some phosphate and micronutrient fertilizers, and liming materials contain elevated levels of arsenic, cadmium, and lead compared to other fertilizer types. Heavy metals also occur naturally in the soils and source materials used to manufacture fertilizers. In addition, heavy metals can be found in fertilizers as a result of blending with recycled industrial wastes, such as steel mill flue dust and mine tailings.

The usage of fertilizers results in the discharge of nitrate, potassium, and phosphates that pollute the water. The contamination of groundwater occurs as a result of leaching due to nitrate. The ground and surface waters are infested with heavy metals, whose concentration poses a threat to humans and animals.

The literature lacks knowledge about the cellular and molecular changes occurring in human cells and altering human genetics. However, studies conducted on animal models have shown that exposure to heavy metals can lead to lipid accumulation in hepatocytes, causing an increase in hepatic toxicity. Exposure to heavy metals has been linked to chronic and acute toxicity, which can cause retardation, neurotoxicity, damage to the kidneys, liver, and lungs, and fragile bones.

Acidification of water

Anhydrous ammonia and urea have a lower acidification potential compared to ammonium-based products as one H+ ion is consumed in the conversion to ammonium. Nitrate-based fertilizers have no acidification potential and can increase soil pH. Intensive agriculture can speed up soil acidification through increasing leaching, the addition of fertilizers, the removal of produce, and the build-up of soil organic matter.

Of all the major fertilizer nutrients, nitrogen is the main nutrient affecting soil pH. Soils can become more acidic or more alkaline depending on the type of nitrogen fertilizer used. Nitrate-based products are the least acidifying of the nitrogen fertilizers, while ammonium-based products have the greatest potential to acidify the soil. Soil acidification due to the use of phosphorus fertilizers is small compared to that attributed to nitrogen due to the lower amounts of this nutrient used and the lower acidification per kg of phosphorus.

Phosphoric acid is the most acidifying phosphorus fertilizer. Potassium fertilizers have little to no effect on soil pH. The use of chemical fertilizers can cause soil acidification, with sulfur-based fertilizers being highly acidifying. Examples include elemental sulfur and iron sulfate, while others like potassium sulfate have no significant effect on soil pH.

Frequently asked questions