Fractional loading isotherm of heavy metals in an arid-zone soil

Environmental problems associated with heavy metals in agricultural soils are increasing as a result of reuse of reclaimed sewage water for irrigation, disposal of wastewater sludge and municipal refusal, application of animal waste and atmospheric fallout. The fractional loading isotherm, proposed here, depicts relationships of heavy metals between the total input and individual solid-phase fractions in contaminated soils by combining isotherm and selective sequential dissolution techniques. The redistribution and transformations of copper (Cu), chromium (Cr), nickel (Ni), and zinc (Zn) in an arid-zone soil were demonstrated through the fractional loading isotherm. The results showed that linear adsorption model better described fractional adsorption data than Freundlich model, and these metals retained in all solid-phase fractions were characterized by linear partitioning behavior under the loading levels used in the present experiments. Fractional loading isotherms not only effectively depicted the transformation direction and pathways, but also reflected effects of the nature of the metals and time period. Compared to the traditional isotherm, fractional loading isotherm is more informative in exploring the adsorption and binding mechanisms, mobility and (bio)availability of metals in the solid-phase components of contaminated soils.