Pesticide in the environment

WHAT IS PESTICIDE?

            Pesticides are substances that protect plants against molds, fungi and insects; therefore decreasing the percent of potential illness. This helps control shortages, higher prices, and income loss and prevents unappealing blemishes. Most pesticides are produced by plants naturally towards repelling-off their predators. Allowed pesticides are very low on the list of risks hazardous to health. Large-scale studies suggest that pesticide residues are unlikely to be an important risk factor for cancer to the general public. Major risk factors include smoking, alcohol consumption, several occupational chemicals and dietary imbalances. Another definition of pesticide is any substance or mixture of substances intended for preventing, destroying, repelling or mitigating any pest.

WHAT ARE THE TYPES OF PESTICIDE?

            Pesticides are often referred to according to the type of pest they control. Another way to think about pesticides is to consider those that are chemical pesticides or are derived from a common source of production method. Other categories include biopesticides, antimicrobials and pest control devices.

1) Chemical pesticides

·         Organophosphate pesticides - Most organophosphates are insecticides. These pesticides such as parathion, malathion, dichlorvos and dimethyldichlorovinylphosphate (DDVP) affect the nervous system by disrupting the enzyme that regulates acetylcholine, a neurotransmitter. They are extremely toxic to mammals, birds and fish (generally 10 to 100 times more poisonous than most chlorinated hydrocarbons). They were developed during the early 19^th century, but their effects on insects, which are similar to their effects on humans, were discovered in 1932. Some are very poisonous (they were used in World War II as nerve agents). However, they usually are not persistent in the environment.

·         Chlorinated hydrocarbons such as dichlorodiphenyltrichloroethane  (DDT), aldrin, dieldrin and lindane are synthetic organic insecticides that inhibit nerve membrane ion transport and block nerve signal transmission. They are fast acting and highly toxic.

·         Carbamates or urethanes such as aldicarb, aminocarb, carbofuran and Mirex share many organophosphate properties, including mode of action, toxicity and lack of environmental persistence and low bioaccumulation. Carbamates generally are extremely toxic to bees and must be used carefully to prevent damage to these beneficial organisms.

·         Inorganic pesticides include compounds of arsenic, copper, lead and mercury. These broad-spectrum poisons are generally highly toxic and essentially indestructible. Seeds are sometimes coated with mercury or arsenic powder to deter insects. They are generally neurotoxins and even a single dose can cause permanent damage.

2)    Biopesticides

Biopesticides are certain types of pesticides derived from such natural materials as animals, plants, bacteria and certain materials. For example, baking soda has pesticidal applications and is considered biopesticides. Biopesticides fall into three major classes:

·    Microbial pesticides consist of microorganisms (e.g. a bacterium, fungus, virus or protozoa) as the active ingredient. Microbial pesticides can control many different kinds of pests, although each separate active ingredient is relatively specific for its target pest. For example, there are fungi that control certain weeds and other fungi that kill specific insects.

·         Plant-Incorparated-Protectants (PIPs) are pesticidal substances that plants produce from genetic material that has been added to the plant. For example, scientists can take the gene for the Bacillus thuringiensis or Bt pesticidal protein and introduce the gene into the plant’s own genetic material. Then the plant, instead of the Bt bacterium, manufactures the substances that destroy the pest.

·   Biochemical pesticides are naturally occurring substances that control pests by non-toxic mechanisms. Conventional pesticides, by contrast are generally synthetic materials that directly kill or inactivate the pest. Biochemical pesticides include substances, such as insect sex pheromones that interfere with mating as well as various scented plant extracts that attract insect pests to traps.

FACTORS INFLUENCING PESTICIDE MOVEMENT TO ENVIRONMENT

1)     Properties of the pesticide 

2)     Properties of the soil 

3)     Site conditions including rainfall and depth to groundwater 

4)     Management practices, including method rate of the application.

WHAT ARE THE PROPERTIES OF THE PESTICIDE?

1)     Persistence

Persistence describes the staying power of a chemical. A pesticide that is persistent will maintain in its structure, or stay a long time. Pesticides are broken down (degraded) at different rates by soil microorganisms, chemical reactions and sunlight. If the soil is moist and warm, microbes use the pesticide molecules as a food source and turn them into harmless molecules such as carbon dioxide and water. Breakdown processes occur mainly in the root zone. Breakdown is considerably slower in deeper soils and sediments. Some pesticides form intermediate substances during the breakdown process, which can be more toxic than the original compound. Persistence is usually measured in terms of half-life.

             What is half-life?

Half-life means how long it takes 50% of the original amount applied to become biologically inactive or broken down. The longer the half-life, the more persistent the chemical. Residues of persistent pesticides may be long lasting in the root zone or they may leach (move downward). Pesticides will continue to degrade upon reaching groundwater. However, breakdown is generally much slower.

           

2)    Adsorption

Persistence and adsorption are the two most important characteristics of a pesticide, affecting its potential to leach to groundwater. Adsorption describes how tightly a compound becomes attached to soil particles. Pesticides that are strongly adsorbed (tightly held) will be less mobile in soil that is leached with water and will be less likely to reach groundwater.

Some pesticides may be too tightly adsorbed to give proper pest control. Injury to sensitive rotational crops may sometimes occur when a pesticide used on the previous crop is later released (desorbed) from the soil particles in amounts great enough to cause injury.

3)    Solubility

Solubility is the tendency of a chemical to dissolve in a solvent. It is another property that affects the behavior of a pesticide in the soil. As water percolates through soil, it carries water-soluble chemicals with it. This process is called leaching. The higher the water solubility value, the more soluble the chemical. For instance, a pesticide with a water-solubility value of 33,000 ppm at 80⁰ Fahrenheit (27⁰ C) is much more water-soluble than a pesticide with a water-solubility value of 33 ppm at 80⁰ Fahrenheit (27⁰ C). It is also more likely to leach.

4)    Volatility

Volatility is the tendency for a liquid or a solid to change into gas. Volatility describes how quickly a liquid will evaporate when it is in contact with air. Highly volatile chemicals are easily lost to the atmosphere. Some pesticides, such as fumigants, must be volatile in order to move and provide uniform distribution through the soil profile.

WHAT ARE THE PROPERTIES OF THE SOIL?

1)    Permeability

Permeability is a measure of how fast water can move vertically through the soil. It is affected by the texture and structure of the soil. Soils with coarse sandy textures are generally more permeable. Soils with higher permeability have greater potential for groundwater contamination than less permeable soils.

2)    Texture

Soil texture is an indication of the relative proportions of sand, silt and clay in the soil. Coarse, sandy soils generally allow water to carry the pesticides rapidly downward. Finer textured soils generally allow water to move at much slower rates. They contain more clay and sometimes organic matter, to which pesticides may cling.

3)    Organic matter

Soil organic matter influences how much water the soil can hold before it begins to move downward. Soil containing organic matter has greater ability to stop the movement of pesticides. Soils in which plants are growing are more likely to prevent pesticide movement than bare soils.

4)    Structure

Soil structure describes how the soil is aggregated. Uncompacted soils allow more water flow. Soils with a loose structure or soils with hollow channels such as dried root channels or animal or worm tunnels, will also allow for increased flow of water through the soil profile. Soils that permit rapid flow of water through the soil profile present a higher potential for groundwater contamination than less permeable soils. Sandy soils with their coarse textures and low water-holding capacity will allow for greater infiltration than finer, heavier clay soils.

5)     Moisture

Soil moisture affects how fast water will travel through the soil. If soils are already wet or saturated before rainfall or irrigation, excess moisture will runoff. Soil moisture also influences pesticide breakdown.

WHAT ARE THE SITE CONDITIONS?

1)    Rainfall

Intense or sustained periods of high rainfall may cause large amounts of water to move through the soil, especially where little runoff occurs.

2)    Depth to groundwater

Depth to groundwater is primary factor affecting the potential for pesticides to reach groundwater. If the top of the water table is shallow, pesticides have less distance to travel to reach groundwater.

3)    Sinkholes and bedrock

The presence of sinkholes, cracked bedrock or confining layers in the bedrock significantly affects vertical movement of water. Sinkholes, cracked bedrock and gravel soils allow dissolved pesticides to freely move to groundwater as long as there are no confining geologic layers. Sinkholes present a high risk for groundwater contamination by pesticides if runoff from fields where they are applied reaches them. Once water enters a sinkhole, it receives little filtration or chance for degradation.

WHAT ABOUT MANAGEMENT PRACTICES?

1)     Select pesticides that are less likely to leach.

2)     Do not exceed recommended application rates.

3)     Calibrate application equipment to applied desired rate.

4)     Mix and load pesticides carefully; prevent spills.

5)     Do not apply a pesticide immediately prior to irrigation or a heavy rain.

6)     Do not over irrigate.

7)    Follow label directions for pesticide storage and disposal.

FACTORS AFFECTING PESTICIDE FATE AFTER APPLICATION

It is important to understand what happens to pesticides after they are applied in the field. Not all of the applied chemical reaches the target site; some may drift downwind and outside the intended application site, possibly to non-target sites, including surface water. Three major processes determine its fate: adsorption, transfer and degradation:

1)    Adsorption

Adsorption is a chemical process that results in a pesticide being bound or adsorbed to a soil particle. For example, portions of a pesticide molecule may bind electrically to clay minerals or organic matter.

 2)     Transfer

Transfer refers to processes that move the pesticide away from the application site and includes volatilization, runoff, leaching, absorption and crop removal. Sometimes pesticide transfer is essential for pest control. For example, certain preemergence herbicides must move within the soil to reach germinating weed seeds. Volatilization occurs when a liquid or solid converts to a gas and moves away from the initial application site. Runoff occurs when water is added to a field faster than it can be absorbed into the soil. Pesticides may move with runoff as compounds dissolved in the water or attached to soil particles. Leaching is the downward movement of chemical through the soil, eventually reaching the groundwater. Absorption is the uptake of pesticides or other chemicals into the plant or animal. After absorption, the pesticide residue may be broken down or remain in the plant or animal until harvest. Crop removal through harvest or grazing may move pesticide residue.

 3)     Degradation

Degradation is the process of pesticide breakdown after application by either microbial action, chemical action of photodegradation. This process may take hours, days, weeks or years, depending on environmental conditions and the chemical characteristics of the pesticide.

PESTICIDE MOVEMENT IN AIR, WATER, SOIL AND LIVING ORGANISMS

1)    Air

Pesticide movement away from the release site in the air is usually called drift. Pesticide particles, dusts, spray droplets and vapors all may be carried offsite in the air. People who mix, load, and apply pesticides outdoors usually are aware of the ease with which pesticides drift offsite.

Moving air easily carries lightweight particles, such as dusts and wetable powders. Granules and pellets are much heavier and tend to settle out of air quickly. Small spray droplets also are easily carried in air currents. High-pressure and fine nozzles produce very small spray droplets that are very likely to drift. Lower pressure and coarse nozzles produce larger droplets with less drift potential.

Pesticide vapors move about easily in air. Fumigant pesticides are intended to form a vapor when they are released. Persons using fumigants must take precautions to make sure the fumigant remains in a sealed container until it is released into the application site, which also must be sealed to prevent the vapor from escaping.

2)     Water

Pesticide particles and liquids may be carried offsite in water. Pesticides can enter water through:

·         Drift, leaching and runoff from nearby applications

·         Spills, leaks and back-siphoning from nearby mixing, loading, storage and equipment cleanup sites

·         Improper disposal of pesticides, rinsates and containers.

Most pesticide movement in water is across the treated surface (runoff) or downward from the surface (leaching). Runoff and leaching may occur when:

·         Too much liquid pesticide is applied, leaked or spilled onto a surface

·         Too much rainwater, irrigation water or other water gets onto a surface containing pesticide residue.

Runoff water in the outdoor environment may travel into drainage ditches, streams, ponds or other surface water where the pesticides can be carried great distances offsite. Pesticides that leach downward through the soil on the outdoor environment sometimes reach the groundwater.

            Runoff water in the indoor environment may get into domestic water system and from there into surface water and groundwater. Runoff can flow into floor, drains or other drains and into the water system. Sometimes a careless pesticide handler washes pesticide down a sink drain and into the water system.

            Some pesticides can leach downwards in indoor environments. In a greenhouse, for example, pesticides may leach through the soil or other planting medium to floors or benches below. Some pesticides used indoors may be absorbed into carpets, wood and other porous surfaces and remain trapped for a long time.

3)    Soil

It might seem that a short half-life would mean a pesticide would not have a chance to move far in the environment. This is generally true. However, if it is also very soluble in water and the conditions are right, it can move rapidly through certain soils. As it moves away from the surface, it moves away from the agents that are degrading it, such as sunlight and bacteria. As it gets deeper into the soil, it degrades more slowly and thus has a chance to get into groundwater.

Figure 1: The fate of pesticides.

The pesticide movement in soil will be discussed more detail in the case study later.

4)    Living organisms

Living organisms may also play a significant role in pesticide distribution. This is particularly important for pesticides that can accumulate in living creatures. An example of accumulation is the uptake of a very water-insoluble pesticide by a creature living in water. Since this pesticide is stored in the organism, the pesticide accumulates and levels increase over time. If this organism is eaten by a higher organism, which also stores this pesticide, levels can reach much higher values in the higher organism that is present in the water in which it lives. Levels in fish, for example, can be tens to hundreds of thousands of times greater than ambient water levels of the same pesticide. This type of accumulation has a specific name. It is called “bio-accumulation”.

In this regard, it should be remembered that humans are at the top of the food chain and so may be exposed to these high levels when they eat food animals that have bio-accumulated pesticides and other organic chemicals. It is not only fish but also domestic farm animals that can be accumulators of pesticides and so care must be taken in the use of pesticides in agricultural situations.

Further information of how pesticide enters fish also will be discussed in the case study later.

CASE STUDY

1)    Uptake of herbicides by leaves or by roots

The upper part of the plant is hydrophobic by virtue of the waxy cuticle of the leaves whereas the lower part is essentially hydrophilic since the major function of roots is to take in water and various water-soluble substances. When a toxic substance with a measure of oil solubility is applied to leaves, it will tend to penetrate through the waxy cuticle. If a leaf-applied herbicide is sufficiently soluble in both oil and water, it may enter the waxy cuticle, penetrate it and then leave on its inside.

Photosynthetic products (assimilates) move through the inter-communicating plasmadesmata of mesophyll cells and thence to the companion cells of the sieve tubes. It is assumed that leaf-applied herbicides move with photosynthetic products. Movement of solutes in the phloem reflects the general metabolic activity of the plant and the majority of systemic foliage-applied herbicides are translocated most readily when the weeds are growing rapidly. Similarly, herbicides usually move out of the leaves rather slowly if poor light intensity restricts photosynthesis. However, some herbicides damage leaf tissue in such a way to reverse the natural flow of water in the xylem. When this happens, xylem transportation of herbicides from foliage can occur.

 The situation as it relates to root uptake is somewhat different. Roots exist to absorb water and some solutes, but the relative amounts of solutes within plants are quite different from their relative amounts in soil water. This difference implies a selective uptake of natural soil constituents and it would not be surprising if herbicidal molecule were also adsorbed in a discriminating manner.

Figure2: Water transportation in plant.

Water is absorbed from soil by roots and other epidermis cells in or near the roots area. Then, it moves via the cortex tissue, across an endodermic layer and perisicle. Then it gets into xylem. Xylem in root is connected to xylem in trunk and allows water to move out from root to the trunk. In the trunk xylem, water moves into leaves by transpiration. Then, it gets into mesophyl cell and evaporates. The vapor is out to atmosphere via stoma.

The root does not have waxy cuticle and water is absorbed directly from soil. Water is absorbed into the root by epidermis cells via osmosis process. Some may move in passively, others may masquerade as natural substances; some may be actively pumped out as they enter, while others may destroy cells and so nullify the plant’s normal protective system. The roots absorb water, which contains nitrate, sulphate and also herbicides. 

The rate of upward movement of herbicide will be influenced by factors such as elevated temperature or reduced humidity, which affect transpiration. Movement in the xylem normally carries most of the herbicides to the leaves, a process that enables those that are photosynthetic inhibitors to reach their site of action. However, a proportion of the total dose absorbed usually escapes from the xylem to the phloem on the way up. 

2)    Pesticides in soil and water

When a pesticide is applied to a field, certain reactions follow. Foliar-applied pesticides stick to leaves, where they are absorbed. But rainfall inevitably washes some of the chemical off the leaf surface onto the soil below and some may be transformed by sunlight. The pathway and reactions of pesticides in soils are shown in Figure 3. There are three mechanisms of pesticide adsorption soils, shown in Figure 4.

  

Figure 3: The pathway and reactions of pesticides in soils.

Sorption is a transfer process by which pesticides are dispersed in soil. The transfer called ‘partitioning’ of a pesticide into organic matter in soil is a somewhat nonspecific mechanism. Much organic matter (humus) generally consists of two systems: a hydrophilic surface and a hydrophobic interior. Nonionic pesticides escape from soil solution into the hydrophobic interior. Pesticides move between organic matter and water in soil. Also, pesticides may undergo an aging process, whereby the chemical moves deeper into organic matter and becomes unavailable to move back into soil solution. Pesticides that are water-soluble tend to remain at the surface of soil organic matter, while those that are insoluble will penetrate to the hydrophobic interior. Sorption to soil particles is also dependent on soil water content because water is necessary for chemical movement and water molecule will compete with pesticide molecules for attachment sites on clay and organic matter. Therefore, pesticide sorption tends to be greater in dry soils than in wet soils. Besides entering the plants and soil, pesticides also can enter water through drift, leaching, runoff and other sources. Now we mention about how pesticides enter water from soil.

 Leaching

Leaching is the term for the transport process of downward movement (infiltration) of pesticides in water. Two kinds of phenomena are associated with leaching: preferential flow and matrix flow. Preferential flow allows pesticide molecules to move rapidly through a section of the soil profile, with reduced likelihood that the molecules will be retained by soil particles or degraded by microbes. Preferential flow is characterized by water that flows rapidly through wormholes, root channels, cracks and large structural voids in soil. Matrix flow results in a slow migration of water and chemical through the soil structure; the pesticide moves slowly with water into small pores in soil and has more time to contact soil particles. 

 Runoff and erosion

Runoff is a movement of water across the soil surface at a rate faster than it can infiltrate the soil. As rain falls, small soil particles become dislodged and are carried laterally by water in a process known as erosion. Because some pesticides are applied directly to the soil, large amounts eventually end up there and as water runs off and soils erode, dissolved and sorbed pesticides go along. Runoff and erosion have the potential to move more pesticide off site than leaching, due to the fact that runoff is a surface phenomenon.

3)    Pesticides enter living organisms

·                                 Bioaccumulation and biomagnification

Living organisms may also play a significant role in pesticide distribution. This is particularly important for pesticides that can accumulate in living creatures. Cells have mechanisms for bioaccumulation, the selective absorption and storage of a great variety of molecules. This allows them to accumulate nutrients and essential minerals, but at the same time, they also may absorb and store harmful substances like pesticides through these some mechanisms. Pesticides that are rather dilute in the environment can reach dangerous levels inside cells and tissues through this process of bioaccumulation.

      The effects of pesticides also are magnified in the environment through food webs. Biomagnification occurs when the pesticide burden of a large number of organisms at a lower trophic level is accumulated and concentrated by a predator in a higher trophic level. Phytoplankton and bacteria in aquatic ecosystems, for instance, take up heavy metals or the pesticide molecules from water or sediments. Their predators- zooplankton and small fish, collect and retain the pesticides from many prey organisms, building up higher concentrations of pesticides. The top carnivores in the food chain- game fish, fish-eating birds and humans can accumulate such high toxin levels that they suffer adverse health effects. One of the first known examples of bioaccumulation and biomagnification was DDT, which accumulated through food chains so that by 1960’s it was shown to be interfering with reproduction of peregrine falcons, brown pelicans and other predatory birds at the top of their food chains.

Figure 5: Bioaccumulation and biomagnification. Organisms lower on the                food chain take up and store toxins from the environment. They are eaten by larger predators, who are eaten, in turn, by even larger predators. The highest members of the food chain can accumulate very high levels of the toxin.

4)            Pesticides enter air - volatilization

Volatilization is the process whereby a solid or liquid evaporates into the atmosphere as a gas. The process provides a significant pathway of transfer for some pesticides. In principle, volatilization is an escape mechanism. Compounds with high vapor pressure and low water solubility have a tendency to volatilize. The tendency of a pesticide to volatilize from water is approximated by the ratio of its vapor pressure to its aqueous solubility. The same is partially true for soils, but the tendency for a pesticide to volatilize from soil also can be inversely proportional to its potential to bind to soil.

Specific environmental factors that tend to increase volatilization include high temperature, low relative humidity and air movement. A pesticide that is tightly sorbed to soil will have a lower solution concentration and be less likely to volatilize. That is, less volatilization occurs from drier soils because the lack of water allows the pesticide to sorb onto soil particles. Volatile pesticides usually are incorporated (plowed into the soil) after application to reduce loss into the atmosphere. However, it has also been shown that pesticide volatilization from soil is complex and highly dependent on the movement of water to and from the soil surface.

Once a pesticide enters the atmosphere as a gas, it can become diluted in water droplets and as a result, highly susceptible to long range transport from the application site. Within the atmosphere, the pesticide may undergo reactions with light (photolysis) and water (hydrolysis) and sorb to suspended materials such as dust particles. Pesticides in a gaseous state may dissolve in atmospheric water.

BIOTECHNOLOGY IN BIOREMEDIATION OF PESTICIDE-CONTAMINATED SITES

Biotechnology has been highly touted as a potential source of safe, inexpensive and effective methods for the remediation of sites heavily contaminated with agrochemicals and for the direct treatment of agrochemical wastes. One area in which much was envisioned of biotechnology but little has yet been realized is the remediation of chemically contaminated sites. An agricultural researcher described which has shown that microorganisms are capable of degrading agricultural chemicals and the use of microbes or microbial systems in waste disposal or remediation of contaminated sites.

Microbial Degradation of Pesticides

Microbial degradation is a transformation process that results when soil microorganisms (bacteria and fungi) either partially or completely metabolize (break down) a pesticide. Microorganisms can cause changes in a pesticide when this activity occurs; in the presence of oxygen it is termed aerobic metabolism and in the absence of oxygen, anaerobic metabolism.

Most microorganisms inhabiting the soil profile where oxygen is plentiful degrade pesticides via aerobic metabolism. As a pesticide undergoes aerobic metabolism, it is normally transformed into carbon dioxide and water. Under anaerobic metabolic conditions, microorganism degradation may produce additional end products such as methane. Those microorganisms using anaerobic metabolism for breaking down pesticides are typical of the microbes inhabiting waterlogged soils in terrestrial systems or living in the bottom sediments of ponds, lakes and rivers. These organisms are also present in groundwater and to some extent, in the soil profile and enter surface water as runoff. Pesticides along with many other naturally occurring organic molecules may serve as a source of food or energy for soil microbes. A pesticide in soil solution has to move to these microbial colonies and cross the microbial cell membrane into the cell to metabolize. Some microbes produce enzymes, which are exported from the cell to predigest pesticides that are poorly transported. Once inside an organism, a pesticide can metabolize via internal enzyme systems. Any energy derived from the breakdown of the chemical can be used for growth and reproduction; any portion not fully degraded to carbon dioxide or incorporated into cells is released back into soil solution as intermediate chemical metabolites.

Degradation of Pesticides by Lignin-peroxidase-producing Phanerochaete sp..

            The white-rot fungus, Phanerochaete chrysosporium was one of the first organisms shown to degrade lignin through the action of a potent lignin peroxidase enzyme. This enzyme converts hydrogen peroxide into hydroxy radical, which can attack lignin, breaking it into smaller components resulting in eventual decomposition of the ligneous material. It has been shown that lignin-peroxidase producing cultures of Phanerochaete chrysosporium can degrade a number of pesticide or pesticide-like compounds, including DDT and methoxychlor, lindane, chlordane and dieldrin and pentachlorophenol. In addition to Phanerochaete there are other white-rot fungi and lignin-degrading actinomyces, which may produce lignin peroxidases that attack pesticides. Through the systematic isolation of such organisms and the characterization of the pesticide degrading ability of the lignin peroxidases they produce, it may be possible to assemble an arsenal of enzymatic weapons for use in remediation of pesticide contaminated soils.

Degradation of Pesticides by Specific Enzymes and Pathways

           

A large number of microorganisms, which produce specific pesticide degrading enzymes or that carry entire pathways for the mineralization of pesticides have been characterized. Parathion hydrolase can degrade coumaphos, methyl parathion and a number of other related compounds while N-mrthylcarbamate hydrolases can degrade aldicarb, carbofuran and carbaryl and a number of other related compounds. These enzymes are stable and the genes have been cloned so that their production for use in detoxification of pesticides is feasible.

TREATMENT OF PESTICIDE WASTE

Cleaning pesticide applications equipment produces rinse water that contains pesticide residues proper management of this pesticide rinse water is necessary to avoid the contaminations of soil, ground water and surface water that can occur when this material is improperly discharged. Concentrations of pesticide in the rinse water range from 1 to 1000 mg/l. Contaminations of soil and water has been documented at a number of sites in the United State where pesticide have been improperly managed. Management options for this rinse water include:

Re-applications of the material as a

·         Dilute pesticide

·         Re-use as a diluents for subsequent batches of pesticide

·         Disposal as a waste

·         Treatment

The first two options are the most widely used by pesticide applicators who are properly managing rinse water. The last two are much less widely used because of the expense of these methods and the difficulties encountered in complying with the regulatory requirements that apply to these management methods.

What is treatment?

The applications of a process that alters the chemical characterizes of the wastewater to the extent that the rinse water can be managed as a non-pesticide or non-hazardous material. The process used may be physical, chemical, biological or combinations of these.

Treatment system that can be used successfully to manage pesticide rinse water must have the following characteristic:

·         Technology appropriate for the pesticide applicator

·         Economic practicality

·         Acceptable treatment capability

·         In compliance with applicable regulatory requirements.

Researchers developing treatment systems must take these four characteristics into account if they hope to see their systems successfully used. Of these four, the regulatory requirements can be the most difficult to accommodate.

Existing treatment systems

The pesticide rinse water treatment systems in used legally in the United State can be divided into two general classes:

• Carbon filtration treatment systems
• Evaporation/degradation treatment systems.

Carbon filtration treatment systems

In United State, the treatment systems employ granulated activated carbon (GAC) to remove the pesticide residue from the rinse water. GAC filtrations systems function by the exposing of the pesticide contaminated rinse water to carbon particles. The organic pesticide are adsorbed onto the carbon and thus removed from the rinse water. Figure 6 is a simplified schematic of this process.

Figure 6: Schematic drawing of simplified carbon filtration system for treatment of pesticide rinse water.

            There are two treatment products to be managed in these systems- the treated rinse water, which may still contain low concentrations of pesticide and the exposed carbon, which now contains pesticide residues. There are a number of firms that produce GAC filtration systems for industrial use. Two that have targeted the treatment of pesticide rinse water are the Wilbur-Ellis Company and Imperial Chemical Industries, Ltd. (ICI). Figure 7 is a schematic of the Wilbur-Ellis system that illustrates these features - a solid particle filter, a settling tank, an oil filter and an ozonation chamber.

 

 Figure 7: Schematic drawing or Wilbur-Ellis Company carbon filtration system for 

                 treatment of pesticide rinse water.

 An ultra-violet light has also been added to the system downstream of the carbon filters to further degrade any bacteria or organics. The solid particle filter and settling tank remove soil particles that can clog pores in the filters downstream. The oil filter removes oil and greases that interfere with the ozonation process and carbon adsorption. The ozonation unit exposes the rinse water to ozone and oxidizes organics in the rinse water as well as any bacteria, algae or other organisms that may act to foul the carbon filters. Oxidation of the organic pesticides in the rinse water may also enhance their adsorption to the carbon. The carbon filters remove any residual ozone from the rinse water.

            Currently, all spent filters and sludges generated through the use of the system are to be disposed of as hazardous wastes. The first carbon filter in the filter series is changed out after treating 50000 gallons of rinse water. The second filter is then rotated into the first position, the third into the second position and a new filter placed into the third position. The water treated is stored for reuse in subsequent cleaning operations and then recycled through the system.

            The ICI system is simpler and is designed to be portable. Pesticide rinse water is treated in discrete batches of about 265 gals (1000 liters). Rinse water is treated first with a flocculation agent and then put through a sand filter and two carbon filters. The carbon filters are supposed to be replaced after 20 batches or 5300 gallons. The flocculation chemicals added during the treatment process contain a dye that serves to indicate when the filters are no longer functioning properly. Sludge settling from the flocculation step and spent filters are to be disposed as solid waste and would have to be disposed of as hazardous waste.

            The GAC filtration system described here has the characteristics necessary for successful treatment systems. The technology used is compatible with the abilities of pesticide users. The systems treat the rinse water to produce a product (the effluent) that is less toxic and more rapidly degradable than the original rinse water.  The effluent has lower concentrations of toxic materials and degradation products. With sufficient treatment, it should be possible to meet water quality standards and obtain a discharge permit for the treated water. In most cases in the United States, however, the treated water is reused as cleaning water for subsequent cleaning operations. The spent carbon and filters are managed as hazardous waste and there is thus no contaminated material released to the environment through this treatment process.

Evaporation/ Degradation Systems

           

The other system type used to legally treat pesticide rinse water in the United States is the evaporation/degradation system. The original systems consisted of a lined pit filled with a soil matrix into which rinse water was placed. The liquid portion of the rinse water evaporated and the pesticide residues were adsorbed onto the soil matrix and eventually degraded by microorganisms in the soil. There was no discharge from the system.

            The systems in use now have been modified to eliminate concerns about possible groundwater contamination. These systems now typically use aboveground tanks to contain the matrix. A secondary containment system is also provided. The replacement of the pit with a tank allows the systems to be operated without the need for groundwater monitoring. Leaks can be detected by inspection and corrected. The secondary containment systems provide extra assurance against groundwater contamination should a leak occur. Figure 8 is a drawing of a system design used in Florida.

  

Figure 8: Drawing of evaporation/degradation system design used in Florida for treatment of pesticide rinse water.

            Evaporation/degradation systems are very simple to operate. Rinse water is collected on a wash down slab for transfer to the tank or emptied directly into the tank. Solar radiation evaporates the water and pesticide residues are adsorbed to the soil matrix. Pesticides are degraded in the tank by bacteria or other mechanisms (such as hydrolysis or photolysis). There is no discharge of liquid from the system. The matrix in the tank is left undisturbed for the life of the system. When the system is dismantled, the matrix can be tested for residues and disposed of as hazardous waste if necessary.

            These systems treat rinse water through the degradation of the pesticide component by microorganisms in the soil matrix. Pesticides are adsorbed by the soil matrix and may be only slowly degraded in these systems.

SUMMARY

            Pesticides are substances that protect plants against molds, fungi, insects or any substance or mixture of substances intended for preventing, destroying, repelling or mitigating any pest. The categories of pesticide are chemical pesticides and biopesticides. The examples of chemical pesticides are organophosphate pesticides, chlorinated hydrocarbons, carbamates and inorganic pesticides. The examples of biopesticides are microbial pesticides, Plant-Incorporated-Protectants (PIPs) and biochemical pesticides. The movement of pesticide to environment is influenced by properties of the pesticides, properties of the soil, site conditions including rainfall and depth to groundwater and management practices, including method rate of the application. The properties of the pesticide include persistence, adsorption, solubility and volatility. The properties of the soil include permeability, texture, organic matter, structure and moisture. The site conditions refer to rainfall, depth to groundwater and sinkholes and bedrock. The best management of pesticides are select pesticides that are less likely to leach, do not exceed recommended application rates, calibrate application equipment to applied desired rate, mix and load pesticide carefully; prevent spills, do not apply a pesticide immediately prior to irrigation or a heavy rain, do not over irrigate or follow label directions for pesticide storage and disposal. It is important to understand what happens to pesticides after they are applied in the field. Three major processes determine its fate such as adsorption, transfer and degradation. Pesticide movement away from the release site in the air is usually called drift. Pesticide particles, dusts, spray droplets and vapors all may be carried offsite in the air. Pesticides also can enter water through drift, leaching and runoff from nearby applications, spill, leaks and back siphoning from nearby mixing, loading, storage and equipment cleanup sites, improper disposal of pesticide rinsates and containers. Runoff and leaching may occur when too much liquid pesticide is applied, leaked or spilled onto a surface and too much rainwater irrigation water or other water gets onto a surface containing pesticide residue. It also can move rapidly through certain soils. Living organisms may also play a significant role in pesticide distribution. Pesticides can accumulate in living creatures. The type of accumulation is called bioaccumulation. Microorganisms are capable of degrading agricultural chemicals. Microbial degradation is a transformation process that results when soil microorganisms either partially or completely breakdown a pesticide. Cleaning pesticide application equipment produces rinse water that contains pesticide residues proper management of these pesticides rinse water is necessary to avoid contamination of soils, groundwater and surface water. Treatment system that can be used successfully to manage pesticide rinse water must have the following characteristics; technology appropriate for the pesticide applicator, economic practicality, acceptable treatment capability and in compliance with applicable regulatory requirements. The pesticide rinse water treatment systems in used legally in the United States can divided into two general classes; carbon filtration treatment systems and evaporation/degradation treatment systems. 

REFERENCES:

1. http://pested .unl.edu
2. http://vm.cfsan.fda.gov
3. http://www.organicconsumers.org/Toxic/braindamage.cfm
4. http://www.ianr.unl.edu/PUBS/water/gll82.htm
5. http://www.agnic.org.
6. http://edis.ifas.ufl.edu
7. http://www.deq.state.or.us/wmc/hw/pesticidedispose.html.
8. Pesticide Waste Management. John B. Bourke, Allan S.Felsot, Thomas J.Gilding, Janice King Jensen and James N.Seiber. American Chemical Society, Washington, 1992.
9. The Chemistry of Pesticides. Kenneth A.Hassall, Verlag Chemie, Florida.
10. Pesticide Transformation Products. L.Somasundaram and Joel. R.Coats. American Chemical Society, Washington.