Correlating soil nutrient test lead with bioaccessible lead in highly-contaminated soils receiving lead-immobilizing amendments

Abstract

Lead (Pb) is one of the most common metals exceeding human health risk guidelines for soil concentrations worldwide. Pb bioaccessibility is known to vary depending on soil physiochemical characteristics and, as a result, in vitro and in vivo tests exist that are used to estimate bioaccessible Pb in contaminated soils. Although in vitro tests such as the relative bioaccessibility leaching procedure (RBALP) present simpler and more cost-effective risk assessments than in vivo methods, soil tests such as Mehlich-3, Modified Morgan, and ammonium bicarbonate-diethylenetriamine pentaacetate (AB-DTPA) extractions are extremely routine and even more cost-effective. Currently, there are few comparisons examining the viability of common soil nutrient tests for assessing Pb bioaccessibility in soils from contaminated sites with extremely high total Pb concentrations or for sites that have received amendments, such as those containing compost, iron, and/or phosphorus, intended to immobilize Pb. Here, we examine the correlation between RBALP Pb and Pb as determined using three commonly utilized soil tests, Mehlich-3, Modified Morgan, and AB-DTPA, in archived samples from one Pb-contaminated site receiving compost amendment (Seattle, WA, USA) and one extremely Pb-contaminated site receiving mixtures of compost, P, and Fe (Joplin, MO, USA). At both the Seattle and Joplin sites separately, RBALP Pb was significantly correlated with all three soil nutrient test values, regardless of soil amendment. However, RBALP was only significantly correlated with Modified Morgan and total Pb when examining the Joplin and Seattle data together, likely resulting from different factors controlling Pb solubility at the two sites. These findings suggest that a diverse suite of relatively inexpensive and accessible soil nutrient test methods correlate with bioaccessible Pb at a specific site, regardless of whether Pb-immobilizing amendments have been used.