Studies on exposure to pesticides in Kibirigwi irrigation scheme,Kirinyaga District
Studies on household and agricultural exposure to pesticides were carried out at Kibirigwi Irrigation Scheme. A questionnaire based survey investigated the practices that farmers used in handling, storage and disposal of pesticides. A sample of sixty-five farmers was Selected from a total of 282 residing in the scheme. All fanners were interviewed guided by the format of a questionnaire covering data on farm size, education level, cropping practices, crop and household pesticide usage, animal husbandry, pesticide storage, handling, labeling and disposal, foods consumed and health ,history. It was found that pests and diseases were a major constraint to production and that 85% of the farmers used pesticides either on crops or animals. Fifty-five pesticide formulations were used or stored including organochlorines, organophosphates, synthetic pyrethroids, dithiocarbamates and other groups. It was also found that although farmers were concerned about potential adverse health effects of pesticides they took little responsibility for handling them carefully. Farmers associated various complaints with handling and spraying pesticides, including: chest pains, coughing and sneezing, colds, swellings, itchiness, stomach upsets, eye irritations, dizziness, fatigue, diarrhea and uneasiness. To investigate the general level of pesticide residues in people in the irrigation scheme, 36breastfeeding mothers residing in the scheme were sampled for milk and the milk was analyzed for organochlorine and organophosphorous pesticides. A wide range of organochlorines were detected; p'pDDE(lOO%), P-BHC(69%), y-BHC (31%), a-BHC (25%),heptachlor(17%), dieldrin(8%),ppDDT(8%), aldrin (8%), opDDT(3%), andDDD(3%). Out of twenty-nine samples analyzed for organophosphates, nine had peaks which were not identified. Studies on exposure while spraying were also carried out. Thirty-nine fanners were randomly selected from the sixty-five surveyed fanners. All exposures were conducted using an organophosphorous pesticide, dimethoate, sprayed on french beans. This was the most common crop-pesticide combination in the scheme. The dimethoate used in the study was provided to the fanners. Prior to mixing and spraying, fanners were fitted with cotton garments covering hands, legs and the back. A mask covering the nose and the mouth was also provided. After spraying, all garments were collected and analyzed for dimethoate and omethoate, a metabolite formed on oxidation of dimethoate. For dimethoate, the hands were the most contaminated (mean= 12.6 ug/cm")and the face the least (mean= 0.2 ug/crrr'). In almost all the fanners, one body part was the most contaminated; usually this was the right hand (21/39), followed by the left hand ,(10/39), the right leg (4/39), left leg (2/39) and the back (2/39). Omethoate was found in 25% of the samples (range 0,01-228 ug). The highest mean omethoate was on the left hand (6.41ug) followed by the right hand (2.77 ug). In addition, blood samples collected 3 days before and a dayafter spraying were analysed for acetycholinesterase using a pH test. There was variation in levels of acetylcholinesterase in whole blood among fanners before spraying (85-] 91 units) and after spraying (102-176 units). In eleven fanners the enzyme level was lower after spraying, in two cases the depression was above 20% and in one of these cases, the level was depressed by 26%. The means for the fanners (before = 138 units and after = 142 units) were significantly different from that of a control group sampled at Kabete Campus (mean = 239 units). In a study to investigate the enzyme levels ofKibirigwi and Kabete residents, 47 persons from Kibirigwi and 15 from Kabete Campus were sampled for serum and plasma and enzyme measurements were taken. It was found that the mean enzyme in serum in pH units for Kibirigwi residents (106.05, s.e=3.27) was significantly lower than that of Kabete Campus residents (124.1, s.e = 6.32) and for plasma, they were 91.234.(s.e. = 2.48) units and 109.86 (s.e.= 5.77) unitsfor Kibirigwi and Kabete residents respectively. Dimethoate exposure during weeding of bean crops was assessed using a sub-sample of five randomly selected farmers. Each of these farmers was advised on the date to spray his beans with dimethoate. Four and ten days after spraying, each fanner was fitted with cotton garments on the hands and legs and he reentered his field to weed for five minutes. Then the garments were collected and taken to the laboratory for analysis. It was found that the cotton garments contained a mean of 0.02 ug dimethoate\patch and O.Olug omethoate\patch. The right hand contained the most dimethoate followed by the left leg while left leg contained the most omethoate followed by the left hand. The forty fanners used in the spraying study were further recruited into a study to assess for exposure during harvesting on re-entering sprayed fields. In this study, farmers were asked to spray a synthetic pyrethroid, 5% cyperrnethrin. It had been established earlier that farmers were advised by extension staff to spray dimethoate on beans from germination to flowering stage after which they switch to the cypennethrin. Harvesting was done on two different days: on the third or fourth day and on the eleventh or twelveth day. Before the start of harvesting, each fanner was again fitted with sleeves on each arm and leggings for each leg. Each farmer would then harvest for five minutes and the garments were removed and taken to the laboratory for analysis. It was found that the garments contained residues of dimethoate, omethoate and cyperrnethrin. The mean levels were 0.19 ug/patch and 0.20 ug/patch for dimethoate and omethoate respectively. Mean levels of cypennethrin were 8.9 ug/patch. Bean samples obtained during the harvesting study were analysed for dimethoate, omethoate and cypermethrin. Mean residues detected were 0.17 ppm, 0.02 ppm and 2.09 ppm for dimethoate, omethoate and cypermethrin respectively. A study was carried out to investigate whether homes in the scheme are generally contaminated with pesticides. In each of forty randomly selected homes in the scheme, a table that is commonly used for meals was swabbed with a cheese cloth measuring 30 em by 30 em dipped in methanol. The clothes were extracted and analysed for a wide range of organophosphorous and synthetic pyrethroids. Twenty-three samples contained organophosphate pesticides. The range was 0.01-8.72 ug/crrr' of table area. These were diazinon (5/40), dimethoate (4/40), malathion (9/40), chloropyrifos (4/40), fenitrothion (1140) Among the synthetic pyrethroids, cypermethrin was detected (9! 40). The range was 2.4*10-6-5.82*10-3 ug/cm' table area. It was concluded that small scale farmers in Kibirigwi who routinely use pesticides receive substantial exposures to pesticides due to mishandling and poor storage of pesticides around the home. Exposures also occur during farm work such as mixing and spraying pesticides as well as weeding and harvesting crops that are sprayed with pesticides. Farmers may also be experiencing adverse health effects for which epidemiological investigations should be carried out in order to quantify the extent to which they occur.