Water : soil ratio influences aqueous phase chemistry of indigenous copper and zinc in soils

Abstract

The effect of dilution on the composition of soil solutions of 8 contrasting soils ranging in pH from 5·3 to 8·8 with reference to zinc (Zn) and copper (Cu) was studied. Soil samples were equilibrated with water in various water:soil ratios for 24 h. Equilibrium solutions were extracted and analysed for dissolved organic carbon (DOC), and major and minor elements. The separation of the soil solution at field capacity (FC) was carried out by a drainage method. Although the concentration of ions decreased upon dilution, the total quantity of sodium (Na), potassium (K), Zn, Cu, and DOC extracted per unit of soil weight increased. In contrast, the total quantity of Ca and Mg decreased in most soils. The ratio of Zn and Cu to Ca correlated to dilution level, whereas the ratio of Zn to monovalent cations decreased in low pH soils. The relationship between the quantity of Zn and Cu at different levels of the water : soil ratio in the soils studied showed that the concentration of these trace metals at FC soil moisture can be estimated from the soil extract. Increases in soil moisture content led to a marked change in the ion-pair, free hydrated metal concentrations, and complexation. Log Zn2+ was linearly related to solution pH. Zinc solubility was not consistent with published solubilities of any common minerals. Also, Zn solubility in alkaline soils tended to be higher than reported values in the literature, indicating that soluble metal–organic ligand complexation was underestimated in these soils. The relationship between pH and log Zn2+ was affected by dilution in several ways.

Fate of some heavy metals in soils: a review

“…Basta et al (1993) recorded that greater retention and lower solubility of metal cations occurred at high soil pH. Both the concentration of trace metals and their speciation vary significantly, with the composition of soil solution and the amount of moisture content in the soil (Fotovat et al, 1997).…”

Soil factors affecting solubility and mobility of zinc in contaminated soils

“…It helps adsorb Zn to the solid phase, therefore decreasing concentrations in soil solutions. And inversely, higher soil organic matter content will also generate higher dissolved organic carbon content, and this would help complex Zn and lead to higher soil solution concentrations of Zn (Cavallaro and McBride 1984;Bar-Tal et al 1988;Fotovat et al 1997;Stephan et al 2008). …”

“…In soil, zinc forms complexes with organic matter quite quickly, and this has a holding back effect on the activity of Zn 2? in the soil solution (Cavallaro and McBride 1984;Bar-Tal et al 1988;Fotovat et al 1997;Hernandez-Soriano and Jimenez-Lopez 2012). The concentration of Zn 2?…”

Bioaccumulation of heavy metals and two organochlorine pesticides (DDT and BHC) in crops irrigated with secondary treated waste water

“…Even after along time of this ban people kept using this pesticide because of its strong action, lack of awareness, easy availability. Soil characteristics such as pH, organic matter, porosity determines availability of elements to plants by controlling the speciation, temporary binding by particle surfaces (adsorptiondesorption processes), precipitation reactions and availability in soil (Fotovat et al 1997). Soil characteristics are among the most important factors affecting the heavy metal content of plants (Appel and Ma 2002;Itanna 2002).…”