Avaliação de hidrocarbonetos policíclicos aromáticos e metais (Cu, Cd, Pb e Zn) em sedimentos do rio Paraibuna, Juiz de Fora, MG

Abstract

Sediments have a great environmental importance due to their ability to adsorb and accumulate substances such as polycyclic aromatic hydrocarbons (PAHs) and metals, which can be later redissolved to the water column or absorbed by the biota. In the present study, concentration levels of PAH and Cu, Cd, Pb and Zn metals were determined at surface sediments of the Paraibuna river, Juiz de Fora (MG). A method for the determination of PAHs at river sediments applying an ultrasound assisted extraction followed by GC/MS quantification, was proposed. Box Behnken 33 planning, with triplicates at the central point, was delineated in order to optimize the extraction process of PAHs, in which the proportion of n-hexane (n-HEX) and dichloromethane (DCM) at the solvents mixture, this mixture volume and sonication time were chosen as variables. The optimum extraction conditions, selected through a response surface methodology study, consisted in a three steps sonication for 15 minutes using a 10 mL solvent mixture, composed by n-HEX/DCM (55:45). This condition was evaluated by means of the recovery percentage obtained for the extraction of a spiked blank and sample using as solvent mixture n-HEX/DCM (55:45) and n-HEX/acetone (55:45). The n-HEX/acetone (55:45) mixture was chosen since it presented a lower relative standard deviation and a greater efficiency at the extraction process.Detection and quantitation limits values ranged from 0.005 mg L-1 to 0.015 mg L-1 and from 0.016 to 0.050 mg L-1, respectively.Thus, the extraction and quantification methodologies were then applied for PAHs at Paraibuna’s river sediment samples. The total PAH concentrations ranged from 10.40 to 246.36 ng g-1 of dry weight, and priority PAH concentrations ranged from 7.34 to 187.56 ng g-1 of dry weight. Flu/ Flu+Pyr and InP/InP+BghiP relationship indicated an introduction by pyrolytic origin, either by combustion of fossil fuel or biomass. For metals determination, sediment samples were treated by the 3050B extraction methodology, described by EPA, and then analyzed by F AAS. Concentration ranges between 4.95 to 40.20 µg g-1 of dry weight for Cu, 1.84 to 4.99 µg g-1 of dry weight for Cd, 4.41 to 40.04 µg g-1 of dry weight for Pb and 39.35 to 344.27 µg g-1 of dry weight for Zn, were obtained. Some Paraibuna river sediment samples showed Zn and Cd concentrations above the established values by the Canadian Environmental Protection Agency, with some probable adverse effects to the biota (PEL).