SOR??O/DESSOR??O E MINERALIZA??O DO INSETICIDA ACEFATO EM SOLO

摘要

Estudou-se a adsor??o/dessor??o e mineraliza??odo inseticida organofosforado acefato aplicado emsolo tropical (argissolo) da regi?o de Campinas-SP(Brasil). Foram usadas técnicas radiométricas nasanálises do solo, do ar e da solu??o aquosa quanto àpresen?a de 14C-acefato no solo tratado. Isotermasde adsor??o e dessor??o foram obtidas tratando-se1, 2 e 4 g de solo com 10 mL de solu??o aquosa deCaCl2 0,01 mol.L-1 com 7 diferentes concentra??esde acefato. Após 24 h de agita??o para atingir oequilíbrio solo/solu??o, a adsor??o foi determinadanos extratos obtidos mediante leitura da atividade do14C-acefato por contagem de cintila??o em líquido.Os parametros, constante de adsor??o/dessor??o (K)e constante exponencial ( n) da equa??o de Freundlichforam obtidos mediante regress?o linear, além daconstante de distribui??o (Kd) e do coeficiente deadsor??o normalizado para conteúdo de carbonoorganico ( Koc). O estudo da mineraliza??o do acefatono solo foi conduzido em frascos biométricos deBartha, com 50 g de solo e 10 mL de KOH 0,2 mol.L-1como solu??o de captura de 14CO2. Acompanhou-sea cinética da degrada??o por meio de doisexperimentos com dura??o de 14 e 64 dias. Alíquotasda solu??o-armadilha e subamostras do solo, apóscombust?o, foram analisadas por contagem decintila??o em líquido. Os resultados das isotermas de adsor??o obtidas para o acefato revelaram que ocomposto é pouco retido em argissolo (as constantesKf e Kd apresentaram valores menores que 5; Koc foide 56). Os valores dos coeficientes de dessor??oindicam processo lento e n?o-completo durante operíodo do experimento. O resultado da mineraliza??oindicou que o acefato é facilmente degradado nos 10primeiros dias, com cerca de 70% do inseticidadesprendido na forma de 14CO2. Sua meia-vida nosolo apresentou os valores de 18,9 e 1.386 dias. SORPTION/DESORPTION AND MINERALIZATION OF THE INSECTICIDE ACEPHATE IN THE SOIL Abstract The sorption/desorption and mineralization of organophosphate insecticide acephate applied in tropical soil (claysoil) ofCampinas-SP region of Brazil was studied. Radioanalitic techniques were used in analysis of soil, air and aqueoussolution to verify the presence of 14C-acephate in treated soil. Adsorption and desorption isotherms were obtained bytreatment of 1, 2 and 4 g of soil with 10 mL of 0.01 mol.L-1 CaCl2 aqueous solution with 7 different concentrations ofacephate. After 24 h agitation in order to reach equilibrium of soil/solution, the adsorption was determined in the extractsobtained by means of 14acephate activity by scintillation counting in the liquid. The parameters, adsorption/desorptionconstant ( K) and the exponential constant ( n) from Freundlich equation were obtained by linear regression, besides thedistribution constant (Kd) and of the adsorption coefficient normalized for organic carbon content (Koc). The mineralizationstudy of acephate in soil was conducted in biometric flasks of Bartha, with 50 g of soil and 10 mL of KOH 0.2 mol.L-1 ascapture solution of 14CO2. The degradation kinetics was followed by two experiments of 14 and 64 days. Trappingsolutions aliquots and sub samples of soil, after combustion, were analyzed by scintillation counting in the liquid. Theresults of adsorption isotherms obtained for acephate revealed that the compound is little retained in claysoil (theconstants Kf and Kd showed values less than 5; the Koc was of 56). The desorption coefficient values indicated a slow andnot complete process during the experiment period. The mineralization result showed that acephate is easily degraded inthe 10th first days, with approximately 70% mineralization of the insecticide to 14CO2. Its half life in soil presented values of18.9 and 1.386 days.