Air Quality Criteria for Lead Volume II of II - (NEPIS)(EPA) - US ...

have included phosphoric acid (H3PO4), triple-super phosphate (TSP), phosphate rock, and/or
hydroxyapatite (HA). Various studies have combined one or more of these phosphorous sources
with or without lime, iron, and/or manganese in an attempt to enhance amendment qualities.
Most amendments are formulated to contain between 0.5 and 1.0% phosphorous by weight.
They are then either applied wet or dry and then mixed or left unmixed with the contaminated
soil. Success of phosphate amendments has been variable, and the degree of success appears to
depend on available phosphorous and the dissolution rate of the original Pb species.
A number of potentially significant problems associated with phosphate amendments have
been recognized, including both phyto- and earthworm toxicity (Ownby et al., 2005; Cao et al.,
2002; and Rusek and Marshall, 2000). Both of these toxicities are primarily associated with very
high applications of phosphorous and/or decreased soil pH. Indications of phytotoxicity are
often balanced by studies such as Zhu et al. (2004) that illustrate a 50 to 70% reduction in shoot-
root uptake of Pb in phosphate-amended soils. Additionally, the added phosphate poses the
potential risk of eutrophication of nearby waterways from soil runoff. Finally, Pb-contaminated
soils from the extractive metals industry or agricultural sites often have elevated concentrations
of arsenic. It has been shown (Impellitteri, 2005; Smith et al., 2002; Chaney and Ryan, 1994;
and Ruby et al., 1994) that the addition of phosphate to such soils would enhance arsenic
mobility (potentially moving arsenic down into the groundwater) through competitive anion
exchange. Some data (Lenoble et al., 2005) indicate that if one could amend arsenic and Pb
contaminated soils with iron(III) phosphate this problem can be mitigated, however the increased
concentrations of both phosphate and iron still exclude the application when drinking water is an
issue.
Biosolid Amendments
Historically, biosolids have been used in the restoration of coal mines (Haering et al.,
2000; Sopper, 1993). More recently, workers have demonstrated the feasibility of their use in
the restoration of mine tailings (Brown et al., 2003a), and urban soils (Brown et al., 2003b;
Farfel et al., 2005). Mine tailings are inherently difficult to remediate in that they pose numerous
obstacles to plant growth. They are most often (1) acidic; (2) high in metal content, thus prone to
phytotoxicity; (3) very low in organic content; and (4) deficient in macro- and micronutrients.
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