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Soil solution interactions may limit Pb remediation using P amendments in an urban soil
Obrycki, J., K. Scheckel, AND N. Basta. Soil solution interactions may limit Pb remediation using P amendments in an urban soil. ENVIRONMENTAL POLLUTION. Elsevier Science Ltd, New York, NY, 220(Part A):549-556, (2017). https://doi.org/10.1016/j.envpol.2016.10.002
Lead (Pb) contaminated soils are a public health concern because they can act as one of several potential exposure sources to elevate blood lead levels in children (Mielke et al., 2011; Binns et al., 2007). One potential management strategy is treating soils with phosphorus (P), specifically phosphates, to encourage formation of several types of Pb phosphates, including chloropyromorphite. These Pb phosphates are less soluble than other Pb mineral forms and could pose less of a Pb soil ingestion hazard when compared to other more soluble Pb minerals (Scheckel et al., 2013). Based on previous findings, in vitro pH conditions influence Pb solubility with lower pH conditions showing P treatments to be less effective. Additionally, in situ soil P treatments might not be effective due to soil solution chemistry interactions. These in vitro and in situ questions remain at the forefront of soil Pb research. This study used a novel approach combing PRSTM-probes (Western Ag Innovations Inc., Saskatoon, Canada), two IVBA Pb tests conducted at pH 1.5 and pH 2.5, and X-ray absorption spectroscopy to quantify changes in the soil solution and soil Pb during the remediation process. The objective was to determine the effect of varying soil pH on in vitro extractable Pb and evaluate the suitability of PRSTM-probes as indicators of how well treatments promoted increased Pb and P solubility. This information is of interest to Regional and Program Office decision makers, States, and local affected communities.
Lead (Pb) contaminated soils are a potential exposure hazard to the public. Amending soils with phosphorus (P) may reduce Pb soil hazards. Soil from Cleveland, OH containing 726 ± 14 mg Pb kg-1 was amended in a laboratory study with bone meal and triple super phosphate (TSP) at 5:1 P:Pb molar ratios. Soil was acidified, neturalized and re-acidified to encourage Pb phosphate formation. PRSTM-probes were used to evaluate changes in soil solution chemistry. Soil acidification did not decrease in vitro bioaccessible (IVBA) Pb using either a pH 1.5, 0.4 M glycine solution or a pH 2.5 solution with organic acids. PRSTM-probe data found soluble Pb increased 10-fold in acidic conditions compared to circumnetural pH conditions. In acidic conditions (pH = 3-4), TSP treated soils increased detected P 10-fold over untreated soils. Bone meal application did not increase PRSTM-probe detected P, indicating there may have been insufficient P to react with Pb. X-ray absorption spectroscopy suggested a 10% increase in pyromorphite formation for the TSP treated soil only. Treatments increased soil electrical conductivity above 16 mS /cm, potentially causing a new salinity hazard. This study used a novel approach by combining the human ingestion endpoint, PRSTM-probes, and X-ray absorption spectroscopy to evaluate treatment efficacy. PRSTM-probe data indicated potentially excess Ca relative to P across incubation steps that could have competed with Pb for soluble P. More research is needed to characterize soil solutions in Pb contaminated urban soils to identify where P treatments might be effective and when competing cations, such as Ca, Fe, and Zn may limit low rate P applications for treating Pb soils.