Submitted to: Journal of Environmental Quality
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/15/2003
Publication Date: 3/15/2004
Citation: Brown, S.L., Chaney, R.L., Hallfrisch, J.G., Xue, Q., Ryan, J.A., Berti, W.R. 2004. In situ soil treatments to reduce the availability of lead, zinc and cadmium. Journal of Environmental Quality. 33(2):522-531. Interpretive Summary: A study was established in Joplin, MO near a former Pb smelter to test treatments to reduce the availability of Pb, Zn, and Cd in situ. Treatments included P added as triple super phosphate (TSP), H3PO4 and rock phosphate; a high Fe municipal biosolids compost, and a high Fe by-product of titanium processing (Iron-Rich). These were applied singly and in combination. Changes in bioavailability and bioaccessibility of soil Pb were measured in the lab with an in vitro test and a feeding study with weanling rats. Field measures included fescue (Festuca arundinaceae cv. KY31) metal levels and in vitro extracts. Reductions were observed across all measurement parameters but were not consistent. In the feeding study, the 1% P as H3PO4 treatment resulted in an average decrease of 26% in rats (across all organs) Pb concentration compared with the untreated control soil. The 2.5%Fe +1%P as TSP and 10% Compost treatments showed an equivalent or greater reduction in Pb (39 and 26%, respectively). The 3.2%P as TSP and the 1%P as H3PO4 treatments showed the most pronounced reduction in in vitro extractable Pb from field samples (59%). However, the in vitro extraction (pH 2.2) did not reflect decreases observed in the in vivo study with the 1% H3PO4 showing a 66% reduction, Compost 39%, and the 2.5%Fe+1%P a 50% reduction. The in vitro (pH 1.5) run on field samples showed no reduction in the Compost or Fe treatments. The most effective treatments at reducing plant and in vitro Pb as well as plant Zn and Cd was TSP applied at 3.2% P per dry weight soil and H3PO4 applied at 1% P per dry weight soil. These results indicate that it is possible to reduce the bioavailability of Pb, Cd, and Zn in field and lab studies but that response across different environments, measurements and elements may vary.
Technical Abstract: Soil lead can comprise risk to young children who ingest soil. A large cooperative field test was conducted to investigate promising amendments to achieve in situ remediation of soil Pb risk. The test was conducted at Joplin, MO, where a smelter contaminated yard soils. A vacant lot was obtained for testing and replicated plots established with several phosphate amendments, biosolids, iron-rich byproduct plus phosphate, and combination of P with composted biosolids or iron-rich. Tall fescue was extablished on all plots after the treatments were installed, incubated, and limestone applied to adjust soils to pH about 7 to minimize Zn and Cd (co-contaminants with Pb) phytoavailability. All treatments reduced uptake of Pb by tall fescue, and the treatments became more effective over several years of the study. Feeding studies with rats showed reduction in soil Pb bioavailability which differed among treatments; bioavailability declined somewhat over years. In vitro bioaccessible soil Pb (a chemical extraction proportional to soil Pb bioavailability) was measured at pH 1.5 (original pH recommended for use), or at pH 2.2. At pH 1.5, the method did not identify significant reductions in soil Pb bioavailability measured with the rats. Bioaccessible Pb measured at pH 2.5 was correlated with the results from rat feeding. Overall the field test has confirmed that addition of phosphate, high Fe biosolids compost, or hydrous Fe oxide plus phosphate can each reduce soil Pb bioavailability to animals. Further, plant availability of soil Pb, Zn and Cd were all reduced by the treatments, and grass cover was effective throughout the test. Method is inexpensive, easy to conduct, and provides protection to families.