Title: Simplified urban soil bioaccessible Pb test correlated with bioavailability of soil-Pb to humans in untreated and phosphate-treated Joplin soils Authors
Submitted to: International Symposium on Biogeochemistry of Trace Elements Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: March 11, 2011
Publication Date: July 4, 2011
Citation: Chaney, R.L., Zia, M.H., Codling, E.E. 2011. Simplified urban soil bioaccessible Pb test correlated with bioavailability of soil-Pb to humans in untreated and phosphate-treated Joplin soils. International Symposium on Biogeochemistry of Trace Elements Proceedings. On disk. Technical Abstract: Urban soils are commonly contaminated with Pb from multiple sources. Total Pb levels commonly exceed 500 mg/kg in center city soils, ranging to above 10,000 where paint residue was incorporated in soils. Many persons seek to grow garden crops in cities, but obtaining useful soil analyses needed to protect themselves against excessive Pb is difficult and expensive. Garden crop accumulation of Pb is less important risk to children than soil ingestion, so the bioavailable soil Pb should be considered in risk assessment rather than total Pb. Chemical extraction methods (bioaccessibility tests) may be used in place of bioavailability tests if the results of the extraction are well correlated with bioavailable soil Pb. However, the Drexler-Brattin bioaccessibility extraction (adopted by US-EPA) run at pH 1.5 strongly underestimated the reduction in soil Pb bioavailability to humans due to phosphate remediation treatment in the Joplin field test (Ryan et al., 2004); but when run at pH 2.5 gave results much closer to bioavailability. The present work sought to develop an extraction test which was inexpensive, simple, reproducible, and which could use inexpensive analytical instruments, but which was well related to the human bioavailability of Pb in the Joplin untreated and treated soils. The method uses pH 2.5, 0.38 M glycine·HCl, room temperature (25°C), with 5 g of air dried soil sieved < 2 mm with 50 mL of extractant, shaken for 2 hr at 100 cycles/min, and filtered before analysis. If levels are high enough to require concern about soil Pb, dissolved Pb may be easily measured by flame atomic absorption rather than more expensive instrumentation. Using the developed Urban Soil Bioaccessible Lead Test (USBLT), 30 urban vegetable garden and orchard soils were tested: Bioaccessible Pb was 10.0±2.2% of total Pb for the garden soils, far lower than the 30% absolute soil Pb bioavailability used in the IEUBK model of US-EPA which was used to develop present US standards for soil Pb in bare play areas near housing (400 mg kg-1). It is likely that repeated fertilizer applications (NPK, manure, compost) have reduced the bioavailability of garden soil Pb and that gardening comprises far lower risk to urban citizens than previously assumed.