Pesticides have revolutionized modern agriculture by effectively controlling pests and increasing crop yields. However, their widespread use has raised concerns about their impact on the environment, particularly in relation to soil contamination. Soil contamination refers to the presence of harmful substances or chemicals in the soil that can adversely affect its quality and the organisms that rely on it. In this article, we will explore the various ways in which pesticides contribute to soil contamination and discuss the potential consequences of their presence in the soil.

What Are Pesticides?

The loose organic or mineral substance that covers the immediate surface of the earth and acts as a natural growing medium for terrestrial plants is known as “soil.” The unconsolidated organic or mineral materials on the earth’s surface have been affected by relief-conditioned macro- and microorganisms, as well as genetic and environmental factors such as climate (including the impacts of water and temperature). Among them was the requirement for maintaining and enhancing the essential elements of soil, such as its physical, biological, and chemical properties, to safeguard the earth and support varied economic development.

The term “pesticide” is a general phrase that refers to all chemicals used to kill or control pests in agricultural fields and other places, including storerooms, human homes, and gardens.

These substances are categorized as herbicides (which control weeds), insecticides (which control insects), fungicides (which control fungi), nematocides (which control nematodes), and rodenticides (which control rodents) (control rodents and their kinds). Moreover, they contain sanitizers, bactericides, insect and animal repellents, antimicrobial disinfectants, molluscicides, and avicides.

While they are effective in controlling pests and increasing crop yields, their improper use or disposal can lead to soil contamination in several ways.

How Do Pesticides Penetrate The Soil?

To manage soil pests, pesticides are applied directly to the soil. They are also released into the ground by granules or treated seeds, spray drift during foliage treatment, wash off from treated leaves, and other means. Following are some ways by which pesticides penetrate the soil:

1. The application of pesticides to the soil to control pests that infest the soil, such as termites and other invasive species, causes insecticides to permeate the soil.

2. Using systemic insecticides to treat seeds or apply them to the soil to prevent soil pests and sucking pests.

3. Pesticides also impact wind-blown dust and surface runoff to untreated soil.

4. Certain insecticides sprayed on crops that run off the roof fall to the ground.

What Is The Role of Pesticides In Soil Contamination?

1. Fungicide

Fungicide usage typically destabilizes soil ecosystems by lowering the diversity and quantity of soil microorganisms essential for nutrient cycling, soil formation, promoting plant development, and pathogen defense. Organic matter in the soil can help protect the soil and water environment from contamination (by firmly binding pollutants and giving them time to be detoxified by microbes). Still, contamination can also prevent organic matter from forming in the first place.

Applications of the common fungicide Captan have been linked to a drop in populations of bacteria and archaea, which fix nitrogen in plants, and an increase in denitrifiers, which are microorganisms that turn plant-available N back into N₂ gas. More fertilizer applications are necessary to inhibit N-fixation, which raises the possibility of higher nitrous oxide (N₂O) emissions. This greenhouse gas is between 265 and 298 times more potent than carbon dioxide.

2. Soil Fumigants

The term “soil fumigants” refers to a class of broad-spectrum pesticides administered directly to the soil in large amounts as gases (or substances that quickly turn into gases) to ensure penetration across the soil profile. By using soil fumigants, crop resilience to both biological and physical disturbance is also reduced. Fumigated soils are negatively impacted, but non-fumigated soils, which have more biodiversity and intact community structures, may survive both temporary heat stress and ongoing chemical stress. Further to having a deleterious effect on soil biology, using the fumigant chloropicrin is linked to 7-8-fold increases in the generation of the highly potent greenhouse gas nitrous oxide (N₂O), and using MITC alone or in conjunction with chloropicrin has a similar impact.

3. Insecticide

The use of insecticides has been demonstrated to cause changes in the dominant species, increasing bacterial biomass and decreasing fungal biomass, as well as the many ecosystem services each species contributes, destabilizing the soil microbial community. Reduced fungal-to-bacterial biomass ratios have been linked to increased sensitivity to disturbance and decreased carbon sequestration, which increases crop damage rates and reduces opportunities for climate change mitigation.

4. Carbamate

On Nitrosomonas, Nitrobacter, and Thiobacillus, all gram-negative bacteria that contribute to nitrification and denitrification processes vital to crop nutrient uptake and strongly associated with high productivity, soil fertility, and yield, carbamate pesticides have been shown to have a toxic effect similar to that of organochlorine pesticides.

5. Neonicotinoid

Neonicotinoid pesticides have long-lasting effects on soil and can have significant adverse effects on essential soil species. According to one study, imidacloprid residues on leaves significantly reduced leaf litter breakdown, negatively affecting earthworms and soil microorganisms. Among other effects, imidacloprid has been linked to decreased fungal abundance and significant changes in nitrate-N, ammonium, nitrite-N, and nitrate reductase enzyme activity levels. The requirement for expensive extra fertilizers and mineral supplements rises due to such declines in soil nutrient content.

Effects of Pesticides on the Soil Biological Properties

1. Effects on soil microorganisms: The microflora plays a crucial role in soil fertility. The primary source of “N” for plant growth is the conversion of organic “N” by microbes into inorganic forms, together with bacterial fixation of atmospheric “N.”

The microflora of the soil aids in the breakdown of carbonaceous organic material. Pesticides harm soil microflora growth, activity, and enzyme production, which negatively impacts soil fertility and health. Fipronil, chlorpyrifos, and cartop hydrochloride had no appreciable negative impact on the collembola population, whereas carbofuran- and phorate-treated plots saw reductions of 27.65% and 13.47% in the rice-maize cropping scheme.

2. Effects on arthropods: Pesticides applied directly or indirectly function as a sink for reservoirs for soil. Earthworms improve soil aeration, aid in the breakdown of organic matter, and raise the number of nutrients in the top layer of soil. Earthworms support human health by consuming decaying trash and serving as a bio-indicator for soil fertility. Certain pesticides kill earthworms, and by eliminating the vegetation that the worms feed on, they may indirectly reduce the population. In the rice-maize cropping system, imidacloprid, chlorpyrifos, and phorate had a detrimental effect on earthworms.

3. Effects on snails and slugs: Insecticides like carbamates and organophosphates can be focused on the bodies of snails and slugs. Although diazinon, phorate, and carbofuran are water-soluble chemicals, their bodies contain high concentrations of these substances. The insecticides are not toxic to them, but they are dangerous to the birds who eat the snails and slugs because they will perish.

To Conclude

Pesticides have adverse ecological effects due to complicated problems, such as waste disposal, agricultural operations, and related industrial issues. These actions have resulted in several contaminations that impact human, water, air, and soil quality. These contaminations can be measured at the global, local, temporary, and permanent levels (i.e., acute or chronic form). However, structural disruptions and chemical concentrations in the soil profile, which may also impact the subsurface water system and the development of soil quality, are the most dangerous soil contaminations. Millions of tiny drops of pesticide chemicals, mixtures of active and inactive substances, make up the surface soil formation. Regular soil analysis that may involve both ex-situ and in-situ technology will be necessary to better understand the effects of soil contamination by pesticides.

To mitigate the role of pesticides in soil contamination, it is important to adopt integrated pest management (IPM) practices that focus on minimizing pesticide use through alternative strategies, such as crop rotation, biological controls, and targeted applications. Proper handling, storage, and disposal of pesticides are also crucial to prevent accidental spills or contamination incidents. Additionally, promoting organic farming practices that avoid or minimize synthetic pesticide use can help reduce soil contamination risks.

Also Read: Ecological Equilibrium: Restoring Harmony