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Vegetable comprises about 15 of the daily food intake of the Mauritian population. Consumers generally demand for better quality vegetables. Quality vegetable to them means healthy, succulent and fresh looking vegetables with no visible rashes or holes caused by pests or diseases. To satisfy this demand farmers have to tackle pest and disease problems by all means. The use of fertilizers and pesticides has been found to be the immediate and cheaper way to produce quality vegetables and increased farm productivity. This practice has unfortunately created numerous problems associated with pesticide abuse such as accidental poisoning to man and toxic residues that are hazardous to health in the environment.
In 2006 and 2007, the world used approximately 5.2 billion pounds of pesticides, with herbicides constituting the biggest part of the world pesticide use at 40%, followed by insecticides (17%) and fungicides (10%). Currently, there are more than 1,055 active ingredients registered as pesticides, which are put together to produce over 20,000 pesticide products that are being marketed in the United States.
The world's herbicide industry is forecast to record close to 5% yearly growth between 2011 and 2016 to exceed 1,350 kilo tons. The market is forecast to record close to 6% yearly growth in revenue generating close to $25,000 million by 2016. This growth will not be across the board, with India and a few other nations recording lower growth. This is largely due to the fact that the country's most-commonly used pesticides are insecticides, which represent 40% of the overall market. The world insecticides market is expected to reach almost 535 kilo tons by 2016, recording in excess of 4% yearly growth for the five preceding years.
According to WHO estimates, one million cases of pesticide poisoning occur every year and consequently there are 20,000 deaths globally (Nasir, 1999). The existence of high concentration of pesticide residues in food chain, together with knowledge of some of their adverse effects, has alerted the public to the need for regulation. There are MRLs (Maximum Residue Levels) that need to be respected by the planters. These MRLs have been set by international health organization such as EFSA( European Food Safety Authority) to ensure food safety.
Although there are human benefits in terms of increasing productivity to a greater extent, the use of pesticides, some also have drawbacks, such as potential toxicity to humans and other animals. According to the Stockholm Convention on Persistent Organic Pollutants, 9 of the 12 most dangerous and persistent organic chemicals are pesticides.
WHAT ARE PESTICIDES?
Pesticides are substances or mixture of substances intended for preventing, destroying, repelling or mitigating any pest to protect crop. They generally protect plants from damaging influences such as weeds, diseases or insects. A pesticide is generally a chemical or biological agent (such as a virus, bacterium, antimicrobial or disinfectant) that through its effect deters, incapacitates, kills or otherwise discourages pests.
There are 2 main type of pesticides:
Contact pesticides generally control a pest as a result of direct contact. Insects are killed when sprayed directly. Weed foliage is killed when enough surface area is covered with a contact herbicide.
Systemic pesticides are pesticides which are absorbed by plants or animals and move to untreated tissues. Systemic herbicides move within the plant to untreated areas of leaves, stems or roots.
They are mainly used in combination, i.e. several types of pesticide, fungicide and insecticide are use in vegetable cultivation. Although most vegetables are washed before sales, it is incorrect to assume that all the pesticides have been removed.
There are 4 common of pesticide:
Organophosphate Pesticides -
These pesticides affect the nervous system by disrupting the enzyme that regulates acetylcholine, a neurotransmitter. Most organophosphates are insecticides. They were developed during the early 19th 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.
These affects the nervous system by disrupting an enzyme that regulates acetylcholine, a neurotransmitter. The enzyme effects are usually reversible. There are several subgroups within the carbamates.
They were commonly used in the past, but many have been removed from the market due to their health and environmental effects and their persistence (e.g. DDT and chlordane).
They were developed as a synthetic version of the naturally occurring pesticide pyrethrin, which is found in chrysanthemums. They have been modified to increase their stability in the environment. Some synthetic pyrethroids are toxic to the nervous system
TOXICITY AND HAZARD
The toxicity of any compound is related to the dose. A highly toxic substance causes severe symptoms of poisoning with small doses. A substance with a low toxicity generally requires large doses to produce mild symptoms. Even common substances like coffee or salt become poisons if large amounts are consumed.
Toxicity can be either acute or chronic.
Acute toxicity is the ability of a substance to cause harmful effects which develop rapidly following absorption, i.e. a few hours or a day.
Chronic toxicity is the ability of a substance to cause adverse health effects resulting from long-term exposure to a substance.
There is a great range in the toxicity of pesticides to humans. The relative hazard of a pesticide is dependent upon the toxicity of the pesticide, the dose received and the length of time exposed.
A hazard can be defined as a source of danger. The hazard in using a pesticide is related to the likelihood of exposure to harmful amounts of the pesticide. Exposure can be influenced by the amount of pesticide used, concentration of the pesticide and how the pesticide and application equipment are handled. A pesticide can be highly toxic as a concentrate, but pose little hazard to the user if:
used in a very dilute formulation,
used in a formulation not readily absorbed through the skin or inhaled,
used only under conditions of no human exposure, or
Used by experienced applicators who are equipped to handle the pesticide safely.
In contrast, a pesticide may have a relatively low toxicity but present a hazard because it is used in the concentrated form which may be readily absorbed or inhaled.
The toxicity of a pesticide can be measured several ways, but generally human toxicity is estimated based on test results on rats and other animals. Toxicity studies are only guidelines. A pesticide that is poisonous to rats is not necessarily equally poisonous to people or other animals. Some pesticides are dangerous after one large dose (acute toxicity). Others can be dangerous after small, repeated doses (chronic toxicity).
Measuring Chronic Toxicity
Chronic toxicity refers to the effects of long-term or repeated lower level exposures to a toxic substance, such as when a pesticide applicator is frequently wetted with spray during unsafe spray practices. The effects of chronic exposure do not appear immediately after first exposure and may take years to produce symptoms. Pesticides which have a tendency to accumulate, or which break down slowly in body tissues, usually represent the greatest chronic exposure hazard. Someone who is frequently exposed to low doses of such pesticides may develop symptoms of poisoning long after the first exposure. Chronic exposure may include chronic oral, chronic dermal or chronic inhalation poisoning.
The symptoms of chronic toxicity develop slowly and persist for a long time after exposure. Such symptoms may occur in three ways:
As a complication of acute poisoning. For example, a severe exposure to a pesticide may cause acute effects such as nausea, chest pain and vomiting as well as chronic effects resulting from kidney, liver and lung damage.
As a slowly progressive condition, without any incident of acute poisoning. For example, increased breathing difficulty or skin sensitization (allergy) after repeated use of a pesticide.
As the occurrence of a disease or condition initiated by previous exposure. For example, the development of cancer years after a period of exposure.
Very few pesticides now in use are known to cause chronic effects, if used according to label directions. However, a few pesticides are suspected or known to cause chronic illness in test animals or humans when exposure levels are high. The registration of some pesticides has been cancelled because the suspected or identified chronic effects represented a significant health hazard.
Chronic toxicity of a pesticide is assessed differently from acute toxicity (LD50 or LC50) A number of different tests are performed on animals which help to predict whether a pesticide will cause long-term effects. Test animals are exposed to sublethal levels of pesticides for periods ranging from about 90 days to several years. They are examined for a wide variety of toxic effects from dermal, oral and respiratory exposure. Such effects include:
Carcinogenicity - ability to produce cancer or to assist carcinogenic chemicals.
Mutagenicity - ability to cause genetic changes.
Teratogenicity - ability to cause birth defects.
Oncogenicity - ability to induce tumor growth (not necessarily cancers).
Liver damage - death of liver cells, jaundice (yellowing of the skin), fibrosis and cirrhosis.
Reproductive disorders - such as reduced sperm count, sterility, and miscarriage.
Nerve damage - including accumulative effects on cholinesterase depression associated with organophosphate insecticides.
Allergenic sensitization - development of allergies to pesticides or chemicals used in formulation of pesticides.
Evidence of chronic effects is usually associated with long-term exposure of test animals to relatively high doses. Thus people who run the greatest risk of developing any chronic effects are workers involved in the manufacture of chemicals or applicators exposed to high levels of pesticides over many years.
Chronic toxicity symptoms may not always be recognized as having been caused by exposure to a toxic chemical months or years in the past. The levels of exposure which might cause chronic effects in a human individual are very difficult to predict. Thus anyone handling pesticides should attempt to minimize their exposure and eliminate the possibility of chronic effects.
Measuring Acute Toxicity (LD50 and LC50 Values)
Acute toxicity of a pesticide refers to the effects from a single dose or repeated exposure over a short time (e.g. one day), such as an accident during mixing or applying pesticides. A pesticide with a high acute toxicity can be deadly even if a small amount is absorbed. Acute exposures may be referred to as acute dermal, acute oral or acute inhalation poisoning. Usually the effects of acute exposure, if any, occur within 24 hours.
LD50 or Lethal Dose 50
The LD50 is the dose of a pesticide that will kill half of a group of test animals from a single exposure by either the dermal, oral or inhalation routes. The larger an animal, the greater the lethal dose required to kill it. The LD50 is expressed in milligrams per kilogram of body weight of the test animal. For example, if a pesticide has an oral LD50 value of 10 mg/kg, and the test animals each weigh 1 kg, 50% of the animals would die of poisoning if each ate 10 mg of the pesticide. If the test animals weigh 25 kg each, the lethal dose to kill 50% of these animals would be 10 mg/kg X 25 kg = 250 mg each.
A pesticide with a lower LD50 is more toxic than a pesticide with a higher number because it takes less of the pesticide to kill half of the test animals. The smaller the LD50 value, the more toxic the pesticide.
LC50 or Lethal Concentration 50
The LC50 value is a measure of the toxicity of a pesticide when test animals breathe air mixed with pesticide dust, vapours or spray mist. The LC50 is the concentration of pesticide which is lethal to 50% of a population of test animals and is usually determined for a specific exposure period (e.g. inhalation for 4 hours). The length of exposure is important because shorter exposure periods generally require higher pesticide concentrations to produce toxic effects. LC50 values for pesticides in air are expressed as the ratio of pesticide to air, in parts per million (ppm) or parts per billion (ppb). LC50 values are also determined for fish and aquatic organisms based on the concentration of pesticide in water for exposure periods of 24 to 96 hours.
If a formulated product contained 125 g/L active ingredient, a 70 kg person would be severely poisoned if he consumed (21 g) / (125 g/L)= 0.168 L = 168 mL of product.
If the product was mixed in a spray solution of 100 mL/10L of spray, then a person would be severely poisoned if he consumed (168 mL) / (10 ml/L) = 16.8 L of spray.
Research shows the susceptibility of mammals to pesticides varies with the species, age, sex and health of the animals being tested. Therefore data on the toxicity of pesticides to test animals can only serve as a guide to the probable toxicity of a pesticide to an individual person. When pesticides are registered, safety factors are included to account for the differences between species and between individuals.
As a general guide, the approximate dose which would cause severe injury or death to an average human adult is illustrated in the table below for various LD50 ranges
Relation of oral LD50 to approximate lethal dose in adult humans.
Oral LD50 of Active Ingredient (a.i.)
Approximate lethal dose to average size adult
(70 kg or 155 lb.)
less than 5 mg/kg
less than 0.3 mL
(one to two drops)
5 to 50 mg/kg
0.3 to 3 mL
(a few drops to half a teaspoon)
50 to 500 mg/kg
3 mL to 30 mL
(half a teaspoon to two tablespoons)
500 to 5,000 mg/kg
30 mL to 300 mL
(1 to 10 fluid ounces)
5,000 to 15,000 mg/kg
300 mL to 900 mL
(10 to 30 fluid ounces)
Tomato Cultivation in Mauritius
Tomato (Lycopersicon esculentum) is one of the various vegetable that is mainly consumed by mauritian on a daily basis either in main dishes (cooked or raw) or as salad. Tomato demand has been on an constant increase during the past few decades, resulting in an large increase in the use of agrochemicals including pesticides to control pest as well as diseases in order to increase productivity.
Tomato is easily grown all over the island in Mauritius due to its favorable climate and its fertile volcanic soil. These are mainly grown in open field. Three types of tomatoes are commonly grown. These are
1. Cooking Tomato
2. Salad Tomato
3. Cherry Tomato
Harvesting begins about 2 months after transplantation, at regular intervals when the tomatoes are well shaped and when they have turned from dark green to light green. These are allowed to ripen in a shady and cool place. When the tomato begins to mature, it has a pink or yellow coloration, which turns to red eventually.
The tomato industry is estimated at a value of around Rs 300 M with an annual production of 14, 700 t over an area of 935 ha and at a market price of Rs 13.00 to 105.00 / Kg. The production of salad tomato crop is estimated to be around 2000 t yearly. In 2006, the production and area harvested has peaked up as compared to a lower production in 2005.
The local production of tomato should be increased to some 28,000 t by 2015 to meet the increasing demand of the growing population and the boost of the tourist industry taking into account our requirements for fresh consumption as well as raw materials for processing.
Pesticide commonly used in Tomato Cultivation
A large number of pesticides are sprayed on tomatoes. "Fresh" tomatoes are for slicing and salads. Tomatoes are also grown for processing into a wide variety of different products. The pesticides used on tomatoes include insect-killers, weed-killers, plant growth regulators and other types of pesticides.
Devrinol 2-E Selective Herbicide, Devrinol 2-EC, Devrinol 4-F
Badge SC, Champ Formula 2 Flowable, Kocide, NU-COP 3L, Ridomil Gold, Copper Fungicide
Ag Streptomycim, Agri-Mycin 17, Bac Master, Firewall Fungicide/Bactericide,
Accu-Pak Ridomil Gold MZ Fungicide, Dithane, F-45 Rainshield, Gavel 75DF,
Bull's Eye Bioinsecticide, Spintor 2SC, SA-50 Conserve Naturalyte Insect
Control, Monterey Garden Insect Spray, Ferti-lome Spray.
Insect & Mite
Abacus Agricultural Miticide/Insecticide, Abba 0.15 EC, Agri-Mek 0.15EC
Miticide/Insecticide, Epi-Mek 0.15EC Miticide/Insecticide
Alais 2F, Areca, Admire, Couraze 1.6F, Macho 2.0 FL, Majesty, Pasada 1.6 F
Monitor 4 Liquid Insecticide
Agri-Star Trigger, Arrow 2EC, Clethodin 2EC, Intensity Post-emergence Grass
Herbicide, Select, V-10139 1.6 EC Herbicide, Valent Prof Prod Envoy Herbicide,
Select 2EC Herbicide, Volunteer Herbicide
Metri D F, Metribuzin, Sencor DF 75% Dry Flowable Herbicide
Warrior LEC, Warrior Insecticide with Zeon Technology
Insect & Mite
Danitol 2.4 EC Spray,
Insect & Mite
Endosulfan 3 EC, Hi-Yield Thiodan Garden Dust, Thiodan Enulsifiable
Concentrate, Phaser 50 WP Insecticide, Thionex 3EC Insecticide
Insect & Mite
Actigard 50WG Plant Activator
Dipel (worm killer) WP, Dipel .86% w.p., Dipel 110 dust, Dipel 2X Biological
Insecticide, Dipel Bio Garden Spray, Dipel ES, Dipel WDG.
Quadris, Bravo, Chloronil 500, Chlorothalonil 500 GK, Chloro Gold, Equus 720
SST, Asana XL
Gramoxone Max Herbicide, Gramoxone Inteon Herbicide
Cabrio EG Fungicide, Cabrio Team Fungicide