Metals and grain size distributions in soil of the middle Rio Grande basin, Texas USA

 This paper deals with the problem of increased heavy metal constituents in agricultural soils due to the expanded use of fertilizers and elevated atmospheric deposition. It discusses the extent of contamination in soil and establishes an environmental monitoring program in the chosen area of concern in the southern coastal region of Texas. Grain size, pH, and metals (Cu, Cd, Zn, Pb, Ni, Ba, As, Cr, Mn, and Fe) were determined in soils of the middle Rio Grande basin. The soils were mainly of sand texture and alkaline in character. Fine sand constituted the major proportion of the soil, and clay and silt ranged from 8–30% of the soil. Correlations of metal concentrations to grain size and iron contents were performed. Metals, except Cd and Pb, gave positive to negative relationships with decreases in grain size. Silt gave no relationship with metal content while clay and silt had a positive relationship. All these metals had a positive correlation with iron in the soil. The results indicate metals are associated with coarse sand, clay, and iron hydroxides surfaces of the soil. The comparison of metal content in soil of the middle Rio Grande basin with metals from other areas of the world suggests that it is relatively uncontaminated. Received: 14 December 1998 · Accepted: 19 Jaunuary 1999