Risks of Using Urea Fertilizer on Human Health

Introduction

• Manufacturers produce urea fertilizer, a widely used nitrogen-based fertilizer in agriculture, from synthechoicetic ammonia and carbon dioxide. It's popular because of its affordability, ease of application, and effectiveness in promoting plant growth. However, its use has been associated with health concerns such as respiratory problems, skin irritation, and kidney damage. Despite these risks, it remains a go-to choose for farmers globally. This article delves into the impact of urea fertilizer on human health and the need to consider alternative sustainable agricultural practices.

1. What is Urea Fertilizer?

• Urea (CO(NH₂)₂) is a simple organic compound that plays a key role in the nitrogen cycle of plants. It is synthesized from ammonia and carbon dioxide, and is valued for its high nitrogen content (46%), making it one of the most concentrated forms of nitrogen fertilizer available. When applied to the soil, urea breaks down into ammonia and carbon dioxide, providing essential nutrients that stimulate plant growth.

• 2. How Urea Fertilizer Works in Agriculture

• Urea is the most important nitrogen fertilizer on the market, a white crystalline solid containing 46 percent nitrogen as an animal feed additive and fertilizer. Urea is used in several ways to provide nitrogen nutrition for plant growth. It is commonly mixed with soil or applied to the soil surface. Because of its high solubility, it can be dissolved in water and applied to the soil as a liquid, added with irrigation water, or sprayed on plant leaves.

  Urea fertilizer is a stable organic fertilizer that can improve soil quality, provide nitrogen to your plants, and increase crop yields.

  The main function of urea fertilizer is to provide plants with nitrogen to promote green leaf growth and make plants look lush. Urea also helps in the photosynthesis process of plants. Since urea fertilizer can only provide nitrogen and not phosphorus or potassium, it is mainly used for flower growth. 

• Mechanism of nitrogen release in the soil.

The mechanism of nitrogen release from urea fertilizer in the soil involves several key chemical and biological processes:

1. Hydrolysis of Urea

• When urea (CO (NH₂)₂) is applied to the soil, it quickly dissolves in water and undergoes hydrolysis—a chemical reaction with water.
• The enzyme urease, found naturally in the soil, catalyzes this reaction, converting urea into ammonium carbonate.

Reaction:

$$\text{CO(NH₂)₂ + H₂O → 2NH₃ + CO₂}$$CO(NH₂)₂ + H₂O → 2NH₃ + CO₂

In this process, urea is broken down into ammonia (NH₃) and carbon dioxide (CO₂).

2. Formation of Ammonium (NH₄⁺)

• The released ammonia (NH₃) reacts with water in the soil to form ammonium ions (NH₄⁺).

Reaction:

$$\text{NH₃ + H₂O → NH₄⁺ + OH⁻}$$NH₃ + H₂O → NH₄⁺ + OH⁻

• The ammonium ions are positively charged and can be adsorbed onto negatively charged clay particles in the soil, preventing them from being immediately washed away by water.

3. Nitrification Process

• Ammonium (NH₄⁺) undergoes a two-step biological process called nitrification, carried out by nitrifying bacteria such as Nitrosomonas and Nitrobacter.

Step 1: Conversion of ammonium to nitrite (NO₂⁻) by Nitrosomonas bacteria.

$$\text{2NH₄⁺ + 3O₂ → 2NO₂⁻ + 4H⁺ + 2H₂O}$$

Step 2: Nitrobacter bacteria convert nitrite to nitrate (NO₃⁻).            

$$\text{2NO₂⁻ + O₂ → 2NO₃⁻}$$

• Nitrate (NO₃⁻) is the final, highly soluble form of nitrogen, which plants can readily absorb through their roots.

4. Plant Uptake

• Plants absorb nitrogen from the soil primarily in the form of nitrate (NO₃⁻) and to a lesser extent as ammonium (NH₄⁺).
• Nitrogen is essential for plant growth, particularly in the synthesis of proteins, enzymes, and chlorophyll.

5. Leaching and Environmental Risks

• Nitrate is highly soluble in water and can easily be lost on the soil through leaching into groundwater or surface water, which can lead to environmental problems like water contamination and eutrophication.
• To mitigate this, urea application should be managed properly, avoiding excessive use or applying it just before heavy rainfall. 

• Role of urea in plant growth and crop yield.

Urea plays a vital role in plant growth and improving crop yield by supplying essential nitrogen, a key nutrient required for various physiological processes in plants. Here’s how urea contributes:

1. Nitrogen Supply

• Nitrogen (N) is one of the most important macronutrients for plant growth. Urea is composed of 46% nitrogen, making it one of the richest nitrogen sources available for fertilizers.
• When applied to soil, urea breaks down into ammonium (NH₄⁺) and nitrate (NO₃⁻), which plants absorb through their roots. These nitrogen forms are essential for synthesizing critical compounds in plants.

2. Protein and Enzyme Synthesis

• Nitrogen is a key component of amino acids, the building blocks of proteins.
• Proteins are crucial for various plant functions, including enzyme activity, which regulates metabolic processes like nutrient uptake, photosynthesis, and respiration.
• Adequate nitrogen from urea promotes efficient enzyme production, supporting overall plant metabolism.

3. Chlorophyll Production and Photosynthesis

• Nitrogen is an integral part of chlorophyll, the green pigment responsible for capturing light energy during photosynthesis.
• Photosynthesis is the process through which plants convert sunlight into energy, which is essential for growth and development.
• A sufficient supply of nitrogen ensures healthy chlorophyll production, resulting in vigorous plant growth and higher crop productivity.

4. Increased Biomass Production

• Nitrogen availability directly influences plant biomass (total plant matter). Sufficient nitrogen from urea promotes leaf development, root growth, and stem elongation.
• Healthy and larger leaves have more surface area for photosynthesis, resulting in increased energy production and a stronger plant.
• Better root systems enhance water and nutrient uptake, contributing to greater overall plant health.

5. Enhanced Crop Yield

• By promoting vegetative growth and improving the plant’s overall health, nitrogen from urea leads to higher crop yields.
• Crops treated with urea have larger grains, more fruits, or more robust flowers, depending on the plant species.
• Urea supports the growth of high-quality produce, which is more marketable and valuable to farmers.

6. Resistance to Stress

• Adequate nitrogen from urea helps plants develop resistance to various environmental stresses such as drought, pests, and disease.
• Healthier plants are better equipped to withstand unfavorable conditions, reducing the chances of crop failure and improving yield stability.

7. Cost-Effective Nitrogen Source

• Urea is not only efficient in terms of nitrogen content,content, but is also relatively inexpensive compared to other nitrogen fertilizers.
• This makes it a cost-effective option for farmers looking to boost crop yield, especially in large-scale agriculture. 

• Advantages of urea over other fertilizers.

Urea has several advantages over other fertilizers, making it one of the most widely used nitrogen sources in agriculture. Below are the key benefits of urea compared to other fertilizers:

1. High Nitrogen Content

• Urea contains approximately 46% nitrogen, which is the highest concentration of nitrogen of any solid fertilizer. This high nitrogen content allows farmers to apply smaller quantities while still meeting the nitrogen requirements of their crops, making it more efficient in terms of transportation, storage, and application.
• In contrast, fertilizers like ammonium nitrate (33-34% nitrogen) or ammonium sulfate (21% nitrogen) require larger amounts to deliver the same nitrogen levels.

2. Cost-Effectiveness

• Urea is more cost-effective than other nitrogen fertilizers due to its high nitrogen content and widespread availability. It is one of the least expensive nitrogen sources on the market, making it a preferred choice for farmers looking to maximize efficiency and minimize costs.
• Its lower cost makes it accessible for large-scale and small-scale farmers alike, allowing for more sustainable crop management.

3. Widely Available and Easy to Manufacture

• Urea is produced on a large scale and is available globally, ensuring a consistent supply. The production process for urea is also relatively straightforward, involving the reaction of ammonia with carbon dioxide, both of which are byproducts of industrial processes.
• This ease of production and availability contributes to its affordability and ensures that farmers can rely on a steady supply of fertilizer.

4. Versatility in Application

• Urea can apply to crops in various forms, including solid granules, prilled, or liquid formulations. This flexibility makes it suitable for different soil and crops.
• It can also be applied through different methods, such as broadcasting, incorporating into the soil, or through fertigation (application with irrigation systems). This adaptability provides farmers with multiple options for efficient use depending on their specific needs.

5. Low Risk of Explosion or Fire

• Compared to other nitrogen fertilizers like ammonium nitrate, which is classified as a potentially explosive material, urea poses a significantly lower safety risk during storage, transport, and application. This makes urea a safer option, especially in regions where regulatory measures on fertilizer storage are strict.
• Urea’s safety profile reduces the risk of accidents, lowering the cost and complexity of safe handling.

6. Less Soil Acidification

• While all nitrogen fertilizers can affect soil pH to some extent, urea has a lower tendency to acidify the soil compared to ammonium sulfate, which is known to cause significant soil acidification because of its sulfur content.
• Maintaining more stable soil pH levels is important for the health of crops and the soil's long-term fertility, making urea a preferable option for maintaining balanced soil chemistry.

7. Minimal Volatilization When Properly Managed

• Urea, when applied properly and incorporated into the soil, can minimize nitrogen volatilization (the loss of nitrogen as ammonia gas). This ensures that more of the nitrogen stays in the soil, available for plant uptake.
• Compared to fertilizers like anhydrous ammonia, which have higher volatilization risks, urea is easier to manage with less nitrogen loss under normal conditions.

8. Compatibility with Other Fertilizers

• Urea is compatible with other fertilizers, such as phosphorus and potassium-based fertilizers, allowing farmers to create custom blends that meet the specific nutrient requirements of their crops.
• This versatility enables farmers to develop balanced fertilization programs that ensure optimal nutrient availability for their plants.

9. Easy to Store and Transport

• Urea is a solid fertilizer, making it easy to store for extended periods without significant degradation. It does not absorb moisture as readily as some other fertilizers, reducing the risk of clumping or spoiling.
• The granular or prilled form of urea is also easier to transport, as it’s less prone to breaking down or causing dust issues compared to powdered fertilizers.

10. Lower Carbon Footprint

• While the production of any nitrogen fertilizer requires energy, urea’s relatively simple production process results in a lower carbon footprint compared to more complex fertilizers. The high nitrogen concentration means that less material needs to be transported and applied to fields, further reducing the environmental impact. 

3. Environmental and Health Risks of Urea Fertilizer

• While urea fertilizer is widely used in agriculture due to its efficiency and cost-effectiveness, its improper use or overuse can lead to significant environmental and health risks. These risks primarily stem from the release of nitrogen compounds into the environment, which can negatively impact ecosystems, water quality, air quality, and human health.

1. Water Pollution and Eutrophication 

When urea is applied to soil, it is converted into ammonium and then nitrate through nitrification. Nitrate is highly soluble and can easily be leached from the soil into groundwater or surface water. 

Nitrate leaching into water bodies can lead to eutrophication, where excess nutrients cause the overgrowth of algae and aquatic plants. This process depletes oxygen levels in the water, leading to the death of fish and other aquatic organisms. 

In regions with high rainfall or excessive irrigation, leaching is a major problem. Excessive nitrate in drinking water can also pose health risks to humans, particularly in infants.

2. Groundwater Contamination 

High levels of nitrate in groundwater, often because of leaching from agricultural fields where urea is used, can lead to contaminated drinking water. This poses serious health risks, particularly in rural areas where groundwater is the primary drinking source. 
Nitrate contamination in drinking water has been linked to health conditions such as methemoglobinemia (blue baby syndrome) in infants, which reduces the blood’s ability to carry oxygen.

3. Ammonia Volatilization 

If urea is not properly incorporated into the soil, it can lead to the release of ammonia gas into the atmosphere through a process known as volatilization. 

Ammonia emissions contribute to the formation of fine particulate matter (PM2.5), a significant air pollutant that can affect respiratory health in humans and animals. It also plays a role in the formation of acid rain, which can harm ecosystems and degrade buildings and infrastructure.

4. Greenhouse Gas Emissions 

 Nitrogen-based fertilizers, including urea, contribute to the emission of nitrous oxide        (N₂O), a potent greenhouse gas. This occurs during the microbial processes of nitrification and denitrification in the soil. 
Nitrous oxide is about 300 times more effective at trapping heat in the atmosphere than carbon dioxide, making it a significant contributor to climate change. Urea application is a key source of nitrous oxide emissions in agriculture.

5. Soil Acidification 

Continuous and excessive use of urea fertilizer can lead to soil acidification. This occurs because the nitrification process produces hydrogen ions (H⁺), which increase soil acidity over time. 
Acidic soils can reduce the availability of essential nutrients such as phosphorus and potassium, harming plant growth. Soil acidification also damages soil structure, decreases microbial activity, and can ultimately reduce agricultural productivity.

6. Disruption of Soil Microbial Balance 

The application of urea can alter the balance of soil microorganisms that play important roles in nutrient cycling and soil fertility. High concentrations of urea can harm beneficial soil microbes, particularly those involved in nitrogen fixation, such as rhizobia in legume crops. 

Disruption of microbial communities can lead to reduced soil health, negatively impacting crop yield and long-term sustainability of agricultural land.

7. Health Risks from Direct Exposure 

Direct exposure to urea fertilizer, particularly in concentrated forms, can cause skin and eye irritation. Farm workers handling urea should take precautions to avoid direct contact with the fertilizer. 
Inhalation of urea dust or ammonia gas (from volatilized urea) can cause respiratory irritation, coughing, or shortness of breath. Prolonged exposure to ammonia emissions in agricultural areas may exacerbate respiratory conditions, particularly in vulnerable populations such as children and the elderly.

8. Nutrient Imbalance and Over-fertilization 

Excessive use of urea can lead to a nutrient imbalance in the soil. High nitrogen levels may cause rapid plant growth but reduce the availability of other essential nutrients such as phosphorus and potassium. 
Over-fertilization can result in excessive vegetative growth at the expense of fruit and flower production, reducing crop quality and yield. It can also increase the risk of pests and diseases, as lush, nitrogen-rich plants are more susceptible to certain types of insects and pathogens.

9. Contribution to Acid Rain 

Ammonia released from urea volatilization can react with pollutants like sulfur dioxide (SO₂) and nitrogen oxides (NOₓ) in the atmosphere to form ammonium sulfate and ammonium nitrate, which contribute to acid rain. 

Acid rain can damage crops, forests, and aquatic ecosystems by lowering the pH of soil and water bodies. This can have long-term detrimental effects on biodiversity and agricultural productivity.  

4. Direct Health Effects on Humans

Direct Health Effects of Urea on Humans

While urea fertilizer is commonly used in agriculture, direct exposure to urea can pose health risks to humans, particularly to those who handle it frequently, such as farmers and agricultural workers. Below are some of the key health effects of urea exposure:

1. Skin Irritation

• Direct contact with urea, especially in its solid or concentrated liquid form, can cause skin irritation. Symptoms may include redness, itching, or a burning sensation.
• Prolonged exposure can lead to dermatitis, a condition that causes the skin to become inflamed, dry, and cracked. Workers who regularly handle urea without proper protective gear are at a higher risk of developing skin problems.

2. Eye Irritation

• Contact with the eyes can cause significant irritation, including redness, tearing, pain, and a sensation of burning. If urea dust or solution accidentally enters the eyes, it can result in discomfort and potential damage to sensitive eye tissues.
• Washing the eyes immediately with water is necessary to prevent prolonged irritation or injury.

3. Respiratory Issues

• Inhalation of urea dust or ammonia gas (which can be released from urea under certain conditions) can irritate the respiratory system. Symptoms may include coughing, wheezing, shortness of breath, and in severe cases, asthma-like symptoms.
• People with pre-existing respiratory conditions, such as asthma or chronic obstructive pulmonary disease (COPD), may experience exacerbation of their symptoms if exposed to urea dust or ammonia gas.

4. Ingestion Hazards

• While urea is not considered highly toxic if ingested in small quantities, accidental ingestion of large amounts can lead to nausea, vomiting, and diarrhea. Ingesting urea in higher doses can cause dehydration and an imbalance in blood electrolytes, which can be dangerous if not treated.
• Although urea is a naturally occurring compound in the body, excessive ingestion disrupts the body's nitrogen balance, potentially leading to metabolic complications.

5. Ammonia Exposure from Urea

• Urea can release ammonia gas during its breakdown, particularly if it is exposed to the atmosphere without being incorporated into the soil. Ammonia inhalation can be harmful and cause:
  • Respiratory tract irritation can result in symptoms such as coughing, difficulty breathing, and chest tightness.
  • Long-term exposure: can exacerbate chronic respiratory conditions, especially in agricultural workers constantly exposed to ammonia from volatilized urea.
  • Acute high-level exposure: can lead to severe respiratory issues, such as bronchospasm and pulmonary edema (fluid buildup in the lungs).

6. Allergic Reactions

• Sometimes, individuals may have an allergic reaction to urea or its byproducts. While uncommon, allergic symptoms can include rash, hives, or more severe reactions such as swelling or difficulty breathing. Individuals with chemical sensitivities are more likely to experience these reactions.

7. Potential Long-term Health Effects

• Chronic exposure to urea, particularly through the inhalation of ammonia gas, may lead to long-term respiratory issues. Continuous irritation of the respiratory system can weaken lung function over time, increasing susceptibility to infections and chronic lung conditions.
• Agricultural workers exposed to fertilizers without proper safety precautions over long periods may experience cumulative health effects.

Safety Precautions

To minimize the direct health effects of urea, the following safety precautions should be taken:

• Personal Protective Equipment (PPE): Workers should wear gloves, protective clothing, and eye protection to prevent skin and eye contact with urea.
• Proper Ventilation: In areas where urea is stored or handled in large quantities, ensuring adequate ventilation can help minimize inhalation risks.
• Incorporation into Soil: Incorporating urea into the soil quickly after application can reduce the risk of ammonia volatilization and subsequent respiratory exposure.
• Immediate Washing: with skin or eye contact, affected areas should be washed immediately with water. 

• 5. Indirect Health Effects Through Food and Water

Indirect health effects of urea fertilizer on humans through food and water.

The widespread use of urea fertilizer in agriculture, while essential for boosting crop yields, can indirectly impact human health through its effects on the environment, particularly through contamination of food and water sources. These indirect health effects often arise because of the overuse or improper management of urea, which leads to the release of harmful nitrogen compounds such as nitrates and ammonia.

1. Nitrate Contamination in Drinking Water

• Nitrate leaching from agricultural fields into groundwater is one of the most significant indirect health risks associated with urea fertilizer. Urea breaks down in the soil to form ammonium, which is then converted to nitrate through nitrification. Nitrates are highly soluble and can easily leach into groundwater, especially in areas with excessive rainfall or irrigation.
• High nitrate levels in drinking water can cause serious health problems, especially for infants. The most well-known condition linked to nitrate contamination is methemoglobinemia (blue baby syndrome). This condition occurs when nitrate is converted into nitrite in the body, which reduces the blood’s ability to carry oxygen, leading to symptoms like shortness of breath, bluish skin, and in severe cases, death.
• Adults may also be affected by long-term exposure to high nitrate levels in drinking water. Some studies suggest a link between nitrate contamination and an increased risk of certain cancers, including stomach and esophageal cancer, as nitrates can form carcinogenic nitrosamines in the digestive system.

2. Bioaccumulation of Nitrates in Food

• Crops that are grown in soil with high nitrogen levels from urea fertilization can accumulate nitrates in their tissues, particularly leafy vegetables like spinach, lettuce, and cabbage. When humans consume these nitrate-rich vegetables, they may be exposed to excessive nitrate levels, which can pose health risks, especially for vulnerable populations like infants and pregnant women.
• High nitrate intake from food can lead to disruption of oxygen transport in the blood, similar to the effects of nitrate-contaminated water. It may also contribute to the formation of nitrosamines, compounds that are potentially carcinogenic and have been linked to various cancers in humans.

3. Eutrophication and Water Quality Degradation

• The over-application of urea fertilizer can lead to nutrient runoff into rivers, lakes, and oceans, contributing to a process known as eutrophication. Excess nitrogen from fertilizers encourages the growth of algae and aquatic plants, leading to algal blooms.
• Harmful algal blooms, especially those caused by cyanobacteria (blue-green algae), can produce toxins that contaminate water supplies. These toxins can cause a range of health issues, including:
• Liver damage: Prolonged exposure to algal toxins in drinking water has been linked to liver disease.
• Neurological effects: Some algal toxins have been associated with neurodegenerative diseases such as ALS (amyotrophic lateral sclerosis).
• Gastrointestinal issues: Ingesting water contaminated with algal toxins can cause nausea, vomiting, and diarrhea.
• Eutrophication also leads to hypoxia (low oxygen levels) in water bodies, which can kill fish and other aquatic life, disrupting ecosystems and reducing the availability of clean water and fish resources for human consumption.

4. Ammonia Emissions and Air Quality

• As urea breaks down, it can release ammonia into the atmosphere, particularly if it is not properly incorporated into the soil. Ammonia emissions contribute to the formation of fine particulate matter (PM2.5), a type of air pollution that is harmful to human health.
• Inhaling PM2.5 particles, which can form when ammonia reacts with other pollutants in the atmosphere, has been linked to respiratory and cardiovascular diseases. Long-term exposure to high levels of PM2.5 increases the risk of asthma, bronchitis, heart attacks, and stroke.
• Ammonia also contributes to the formation of acid rain, which can damage crops and contaminate water sources, indirectly affecting food safety and the availability of clean water for human consumption.

5. Heavy Metal Contamination

• While urea itself does not contain heavy metals, its frequent use can alter the soil's pH and chemical properties, potentially increasing the mobility of heavy metals such as cadmium, lead, and mercury in the soil. These metals can be taken up by crops and accumulate in the food chain, posing a risk to human health.
• Consuming crops contaminated with heavy metals can lead to a range of health problems, including:
• Kidney damage: Heavy metals like cadmium are known to cause kidney dysfunction.
• Neurological disorders: Lead exposure is particularly dangerous for children, as it can impair cognitive development and cause behavioral issues.
• Bone fragility: Long-term exposure to heavy metals can weaken bones and contribute to conditions like osteoporosis.

6. Impact on Soil Health and Food Quality

• Overuse of urea fertilizer can lead to soil acidification over time. Acidic soils can reduce the availability of essential nutrients for crops, leading to a decrease in the nutritional quality of food. For example, crops grown in acidic soils may have lower concentrations of important minerals like calcium, magnesium, and potassium.
• Additionally, soil degradation caused by the long-term use of urea can reduce the overall health of the soil, making it less fertile and less able to support sustainable agriculture. This can lead to a decline in food production and quality, indirectly affecting human health through reduced food security and availability.

7. Increased Risk of Pesticide Use

• Excessive nitrogen from urea fertilizer can lead to excessive vegetative growth in crops, making them more susceptible to pests and diseases. To combat this, farmers may increase their use of pesticides, which can introduce harmful chemicals into the food supply and water systems.
• Pesticide residues on food can pose health risks to humans, including hormonal disruptions, reproductive issues, and an increased risk of certain cancers. Pesticides can also leach into water sources, further contributing to water contamination and the indirect health effects on nearby communities.