In this article we will discuss about the impact of pesticides on environment.
Impact # 1. Insecticide Resistance:
Resistance is the development of an ability to tolerate a dose of an insecticide, which would prove lethal to the majority of individuals in the normal population of the same species. Large scale use of pesticides to control pests has resulted in the development of resistance which is most serious bottleneck in the successful use of pesticides. Since the first report of development of resistance in San Jose scale to lime sulphur in 1908, more than 577 species of insects and mites have developed resistance to insecticides by 2012.
The resistant species represent 15 different arthropod orders and among these the top seven orders (Diptera, Homoptera, Lepidoptera, Thysanoptera, Coleoptera, Hemiptera and Acari) comprise approximately 93 per cent of the resistant species. Seven of the top 10 species to show resistance are agricultural pests and 3 are medically important.
Most of these pest species belong to a relatively small number of families of arthropods, viz. Tetranychidae (mites), Culicidae (mosquitoes), Noctuidae (moths) and Aphididae (aphids).
Following are the biological factors which help to explain why these species have repeatedly evolved insecticide resistance:
i. These species are under rintense selection for resistance. All of these pests are major targets of insecticide use because of their significant economic and in some cases, human health impact. For example, many of the harbivorous species are pests of cotton, where insecticide use is particularly high. Similarly, diamondback moth is a pest of cruciferous vegetables which are sold primarily damage-free, requiring significant insecticide use.
ii. Many of the herbivorous pests in this group, such as the heliothines and the sucking pests are pests of several major crops, resulting in their being exposed to the same or similar insecticides on different crops.
iii. These species are biochemically pre-adapted to evolve insecticide resistance. The herbivorous species are polyphagous and evolved to deal with a variety of plant defensive chemicals, particularly alkaloids (Colorado potato beetle and cotton pests) and, therefore, had mechanisms available to detoxify and excrete novel toxins.
iv. Several of these species are capable of asexual reproduction (aphids, whiteflies and mites), which can speed the rate of adaptation to insecticides.
v. These species are typified by high rates of dispersal, with the adults being highly mobile and/or human activities contributing to their long distance movement, e.g., whitefly and diamond-back moth may be moved on host plants that have been grown in one area to be sold in another and many of the pest species may be found inside ships or aeroplanes.
vi. Many of the above biological characteristics are common to related species which helps to explain why multiple species within particular arthropod families appear to have a strong tendency to evolve insecticide resistance.
Resistance to organochlorine a pesticide is most common and comprises approximately 66 per cent of the top 10 insecticides/acaricides or formulations that have an arthropod species resistant to them. Organophosphorous products make up an additional 29 per cent and the carbamates are 5 per cent of this total.
Development of resistance has become more prevalent during the last 50 years, but the number of new resistant species recorded recently is less than in previous decades. This is due to many recent reports adding to the resistance spectrum in species already reported as resistant to other compounds.
This phenomenon has also appeared in 100 species of plant pathogens and 55 species of weeds, as well as in some nematodes and rodents. In India, 14 insect pests of public health and household importance, 7 insect pests of agricultural crops and 6 stored grain insects have developed resistance to insecticides.
In Asian countries, the first report of development of pesticide resistance was reported from India in 1963, when Singhara beetle, Galerucella birmanica (Jacoby) was found resistant to DDT and HCH. Since then, 14 other pests have been demonstrated to become resistant to different insecticides in one or more countries.
Widespread occurrence of resistance in this pest has also been reported from Indonesia and Thailand. Similarly, another polyphagous pest, Spodoptera litura (Fabricius) has become resistant to nearly all the available groups of pesticides in India. In Plutella xylostella (Linnaeus) high levels of resistance to quinalphos (>600 folds), fenvalerate (2700 folds), cypermethin (2880 folds) and other insecticides have been reported.
Brown planthopper of rice has been reported to have developed resistance to one or more pesticides in Fiji, Malaysia, the Philippines, Sri Lanka and Vietnam. Moderate to high levels of resistance to most of the insecticides have been reported in Bemisia tabaci (Gennadius) in Pakistan and India. In case of other pests, the problem is not yet widespread and can be tackled by undertaking timely remedial measures.
The problem of pesticide resistance can be contained by following one or the combination of the following methods:
(i) Pesticides should be used only if their use is essential and is based on monitoring the pest population in the field.
(ii) Increase the dose applied so that even potentially resistant genotypes are killed.
(iii) Use of synergist which will enhance the toxicity of a given pesticide by inhibiting the detoxification mechanism.
(iv) Alteration of pesticides with unrelated mode of action.
(v) Incorporation of non-insecticidal strategies in an integrated pest management approach.
Impact # 2. Pest Resurgence:
Resurgence refers to an abnormal increase in pest population or damage following insecticide application often far exceeding the economic injury level. Pest resurgence may broadly be classified into two categories, i.e. primary pest resurgence and secondary pest resurgence (replacement).
Primary Pest Resurgence:
Primary pest resurgence occurs when the target pest population responds to a pesticide treatment by increasing to a level at least as high or higher than in an untreated control or higher than the population level observed before the treatment. The resurgence may occur after the first application or after several applications of the pesticide. Pest population outbreaks can be caused by many factors, but pest resurgence occurs after a treatment of the crop with a chemical, targeted at the pest population that is intended and expected to control the targeted pest.
Secondary Pest Resurgence:
Secondary pest resurgence refers to the replacement of a primary pest with a secondary pest or a secondary pest outbreak occurs when a non-target, but injurious pest population increases in a crop, after it is treated with a pesticide to control a primary pest population. The increase is an unintended and unexpected consequence of the pesticide treatment.
For example, pesticide sprays to control the codling moth, apple maggot and plum curculio on apple lead to resurgence of populations of white apple leafhopper, spotted tentiform leafminer, and European red mite. Season long sulphur sprays for control of powdery mildew on grapes often lead to resurgence of the red spider mite, Tetranychus pacificus McGregor.
Resurgence of insect pests following application of insecticides has been known for a long time. As early as 1956, more than 50 species of insect pests and mites whose populations showed resurgence after insecticidal treatments with diverse chemicals were known.
Maximum cases of resurgence belong to Homoptera (44%) followed by Lepidoptera (24%) and phytophagous mites (26%). It is interesting to note that homopteran insects are protected from contact insecticides by a waxy covering and many of the Lepidoptera exhibiting resurgence are borers and leafminers which also escape direct contact with the insecticides.
Interestingly, Homoptera (66%) and Lepidoptera (18%) head the list for classical biological control successes associated with each insect order. It thus appears that resurgence is associated with pests which have effective natural enemies and which are also less affected by contact pesticides than their natural enemies.
Maximum reports of resurgence pertain to planthoppers especially brown planthopper (BPH) of rice. BPH was a minor pest of rice crop during 1950s in India but extensive use of insecticides has elevated it to the status of a major pest not only in India but whole of Asia. Reports of insecticide-induced resurgence in BPH have been received from Bangladesh, India, Indonesia, and Solomon Islands.
As many as 27 insecticides have been reported to cause resurgence in BPH. The factors implicated in BPH resurgence include reduction in duration of nymphal stage, longer oviposition period, shortened life cycle, enhanced reproductive rate, higher feeding rate and destruction of natural enemies especially Cyrtorhinus lividipennis Reuter.
The use of synthetic pyrethroids on cotton during the last two decades has resulted in increasing incidence of serveral sucking pests including whitefly, aphid, red mite and mealybugs. Over-reliance on SPs for the control of bollworms has been the major factor responsible for whitefly outbreaks in Andhra Pradesh, Gujarat, Tamil Nadu and other parts of the country.
SPs have also been reported to cause resurgence of mustard aphid infesting Indian mustard. It was found that the application of SPs to the host plants increased the concentration of glucose and some amino acids especially arginine, lysine, isoleucine, leucine and cystine.
These changes might be responsible for stimulation of aphid reproduction and increased weight of such aphids. On the other hand, endosulfan did not affect the quality of leaf sap of the host plants but still caused enhanced reproduction in the aphid.
It was found that endosulfan reduced the excretion of some amino acids in the honeydew of the aphid indicating that better utilization of these amino acids was responsible for the increased fecundity of such aphids. It is, thus, clear that different insecticides may cause resurgence of the same insect by different mechanisms and even the same insecticides may produce variable effects at different sub-lethal concentrations.
The use of right type of insecticide, dosage, time and method of application can play a significant role in reducing the risk of insecticide resurgence. The agronomic practices like date of sowing, judicious use of fertilizer and irrigation water can help in reducing the insecticide-induced resurgence. The cultivation of healthy crop, conservation of natural enemies with the use of ecofriendly insecticides, proper surveillance and making farmers IPM experts can help in avoiding insecticide-induced resurgence.
Impact # 3. Effect on Non-Target Organisms:
Repeated use of pesticides on cotton, fruits, tobacco and other crops has disruptive effects on beneficial insects like pollinators, biocontrol agents, soil, wild and aquatic life. Many invertebrates take up pesticides from soil into their bodies and may concentrate pesticides several times greater in their tissues than those in the surrounding soil.
The animals that feed upon these invertebrates may, in turn, concentrate these residues to levels that may kill them or affect their normal activities. Soil microorganisms which cause breakdown of cellulose, nitrification, turn-over of organic matter and other biological materials may also be adversely influenced by pesticides.
Indiscriminate use of insecticides on the field crops has resulted in widespread mortality of honey bees and wild bees which are essential for pollination. Studies conducted in Punjab have revealed that application of carbaryl, endosulfan, fluvalinate and monocrotophos for bollworm control caused 94, 74, 44 and 100 per cent mortality, respectively of the bees present in cotton fields. In raya crop, quinalphos, anthio and endosulfan caused 100, 98 and 25 per cent bee mortality, respectively by direct spray.
A list of pesticides according to their toxicity to honey bees is given below:
1. Highly toxic (LD50 0.001 – 1.99 µg/bee):
ii. Calcium / Lead arsenate
2. Moderately toxic (LD50 2.0 – 10.0 µg/bee):
v. Ethyl parathion
xv. Methyl demeton
xvi. Methyl parathion
3. Relatively non-toxic (LD50 >11.0 µg/bee):
i. Bacillus thuringiensis
vii. Nuclear polyhedrosis
iii. Bordeaux mixture
vi. Cuprous oxide
III. Herbicides, defoliants and desiccants:
x. Oil sprays
Impact # 4. Pesticide Residues:
Pesticide residue is any substance or a mixture of substances in or on any substrate resulting from the use of pesticides. It has been demonstrated that less than one per cent of the pesticide applied to a crop reaches the target pests and the remaining quantity gets into different components of the environment.
Since most of the chlorinated pesticides are non-biodegradable, they leave excessive residues in various food commodities. The presence of residues of these pesticides in food commodities and other components of the environment is a matter of serious concern.
Monitoring surveys in different parts of India have revealed widespread pesticidal contamination of all types of food materials including cereals, pulses, vegetables, fruits, animal products, vegetable oils, spices, honey, milk and milk products.
Twenty per cent of the market samples of non-fatty food commodities have been found to contain residues above the legal maximum residue limits (MRLs). A broader picture of the magnitude of contamination of milk has been provided by the analysis of 458 samples collected from different parts of the country under the All India Coordinated Research Project (AICRP) on Pesticide Residues.
About 87 per cent samples were contaminated with DDT, with 43 per cent above the legal limit of 0.05 mg/kg. Similarly, 90 per cent of samples were contaminated with HCH, 78 per cent of which had total HCH above the legal limit of 0.1 mg/kg. In contrast, only 1-2 per cent of the samples of food commodities have been found to be contaminated with pesticide residues above MRL at the global level. Even human milk samples have been found to be contaminated with high levels of DDT and HCH.
Recent surveys conducted in Punjab reveal significant reduction in the residues of these insecticides in food commodities. However, lindane residues were found to be present in 53 per cent of milk above the legal limit. The presence of commonly used organophosphorus insecticides in 71 per cent samples of vegetables and 85 per cent of fruits is a matter of concern.
The population of developing countries is known to carry heavy burden of pesticides in their bodies. The principal source of these residues is believed to be the diet which contains significant quantities of the persistent pesticides. It has been estimated that the estimated dietary intake of DDT and HCH exceeds the acceptable daily intake (ADI) in India.
In addition, pesticide residues in agricultural commodities have a significant influence in the area of international trade. Commodities bearing pesticide residues above the legally permitted levels may be rejected by the importing country, thereby causing appreciable economic loss to the exporting country.
The Government of India has withdrawn the use of DDT in agriculture in 1989. In very special circumstances warranting the use of DDT in plant protection work, the State or Central Government may purchase it directly from M/s Hindustan Insecticides Ltd, to be used under expert Government supervision.
The use of DDT for the public health programme has been restricted to 10,000 metric tonnes, except in case of any major outbreak of epidemic. The manufacture and use of HCH stands totally banned with effect from 1st April, 1997. With this, the pesticide residue scenario is likely to change if this recommendation is strictly adhered to in the country.
List of pesticides not approved, withdrawn or banned in India:
1. Pesticides Refused Registration:
i. Ammonium sulphamate
ii. Azinphos ethyl
iii. Azinphos methyl
v. Calcium arsonate
x. Fentin acetate
xi. Fentin hydroxide
xii. Lead arsenate
xvi. 2, 4, 5-T
2. Pesticides Withdrawn:
iv. Nickel chloride
v. Pentachlorobenzene (PCB)
3. Pesticides banned for manufacture, import and use:
iii. Calcium cyanide
vii. Copper acetoarsenite
viii. Dibromochloropropane (DBCP)
xi. Ethyl mercury chloride
xii. Ethyl parathion
xiii. Ethylene dibromide
xv. Hexachlorocyclohexane (HCH)
xvi. Lindane (Gamma-HCH)
xvii. Maleic hydrazide
xxi. Paraquat dimethyl sulphate
xxii. Pentachloronitrobenzene (PCNB)
xxiii. Pentachlorophenol (PCP)
xxiv. Phenyl mercury acetate (PMA)
xxv. Sodium methane arsonate (MSMA)
xxiii. Trichloro acetic acid (TCA)
4. Festicide formulations banned for import, manufacture and use:
i. Carbofuran 50% SP
ii. Methomyl 12.5% L
iii. Methomyl 24% formulation
iv. Phosphamidon 85% SL.
The levels of pesticide residues can be minimized if the following precautions are followed:
i. Pesticides should be used only when it is absolutely essential. The non-chemical methods of pest control should be encouraged.
ii. Only recommended pesticides should be applied at the right time and at the prescribed dosages.
iii. Preference should be given to the use of less persistent pesticides. Never use the banned one.
iv. Restricted pesticides should be used only under specific conditions.
v. Ripe fruits and vegetables should be plucked before pesticide application. After pesticide use, the crop should be harvested only after the recommended waiting period.
vi. Pesticide residues on the produce can also be reduced by washing along with rubbing and peeling of vegetables.
List of pesticides restricted for use in India:
i. Aluminium phosphide – Pest control operations to be carried out by Govt. /Govt. organizations/undertakings/pest control operators under strict supervision of experts.
ii. Captafol – Use as foliar spray banned, to be used only as seed dresser.
iii. Cypermethrin – Cypermethrin 3% smoke generator to be used only through pest control operators, not allowed to be used by general public.
iv. Dazomet – Use not permitted on tea.
v. DDT – Use for domestic public health programme is restricted upto 10,000 metric tonnes per annum, except in case of any major outbreak of epidemic.
vi. Diazinon – Banned for use in agriculture except for household use.
vii. Fenitrothion – Use banned in agriculture except for locust control in scheduled desert area and public health.
viii. Fenthion – Use banned in agriculture except for locust control, household and public health.
ix. Methoxy ethyl mercuric chloride (MEMC) – Use banned completely except for seed treatment of potato and sugarcane.
x. Methyl bromide – May be used only by Govt./Govt. organizations/undertakings/ pest control operators under the strict supervision of experts.
xi. Methyl parathion – Use permitted only on those crops approved by Registration Committee where honey bees are not acting as pollinators.
xii. Monocrotophos – Banned for use on vegetables.
xiii. Sodium cyanide – Use restricted for fumigation of cotton bales under expert supervision.
Impact # 5. Pesticide Poisoning:
Human pesticide poisoning is a major concern in producing and using pesticides in agricultural and public health programmes. The World Health Organization has estimated that more than 3 million occupational or accidental poisoning cases occur in the world annually with about 2,20,000 deaths.
More than half of these poisoning cases and three-fourth of the documented deaths take place in the third world, even though these consume only 15 per cent of the total world pesticide output. India accounts for one third of the total pesticide poisoning cases in the world.
In the first major accident involving pesticides in India, more than 100 people died in Kerala in 1958 due to consumption of wheat flour and sugar contaminated with parathion leakage during shipment from Bombay to Cochin. More than 3000 people died due to inhaling of vapours of methyl isocyanate, leaked from a carbaryl manufacturing plant in Bhopal in 1984. More than 30,000 people were disabled to varying degrees.
The surviving population is still expressing teratogenic, mutagenic, carcinogenic and other effects involving vital body organs. Cases of blindness, cancer, diseases of liver and nervous system from pesticide poisoning have been identified in cotton growing areas of Maharashtra and Andhra Pradesh.
In case the poison is swallowed accidently, the victim should be taken immediately to the nearest physician or preferably to a hospital. It is most important that the insecticide container from which the poison was swallowed should be shown to the physician.
The medical treatment for each pesticide is given below:
1. DDT and HCH:
(i) Give universal antidote (activated charcoal 2 parts, magnesium oxide 1 part, tannic acid 1 part; 15 g of the mixture in half a glass of warm water) to absorb or neutralize poisons, to be followed by gastric lavage to evacuate stomach contents. If patient is vomiting do not give an emetic but give large amounts of warm water. If an emetic is needed give 15 g sodium chloride in warm water and repeat until vomit fluid is clear,
(ii) Give magnesium sulphate 30 g in water as a cathartic and force fluid,
(iii) Give caffeine sodium benzoate 0.5 g subcutaneously or intravenously or give hot tea or coffee drink,
(iv) Give calcium gluconate 10 ml of 10% solution intravenously for incoordination and tremors or pentobarbital sodium 0.1 g intravenously if necessary,
(v) To prevent any liver damage use diet having high carbohydrate and calcium.
(i) If ingested, give universal antidote,
(ii) Give a saline purgative but not oil laxative,
(iii) Give phenobarbital up to 0.7 g or pentobarbital 0.25-0.50 g per day to induce sedation and control convulsions,
(iv) Give calcium gluconate 10% intravenously.
(v) Oxygen therapy and artificial respiration may be needed during depression.
(i) Atropinize the patient immediately and repeat doses of 2-4 mg at 5-10 minutes intervals till the continuance of symptoms. As much as 50 mg of atropine may be given per day without any side effects,
(ii) Administer 1g of 2-pyridine-2 aldoxine-N-methyliodide (2 P.A.M.) intravenously. This should be done very slowly in 5-10 minutes,
(iii) Give gastric lavage with 5 per cent sodium bicarbonate,
(iv) Wash contaminated skin and irrigate eyes with normal saline,
(v) Maintain electrolyte balance but avoid large amounts of intravenous fluids,
(vi) Apply artificial respiration if necessary to remove upper respiratory obstruction,
(vii) Do not give morphine, theophyline or aminophyline.
4. Zinc Phosphide:
(i) Give gastric lavage with 1: 5000 potassium permanganate solutions.
(ii) Give 0.02% cupric sulphate. This may act as an emetic and produce insoluble cupric phosphide which should be removed by lavage,
(iii) Use morphine for sedation and salivation,
(iv) Give large doses of vitamin K.
5. Mercurial Fungicides:
(i) Give universal antidote as for DDT followed by gastric lavage.
(ii) Give high colonic irrigation with sodium formaldehyde sulphoxylate solution allowing small amounts to remain inside,
(iii) Inject 100-200 ml of freshly prepared 5-10% sodium formaldehyde sulphoxylate solution intravenously. For later treatment give sodium citrate 1-4 g every 4 hours by mouth,
(iv) Give calcium gulconate 10 ml of 10% solution intramuscularly or intravenously for muscle spasm.
6. Strychnine Hydrochloride:
(i) Give universal antidote followed by gastric lavage with 240 ml of potassium permanganate 1: 1000 solution leaving one fourth in the stomach,
(ii) Give pentobarbital sodium 0.1 g intravenously,
(iii) Do not use morphine or its derivatives.
(i) Keep the patient lying and warm,
(ii) Give sodium chloride 15 g in a glass of warm water, repeat until vomit fluid is clear and give 30 g of magnesium sulphate.
(iii) Give strong tea or coffee or one tablespoonful of aromatic spirit of ammonia in water.
8. Methyl Bromide:
(i) Correct the metabolic acidosia.
(ii) Give artificial respiration and guard against respiratory infection,
(iii) Inject caffeine sodium benzoate 0.5 g and if necessary epinephrine 0.5 ml 1: 1000.
(iv) Keep the mouth rinsed with 10% solution of sodium thiosulphate.
(v) When revived give hot tea or coffee.
9. Aluminium Phosphide:
(i) Take the patient immediately into air and let him lie down in a comfortable position,
(ii) Apply artificial respiration, if necessary,
(iii) Inject glucose solution.
10. Ethylene Dibromide:
(i) Give oxygen therapy, respiratory stimulants such as nikethamide or caffeine.
(ii) After acute nervous symptoms subside, give adrenergic blocking agents like dibenzyl betachloroethyl amine hydrochloride to prevent damage to liver and kidneys.
(iii) If the poison has been swallowed, give gastric lavage and saline purgatives.