Pesticide use in rice cultivation in Tarapoto, Peru : usage patterns and pesticide residues in water sources

Sammanfattning: A study concerning the use of pesticides in rice cultivation was performed in the Tarapoto-region, department of San Martín, Peru. The department is the second most important rice production in Peru with a large in-put of pesticides and water consumption. Large amounts of pesticides classified by WHO as highly hazardous are used, even those that are not manufactured or recommended for rice. This study was a part of a larger interdisciplinary project. The objectives in this specific study were to identify the usage of pesticides among rice farmers in the study area, and to identify pathways for pesticides by analysing water sources for pesticide residues. Semi-structured interviews with PRA/RRA tools took place with seven voluntary rice farmers. The aim of the interviews was to understand the socio-economic conditions, found out about rice cultivations practices, the usage patterns of pesticides and to identify suitable water sampling sites. Twenty-four water samples in total were collected from irrigation canals, surface waters, groundwater, and field waters. The Solid-Phase Extraction (SPE) technique was used, and the water and filter samples were analysed on GC-ECD after extraction, and screened for 23 active ingredients. According to the interviews, the seven farmers included in the study were handling pesticides in the same way. All farmers sprayed or mixed the pesticides, and washed the backpack sprayer in irrigation canals or surface water. Six of the seven store the pesticides in their living quarters. Five farmers have had symptoms of intoxication and no one used recommended protective equipment. The most commonly used pesticides are Tamaron and Thiodan with the active substances methamidophos and endosulfan respectively. In the water samples were α- endosulfan, β-endosulfan, endosulfan-sulfate, butachlor, paration-ethyl, alpha-cypermethrin, DDT-o,p, DDE-p,p, DDD-p,p, methamidophos, carbofuran, and carbosulfan detected. Methamidophos, carbofuran and carbosulfan were detected in all samples in the study, but there concentrations could not be determined due to a contaminated blank sample. The endosulfans (α- and β-) and its degradation product endosulfan-sulfate was the second most detected compound. Butachlor was mainly detected in surface waters and alpha-cypermethrin was only detected in a special case from a field right after spraying with the substance. Parathion-ethyl was detected in the stream of Mishquiyacu and in an irrigation canal. The results from the study are fairly similar where no concentrations reach 1 µg/l, except for butachlor and alpha-cypermethrin. Pesticides bound to particle from the filters were detected despite the low content of particles. Besides methamidophos, carbofuran, carbosulfan, were also α- endosulfan, β-endosulfan, endosulfan-sulfate, alpha-cypermethrin and DDT-p,p, detected. The results show that all the farmers in the study are using the pesticides in a manner that is both unsafe and inadequate. There is no correlation between the numbers of applications per harvest and concentrations detected in the study. There are neither correlation between from which lateral the fields are irrigated, the allocation of the field and the results. The in- and out flow of water in the irrigation system is fairly unpredictable, and the area has problem with water scarcity.