Herbicides and Human Health - An Overview

Introduction

The growth of unwanted plants in the agricultural fields results in overall yield loss. Herbicides are chemicals introduced to prevent the growth of unwanted plants in agricultural lands, lawns, and areas of commercial forests. Herbicides contain harmful chemical substances which cause environmental toxicity and adverse health issues in humans. These harmful chemicals leach into the soil and underwater sources and remain for a long period. Long-term exposure to chemicals will cause multisystem defects in humans. Proper handling methods should be followed to prevent accidental exposure and after-effects.

What Are Herbicides?

Herbicides (weed killers) are chemicals that kill or prevent the growth of unwanted plants in agricultural feeds, lawns, and commercial forests. These unwanted plants are called weeds or plant pests. They compete with wanted plants for water, light, and nutrients, decreasing agricultural crops' productivity and yield. Herbicides can be applied to the agricultural fields before or after planting. Herbicides are classified based on the mode of action as selective herbicides and non-selective herbicides. Selective herbicides inhibit the growth of a specific type of weed. Non-selective herbicides control the growth of both the wanted and unwanted plants.

What Are the Advantages of Using Herbicides?

• It helps to prevent the growth of unwanted plants.

• They are comparatively easy to use.

• Cheaper as compared to manual weeding methods.

• Destroy plant-bearing diseases.

• Long-lasting effects compared to other weed control methods.

• One-time application is enough, whereas other methods have to be continuously used.

• They help the crops to grow better by destroying unwanted plants (weeds) that utilize water, nutrients, and sunlight.

What Are the Different Types of Herbicides?

• Pre-emergent Type - It is used as a preventive method against unwanted plants rather than a control method. These herbicides help to prevent the germination of unwanted seeds. They are applied before the seed develops into a plant.

• Post-emergent Type - They are applied after the seed develops into a plant. They prevent and kill the growth of leaves and other structures of unwanted plants (commonly used is round-up).

• Contact Herbicide - Applied on the leaves of unwanted plants, and after contact, they slowly start killing the plant within a few hours. They are comparatively cost-effective and easily available (example - paraquat). However, contact herbicides do not provide a long-lasting effect as they only affect the leaves, not the root.

• Systemic Herbicides - They are also known as translocated herbicides. Systemic herbicides reach the tissues of unwanted plants through transport mechanisms (xylem and phloem). These harmful chemicals present in the plant tissues eventually result in their destruction. Systemic herbicides are effective as compared to other herbicides, as they destroy the shoot and root of unwanted plants. After application, these chemicals will take more than two weeks for their action (commonly used is Glyphosate herbicide).

• Selective Herbicides - They help to prevent the growth of specific categories of unwanted plants. They can be either systemic or contact types.

• Non-selective Herbicides (Knockdown) - It prevents the growth of all categories of plants and takes three to four days for their action. However, they are not able to differentiate between weeds and crops.

• Residual Herbicides - They are used for highly resistant types of weeds. Due to continuous application, some weeds will develop resistance to chemical substances. Residual herbicides have been effective for a long time.

• Drench Herbicides - It helps eliminate unwanted plants for a very long time. They are highly effective as compared to others.

How Do Herbicides Affect Human Health?

Improper handling and application of herbicides will result in environmental pollution and adverse health effects. Short-term and long-term poisoning occurs due to inadequate safety measures during application and exposure. The toxicity of commercially available herbicides depends on the chemical composition and the application measures.

1. Short-Term Effects of Herbicides: These adverse effects occur due to the absence of proper application procedures, resulting in direct contact with harmful chemical substances. It includes the following.

• Skin Rashes -Contact with the chemicals present in herbicides causes redness, irritation, and inflammation of the skin.

• Nausea - An increased tendency for vomiting.

• Diarrhea- Toxic chemicals reach the stomach and result in frequent, watery stools.

• Blisters - Contact with skin results in the formation of fluid-filled space between the skin layers.

• Dizziness - Occupational exposure will lead to a state of weakness.

• Blindness - Direct eye contact with the harmful chemicals present in herbicides due to accidental exposure can result in complete loss of vision.

• Stinging Eyes - Chemicals present in herbicides cause allergic responses and eye irritation.

• Increased Salivation - Chemicals in herbicides can reach the mouth due to improper handling and increase saliva production.

• Mouth Burns - Burning sensation in the oral mucosa occurs when the chemicals reach the mouth due to accidental contact.

• Pain and Discomfort -It occurs in the areas of contact.

2. Long-Term Effects of Herbicides: Long-term exposure to chemicals present in herbicides causes adverse health effects. Glyphosate-containing herbicides (Roundup) are the most commonly used chemical for weed control. Exposure to harmful chemicals will lead to long-term health effects. It includes the following.

• DNA Defects - Harmful chemicals present in the herbicides may cause DNA damage and resultant mutations. The chemicals in herbicides reach the cells and produce free radicals, producing reactive oxygen species (ROS). Increased levels of reactive oxygen species in the body will result in the oxidation of proteins, nucleic acids, lipids, and other cellular components resulting in DNA damage.

• Cell Death and Damage - It results in the inhibition of various enzymes and cellular cycles.

• Cancer- Phenoxy group of herbicides interacts with organic pollutants present in the atmosphere (like dioxins) and increases the risk of developing cancer.

• Parkinsonism - Contact herbicides like paraquat are associated with the incidence of central nervous system degenerative diseases like parkinsonism.

• Kidney Damage - Studies have shown kidney diseases in farmers who are exposed to chemicals present in herbicides.

• Developmental Disorders- Long-term exposure to toxic chemicals results in developmental defects in children. It includes behavioral changes, delayed milestones, learning disabilities, attention deficit hyperactivity disorder (ADHD), and emotional disabilities.

• Pregnancy - Glyphosate herbicides are associated with an increased risk of birth defects.

How to Avoid Herbicide Toxicity?

• Proper handwashing before and after the application of herbicides.

• Wear protective measures like a face mask, protective eyewear, and hand gloves before the application of herbicides.

• Avoid drinking contaminated water from areas near land fields used for agriculture.

• Wash fruits and vegetables thoroughly before consuming them.

• Remove clothes used during the application and proper disposal if contaminated with chemicals.

Conclusion

Herbicides are chemical substances used to destroy, prevent or reduce the growth of unwanted plants (weeds). They contain harmful chemicals which can cause damage to the environment and human health. Proper precautions must be taken during the application of herbicides to prevent accidental exposure and its side effects. Studies show workers' increased incidence of cancer, DNA damage, and kidney diseases due to long-term exposure. Therefore, proper herbicide management and safety standards must be followed to reduce the harmful effects.