Electroanalytical methodology was employed aiming to study the behaviour of the triazinic pesticides Atrazine and Ametrine in water and sediment collected from the Mogi-Guaçu river. /

Maria Raimunda Chagas Silva

An electroanalytical methodology was employed aiming to study the behaviour of the triazinic pesticides Atrazine and Ametrine in water and sediment collected from the Mogi-Guaçu River. The square wave voltammetry (SWV) and the hanging mercury drop electrode (HMDE) were employed. In a first step, the experimental (and voltammetric) parameters were optimized in order to yield the highest current signals as well as the most well defined voltammetric profiles. The best conditions were achieved as: 0.01 mol L-1 CaCl2 as the support electrolyte at pH 3.0 and 2.3 for Ametrine and Atrazine respectively, f = 100 s-1, a = 50 mV and ?Es = 2.0 and 10.0 for Ametrine and Atrazine respectively. After this initial step, analytical curves were obtained for both pesticides. The corresponding detection (LD) and determination (LQ) limits were calculated, as well as the recovering factors, repeatability, reproducibility and sensibility for the analytical methodology, which was compared with those, obtained using the HPLC-UV. For Ametrine and Atrazine, in pure electrolyte the LD values were 2.12 and 1.16 ?g L-1, while the LQ ones were 7.06 and 3.90 ?g L-1, respectively. The same parameters, obtained with HPLC-UV yielded LD values of 2.69 and 1.37 ?g L-1 for Ametrine and Atrazine, respectively, while the LQ ones were 9.01 and 10.62 ?g L-1, respectively. In this way, it is apparent that the results obtained in this work were very close for both techniques and lower than the minimum limit allowed by the Conselho Nacional do Meio Ambiente (CONAMA) for waste water or industrial effluents, 50 ?g L-1. Moreover, they are close to the maximum allowed value for drinking water postulated by the Environmental Protection Agency (EPA USA), 3 ?g L-1 and the Agência Nacional de Vigilância Sanitária (ANVISA), 2 ?g L-1. The application of the same methodology for natural water samples yielded important parameters to establish the behaviour of pesticides, mainly concerning with its persistency. It were determined the detection and quantification limits and recovering factors by the SWV technique, for river water samples collected in three different points. For Ametrine, the LD values for electrolytes prepared with river waters, varied between 15.41 and 29.54 ?g L-1, while the values for LQ were between 51.38 and 98.49 ?g L-1. The same values for Atrazine were determined between 4.90 and 6.19 for LD and 16.36 and 20.65 for LQ. The recovering factors for Ametrine were found to be between 91.12 and 98.50% and for Atrazine between 98 and 98.8%. The photodegradations of pesticide molecules were studied by exposition to daylight of solutions containing the pesticides prepared with Milli-Q water, river water and river water containing sediments. The peak current decaying for Ametrine and Atrazine with exposition time varied accordingly the water collection point in the Mogi-Guaçu River and the nature of the pesticide. In this way, for Ametrine the percentage of decaying after 32 hours of exposition were 19.10% for Milli-Q water, 28.24% point 1, 47.62% point 2 and 30.92% point 3. For Atrazine, the respective decaying percentages of peak currents were 37.5%, 45.90%, 46.10% and 36.53% respectively. For solutions containing sediments (also collected in points 1, 2 and 3) the degradation percentage was around 30% for Ametrine, while for Atrazine the difference, around 86%. The coefficients from Freundlich adsorption isotherms presented values depending on the organic matter and clay present in the sediment samples. The pesticides presented low adsorption characteristic on the sediments. The 1/n values from Freundlich isotherm varied between 1.00 and 1.15, indicating a linear partition coefficient characteristic in all points. In this way, it is possible to associate the Kf values with the partition coefficients (Kd). The organic matter content for the three collection points varied between 5.45 and 15.15. The organic matter is found to be covering the mineral fractions of soils and sediments. These mineral fractions varied from 15.7 to 20.8%, while silt content were among 12.3 and 16.3%.

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