Pesticide Residues in Agro-Horticultural Ecosystems
Agro-horticultural produce constitutes an essential part of human diet, and as per the recommendation of World Health Organization (WHO), there should be at least 30% fruits and vegetables in our daily diet, depending on the body weight of the person. Vegetables are the major source of vital nutrients.
But it is not heartening to know that instead of fulfilling the nutritional requirements, these fruits and vegetables carry pesticide residue harmful to the health of the consumers. Main reasons of finding the pesticide residues in these food stuffs may be because of providing shiny and fresh appearance and good color to the crop. This leads to usage of synthetic chemicals beyond the safe limits. Due to the persistent nature of some of the highly toxic pesticides, or maybe due to illegal use of prohibited/banned pesticides, these compounds have been detected in the environment worldwide.1451 So, usage of restricted pesticides is a matter of concern especially in case of vegetables. There is a general belief that these food items are much harmful if impregnated with pesticides in comparison to other food stuffs, because they are generally consumed raw or semi-cooked. Many studies support the presence of pesticide residues in vegetables, on an average, this percentage is 50%-70% in India as mentioned by I46-48!. In India, 51% of the food commodities have been detected with pesticide residues.1491 A study conducted by Charan et al. in 2010|47l revealed that 67% of total contaminated samples exceeded the maximum residue limit (MRL) values recommended by the Food and Agriculture Organization (FAO)/WHO. Another study revealed the presence of monocrotophos, chlorpyrifos, cypermethrin, and endosulfan, etc. in the vegetables.1481 According to a report, over 98% of sprayed insecticides and 95% of herbicides reached nontarget destinations such as other species, air, water, and soil.
Most of the pesticides used on crops are persistent, especially organochlorines, which persist for a longer period in the environment (substrate). The organochlorine insecticides (such as DDT and BHC) that were banned still persist in soil and contaminate both organic and conventional crop produce. Baker and co-workers observed pesticide residues in organic fruit samples. The reasons for residues in organic fruit samples were in violation of organic methods of cultivation, pesticide-contaminated water used for irrigation, or pesticide residues left in the soil, if previously used to grow conventional crops.1501
Apple fruit crop is attacked by a number of insect pests and diseases such as apple scab, San Jose scale, wooly apple aphid, fruit scrapper, defoliating beetles, and tent caterpillar. Pesticides such as chlorpyrifos, endosulfan, carbendazim, propineb, and mancozeb are applied to control these pests. After spraying/ treatment, pesticide residues get deposited on the fruits and dissipate slowly depending upon the number of factors such as physiochemical characteristics of pesticide, weather conditions, and time after treatment. Preharvest or postharvest interval or waiting period between spray and harvest is required for safe consumption of fruits. Sometimes, the produce is sent to the market immediately after spraying, and consumers unknowingly consume the product and may be badly affected. Similarly, under Indian conditions, a number of synthetic pesticides, such as deltamethrin, cypermethrin, dimethoate, quinalphos, oxydemeton methyl and carbaryl, are used to control mango crop pests such as mango hopper, mango mealy bug, and fruit fly, as well as powdery mildew and malformations. Deltamethrin at 0.002% does not require any waiting period, but cypermethrin requires 11 days of waiting period. Mango is eaten after removing the peel, but the residues on its peel also find their way into the consumer by contact. Residues of mancozeb and lindane though within the permissible limit were detected in mango fruit samples.1511 The repeated spray of bifenthrin on mango from flowering to 1 month before harvest resulted in residues that persisted on the peel for more than a month, and rate of degradation was very low.1521
The consumption of pesticide in India is low as compared to other countries, in spite of this, there is widespread contamination of food commodities with pesticide residues due to non-judicious use of pesticides. An earlier survey carried out by the Indian Council of Medical Research, New Delhi, revealed that 51% of food commodities contained pesticide residues, and out of these, 20% had pesticide residues above the MRL values, as compared to 21% contamination with only 2% of samples above the MRL on a worldwide basis.1521
Now, the scenario in India has started changing very rapidly as new pesticide molecules, whose application rate (as well as persistence in the environment) is very low, are being introduced every year. Heavy-duty pesticides have been either banned or put under restricted use. The pesticide load on the agro-horticultural ecosystem has declined as compared to the last decades. Maximum pesticides in India are used on cotton and rice. The Malwa area of Punjab, which is famous for cotton growing, has been named as the cancer belt of Punjab because pesticides have contaminated the whole environment, including groundwater, and caused cancer among its people. Out of the total pesticides used in India, only 13%—14% is used on fruits and vegetables; despite this, half of the fruits and vegetables were found contaminated with pesticide residues.1521 Pesticide residues in 10% of the samples were above the MRL value. Residues of methyl parathion, endosulfan, chlorpyrifos, Dimethyl 2,2-Dichlorovinyl Phosphate (DDVP), dimethoate, fenitrothion, monocrotophos, cypermethrin, deltamethrin, copper, etc., were above the MRL in fruits and vegetables.1521
Approaches for Pesticide Use Reduction
Since the excessive and indiscriminate use of pesticides has polluted every component of the environment, people all over the world have realized the need for pesticide reduction so as to prevent the environment from further deterioration. The use of pesticides in fruits and vegetable production has been developed in many countries and the range of pesticides is very large, most of them are chemicals used since the 1950s, quite often pesticides not licensed for use on food crops (typically cotton pesticides and consumers health).
However, it is not an easy task, as agrochemical market and crop protection knowledge are increasingly controlled by few multinationals. Today, more than 80% of worldwide pesticide sales fall to the share of only six companies. Presently, efforts are being made to reduce pesticide applications worldwide by organic and integrated pest management (IPM) approaches. IPM system relies on biological, cultural, and other less chemically intensive approaches to pest management and are best options to minimize residues in several horticultural commodities requiring cooperation between farming community and pesticide dealers while providing high quality and pest-free produce in developing countries. IPM strategies need to be concentrated on improving the cultural practices and reducing pesticide use, substituting less costly ecofriendly pesticide, continuous monitoring of the pest menace, and finally, training the extension officers/farming community to make IPM a successful event.
However, in countries like India, this alternative pest management approach to reduce pesticide use could not find much success due to poor farmer participation. An all-India survey confirmed that 34% of the respondents have no idea about IPM and only less than 5% of them follow complete IPM technology.1531 Nowadays in many states of India, government authorities are promoting natural farming and urging the farming community to adopt it in order to discourage the use of chemical pesticides.
However, IPM techniques are still characterized by a large amount of pesticide use and by the application of many different pesticides, e.g. organic apple production does not use any herbicides and applies only biological control, but fungal diseases like apple scab demand for the intensive use of sulfur and copper in organic apple orchards and copper has a negative impact on the environment. IPM techniques have not been widely implemented on many crops, e.g., wheat. There is a great need to modify “good agricultural practice” and change it to “pesticide avoidance practice” and to improve the education of farmers so as to promote organic farming or natural farming and IPM as the best alternatives for pesticides.
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