Avaliação temporal dos parâmetros físico-químicos da água e da concentração de metais em material particulado do Rio Grande, Barreiras, Bahia

Abstract

The objective of this study was to evaluate the physico-chemical characteristics of water and the concentration of metals associated with suspended particulate matter at different time scales (hours, days, weeks, months and seasons), considering two locations in Grand River, Barriers in the city of Bahia, Brazil. Samples were taken following a hierarchical sampling design, between September and October 2010 (dry season) and between March and April 2011 (rainy season). The pH, temperature, conductivity and dissolved oxygen were measured at sampling location. In the laboratory the water samples were filtered and the concentration of suspended particulate matter (SPM) was determined. The filters containing the MPS underwent extraction with HCl 1 mol L-1, and the metals associated with the MPS were determined by optical spectrometry with inductively coupled plasma emission (ICP OES). The values obtained for the variables studied in the two sampling sites were: pH 6.45 to 8.87, water temperature 23.3 to 28.5 ºC, electrical conductivity from 17.0 to 41.0 μS cm-1, dissolved oxygen of 6.04 to 10.5 mg L-1, MPS 2.10 to 14.7 mg L-1. For metals, the concentrations ranged between 2.34 and 4.29 mg g-1 for Al, 0.15 mg g-1 and 0.32 mg g-1 to Ba, 3.97 and 10.9 mg g-1 here, 15.1 to 97.4 mg g-1 for Fe, 0.26 and 3.32 mg g-1 to K, 0.43 and 2.49 mg g-1 for mg, and 1.10 and 3.22 mg g-1 for Mn. For variables MPS , Fe and K , variation in small time scale (days and weeks) was important, while for conductivity, pH, Ba, Ca and temperature variations on a larger scale (months and seasons) were determining the temporal distribution pattern. For most variables was observed temporal variability of natural origin, related to hydrological parameters, for potassium may have been the anthropic contribution. The use of principal component analysis and hierarchical analysis illustrated the formation of two distinct groups of samples corresponding to the dry and rainy season. The rainy season was divided into two groups corresponding to the two months of collecting this period because of the difference in the amount of rainfall during these months. There was no spatial distinction between the two sampling sites studied. With this study we observed the behavior of each variable on different time scales and the importance of nested hierarchical sampling design to select the appropriate time scale of sampling for subsequent monitoring programs environmentalist in the region.