Chemical Immobilization of Lead, Zinc, and Cadmium in Smelter‐Contaminated Soils Using Biosolids and Rock Phosphate

Abstract

Chemical immobilization, an in situ remediation method where inexpensive chemicals are used to reduce contaminant solubility in contaminated soil, has gained attention. We investigated the effectiveness of lime-stabilized biosolid (LSB), N-Viro Soil (NV), rock phosphate (RP), and anaerobic biosolid (AB) to reduce extractability and plant and gastrointestinal (GI) bioavailability in three Cd-, Pb-, and Zn-contaminated soils from smelter sites. Treated (100 g kg(-1) soil) and control soils were incubated at 27 degrees C and -0.033 MPa (0.33 bar) water content for 90 d. The effect of soil treatment on metal extractability was evaluated by sequential extraction, on phytoavailability by a lettuce bioassay (Lactuca sativa L.), on human GI availability of Pb from soil ingestion by the Physiologically Based Extraction Test. The largest reductions in metal extractability and phytoavailability were from alkaline organic treatments (LSB and NV). Phytotoxic Zn [1188 mg Zn kg(-1) extracted with 0.5 M Ca(NO3)2] in Blackwell soil (disturbed soil) was reduced by LSB, NV, and RP to 166, 25, and 784 mg Zn kg(-1), respectively. Rock phosphate was the only treatment that reduced GI-available Pb in both gastric and intestinal solutions, 23 and 92%, respectively. Alkaline organic treatments (LSB, NV) decreases Cd transmission through the food chain pathway, whereas rock phosphate decreases risk from exposure to Pb via the soil ingestion pathway. Alkaline organic treatments can reduce human exposure to Cd and Pb by reducing Zn phytotoxicity and revegetation of contaminated sites.

Immobilization of lead in shooting range soils by means of cement, quicklime, and phosphate amendments

“…Chemical-based S/S approach is based on the formation of thermodynamically stable and insoluble precipitate end-products with the contaminants. More effective chemical additives include phosphates and Fe-Mn oxides (Ma et al 1995, Hettiarachchi et al 2000, Basta et al 2001, Seaman et al 2001, Cao et al 2002. Phosphate has been proven to be effective in immobilizing Pb from labile soil Pb forms via formation of lead phosphate compounds such as pyromorphite-like minerals (Pb 5 (PO 4 ) 3 X, X=F, Cl, OH) by scavenging Pb from soluble Pb compounds such as cerussite (PbCO 3 ) and litharge (PbO) (Zhang & Ryan 1999, Cao et al 2002, Scheckel & Ryan 2004.…”

Mechanisms of lead, copper, and zinc retention by phosphate rock

“…Significant effort has been made to evaluate the effec tiveness of phosphate on in situ remediation of contam inated waters and soils (Basta et al, 2001;Cotter-Howells and Caporn, 1996;Hettiarachchi et al, 2000;Ma et al, 1995;Yang et al, 2001). Phosphate minerals, i.e.…”

Effect of Sludge Amendment on Remediation of Metal Contaminated Soils

“…Basta et al [20] showed the effectiveness of lime-stabilized biosolids at reducing the extractability and bioavailability of Cd, Pb and Zn from smelter-contaminated soils, and indicated that alkaline organic treatments reduced metal extractability and phytoavailability.…”