Soil Pollution: Pesticides' Impact And Dangers

The use of pesticides can have a detrimental effect on soil quality and quantity. Pesticides are chemical compounds used to eliminate pests, and are used to protect and maximise the yield and quality of crops. However, the excessive use of pesticides can lead to serious problems, such as soil, water and air pollution, and can cause harmful effects to the ecosystem and along the food chain.

Pesticides can be more or less toxic to soil organisms, and can persist in the soil for longer periods. They can be taken up by plant roots and moved to other plant tissues, including fruit. They can also leach through the soil and contaminate groundwater.

The microbial metabolism of indigenous microorganisms can be exploited for degradation, as bioremediation is an eco-friendly, cost-effective method compared to physical and chemical ones.

Pesticides can be more or less toxic to soil organisms, depending on the type of pesticide and the type of soil

Pesticides can be more or less toxic to soil organisms depending on the type of pesticide and the type of soil.

The toxicity of pesticides depends on the electronic properties and the structure of the molecule, dosage, and exposure times. The type of soil and the type of pesticide can also affect pesticide persistence.

Pesticides with low affinity for adsorption tend to spread more easily into the environment. Several soil parameters influence the adsorption process, namely soil organic matter content, clay content, clay mineralogy, and pH.

The removal efficiencies of these processes depend on the type of pollutant and the chemical and physical conditions of the soil.

The regulation on the use of pesticides is strictly connected to their environmental impacts. Nowadays, every country can adopt regulations to restrict the consumption of pesticides, prohibit the most harmful ones, and define the admissible concentrations in the soil.

Pesticides can persist in the soil for longer or shorter periods, depending on the type of pesticide and the type of soil

The persistence of pesticides in the soil depends on several factors, including the type of pesticide, the type of soil, and environmental conditions.

Pesticides can be classified into several groups, including insecticides, herbicides, rodenticides, bactericides, and fungicides. Insecticides, for example, include organochlorines, organophosphates, carbamates, and pyrethrins and pyrethroids.

The persistence of pesticides in the soil can vary from a few hours to several years. For instance, the herbicide glyphosate was originally believed to break down within 14 days, but recent research indicates that it may persist in the soil for at least a year. Some chemical herbicides can remain in the soil for over a month, while others can last for years.

The properties of the soil, such as its composition and chemistry, can also affect the persistence of pesticides. Soils that are high in clay and organic matter, for instance, tend to cause herbicide carryover problems because herbicides bind more strongly to their particles.

Environmental conditions, such as temperature, moisture, and sunlight, can also influence the breakdown of pesticides. Microbial and chemical degradation, for example, typically increase with higher temperatures and moisture levels. Sunlight can also break down certain chemicals in pesticides.

Overall, the persistence of pesticides in the soil is influenced by a variety of factors, and understanding these factors can help minimize the potential risks associated with their use.

Pesticides can be taken up by plant roots and moved to other plant tissues, including fruit

Soil can be polluted by pesticides in several ways. One common cause is the improper storage of obsolete agrochemicals, which can result in spills that seep into the soil or are dispersed by the wind. In some cases, this spillage has been ongoing for many years, leading to serious soil or groundwater contamination. The overuse or misuse of pesticides can also degrade the soil and damage the community of organisms living within it. Some pesticides are more toxic to soil organisms and persist in the environment for longer periods, while others break down quickly. The type of soil and the type of pesticide can also affect how long the pesticide remains in the soil.

Once pesticides enter the soil, they can be absorbed by plant roots and transported to other plant tissues, including the fruit. This process is known as root absorption, and it occurs more readily with lipophilic herbicides. Root absorption is a simpler process than foliar absorption because roots do not have cuticles like leaves, although mature roots may be covered by a suberized layer. The absence of cuticles means there are fewer barriers to herbicide absorption by plant roots. The absorption typically occurs in the area a few millimetres behind the root tip, which is where most water and nutrient absorption takes place and is characterised by a profusion of root hairs that increase the surface area of the root.

Herbicides can be divided into four categories based on the site of absorption. The first group includes herbicides that are absorbed by roots only and have activity at root meristems. These herbicides do not translocate to the shoot because they are very lipophilic and tend to partition into cell membranes and other lipophilic areas. An example of this type of herbicide is Pendimethalin (Prowl®), which controls certain small-seeded grasses and broadleaf weeds by being rapidly absorbed by primary roots and stopping their development.

The second group of herbicides is absorbed by both roots and shoots, with some movement in the developing seedling. These herbicides do not stop germination but kill seedlings before emergence. An example of this group is Metolachlor (Dual Magnum or Dual II Magnum). The third group of herbicides is absorbed primarily by the shoot in the vapour phase and has some movement into developing seedlings. EPTC (Eptam) is an example of this group, which has very low water solubility and high vapour pressure, allowing it to move from the soil solution to become a gas or vapour. The final group of herbicides is absorbed by roots but does not have herbicidal activity in the root system. These herbicides require translocation to the developing above-ground shoot to be effective. Sulfentrazone (Spartan/Authority) and atrazine are examples of this group, and their mode of action involves light energy.

It is important to note that the impact of pesticide-contaminated soil can be mitigated through various methods. These include removing the contamination by excavating the soil and pumping up groundwater, containing the contamination by covering the polluted soil, or preventing human contact with the contamination by covering the polluted soil with clean soil and fencing off polluted areas.

Pesticides applied to sandy or course-grained soils are more likely to leach through the soil and contaminate groundwater

Soil can be polluted by pesticides in several ways. Hazardous pesticide contamination often results from the improper storage of agrochemicals, which can cause pesticides to be spilled and seep into the soil or be dispersed by the wind. Pesticides can also enter the soil through discarded pesticide containers, which can be as dangerous as the pesticides themselves.

Pesticides applied to sandy or coarse-grained soils are more likely to leach through the soil and contaminate groundwater. This is due to several factors. Firstly, sandy soils have larger particles and voids, which allow water and dissolved pesticides to move through them more freely. The increased space between particles means sandy soils have fewer binding sites available for the adsorption of dissolved chemicals compared to clay or silt soils. As a result, pesticides are less likely to stick to sandy soil particles and are more likely to be washed through the soil.

Additionally, sandy soils tend to have lower levels of organic matter. Organic matter consists of decaying plant material, and soils with higher organic matter content have a greater ability to hold both water and adsorbed pesticides. Therefore, pesticides applied to sandy soils with low organic matter are at an increased risk of leaching through the soil and contaminating groundwater.

The depth of the groundwater also plays a role in the likelihood of pesticide leaching. Shallow groundwater increases the risk of contamination because there is less soil available to act as a filter, reducing the opportunities for pesticide degradation or adsorption. When groundwater is deeper, there is more soil available to filter pesticides, decreasing the chances of leaching.

Overall, pesticides applied to sandy or coarse-grained soils with low organic matter and shallow groundwater are more likely to leach through the soil and contaminate water sources.

Pesticides can cause soil degradation and damage the community of organisms living in the soil

Soil Degradation

Soil degradation is caused by the uncontrolled application of pesticides. Pesticides can contaminate the soil and kill non-target organisms. The excessive application of pesticides shows the land degradation potential.

Pesticides can also damage soil biomass and microorganisms such as bacteria, fungi, and earthworms.

Damage to Organisms Living in the Soil

Pesticides can have a negative impact on a wide range of soil organisms, including:

• Insects
• Bees
• Worms
• Beetles
• Bacteria
• Fungi
• Nematodes
• Mites
• Millipedes
• Woodlice
• Springtails
• Coneheads
• Termites
• Ants
• Ground-nesting bees
• Parasitic wasps
• Water bears
• Centipedes
• Spiders
• Flies
• Mosquitoes
• Ticks
• Birds
• Fish
• Mammals
• Humans

Pesticides can negatively affect these organisms in a variety of ways, including:

• Mortality
• Reduced abundance
• Reduced biomass
• Altered behaviour
• Reduced reproduction
• Biochemical biomarkers
• Reduced growth
• Reduced richness and diversity
• Structural changes

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