Estudo dos parâmetros de otimização e aplicação da micro-extração em fase sólida para determinação de agrotóxicos organoclorados em alface (Lactuva sativa L.) e água

Abstract

Predatory practice of agricultural production has led to the accumulation of agricultural pesticides in the environment, contaminating the ground, water resources and even virgin areas, those that never received application agrochemicals. Although many of the carcinogenic, toxic agrochemicals, considered as highly persistent pollutants have already been forbidden in Brazil (DDT, BHC, etc), there are others, less persistent, that can be degraded into others, as toxic, or even more toxic. Currently, the quality of all the foodstuffs is defined not only by its nutritional composition and state of conservation, but also by the levels of residual substances, toxic to man. It is important to develop and apply the philosophy of the good agronomic practices; environmental education; consumer education; legislation with strong repression for the infractors; routine fiscal analyses by competent official agencies, control of levels of the maximum residual limits (MRL) in foodstuffs and water for human consumption. With this end, a simple methodology, efficient and economic, was developed, based in the use of solid phase micro-extraction (SPME) for determination of pesticides (Lindane®, Aldrin®, DDE, Dieldrin®, TDE and Mirex®) in samples of water and of lettuce, using gas chromatography with electron capture detector (GC-ECD). This method can be applied in small volumes of sample (ca. 1,0 mL), it does no need the use of solvents and, in the multi-residue analysis there is no need to modify the ionic force or pH of the matrix. Of the analyzed samples, after screening, the organochlorine pesticide DDE was found only in the samples of lettuce, in the range 29 – 262 ng/g, with RSD average of 13 %. The accuracy of the quantification of DDE in the samples of lettuce was tested by % of recovery and comparison with an official method for determination of pesticides, when recoveries in the range 93 – 96 % with average RSD of 14 % were obtained. Using ELL extraction (official method) a value for the DDE in the four samples of lettuce in the band of 25 – 240 ng/g was found, with average RSD of 14 %, and recovery between 92 and 98 %, with RSD average of 12 %. The two methods do not differ statistically, to a level of confidence of 95 %. The presence of DDE as contaminant can be related with the application of DDT instead of DDE itself, since DDT was used world-wide in wide scale up to 1985, when its use was forbidden in Brazil. The results obtained for the lettuce samples are indicative of the environmental persistence of organochlorine pesticides