Evaluation of a Field-Deployable Soil Lead Screening Method: LFIA Test Strips with Organic Acid Extraction Benchmarked Against XRF and ICP-MS

Lead contamination in soil remains a persistent public health concern, particularly in communities where legacy pollution from leaded gasoline, paint, and industrial activity persists. Children are disproportionately at risk due to hand-to-mouth behaviors that increase soil and dust ingestion. Current child lead poisoning prevention relies primarily on blood lead level (BLL) screening, a reactive approach that typically occurs after harmful exposure has already occurred. Proactive soil monitoring could help identify hazardous environments before children are exposed, but existing analytical methods present significant barriers. Standard approaches such as acid digestion with inductively coupled plasma mass spectrometry (ICP-MS) and handheld X-ray fluorescence (XRF) spectrometry provide accurate, regulatory-accepted measurements but require specialized equipment, trained personnel, and laboratory infrastructure that many affected communities cannot access. Lateral flow immunoassay (LFIA) test strips offer a potentially affordable and rapid alternative, but their reliability in heterogeneous environmental soil matrices had not been systematically validated prior to this work. This study developed and evaluated a low-cost soil lead testing method combining a weak organic acid extraction protocol, citric acid with sodium percarbonate as a mild oxidant, with commercially available LFIA test strips. Twenty-one environmental soil samples were collected from public parks, trails, and high-traffic areas across Chapel Hill, NC, along with a series of laboratory-spiked reference soils spanning 50–1,000 ppm. All samples were analyzed using a volume-scaled modification of EPA Method 3050B acid digestion followed by ICP-MS, with XRF providing an independent fieldrelevant benchmark. Photographs of LFIA test strips were captured and analyzed using ImageJ software to quantify band intensity as a ratio of test line to control line signal (ROI), improving reproducibility and reducing subjective interpretation error. Performance was assessed in terms of extraction percent recovery, Spearman rank correlation, coefficient of variation, and Bland-Altman agreement across methods. ICP-MS concentrations across environmental sites ranged from 4.9 to 3,022.5 ppm. XRF correlated strongly with ICP-MS across all sites (Spearman ρ > 0.93). The citric acid-sodium percarbonate extraction achieved a mean lead recovery of approximately 4.4% relative to ICP-MS, reflecting the difficulty of mobilizing lead from iron oxide-rich Piedmont soils with a mild organic acid. Despite low extraction recovery, LFIA ROI values were significantly correlated with ICP-MS concentrations (ρ = 0.758, p < 0.001) and successfully distinguished the above-threshold site from all subthreshold sites at the ROI = 1 cutoff. These findings demonstrate proof of concept for LFIA-based soil lead screening while identifying extraction optimization as the primary bottleneck for sensitivity improvement near the 200-ppm regulatory threshold. Stronger biodegradable chelating agents represent promising next steps. This work contributes to expanding access to affordable, community-deployable lead screening tools that support proactive environmental health monitoring and locally driven risk assessment, particularly in communities facing legacy contamination and limited access to conventional testing.