Inventory of Soil Heavy Metal Concentrations in Lafayette, Louisiana Using X-ray Fluorescence Analysis

Description

The hypothesis of this study is that soil lead (Pb) contamination in urban areas of Lafayette, LA, is significantly influenced by socioeconomic factors and historical land use. The study aims to comprehensively map and analyze soil contamination, understand its socioeconomic impacts. The ultimate goal is to equip the community with critical data to mitigate heavy metal exposure and inform future urban planning and public health policies. Key Findings: - Soil Pb Concentrations: The median soil Pb concentration across all samples was 27 mg/kg, below the median geochemical background of 33 mg/kg measured in sediment samples from a small Louisiana drainage basin. However, significant variability was observed, with concentrations ranging from <8 to 6877 mg/kg. - Spatial Distribution: The highest soil Pb concentrations were found in the historic city center, with census tracts 1, 22, 8, and 9 exhibiting the highest median concentrations. These areas have a higher prevalence of older housing, which is a significant predictor of increased soil Pb contamination. - Public Areas vs. Residential Areas: Residential areas, particularly near house foundations and street sides, showed higher Pb concentrations compared to public parks and open spaces. This highlights the influence of historical use of lead-based paints and proximity to traffic emissions. The study's findings can be used to: - Inform Urban Planning: Data on Pb hotspots can guide urban planners in prioritizing soil remediation. - Public Health Policies: Health departments can use this data to focus on high-risk areas for lead exposure and implement community health interventions. - Community Engagement: By sharing these results with the community, awareness can be raised about soil contamination risks and the importance of soil testing and remediation. This study provides critical insights into the distribution of heavy metals in urban settings, emphasizing the need for preventative measures and targeted interventions to mitigate exposure risks. The comprehensive mapping and analysis of soil contamination in Lafayette, LA, serve as a model for addressing similar issues in other urban areas, contributing to the broader understanding of environmental justice and public health.

Steps to reproduce

Between 2021 and 2023, we collected 1,290 composite topsoil samples from 24 selected census tracts within Lafayette, Louisiana (USA). The goal was to comprehensively map soil heavy metal(loid) contamination and understand its health and socioeconomic impacts. Samples were collected from both public and residential areas, including high-traffic roadways, industrial zones, parks, and residential regions near house foundations, street sides, open spaces, and gardens. Typically, one representative sample with five subsamples was collected. In residential areas, five samples were collected within one meter of house foundations, five within one meter of street sides, and five from open spaces. All samples were collected from the topsoil layer (0-2.5 cm depth), which is the primary zone of contact for children and the layer where heavy metals tend to accumulate. Collected soil samples were oven-dried for 24 hours at 105 degrees Celsius, ground, and sieved through a <2 mm sieve to ensure uniformity. Laboratory analysis was performed in the Delta Urban Soils Laboratory at the University of Louisiana at Lafayette, utilizing a handheld X-ray fluorescence (XRF) analyzer in a benchtop stand (Thermo Niton XL3t 955 Ultra). The detection limit of the instrument in the Standard Reference Material (SRM) matrix is 8 mg/kg, according to the manufacturer (Thermo Scientific, 2024). Measurements resulting in a reading of less than the limit of detection were substituted with 8 mg/kg for statistical purposes. The soil samples were analyzed in low-density polyethylene bags using the XRF for 90 seconds each. Each batch included testing SRM reference standards. Results from the XRF analysis for soils were compared to U.S. National Institute of Standards and Technology (NIST) Standard Reference Materials (SRM) soils: SRM 2710a, SRM 2711a, SRM 2704, and SRM 2709a. The readings were not adjusted. In the dataset, elemental concentrations are reported by census tract to ensure the privacy and confidentiality of individual site owners. Values of 0 in the columns represent measurements below the detection limit of the XRF instrument.

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