Residues of cypermethrin, dimethoate and metalaxyl in locally harvested carrots

Abstract

Importation of pesticides in Malta during 1997 was of over 220,000 kg and over 20,000L, indicating the high use of pesticides on crops that are grown locally and most of which are also consumed locally. The study had principally two aims. One of them was the participation in an interlaboratory study within the European Union in order to validate and extraction method. This study was organized by the European Commission while Central Science Laboratory in England acted as the co-ordinating laboratory. Excluding Malta 25 laboratories participated in this study. Although Malta is not a member of the European Union, the co-ordinating laboratory still gave us this opportunity to participate in this study. For this part of the study 6 pesticides were studied: chlorfenvinphos, cypermethrin, dimethoate, omethoate, metalaxyl and triazophos. The presence or absence of 3 of these pesticides in locally harvested carrots was then studied. These 3 pesticides were: cypermethrin, dimethoate and metalaxyl. This since in Malta importation of chlorfenvinphos is banned, while that of omethoate and triazophos is restricted. This however does not exclude the possibility that such pesticides could be present in locally produced carrots. In fact this same study could be continued and testing for these other three pesticides will be carried out. The results obtained in testing for pesticide residues can be influenced by a number of factors including: training of scientific and technical personnel, working state of the equipment used which is of high technology, and degree of purity of solvents and reagents. For the study, certified pesticide standards were used and all other reagents and solvents were purchased from reliable suppliers ensuring on labels that such products could be used for analysis involving the use of equipment of high technology. The instrumentation employed in this study for both the validation of the extraction method and the final determination of presence or absence of pesticide residues in locally produced carrots was the gas chromatograph with an electron capture detector. It should be noted here that the carrot samples were collected from various supermarkets and vegetable hawkers all over Malta and Gozo. Gozo - Marsalforn, Victoria, Xlendi, Sannat and Xewkija. Malta - Mellieha, Burmarrad, Mosta, Birkirkara, Rabat, Qormi, Msida, Valletta, Zabbar, Marsaxlokk, Birzebbugia. Pesticide residue analysis is not an easy task involving a number of steps before eventually concentration of pesticide in a crop is found. Such steps include: • preparation of stock solutions; • preparation of working stock solutions; • preparation of standard solutions; • preparation of spiked solutions; • injecting of standard solutions in gas chromatograph so that peak area for each pesticide is determined and thus calibration curves for each one could be prepared; • injecting once again with the spiked solutions. Such solutions would have present a representative sample of the homogenised crop besides that particular pesticide whose concentration is being assessed; • from peak areas, that are given automatically by the gas chromatograph for the spiked solutions, calibration curves are prepared; • comparison of calibration curves for standard and spiked solutions for percentage recovery. From the results obtained it can be concluded that percentage recovery of the pesticides was not 100% as was expected. This could have been due to various experimental errors including: • losses while performing the injections which were performed manually; • although same solution was injected more than once, no replications were done; • there was not enough time to repeat the whole experiment; • the extraction method is still in its validation stage in the European Union; • studies of recovery are also still in their validation stage in the European Union. Regarding the second aim, none of the 3 pesticides studied were found to be present in the locally harvested carrot samples. Keeping in mind the quantities of pesticides imported locally; the ambitions of our local farmers to export locally grown crops to countries within the European Union; and the tourist industry; studies similar to this one should be further encouraged. Such studies will not only help farmers in regulating amounts of pesticides used, but would also ensure a better life quality to all concerned.