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 atmo spheric deposition. It discusses the extent of contamination in soil and es tablishes an environmental monitoring program in the chosen area of concern in the southern coastal region of Texas. Grain size, pH, and metals (Cu, C d, Zn, Pb, Ni, Ba, As, Cr, Mn, and Pe) were determined in soils of the midd le Rio Grande basin. The sails 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 concentratio ns to grain size and iron contents were performed. Metals, except Cd and Pb , gave positive to negative relationships with decreases in grain size. Sil t gave no relationship with metal content while clay and silt had a positiv e relationship. All these metals had a positive correlation with iron in th e soil. The results indicate metals are associated with coarse sand, clay, and iron hydroxides surfaces of the soil. The comparison of metal content i n soil of the middle Rio Grande basin with metals from other areas of the w orld suggests that it is relatively uncontaminated. areas of the world sugg ests that it is relatively uncontaminated.