Transfer functions simulating the coprecipitation of trace elements in unsaturated soils

Transfer functions describing the coprecipitation of various trace elements (TE; As, Cd, Co, Cu, Cr, Mo, Ni, Pb, Zn), precipitating with iron(oxihydr)oxides from an aqueous solution, were developed and implemented in the computer model ‘Seeper’. ‘Seeper’ was developed to predict the progression of the concentrations of inorganic pollutants in unsaturated soils underneath contaminated areas and to evaluate the prospective contamination of the groundwater. Transfer functions provide a straight and simple relation between the coprecipitation of TE and easy to obtain standard soil parameters, without excessive repercussions on the usability and computation time of the model. Laboratory experiments were conducted to quantify coprecipitation in solutions with pH values ranging from 5 to 12 and containing various iron and TE concentrations. For the examined TE, the transfer functions describe the coprecipitated fraction as a function of the pH value and the concentration ratio between precipitated iron and a TE. The transfer functions yielded a good prediction of cadmium, cobalt, copper, molybdenum, nickel, and zinc (R ² from 0.73 to 0.83). As for arsenic, chromium, and lead the correlation was not as good albeit a significant influence of precipitating iron on the mobility of these elements was observed and represented in the corresponding transfer functions.