Pesticides and Their Impact on Environment, Animal & Human Health

Introduction

As defined by the Environmental Protection Agency (EPA), pesticides encompass a category of chemical compounds employed for the purpose of controlling and repelling pest populations. This group comprises substances or combinations thereof that find primary usage in agriculture and public health initiatives. Their role is to safeguard plants against pests, weeds, and diseases, while also providing protection against vector-borne illnesses like malaria, dengue fever, and schistosomiasis. Various types of pesticides exist, including insecticides, fungicides, herbicides, rodenticides, and plant growth regulators.

Classification of pesticides

• Based on the pests they control
  • Insecticides: combat insect growth or survival
  • Herbicides: work against plants, weeds and grasses
  • Rodenticides: against rats and other rodents
  • Avicides: against bird population
  • Fungicides: attack fungi
  • Nematicides: combat nematodes

• Based on their chemical structure
  • Organophosphorus: chlorpyrifos and diazinon,
  • Carbamates (carbaryl and aldicarb)
  • Organochlorine (DDT and aldrin)
  • Pyrethrins and pyrethroids (cyfluthrin and cypermethrin)
  • Benzoic acids (dicamba)
  • Triazines (atrazine and simazine)
  • Phenoxyacetic derivatives (2,4-D)
  • Dipyridyl derivatives (diquat and paraquat)
  • Glycine derivatives (glyphosate)
  • Dithiocarbamates (maneb and ziram)

Consumption pattern of pesticides

Aktar et al., (2009)

The utilization pattern of pesticides in India differs from the global trend. As illustrated in the figure, insecticides constitute 76% of the total pesticide usage in India, in contrast to the global average of 44%. Conversely, the application of herbicides and fungicides is comparably lower. Notably, the primary purpose for employing pesticides in India is to protect cotton crops (45%), followed by paddy and wheat cultivation.

Benefits of Pesticides

Pesticides serve several key purposes, which include:

1. Enhanced Productivity: Pesticides contribute to improved agricultural output by managing pest populations and minimizing crop losses, thus boosting overall productivity.
2. Safeguarding Crop Yields: Pesticides play a pivotal role in shielding crops from yield reduction caused by pests, thereby ensuring optimal harvests.
3. Vector-Borne Disease Management: Pesticides are crucial for controlling disease-carrying vectors, helping to prevent the spread of illnesses like malaria, dengue fever, and other vector-borne diseases.
4. Diverse Applications: Pesticides find utility in various domains, such as:
   1. Sports Facilities: Herbicides and insecticides are employed to maintain the quality of turf on sports fields, cricket pitches, and golf courses.
   1. Structural Protection: Insecticides are used to safeguard buildings and wooden structures from termites and woodboring insects, averting potential damage.

Impact on environment

• Air pollution

Pesticide Drift occurs when pesticides, existing as airborne particles, are carried by the wind to unintended locations, thereby contaminating those areas. Higher wind velocities amplify the occurrence of spray drift and associated exposure. Factors like low relative humidity and high temperatures contribute to increased spray evaporation. Pesticides applied to crops can undergo volatilization, turning into vapor and being carried by winds to neighboring regions, potentially endangering wildlife. Pesticides used for soil fumigation can emit volatile organic compounds, which can react with other chemicals and give rise to a pollutant known as tropospheric ozone.

• Water pollution

Pesticides have the potential to contribute to water pollution through various pathways. These include unintended drift during application, percolation or leaching through soil layers, runoff into water bodies, and accidental or negligent spills. Several factors determine a pesticide’s capacity to contaminate waterincluding its water solubility, distance from application site to water body, weather conditions, such as rainfall and wind patterns, soil type and its characteristics, presence of a growing crop and application techniques.

• Soil pollution

Chemical compounds found in pesticides can persistently linger within the soil, exerting lasting effects that may span decades and pose detrimental effects to soil preservation efforts. Pesticide application contributes to a reduction in overall soil biodiversity and the depletion of organic matter within the soil composition. The persistence of pesticides in soil is influenced by both degradation and absorption processes. Depending on the specific chemical attributes of the pesticide, certain mechanisms directly regulate its movement from the soil to water bodies, subsequently impacting air quality and the safety of our food sources.

• Effects on soil organisms

Soil microorganisms play a crucial role in upholding soil integrity, facilitating the conversion and breakdown of organic matter, and facilitating the release of nutrients for plant utilization. While soil microorganisms possess the capacity to metabolize and break down numerous pollutants and pesticides, the latter can exert detrimental impacts on the growth and reproductive capabilities of earthworms. Pesticides disrupt enzymatic functions, elevate individual mortality rates, diminish reproductive capacity and physical growth, alter behaviors like feeding rates, and ultimately lead to a reduction in overall community biomass and population density.

• Effects on plants

Pesticides in the soil impede nitrogen fixation, a crucial process for the growth of higher plants. This results in direct negative impacts on plants, including inadequate root hair development, yellowing of shoots, and diminished overall plant growth. When pesticides are applied to flowering crops, it can lead to the mortality of honeybees, vital pollinators responsible for plant reproduction.

Impact on animal health

Pesticide residues left on food can poison animals as these residues move through the food chain. Some animals may face a loss of critical food sources due to pesticide usage, leading them to migrate, alter their diet, or face the risk of starvation. Pesticide exposure can result in weakened immune system responses, reproductive consequences such as decreased birth weight and lower conception rates, as well as neurological and endocrine disruptions.

Aquatic animals, including fish, can face harm when exposed to water contaminated with pesticides. Repetitive contact with sub-lethal amounts of certain pesticides can induce alterations in physiology and behavior among fish, leading to population declines, abandonment of nests and offspring, lowered disease resistance, and compromised evasion from predators. Pesticides can accumulate within water bodies to levels that result in the eradication of zooplankton, a primary food source for juvenile fish.

Impact on human health

Pesticides can infiltrate the body through various pathways: inhalation of aerosols, dust, and vapor; ingestion via food and water; and skin contact through direct touch.The impact of pesticides on human health depends on both the toxicity of the chemical and the duration and intensity of exposure.Children, due to their ongoing development and weaker immune systems compared to adults, are more vulnerable and responsive to the effects of pesticides.Adverse health effects encompass a range of symptoms such as headaches, fatigue, respiratory ailments, cardiovascular issues, gastroenteritis, and skin irritation, among others.Pesticides have also been linked to developmental anomalies. The consequences of exposure can vary from mild skin irritation to birth defects, tumors, genetic alterations, blood and nerve disorders, disruptions in the endocrine system, and even extreme outcomes like coma or fatality.

Conclusions

A practical stance is essential when dealing with pesticide utilization. This implies that all actions related to pesticides must be based on scientific assessment rather than driven solely by commercial motives. It is imperative to provide education and training to workers to ensure the safe and proper application of pesticides. Monitoring the residual levels of pesticides in body fluids and tissues of the general population serves as a valuable means of gathering information about the ultimate outcomes of human exposure.