Fertilizers: A Friend Or Foe To Nature?

Fertilizers are essential for crop growth and development, but they can become pollutants when overapplied. Excessive use of fertilizers, whether artificial or organic, can contaminate freshwater and marine ecosystems. The nutrients in fertilizers, such as nitrogen and phosphorus, can cause rapid growth of algae, known as algal blooms, which deplete oxygen levels in water bodies, leading to the death of aquatic life. This process, called eutrophication, also results in the formation of toxic environments that can be harmful to humans and other organisms. The impact of fertilizer pollution extends beyond water bodies, as nitrogen compounds can be released as gases, contributing to air pollution, acid rain, and climate change.

Eutrophication and hypoxia

Fertilizers, whether artificial or organic, can contaminate freshwater and marine ecosystems. They contain nutrients such as nitrogen and phosphorus, which can cause the rapid growth of algae, also known as algal blooms. When the algae die, they are consumed by bacteria, which then deplete the oxygen levels in the water, leading to the death of fish and plants. This process is known as eutrophication, which can further lead to hypoxia or oxygen depletion.

Eutrophication is the over-enrichment of water bodies by nutrients, mainly nitrogen and phosphorus. It has emerged as a leading cause of water quality impairment and can result in harmful algal blooms, dead zones, and fish kills. Hypoxia occurs when a water body has dissolved oxygen concentrations of less than 2-3 mg/L, which is often caused by excess nutrients and waterbody stratification. Eutrophication and hypoxia can have severe impacts on aquatic life and ecosystems, including the loss of subaquatic vegetation, changes in species composition, coral reef damage, and the formation of dead zones.

The rise in eutrophication and hypoxia is attributed to various factors, including intensive agricultural practices, industrial activities, and population growth, which have increased nitrogen and phosphorus levels in the environment. Eutrophication can also be influenced by climate change and overfishing, further exacerbating the problem.

Addressing eutrophication and hypoxia requires a comprehensive approach beyond traditional command-and-control measures. It involves education, research, fiscal incentives, ecosystem preservation, and exploiting synergies with other environmental goals. By understanding the complex interactions between eutrophication, hypoxia, and various environmental factors, we can work towards mitigating their impacts and preserving aquatic ecosystems.

Algal blooms

Fertilizers, whether artificial or organic, can contaminate freshwater and marine ecosystems. Nitrogen and phosphorus are the primary plant nutrients in fertilizers. When there is an overabundance of these nutrients in bodies of water, they act as fertilizers, causing the rapid growth of algae, also known as algal blooms.

Agricultural runoff of synthetic fertilizer and manure is the leading source of nutrients that toxic algae thrive on. However, contamination can also occur from failing septic systems, municipal and industrial wastewater, and residential lawn fertilizers.

Fertilizer composition

Fertilizers are any materials of natural or synthetic origin that are applied to soil or plant tissues to supply plant nutrients. They can be natural or industrially produced.

Macronutrients

The three main macronutrients found in fertilizers are nitrogen, phosphorus, and potassium.

Nitrogen (N)

Nitrogen fuels new growth. All vegetables and herbs need some nitrogen, with some crops, like corn, requiring more than others, like sweet peas. Nitrogen-based fertilizers are made from ammonia, which is produced from natural gas and air. Nitrogen fertilizers containing nitrates can contaminate groundwater because nitrates are highly soluble in water. At high levels, nitrates can be poisonous to humans, especially children. Certain forms of nitrogen are released as gases, contributing to acid rain and climate change.

Phosphorus (P)

Phosphorus promotes root development, which helps to strengthen plants. It also increases blooms. Phosphate fertilizers are obtained by extracting phosphate rock, which contains two principal phosphorus-containing minerals: fluorapatite and hydroxyapatite.

Potassium (K)

Potassium is essential to many plant functions and their overall health. It also helps plants withstand stressful weather and defend against diseases. Potassium fertilizers are usually potassium chloride, potassium sulfate, potassium carbonate, or potassium nitrate.

Secondary Macronutrients

Calcium, magnesium, and sulfur are considered secondary macronutrients.

Calcium (Ca)

Calcium improves general plant vigour and promotes the growth of young roots and shoots.

Magnesium (Mg)

Magnesium helps regulate the uptake of other plant foods and aids in seed-making. It is also important to the dark green colour of plants.

Sulfur (S)

Sulfur helps foliage maintain a dark green colour while encouraging vigorous plant growth.

Micronutrients

Micronutrients are consumed in smaller quantities but are still essential to plant health. Iron is commonly added to fertilizer because it is often lacking in poor soils. It aids in the conversion of sunlight to energy and helps plant foliage maintain a dark green colour. Other micronutrients include manganese, boron, zinc, copper, and molybdenum.

Straight vs Multinutrient Fertilizers

Fertilizers are classified as either "straight fertilizers", which provide a single nutrient, or "multinutrient fertilizers" (or "complex fertilizers"), which provide two or more nutrients.

Organic vs Inorganic Fertilizers

Fertilizers are also sometimes classified as organic or inorganic. Organic fertilizers are usually (recycled) plant- or animal-derived matter. Inorganic fertilizers are sometimes called synthetic fertilizers as they require various chemical treatments for their manufacture.

Groundwater contamination

Fertilizers, whether artificial or organic, can contaminate groundwater and cause serious problems. Nitrogen-based fertilizers are water-soluble and can easily pass through the soil to the groundwater table. Nitrate contamination of groundwater is a particular concern, as it can be fatal to humans, especially children, and deadly to amphibians.

Nitrogen fertilizers are widely used in agriculture to increase crop production, but excess nitrogen can cause air, soil, and water pollution. One of the most damaging impacts of over-application of nitrogen fertilizers is the degradation of groundwater quality and contamination of drinking water supplies. This poses immediate risks to human health, especially to infants, who are vulnerable to low oxygen levels in the blood caused by nitrate ingestion.

The risk of groundwater contamination by nitrate depends on both the nitrogen input to the land surface and the degree to which an aquifer is vulnerable to nitrate leaching and accumulation. Nitrogen input includes nitrogen from inorganic fertilizers, animal manure, atmospheric deposition of airborne nitrogen compounds, residential fertilizers, septic systems, and domestic animal waste in urban areas. Aquifer vulnerability is influenced by soil-drainage characteristics and the extent of cropland versus woodland in agricultural areas.

Areas with high nitrogen input and vulnerable aquifers are at the highest risk of groundwater contamination by nitrate. These areas include the Midwest, parts of the western United States, and some regions in the Northeast. In these regions, nitrate concentrations in groundwater can reach levels that exceed the U.S. Environmental Protection Agency's (EPA) drinking-water standard of 10 milligrams per liter (mg/L).

To mitigate the risk of groundwater contamination, it is essential to consider factors such as nitrogen input, aquifer vulnerability, soil type, drainage characteristics, and the presence of woodlands or croplands. Protecting groundwater resources requires effective management practices and regular water-quality testing, especially in areas with a high risk of contamination.

Air pollution

Fertilizers are a significant contributor to air pollution. While they have been instrumental in boosting agricultural production, their excessive use has led to environmental and health issues.

Agricultural Air Pollution

Agricultural air pollution is mainly in the form of ammonia, which enters the air as a gas from heavily fertilized fields. Ammonia combines with pollutants from combustion, such as nitrogen oxides and sulfates from vehicles, power plants, and industrial processes, to create tiny solid particles or aerosols. These aerosols are about 1/30th the width of a human hair and can penetrate deep into the lungs, causing heart or pulmonary disease. According to a 2015 study in the journal Nature, these fine particles cause at least 3.3 million deaths each year globally.

A study published in Geophysical Research Letters found that emissions from farms outweigh all other human sources of fine-particulate air pollution in much of the United States, Europe, Russia, and China. The study also projected that if industrial emissions decline in the coming decades, as most projections indicate, fine-particle pollution will decrease even if fertilizer use doubles.

Nitrogen-based Fertilizers

Nitrogen-based fertilizers have played a pivotal role in the industrialization of agriculture over the past century, enabling high yields even on overtaxed land. However, they have severe drawbacks for water supplies and the climate. When excess nitrogen is released into the atmosphere, it can become nitrous oxide, a potent greenhouse gas, or nitrogen oxide, contributing to ground-level smog.

Nitrogen-based fertilizers also contribute to nutrient runoff, which occurs when nutrient-rich materials like fertilizer or manure, high in nitrogen and phosphorus, find their way into nearby rivers, oceans, and lakes, wreaking havoc on freshwater and marine ecosystems. This nutrient runoff has led to the decimation of ecosystems such as the Chesapeake Bay and the recurring "dead zone" in the Gulf of Mexico.

Health Impact of Air Pollution from Fertilizers

The presence of nitrogen compounds in the air seriously affects public health. It damages the respiratory tract and is linked to various conditions affecting the circulatory and immune systems, as well as pathologies in organs like the liver and spleen. According to a 2022 study in The Lancet, antibiotic-resistant bacteria, which can develop due to the widespread use of antibiotics in meat production, contribute to approximately 4.95 million deaths globally each year.

Additionally, pesticides used in agriculture have been linked to various chronic diseases, including endocrine (hormone) and neurological disorders and cancer. Children are especially vulnerable to the toxic effects of pesticides due to their developing bodies.

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