Pesticides and their Context in terms of Environmental, Agricultural and Social Development. Part 1 Definitions.

Pesticides, according to FAO relate to "any substance or mixture of substances intended for preventing, destroying or controlling any pest, including vectors of human or animal, plant species or pests that cause damage or otherwise interfere with the production, processing, storage, transport or marketing of food, agricultural products, wood, or wood products or animal feed, or can be administered to animals to combat insects, arachnids or other pests in or on their bodies. Includes substances intended for use as growth regulators in plants, defoliants, desiccants, agents for thinning fruit or preventing the premature fall of fruit, and substances applied to crops either before or after harvest to protect commodity from deterioration during storage and transportation. "  (FAO. 2002. Code of Conduct on the Distribution and Use of Pesticides. ftp://ftp.fao.org/docrep/fao/006/y4544s/y4544s00.pdf). 

Pesticide Aplication 

There are several types or classifications of pesticides, the most common corresponds to a classification according to the target species (to which the attacks), this classification can be grouped into the following groups, according to U. S. Environmental Protection Agency (http://www.epa.gov/pesticides/about/types.htm#type) :

• Algicides: Control algae in lakes, canals, swimming pools, water tanks, and other sites.
• Antifouling agents: Kill or repel organisms that attach to underwater surfaces, such as boat bottoms.
• Antimicrobials: Kill microorganisms (such as bacteria and viruses).
• Attractants: Attract pests (for example, to lure an insect or rodent to a trap). (However, food is not considered a pesticide when used as an attractant.)
• Biopesticides: Biopesticides are certain types of pesticides derived from such natural materials as animals, plants, bacteria, and certain minerals.
• Biocides: Kill microorganisms.
• Disinfectants and sanitizers: Kill or inactivate disease-producing microorganisms on inanimate objects.
• Fungicides: Kill fungi (including blights, mildews, molds, and rusts).
• Fumigants: Produce gas or vapor intended to destroy pests in buildings or soil.
• Herbicides: Kill weeds and other plants that grow where they are not wanted.
• Insecticides: Kill insects and other arthropods.
• Miticides (also called Acaricides): Kill mites that feed on plants and animals.
• Microbial pesticides: Microorganisms that kill, inhibit, or out compete pests, including insects or other microorganisms.
• Molluscicides: Kill snails and slugs.
• Nematicides: Kill nematodes (microscopic, worm-like organisms that feed on plant roots).
• Ovicides: Kill eggs of insects and mites.
• Pheromones: Biochemicals used to disrupt the mating behavior of insects.
• Repellents: Repel pests, including insects (such as mosquitoes) and birds.
• Rodenticides: Control mice and other rodents.

The term pesticide also includes these substances:

• Defoliants: Cause leaves or other foliage to drop from a plant, usually to facilitate harvest.
• Desiccants: Promote drying of living tissues, such as unwanted plant tops.
• Insect growth regulators: Disrupt the molting, maturity from pupal stage to adult, or other life processes of insects.
• Plant growth regulators: Substances (excluding fertilizers or other plant nutrients) that alter the expected growth, flowering, or reproduction rate of plants.

The most widely used worldwide for agriculture corresponds to 3 major groups: herbicides, insecticides and fungicides.

Pesticides have 3 components in its formulation (how they are traded):

• Active Ingredient(s): This is the component that actually has abiological effect on the pest which is acting.
• Solvents and thinners: They act as a vehicle of the active ingredient, diluting it and allow to reach a timely manner to the plague.
• Adjuvant: Those components that help the active ingredient in its role in reducing the pest, sometimes enhancing the action of the pesticide. 

From the agronomic and management, pesticides have had a substantial contribution to increasing crop productivity, avoiding losses associated with pest and disease attacks, which often ledto partial or total loss of crops, and the best forecasts a decline in product quality. However, when products are designed to bring an action "to kill" their targets, these products are not without risk to health nor the environment. A short walk from the use of these pesticides, research reported that they talked about the environmental effects of these compounds, especially related to wildlife (fish and birds) that were exposed to these pesticides or their residues. From then to now, we have designed protocols for evaluation of substances that make these products and the laboratories should be made ​​very large and expensive studies in order to place a substance on the market. These studies in turn have the quality to be reserved between the evaluator agent and the company seeking his release for commercial use. 

Among the requirements that must be met for the provision of a commercial product should be performed, among other studies, the following:

• Toxicological Testing (confidential).
• Qualitative and Quantitative Analysis of Active Ingredient and Formulation Testing.
• Quantitative and Qualitative Analysis Product (Additives, adjuvants, inert, etc..) and its %.
• Physical and chemical characteristics of the preparation. 
• Product Use: 
•   Method of application, including description of the system used.
• Application rates and, where appropriate, and biocide final concentration of the active substance in the system to be used in the preparation.
• Number and rate of applications. 
• Waiting periods necessary to protect human beings.
• Precautions.
• Stability.
• Information concerning to residues.
• Incompatibility with other products.
• Storage conditions. 
• Type of packaging and net content.
• Documentation for the environment.
• Safety data sheet date. 
• Safety Data Sheet for each of the components that are part of the formula.
• Draft label (depending on use Environmental, Domestic or both).

One way to measure or quantify the toxicity (environmental or human risk) of a pesticide in a theoretical way is through a test QSAR, explained below that corresponds:

QSAR: It comes from Quantitive Structure Activity Relationships, method that assumes an implicit relationship between the toxicity of a xenobiotic (pesticide active ingredient) and chemical properties. It is based on simple mathematical relationships to describe and extrapolate one or more of these properties to agroup of compounds that usually belong to the same chemical family. The mathematical relationships can be established by multi-linear regression or nonlinear methods. So you can predict the activity of the molecule relative to its fundamental properties (structure, physical and chemical properties).

Once a pesticide and accepted its use must comply with certain levels of pesticide residues, which should not have deleterious or toxic effects on the health of consumers of the products in which they apply.

To understand this, one must first define what is pesticide residue, and not any errors of concept to talk about it.

The term "pesticide residue" means any specified substance in food, agricultural products or animal feed as a result of the use of a pesticide. The term includes any derivatives of a pesticide, such as conversion products, metabolites, reaction products and impurities of toxicological concern, expressed in mg/kg. (Note:The term "pesticide residue" includes residues from unknown or unavoidable causes (environmental), as the known uses of the chemical). 

Pesticide residues may vary according to their nature and are expressed as follows:

• Residues of the Original Substance: When the original substance (active ingredient) is not metabolized and metabolites derived are molecularly close to the original substance (the risk is inherent to the direct toxicity of it).
• Residues of a specific metabolite: All active substance is metabolized and removed a large amount of metabolite derived from the conversion and some active material. (half-life short but very toxic). 
• Residues of the Original Substance and Metabolites Derived:  The original substance is not fully metabolized and removed a large amount of original substance and metabolites. Both values ​​are presented. 

These pesticide residues must be consistent with the residue levels permitted or tolerated for that pesticide in the legislation. The concentration levels of residues must be under the levels established as MRLs (Maximum Residues Limit) and MRLSs (Maximum Residues Limit Strangers), established by law for each market and each particular foodstuff.
MRLs correspond to concentration levels of pesticide residues concerned and that being in the diet of these quantities would have no effect on the health of the population, this shows clearly that for each country or market the standard varies according to the characteristics of population (eg the average weight and design of risk population especially children, seniors, women who are pregnant or breastfeeding and the unborn). 

To set MRLs for pesticides, there are still 2 complementary ways, a laboratory animal models (rats, rabbits, dogs, etc.) and another field which shows the results of applications under conditions of Good Agricultural Practices. A brief description of what each one:

• Toxicological criteria (laboratory):  makes toxicities to humans and animals through previously established no-effect level (NOEL,NEL, NOAEL) for animal models (rats and dogs), this no-effect level corresponds to a continuous exposure to pesticide where no evidence of effects at the molecular level, metabolism and behavior. After the no-effect level, using a safety factor to extrapolate values ​​from animal models to humans, this factor is normally 100, means that multiplies 100 times the accepted maximum concentration threshold for increased security against the product (100 result of: 10 inter-specific and 10 intra-specific), but sometimes you can use values ​​up to 1000 or 10000. After this the No Effect for Human corresponds to the ADI (Acceptable Daily Intake) in mg residue / kg of human weight, and then determines the allowable level for the crop residue, the permissible level, using the IDA and multiplies worth an average weight of the population (the highest risk children or the elderly) and a correction factor according to the diet of the population (also the most risky such as vegetarians).
• Agronomic approach: Set Field tests by GAPs procedures (calibration of machinery, enforcement of waiting periods, etc.) and the values ​​of pesticide residues in the tested product must be less than the permissible levels of certain by previous method , if lower, taking this value as MRLs , as this will prevent overuse of pesticides or close exposure to the permissible residual value , otherwise, if the residue values ​​are higher than the previous method , the results are ignored and considered only the toxicological criteria, with which this is achieved wait between the time of application and harvest the product. This method is intended to reduce as far as possible the use of pesticides according to optimal conditions for its application in precision agriculture.

If not complied with the MRL (if exceed their value) is likely two things, first there is a risk of poisoning due to exposure, this would correspond to Acute poisoning (which is immediate and their effects should be treated the same as very fast), however this is only possible if residue levels are excessively high in relation to the establishment, the other option is that the long-term consumption of products with higher than normal MRL exercise chronic poisoning, which effects are not immediate but long term, taking years to express a related condition, so it is very important to respect and constantly MRLs would audit. This type of chronic poisoning may be comparable to that which may affect pesticide handlers and those products may be exposed in areas used continuously these treatments. Hence the importance of the certification of pesticide handlers and community access to information of those who live near agricultural areas where pesticide treatments are performed. 

However, the MRLs for residues are within the range set by law, we can ensure that consumers do not have a harmful effect on your health. Remember that the values ​​of MRLs are constantly evaluated and corrected when they have shown a higher risk, otherwise they are taken for review to be removed or excluded from the list of approved products and prohibits their use.