Studies on the removal of pesticide residues from various vegetables through traditional processing methods

Abstract

Pesticides are used in agriculture to safe guard the crops and new vegetation/plantation against pests, diseases, and weeds. Vegetable crops are usually attacked by insect pests round the year from seedling stage up to maturity of the crop because of their attractive colors. The insects, pests cause high damage to the production. It is observed that these pests destroy nearly half of the world's agricultural crops which not only affects the yield and economy but also leads to lesser economic returns to farmers coupled with decreased supply of food to huge population. It therefore warrants to enhance the yield of crops to feed the ever growing population particularly in developing countries.

The study was conducted in two parts. In the first part, the selection of pesticides was carried out through the survey conducted in six districts of lower Sindh to assess the knowledge, perception and use of pesticides amongst farmers. It was observed that farmers were using 27 different types of pesticides belonging to different groups. Out of these, six were most commonly and frequently used. It was further observed that farmers were not applying pesticides in recommended doses, time, frequency, safety interval after last spray and were also not following safety measures during pesticides spray on the crops.

Sixty dealers (10 from each district) were allowed to participate in the survey. Questions were asked from the pesticide dealers as per structured questionnaire and it was noticed that 2 dealers of total (3.34%) were postgraduate, 34 (56.66%) were graduate and 15 dealers (25%) had education up to secondary level and 9 dealers (15%) had education up to middle. Majority of the pesticide dealers were not agricultural graduates but these dealers got briefings periodically from pesticide sales representatives of different companies. These sales representatives are competent agriculture graduates with specialization in plant protection, entomology, plant pathology or agronomy. Pesticide companies and other agricultural representatives periodically visited pesticide dealers in different areas explained briefly and provided literature in the form of leaflets and brochures mostly in the local language (Sindhi/Urdu) and/or English of pesticide products.

Twenty seven dealers (45%) of them on a quarry replied that they did nothing for the use or reuse of the expired products, whereas 19 dealers (31.67%) returned the pesticides to the respective companies after expiry date, 3 dealers (5%) of them threw them away, whereas 11dealers (18.33%) buried them in the soil. It was also observed that 66.67% farmers demanded the pesticides most frequently in the Kharif season (summer) than in Rabi season (winter) i.e., 33.33% from the pesticide dealers. About 22 dealers explained that there is a high demand of pesticides on cauliflower crop (36.67%) followed by brinjal (25%), tomato (16.67%), bitter gourd (11.66%) and onion (10%). Pesticide dealers further explained that most of the farmers demanded endosulfan (35%) followed by imidaclopride (21.67%), bifenthrin (20%), prefenofos (11.67%), emamectin benzoate (8.33%) and diafenthiuron (3.33%).

Five (8.33%) famers brought slips for the pesticide purchase, while 95 (91.67% pesticides were purchased on the recommendation of pesticide dealers. Fifty seven (95%) dealers briefly explained the use of pesticides to the farmer regarding pesticide usage and 34 (56.67%) dealers informed the farmers regarding residual effects of pesticides.

The spray of pesticide depended upon many factors such as the price of vegetable in the market, advice from the fellow farmers, pesticide sales representative, etc. 96 (80%) of farmers had their own decision to spray, but 4 (3.33%) farmers have other sources such as Neighbors, Agriculture extension workers, Agriculture Research and Pesticides agents.

The time of spray by 49 farmers (40.83%) was in the morning, whereas 71 farmers (59.17%) sprayed in the evening. Only 5 farmers (4.17%) used the protective cloths in winter but in summer they did not use because of high temperature and high moisture and 115 farmers (95.83%) farmers did not use the protective clothes & tools in lower Sindh. They put off shoes deliberately while spraying. For increasing the effect of pesticides, farmers also used the mixed pesticides as suggested to them by different sources such as Agriculture extension department, Pesticides dealer or by their own decision. About 118 (98.33%) farmers had used the mixed pesticides on their crop in which 92 farmers (76.67%) farmers’ source was pesticides dealer. Answers about interval between pesticide application and harvest depended on farmer’s need of vegetables not on the kind of the pesticides.

In the second part, in order to reduce the risk of vegetables poisoning due to residues, the study was conducted on farmer’s field to reduce the pesticide residues from vegetables through various traditional processing being practiced at various homes of Sindh province of Pakistan. Five vegetables i.e. onion, cauliflower, bitter gourd, brinjal and tomato were grown on farmers field and were sprayed with different insecticides/pesticides at recommended dosages. Onion was harvested one week after the application of pesticides, while cauliflower, bitter gourd, tomato and brinjal were harvested one day after the spray of pesticides. After harvesting, the samples were packed in polythene bags, labeled and brought to the laboratory of Institute of Food Sciences and Technology for traditional processing such as plain water washing, detergent washing, blanching, salt washing, drying under sun and in cabinet dehydrator and boiling/frying etc. The samples were further processed for extraction, clean up and analyses. The results revealed that some traditional processing methods were mildly effective and others were highly effective. Plain water washing reduced the residues up to 45% whereas, detergent water washing deceased it up to 50%. The blanching treatment of vegetable further removed the pesticide residues up to 60%. The washing was followed by sun drying, drying in cabinet and dehydrator and/or frying which reduced the pesticide residues by more than 80% from all the five vegetables and were found highly effective. The results further suggest that every traditional method played its significant role in reducing the residues depending upon the kind of vegetables and the type and nature of pesticides.

Commercially produced samples of all the vegetables taken from Hyderabad market were found contaminated with residues of more than one pesticide and most of the samples contained residues above their respective MRLs.

It is therefore, concluded from the study that traditional/house hold processing methods play a significant role in reducing the insecticides/pesticides. However, indiscriminate use of pesticides and lack of good agricultural practices lead to residue problems in vegetables and the consumption of pesticide residue contaminated vegetables may cause severe health haz