Metales pesados en humedales de arroz en la cuenca baja del río Guayas

Abstract

In the lower basin of Guayas, more in particular in the wetland area, the rice is cultivated on 350.000 ha. An area of 100 km2, covering both sides of the tributary river Babahoyo, situated in the cantons Samborondón and Yaguachi, was selected to study the presence of heavy metals in the top soil and plants. Soil samples were collected in 26 sites, whereas plants were sampled in 5 sampling stations. The concentration of heavy metals in the top soil was related to soil edaphological properties and the concentration in the rice plants, using multivariate analysis. At each site 12 variables were measured resulting over the 26 sites in the following average values: MO 4%, clay 32,7%, loam 49,8%, sand 17,5%, pH 6,6, CE 7,9 mS m-1, metal concentration in mg kg-1 Cu 48,8, Fe 8.734, Mn 343, Zn 34, Hg not detected, Cd 0,15 y Pb 4,4. Statistical analysis revealed that 40,7% of the spatial variability in heavy metals in the top soil is explained by the first two principal components, loam and clay (CP1) and clay and cadmium (CP2). In addition, the 26 sites could be grouped in 6 distinct classes at an euclidian distance of 3,22. Based on the concentration the heavy metals in the top soil rank from high to low as follows: Fe > Mn > Cu > Zn > Pb > Cd and Hg not detected. The concentration of lead in the sites where also the lead concentration was measured in the rice plants, 5 locations in total, ranged in the top soil between 6,55-8,87 mg kg-1, in the roots between 3,30-4,40 mg kg-1, in the stems between 2,01-2,60 mg kg-1, and in the leaves between 1,80 and 2,00 mg kg-1.