Studies of purity of some pesticides applied in vegetables and fishes

Abstract

Human health is under threat due to the exposure to toxic chemicals used either in agricultural or industrial sectors. The use of toxic chemicals both in agriculture and aquaculture gradually increasing due to increasing food demand. Vegetables and fishes are important food stuff for local consumption as well as to earn foreign currency. The presence of residual amounts of these chemicals above the maximum residue limit (MRL) in food products is hazardous for local consumption as well as for export. Vegetables are being consumed by the local people of Bangladesh almost every day. Pesticides are being used to protect the crops and there is no guide line about the safe harvesting period of the crops and MRL values for any pesticides in Bangladesh. Purity of selected commercial pesticides is found 87.01% which was applied in experimental field. Calibration curves of certified standard and commercial cypermethrin were constructed. The curves followed linear relationship with good correlation coefficients (R2>0.95). Studies of dissipation pattern of pesticides in growing crops is necessary which will give a safe harvesting period as well as MRL value after final application. Dissipation patterns of cypermethrin on bean and cauliflower at recommended dose were studied after the applications in the respective experimental fields. Recoveries were found to be 105.95-106.89%, 75.71-82.54% for bean and cauliflower respectively. Amount of cypermethrin in edible part of bean and cauliflower was found to be below MRL (0.5 ppm) and (1.0ppm) on 10 and 7 days after application at the recommended dose respectively. Monitoring system of POPs including DDTs in Bangladesh is very poor and hardly any expertise is available in the country. Our preliminary studies DDTs were found very poor amount in different kind of experimental fish samples like Gulsha and Taki fish. Due to bioaccumulation and biomagnification it is found in detected level, though it is far away of MRL (5.0 ppm for total DDT in fish) of Maximum Residue Limit (MRL) suggested by FAO/WHO (Codex, 1993). The calibration curves were linear over the range of the tested concentrations as shown by the fact that the correlation coefficients (r2) for the linearity range were 0.995-0.999. The detection limit was found to be 5ppb for DDTs and the quantification limit was 6.5ppb. Recoveries were found (70-130%); this is acceptable for fish samples according to standard methodology. Taki fish was found to contain detectable amount of residual targeted pesticides DDTs (8.415 ppb in digestive tract, 4.037 ppb in gill, 56.442 ppb in gonad and 23.146 ppb in muscle) and (64.212 ppb in digestive tract, 75.234 ppb in gill, 119.819 ppb in gonad and 45.839 ppb in muscle) for Gulsha fish. Gonad is the main target of DDT and its metabolites. Because highest amount of DDT found in gonad 56.442 ppb, 119.819 ppb for taki and gulsha respectively. No detectable amount of residues of DDTs was found in liver of both experimental fishes.