Impact of pesticides on abiotic and biotic components in rice ecosystem of Kuttanadu

Abstract

Investigations were carried out in the main crop seasons of Kuttanadu during the years 2007-08 and 2008-09 to study the pesticide use pattern and extent of contamination in rice ecosystem of Kuttanadu, to assess the relative impact of conventional and IPM practices and to suggest measures for minimizing the residue hazards. The survey conducted on the pesticide use and consumption pattern in the three river catchments in Kuttanadu viz., Pampa, Manimala and Meenachil revealed that the herbicide use in Kuttanadu has increased during the past five years while a decreasing trend was noticed the case of insecticides. The consumption of pesticides in Kuttanadu ranged from 0.56 to 3.38 kg ai ha-1 with 0.3 to 1.63, 0.04 to 0.0973 and 0.09 to 0.947 kg ai -1 for herbicides, fungicides and insecticides respectively. The most popular herbicide, fungicide and insecticide were 2,4-D, hexaconazole and acephate respectively. The survey further revealed that during pesticides application, the spray men were not using any protective gadgets as per FAO guidelines while 18 per cent of the spray men were using partial protective measures. The label information on the pesticides as well as the safety guidelines for disposal of used pesticide bottles and wash water of sprayer were not followed by the majority of farmers. Health problems like head ache and dizziness, skin irritation etc were reported by the spray men. Multi Residue Methods in water, soil, paddy grains, paddy straw, duck meat and fish were developed and validated by conducting recovery studies. Five important validation parameters viz., recovery per cent age, repeatability, reproducibility, linearity, limit of detection and limit of quantification were established for eleven candidate pesticides viz., phorate, dimethoate, lindane, methyl parathion, malathion, chlorpyriphos, alpha endosulfan, hexaconazole, ediphenphos, lambda cyhalothrin and deltamethrin. These methods were found to be suitable for analyzing multiple pesticide residues in different components of Kuttanadu rice ecosystem. The estimation of residues from different components were performed using gas chromatograph (GC) and high performance liquid chromatograph (HPLC). Monitoring studies were conducted in three different river catchments in Kuttanadu. Samples of soil and water were collected from rice field, field outlet, drainage channel, stream and river at different growth stages of the crop viz., seedling stage, tillering stage, booting stage, milky stage and after the harvest. Samples of rice grains, straw, fish, mollusk, duck meat, eggs and animal meat (beef) were collected from the rice ecosystem. Data revealed that the pesticides detected included 2,4-D, chlorpyriphos, dimethoate, phorate, phorate sulphone, carbaryl, triazophos,monocrotophos, quinalphos and malathion. The pesticide residues were below detectable limit in samples of rice grains, straw, fish,mollusk, duck meat, eggs and beef collected from the rice ecosystem. Studies conducted on the impact of IPM and conventional practices on major pests, natural enemies and neutrals revealed that during the initial stages (25DAS), the pest : defender ratio was 1.031 and 1.141 in the IPM and conventional plots, while at 45 DAS the pest: defender (P:D) ratio was 1.836 and 2.118 respectively. At 65 DAS the P:D ratio was 1.763 and 3.037 respectively in IPM and conventional plots. The mean yield of paddy grains and straw were higher in IPM plots. Studies on the dissipation of pesticides being used in Kuttanadu revealed that the dissipation in field conditions was mainly influenced by the water management practices prevailing in the region. The half life of 2,4-D, chlorpyriphos, acephate, hexaconazole, moncrotophos and triazophos in soil were found to be 0.59, 2.24, 0.75, 1.36,1.23 and 2.79 days respectively. The half life of lambda cyhalothrin and methyl parathion in rice plants were 1.51 and 1.38 days respectively. The present studies revealed that appreciable quantity of pesticide residues were present in the field and field outlet while the quantity of pesticide residues present in the drainage channel was low. The pesticide residues in river and stream were below detectable limit. Estimation of dermal exposure of spray men to pesticides during application of pesticides in Kuttanadu rice ecosystem revealed that the dermal exposure of hexaconazole and triazophos per man were calculated to be 3.76 +0.116 mg man-1h-1, 6.20 +0.152 mg man-1h-1respectively. The study emphasizes the need for extensive study to be conducted at compartmental level to assess the exact route of dissipation of the pesticides applied and to arrive at the extent of environmental impact due to their application. A safe pest control strategy envisaging the use of pesticides need to be developed and recommended based on the detailed study in the ecosystem. The farmers and the workers are to be trained properly so as to follow judicious plant protection procedures to ensure Good Agricultural Practices in rice cultivation in the region without disturbing the natural eco system for sustainable development.