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Saturday, 19 February 2011 03:23

Agricultural Chemicals

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Agricultural chemicals are usually defined as pesticides, fertilizers and health products. The US Environmental Protection Agency (EPA) defines pesticides as any materials manufactured or formulated to kill a pest. This means that herbicides, fungicides, insecticides and miticides are pesticides. Fertilizers are nutrient chemicals that enhance the growth of the plant. The important elements in the fertilizers are nitrogen, phosphorus and potassium. Nitrogen is usually in the form of ammonia, ammonium nitrate, ammonium sulphate, ammonium phosphate or solutions of these materials. Other nitrogen-containing chemicals are used for some special nutrient needs. Ammonium phosphate is the normal source of phosphorous. Potash (potassium oxide) is the potassium nutrient. Animal health products are any chemicals that are used to promote the health or growth of an animal. This includes products that are used topically by drenching or pouring-on, orally as a tablet or gel, and injectibles.


The most significant development in the pesticide manufacturing industry has been the introduction of the environmentally friendly pesticides. The imidazolinone family of herbicides has been a benefit to soybean and other field crops, as the herbicides are much more effective pound for pound; are less toxic to humans, animals and fish; have less persistence in the soil; and are formulated using water instead of flammable solvents, as compared to the old generation nitroaromatics. Concurrent with these innovations is the development of imidazolinones-resistant seeds that can be protected from weed growth. Corn is in the forefront in this area and has been successfully grown, protected by the imidazolinones. This also makes carry-over from year to year of the herbicide an insignificant problem, as in many areas soybeans and corn are rotated.

A newer development is the production of the synthetic pyrethroids, which are broad-range pesticides. These products are effective pesticides and are less toxic to animals and humans than the old organophosphates and carbamates. They are activated by the insect’s biological system and therefore not a danger to vertebrates. They are also less persistent in the environment, as they are biodegradable.

There have also been developments in the use of the old generation pesticides and herbicides. Herbicide formulations have been developed that utilize water dispersion technology that eliminates the use of volatile solvents. This not only reduces the amount of volatile organic chemicals that go to the atmosphere, but also makes handling, storage, formulation and transportation much safer. In the area of pesticides, a superior method of handling the toxic pesticides has been developed that uses closed container transfer of the material from the package to the spreader, called “Lock-N-Load”. This reduces the chances of exposure to these toxic materials. Organophosphates are still being used successfully to help eradicate health problems such as malaria and river blindness. Some of the less toxic organophosphates are effective in the treatment of animals for insects, worms and mites by direct application to the skin using pour-on or aerosol formulations.

The pesticide industry is regulated by many countries, and labelling, application to plants and soil, training in pesticide use, and transportation are controlled. Many pesticides can only be spread by licensed applicators. Precautions during pesticide application are discussed elsewhere in this Encyclopaedia. Bulk transportation vehicles can only be operated by qualified drivers. The producers of pesticide have a legal obligation to provide safe handling and application methods. This is usually accomplished by providing comprehensive labelling, training and material safety data sheets (MSDSs) (see the chapter Using, storing and transporting chemicals).

Another problem is the disposal of empty containers. It is not advisable, and in many places it is illegal, to reuse pesticide containers. Many advances have been made to mitigate this problem. Plastic containers have been collected by the distributors and reprocessed into plastic pipe. Bulk, refillable containers have been used. With the advent of the wettable powders and water-based dispersions, triple rinsing the container into the solutions tank gives the applicator a method to decontaminate the container before landfilling or recycling. Hand lances with spray nozzles that can pierce the container are used to assure proper cleaning and the destruction of the container so that it can not be reused.

Pesticides are made to kill; therefore, care is necessary to handle them safely. Some of the problems have been lessened by the product advances. In most cases, copious quantities of water are the best first-aid treatment for superficial exposures to skin and eyes. For ingestion, it is best to have a specific antidote available. It is important that the nearest health facility know what is being used and have a supply of the appropriate antidote on hand. For instance, organophosphates and carbamates cause cholinesterase inhibition. Atropine, the specific antidote for the treatment of this reaction, should be available wherever these pesticides are used.

For further discussion of pesticides, see the eponymous article in this chapter.


Ammonia is the base of most important fertilizers. The major fertilizers are ammonia itself, ammonium nitrate, urea, ammonium sulphate and ammonium phosphate. There appears to be an environmental problem associated with nitrogen use, as the ground water in many farming areas is contaminated with nitrates, which causes health problems when the water is consumed as drinking water. There are pressures for farmers to use less fertilizer and to rotate crops of nitrogen-using legumes such as soy beans and rye grass. Ammonium nitrate, an oxidizer, is explosive if heated. The dangers of ammonium nitrate as a blasting agent were demonstrated by the destruction of a US federal building in Oklahoma City, Oklahoma, in 1995. There is some movement to add inert ingredients to make fertilizer-grade ammonium nitrate detonation-resistant. An industrial explosion resulting in multiple fatalities which occurred in an ammonium nitrate solutions plant that was thought to be safe from detonation because the ammonium nitrate was handled as an 85% solution is anonther example. Investigation results indicated that an intricate condition of temperature and contamination caused the incident. These conditions would not exist in the retail or farming sector. Anhydrous ammonia is a moderately toxic gas at room temperature and must be kept under pressure or refrigeration during storage and use. It is a skin, eye and respiratory irritant, can cause burns, and is flammable. It is directly applied to the soil or used as an aqueous solution. There is significant anhydrous ammonia storage in many farming areas. A hazardous condition is created if the storage is not managed correctly. This should include monitoring for leaks and emergency leak procedures.

Animal Health Products

The development and marketing of bovine somatotropin (BST) has caused controversy. BST, a fermentation product, raises the productivity of milk cows by 10 to 20%. Many people are opposed to the product because it introduces a chemical into the production of milk. However, the BST milk is indistinguishable from ordinary milk since BST is produced naturally by the milk cow. A problem seems to be an increase in infections of the cow’s udder. Antibiotics for these infections are available, but the use of these antibiotics is also controversial. The important benefits of BST are the increased production of milk with a reduction in food consumption and a similar reduction in cow manure, a material that is a solid-waste problem in many areas. A similar product, porcine somatotropin (PST), is still in the testing stage. It produces bigger hogs quickly, utilizing less feed, and results in pork containing less fat.

Antibiotic use in the beef-raising industry is also causing controversy. There is fear that consumption of large amounts of beef will result in hormonal problems in humans. There has been little in the way of confirmed problems, but the concern persists. Animal health products have been developed that control worms in animals. The previous generation was a synthetic chemical product, but the new generation products are the result of biological fermentation technology. These products are effective in many types of animals at very low use levels, and include domestic pets in their protection arena. These products are very toxic to aquatic life, though, so much care must be taken to avoid contamination of creeks and streams. These materials do biodegrade, so there appear to be no long-term or residual aquatic problems.

Manufacture of Agricultural Chemicals

The manufacturing of agricultural chemicals entails many processes and raw materials. Some agricultural chemicals are batch chemical syntheses that involve exothermic reactions where temperature control and emergency relief sizing are an issue. Hazard evaluations are necessary to assure that all the hazards are discovered and addressed. Hazard and operability studies (HAZOP) are recommended for conducting reviews. Relief sizing must be conducted using Design Institute for Emergency Relief Systems (DIERS) technology and data from calorimetric equipment. Usually, because of the complexity of the molecules, the production of agricultural chemicals involves many steps. Sometimes there is considerable aqueous and organic liquid waste. Some of the organics may be recyclable, but most of the aqueous waste must be biologically treated or incinerated. Both methods are difficult because of the presence of organic and inorganic salts. The previous generation herbicides, because they involved nitrations, were produced using continuous reactors to minimize the quantities of the nitrated materials at reaction temperatures. Severe runaway reactions, resulting in property damage and injuries, have occurred when batch reactors of nitrated organics have been subjected to a temperature excursion or contamination.

Many modern pesticide products are dry powders. If the concentration, particle size, oxygen concentration and a source of ignition are present at the same time, a dust explosion can occur. The use of inerting, the exclusion of oxygen, and utilization of nitrogen or carbon dioxide minimizes the oxygen source and can make the processes safer. These dusts may also be an industrial hygiene issue. Ventilation, both general and local, is a solutions to these problems.

The major fertilizers are made continuously rather than by the batch process. Ammonia is made by reforming methane at high temperatures utilizing a specific catalyst. Carbon dioxide and hydrogen are also formed and must be separated from the ammonia. Ammonium nitrate is made from ammonia and nitric acid in a continuous reactor. The nitric acid is formed by the continuous oxidation of ammonia on a catalytic surface. Ammonium phosphate is a reaction of ammonia and phosphoric acid. Phosphoric acid is made by reacting sulphuric acid with phosphate -containing ores. Sulphuric acid is formed by burning sulphur to sulphur dioxide, and catalytically converting the sulphur dioxide continuously to sulphur trioxide, and then adding water to form the sulphuric acid. Urea is a continuous high-pressure reaction of carbon dioxide and ammonia, the carbon dioxide usually coming from the ammonia continuous reaction by-product.

Many of these raw materials are toxic and volatile. Release of the raw materials or finished products, through an equipment failure or operator error, can expose employees and others in the community. A detailed emergency response plan is a necessary tool to minimize the effects of a release. This plan should be developed by determining a credible worst-case event through hazard evaluations and then forecasting consequences using dispersion modelling. This plan should include a method to notify employees and the community, an evacuation plan, emergency services and a recovery plan.

Transportation of agricultural chemicals should be thoroughly investigated to choose the safest route—one that minimizes the exposures if an incident occurs. A transportation emergency response plan should be implemented to address transportation incidents. This plan should include a published emergency response telephone number, company personnel to respond to calls and, in some cases, an accident site emergency response team.

Fermentation is the method of producing some of the animal health products. Fermentation is usually not a hazardous process, as it involves growing a culture using a nutritional medium such as lard oil, glucose, or starch. Sometimes anhydrous ammonia is used for pH (acidity) control or as a nutrient, so the process can involve hazards. Solvents may be used to extract the active cells, but the quantities and the methodology are such that is can be done safely. Recycling these solvents is often part of the process.



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