Relative bioaccessibility of Pb-based paint in soil

Area of Science:

• Environmental Science
• Toxicology
• Public Health

Background:

• Lead (Pb) in soil is a significant public health concern, particularly for children.
• Old lead-based paint is a primary source of soil lead contamination in residential areas.
• The health risks of soil lead depend on paint quantity, composition, and aging.

Purpose of the Study:

• To assess the relative bioavailability (RBA) of lead (Pb) in different types of lead-bearing paint.
• To investigate how mixing paint with soil and phosphate amendments affects Pb RBA.

Main Methods:

• Analyzed thirteen lead-bearing paint samples, including <100 µm and 100-250 µm fractions.
• Used simulated gastric fluid (SGF) at pH 1.5 for RBA extraction (2-hour agitation).
• Examined paint and residues using SEM/EDX, XRD, and measured Pb concentration via AAS.

Main Results:

• Lead mobilization was approximately tenfold lower in paint-soil mixes compared to paint-only samples.
• The difference in Pb extracted from paint-soil versus paint-soil-phosphate mixes was minimal.
• Observed PbCl precipitate in paint-soil residues and PbClP phases in paint-soil-apatite II residues.

Conclusions:

• Soil mixing significantly reduces extractable lead from paint, potentially altering RBA assessments.
• Phosphate amendments had a minimal impact on lead extraction in this study.
• Secondary phase precipitation (PbCl, PbClP) during extraction may lead to under-reporting of bioavailable lead.