Organic Farming: Contamination Control

Introduction

Contaminants are prohibited substances or organisms. The contamination control refers to efforts to prevent or minimize the possibility of unintended contact with those substances or organisms which are contaminants. The contaminants depend on agricultural activities and are generated from either well-defined sources or from sources that are not so well defined. The sources could be either point or non-point sources. A point source of pollution is effluent discharged from one location such as a pipe, tank, pit, or ditch. Non-point source of pollution originates from not a well-defined source, such as runoff from a field or from streets in a city, making identification and assessment of sources difficult. Contaminants related to cropping practices include nutrients [nitrogen and phosphorus], herbicides, insecticides, sediments, salts, and trace elements. The contaminants are carried over to the surface and groundwater through all phases of the hydrologic cycle.

Contamination control approaches help containing the spread of the contaminants in the environment, soil, water courses, reservoirs, and wells. The tillage, irrigation, and drainage practices, the volume, timing, and placement of fertilizer, herbicide, and insecticide, the sequence of crop rotation, soil characteristics, and weather conditions may also influence the contamination and its control. The control measures aim producing organic farm items that can meet the standards of certifying agencies besides achieving sustainability and safety of agricultural production system.

• Contamination Risks In Organic Farming:

Now, we shall see the potent contaminants, which if not prevented may risk in organic farming. In many situations, there is a risk of contamination from activities happening on the adjacent farm. Like in the case of the aerial spray of pesticide on horticultural crops through spray drift. Treatment applied by the government agencies for the treatment of malaria, control of obnoxious weeds and pests also causes contamination. We may visualize the risk through the import of compost, implement, and other inputs or materials from non-organic fields. Genetically Modified Organisms [GMO] like seeds or any other input are the other source of contamination.

We should develop a comprehensive contamination risk management strategy for our organic farming system. We shall study the contamination and its impact on different systems. Also, describe the methodologies to decontaminate them.

 

Soil Contamination

The soil contamination refers to the presence of inorganic ingredients in the soil. Soil contamination arises mainly from the application of fertilizers and pesticides. In addition, direct discharge of industrial wastes to the soil and percolation of contaminated surface water to sub-surface contaminates the soil. The most common chemicals involved are petroleum hydrocarbons, solvents, pesticides, lead, and other heavy metals.

Percolation of pesticides and herbicides into the soil, when used for agriculture, is the common mode of soil contamination. It includes a variety of chemicals including DDT, lindane, organochlorines, organophosphates carbonates, and cyclodienes. Besides this direct contamination of the soil, run-off water may also carry contaminants to the organic fields. The contaminants like lead, mercury, chromium, cadmium, bacteria, hydrocarbons from solid waste disposal sites may also leach into the organic farm. Dust containing zinc, cadmium, lead and mercury emanating from coal burning power plants and smelting operations may also drift on to the soil in an organic farm.

• Nature Of Soil Contamination

Contaminants become entrained in soil by a variety of mechanisms. One has to understand these mechanisms to comprehend the fundamental nature of soil contamination.

Soil particulates are composed of organic and inorganic chemicals. They vary in their cation exchange capacity, buffering capacity, and redox potential. At one extreme, the sand component is a coarse-grained, totally inorganic substance that is inert. On the other extreme, peat soils are fine organic materials that are highly active. In general, many soil subtypes comprise soil, which have complex characteristics. The soils are diverse in soil porosity [ranging from gravels to sands to silt to clay] and pore size. This leads to variations in chemical bonding or adhesion characteristics. Hence, each contaminant has a different bonding mechanism with a given soil type.

Some contaminants may drain through soils move to other soils or deeper aquifers. Organic chemicals discharged into clay soil will have very high adsorption. In most occasions, the contaminants adhere to the surface of soil particles or stay in the interstices of a soil matrix resulting in soil contamination. There exists a dynamic equilibrium, where new contaminants may adhere to new soil particles. Further, the movement of groundwater may transport some of the soil contaminates to other locations or depths.

Spilling or burying of hazardous substances contaminates the soil. Migration of the spill that occurred elsewhere also contaminates the soil. Smelting operations, smokestacks, or other similar activities release small particles containing hazardous substances into the air that fall and adhere on the surface of soil particles. Hazardous substances that are deposited on the soil are washed away when rain comes or during irrigation and contaminate the soil at the destination or on the way.

• Impact Of Soil Contaminants On Ecosystems

Soil contaminants can have a significant impact on ecosystems. Presence of many hazardous chemicals even at low concentrations may create drastic changes in the soil chemistry. These changes may influence the metabolism of microorganisms and arthropods living in the soil. Such a contamination may eliminate some components, especially in the primary food chain. This may deprive the predator or consumer species. The impact of such contaminants may be limited to lower life forms. But it may be carried to the higher levels of the food chain by an enhanced concentration in each stage of the food web. This bio-accumulation or bio-magnification has lead to the extinction of many species. For instance, bio-magnification of the persistent DDT material in the food sources of many birds has led to the extinction of those species.

On the other hand, soil contamination in agricultural lands change plant metabolism thereby reducing crop yields. This may eliminate the crop cover of the soil making the soil more prone to soil erosion. Half life period of some of the contaminants is usually longer. In some cases, primary soil contaminants decay in due course resulting in chemical derivatives. These also significantly influence crop yields.

 

Water Contamination

Water contamination may occur in both the surface and groundwater. The contamination of surface water could be easily controlled compared to that of groundwater. It is complex because the groundwater moves over long distances through aquifers. In clay soils with non-porous aquifers, the contaminants like bacteria may be easily removed by simple filtration [adsorption and absorption] or by chemical reactions and the biological activity of water. In other cases, where filtration or other soil processes are not effective, the contaminants are simply transported. Ineffective filtration also enables the contaminants in the groundwater to move through cracks and reach the surface water.

• Nature Of Water Contamination

The process of water contamination is complex. The water contamination increases the nutrients that may lead to eutrophication. Oxygen demand increases in water when organic wastes are dumped. Such a situation depletes oxygen that ultimately affects the ecosystem. Industrial effluents carry heavy metals, organic toxins, oils, and solids that constraints oxygen availability. Run-off water with silt and other contaminants blanket the lake or river bed inhibiting the penetration of sunlight through the water column. This damages the ecological system.

• Sources Of Water Contamination

Water may be contaminated by various sources. Pesticides or fertilizers carried by the surface run-off constitute the primary source of contamination of water for organic farming. Slash and burn farming practice, usually associated with ‘jhum‘ cultivation is also a source of water contamination. Discharge of industrial effluents, untreated sewage, spilled petroleum products and seepage from underground storage tanks are the other sources of contamination affecting water. Sulfur dioxide emanating from the burning of fossil fuels leads to acid rains also contaminates water. Surface run-off water carrying silt from construction sites, farms, and other impervious surfaces may also cause water contamination.

• Organic And Inorganic Contaminants

The organic contaminants may be insecticides, herbicides, and other chemicals. Bacteria from sewage or livestock operations, pathogens from food processing wastes may also contaminate water. Debris from logging operations in forests contaminates water sources. Industrial solvents escaping from improper storage structures also contaminate water.

Inorganic contaminants of water include heavy metals, industrial discharges especially sulfur dioxide from power plants, nitrates, and phosphates in the fertilizers.

• Mode Of Water Contamination

Water contamination may occur either directly or indirectly. The direct contamination of water is mainly because of spraying operations. Spillage of pesticide concentrate when mixing and loading in the sprayers, leakage of stored concentrate or discarding unwashed ’empty’ containers in or near a water supply, back siphoning or overfilling of sprayer tanks, rinsing or washing spray equipment, and spray drift under windy conditions or application too close to open water are the common modes of direct contamination of water. In porous soil, pesticides can readily leak in and contaminate the well water. In clay soils, rain water percolates down into the well carrying the pesticides. Indirect contamination of water occurs due to the movement of pesticides from treated land. Heavy rains and run-off water facilitate the movement of pesticides. Ultimately it seeps into the groundwater through aquifers.

Soil particles and pesticides from treated fields or spills are carried by surface run off into streams, ditches, ponds, and wells. This normally occurs when heavy rain follows within a few days of a spray operation, although it can also happen any time of the year with pesticides that persist in soil. The greatest loss occurs when rains fall within 24 hours of the application of pesticide. Removal of pesticides from the soil surface decreases with time following the application and is usually negligible one week after spraying. Run-off is normally more severe on clay soils than on sandy soils.

There are pesticides that are persistent and water-soluble. These will move through the soil and reach the water table ultimately.

 

Air Contamination

Controlled burn practices used in agriculture and forestry management, dust particles emanating from industries, fly ash from thermal stations, automobile exhausts are the main sources to contaminate the air. Impact of air contamination in organic farming especially in developing countries like India is minimal.

 

Groundwater Contamination

Groundwater is most crucial source of water for drinking and agriculture [irrigation]. Its safety decides the safety of plants and animals [including humans] on the earth. Groundwater is a body of water that is contained in underground waterways known as aquifers. Because groundwater flows through compressed gravel and soil deposits, it flows very slowly.

We know, the groundwater is replenished through two sources those are percolating rain or snowmelt water and recharge zones where the aquifer contacts the surface. During its replenishment, the groundwater is vulnerable to contaminants that may be in the surface water or the soil. The aquifer may be protected from surface contamination by the presence of underground deposits of impervious materials such as clay or bedrock. For example, a sanitary landfill constructed in sand and gravel deposits is more likely to lead to groundwater contamination than a landfill constructed in clay deposits.

Microorganisms, inorganic chemicals, and organic chemicals from many sources may contaminate groundwater. Joseph Salvato, in Environmental Sanitation and Engineering, lists sources of groundwater contaminants that fall into the following four categories:

Waste Category I: These are systems designed to discharge wastewater onto the surface of the land or to the groundwater. This category includes land application of wastewater, septic systems, waste disposal wells, and brine injection wells.

Waste Category II: These are systems that may discharge wastewater to the land or groundwater but are not designed to do so. This category includes surface impoundments such as lagoons, landfills, and other excavations, animal feedlots, leaky sanitary sewer lines, and acid mine drainage.

Non-Waste Category III: These are non-waste systems that may discharge contamination to the soil or the groundwater. This category includes buried storage tanks or pipelines, stockpiles of such things as agricultural activities, and accidental spills.

Non-Waste Category IV: These are non-waste and non-discharge sources of contamination. This category includes saltwater intrusion, river infiltration, improperly constructed or abandoned wells, and farming practices.

Groundwater contamination presents very complex issues. Once an aquifer is contaminated, merely removing the source of contamination will not clean it up. Control of groundwater contamination is dependent on four interrelated systems: Regulation, Design, Monitoring, and Remediation.

Regulations intended to control groundwater contamination are very difficult to enforce. Numerous federal acts in European and American countries have been enacted. Some of them are Resource Conservation and Recovery Act, the Superfund Act, and the Safe Drinking Water Act are designed to protect groundwater. Building control and monitoring measures into new facilities is the most promising method for long-term regulation of groundwater contamination. Finally, remediation or cleanup of a contaminated aquifer through air stripping, a process by which water is removed from an aquifer, treated to remove contaminants, then returned to the aquifer should be performed in limited situations.

 

Contamination Control

As stated above, contamination control refers to containing the spread of the pesticide to prevent further contamination of the environment, in particular watercourses, reservoirs, and wells.

• National Guidelines

The National Organic Certification Program stipulates that all relevant measures should be taken to minimize contamination from outside and within the organic farm. It states that the certification program should set limits for the maximum application levels of heavy metals and other contaminants if there is a risk or reasonable suspicion of contamination. However, the accumulation of heavy metals and other pollutants should be within the prescribed standards. If there is a reasonable suspicion of contamination, the certification program shall carry out an analysis of the relevant products and possible sources of soil and water contamination to determine the level of contamination.

In organic farming system, only products based on polyethylene and polypropylene or other polycarbonates are allowed for protected structure coverings, plastic mulches, insect netting, and silage rapping. These products shall be removed from the soil after use and should not be burnt on the farmland. The use of polychloride based products is prohibited.

• Protecting The Farm Ponds and Wells

Farm ponds and wells can be protected against surface run-off water that carries contaminants by creating a berm. Berm denotes the area of level ground between the raised earthwork and the ditch surrounding it. The location and protection of the well and farm ponds are also important. If the well or pond is to be located in a treated field where surface water can run off, the contamination can be reduced by excavating ditches or by providing a grassed buffer strip between the pond or well and the treated area. General recommendations on controlling soil erosion is also useful to contain the passage of pesticides to ditches and streams.

• Decontaminating Farm Wells

Well waters are quite cold and often alkaline. Most pesticides are less soluble under these conditions than in waters of higher temperature and at a neutral pH. Emptying the water of the well frequently may be adequate to decontaminate the water if low amounts of contaminants have entered as spray drift. Often the bottom of the well should be scraped and the sediment is removed.

Often the toxicant is spilled down the sides of the well and hence removal must include washing or scrapping. In the case of stone or cement walls, washing the walls is adequate; if the walls are earthen, the walls should be scrapped to effect a cleanup. This would be followed by emptying the well frequently and releasing the water for at least 30 m from the well. If there is a pesticide spill around the lip of the well, the contaminated surface soil should also be removed.

Decontamination may take from 6 months to 3 years or in some cases the well has to be abandoned. Clean-up should be rapid when the well is decontaminated by scraping and removing water.

Sometimes, a large quantity of contaminants is spilled close to the well, especially on sandy or gravelly soils. Then, the pesticide may soak deep into the soil and seep into the well in succeeding years especially under heavy rainfall conditions. If such conditions happens, the well has to be abandoned.

There are no adequate means of preventing contamination from subterranean seepage. With subterranean contamination, wells cannot be decontaminated. Abandonment of the well is the only option available.

• Contamination Control For Pesticide Spill

If there is a leak from the pesticide container, it has to be stopped. A barrier made of soil, sawdust, newspaper, activated charcoal, and vermiculite should be constructed to soak up the pesticide. The spill up area should be cleaned. Surplus liquid product should be pumped into drums.

Damp soil or sawdust should be used to make the dry powder or granular product lightly wet and then this material should be put into a drum. If the spill occurs on the ground, it is necessary to dig up the contaminated area and place the soil in drums. Leaky or damaged containers should be placed in a drum or heavy plastic bag. If contamination happens inside a building, the area has to be ventilated to prevent the build-up of toxic fumes.

If possible, the spill area should be decontaminated. After removing the spilled pesticide, the contaminated area should be soaked with a mixture of equal parts of bleach and water. A dike should be placed around the spill area to prevent the spread of the decontamination solution. All equipment used in the clean-up and the vehicles contaminated by the spill should be decontaminated by following the same procedures.

• Human Relations

The most effective contamination control is a cordial relationship with neighbors. Organic producers may enlighten their neighbors about the organic production, certification, and problems of contamination; then, the neighbors will take care and help avoid possible contaminants across the boundaries from their fields.

 

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