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Unmarked glass laboratory vessels, a closed notebook, sampling spoon and empty specimen dish illustrating Lard and colleagues 2026 source research context.

Changes in community members' toenail metal concentrations after cessation of nearby open-burn thermal treatment of munitions waste

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This paper measured 22 metals by inductively coupled plasma optical emission spectrometry (ICP-OES) in toenail samples collected from residents of Coifax, Louisiana, before and after the cessation of an open-burn/open-detonation (OB/OD) hazardous waste thermal treatment facility that had operated adjacent to the community until December 2023. The facility processed fireworks, propellants, and military waste including Superfund site materials. Statistically significant decreases in toenail nickel, lead, and molybdenum concentrations were observed after the facility ceased operating, providing evidence that OB/OD operations had contributed to elevated community metal body burden.

Key numbers

  • Sampling periods: 2023-2024 (during OB/OD operations; n=52 participants, 36 samples within 7.5 km) and March 2025 (post-cessation; n=36 repeat participants).
  • 22 metals analyzed (ICP-OES): Ag, aluminum (Al), total arsenic (tAs), B, Ba, Be, cadmium (Cd), Co, chromium (Cr), Cu, Fe, Mg, Mn, Mo, nickel (Ni), lead (Pb), Sb, Ti, V, W, Zn.
  • Detectable concentrations in 2023-2024 samples for 17 of 22 metals; most prevalent were Fe, Ca, Mg (maximum concentrations 9270, 1859, and 288 mg/kg respectively).
  • Harmful heavy metals detected in 2023-2024: Sb and Pb detectable; arsenic (As) and Cd below the limit of detection.
  • 2025 (post-cessation) samples: 15 of 22 metals detectable; Sb no longer detectable; Mo not present in 2025.
  • Statistically significant decreases (Mann-Whitney) between 2023-2024 and 2025: Ni (p value significant), Pb (p value significant), Mo (p value significant). See Supplementary Table S4.
  • Spatial comparison 2023-2024: residents within 7.5 km of the facility more likely to have toenail Al, Fe, Ni, and Pb concentrations above the median for residents living beyond 7.5 km (chi-squared analysis).
  • Maximum concentration reductions from 2023-2024 to 2025: Fe decreased from 4811 to 277 mg/kg; Ni decreased from 495 to 31.4 mg/kg (more than fivefold); Mn and Pb both reduced more than twofold (2.86x reduction for Mn, 2.06x for Pb).
  • Comparison to literature: 2023-2024 Coifax Cr, Fe, Ni, Pb, and Zn concentrations were above reported mean values (1.91 +/- 1.66 mg/kg for Cr; 5.05 +/- 4.64 mg/kg for Fe; 41.4 +/- 43.6 mg/kg for Ni; 32.9 +/- 69.0 mg/kg for Pb; 0.74 +/- 1.23 mg/kg for Mn; 120.0 +/- 51.5 mg/kg for Zn) in US toenail exposure studies; 2025 averages were lower than those prior study averages.

Methods (brief)

Toenail samples from 52 Coifax residents (50% Black or African American, 50% White; 62% female; ages 24-89) were collected at participants’ homes in 2023-2024 during OB/OD operations. Repeat samples were collected in March 2025, 15 months after cessation of OB/OD operations, from 36 of the 52 original participants. Nails were sonicated 1 hour in 1% Triton X-100, rinsed twice with deionized water (18.2 MOhm-cm), dried at 60 degrees C for 18 hours, equilibrated at room temperature 30 minutes before weighing. Dried samples were acid digested in a precleared Teflon vial with 1.8 mL concentrated HNO3 (AristarPlus, VWR) and 0.3 mL H2O2 (Aristar Ultra, VWR), heated to 110 degrees C for 1 hour, with post-cooling addition of 0.3 mL H2O2, transfer to 25 mL volumetric flasks, diluted to volume, and photo-oxidized (7900, ultra-violet, Ace Glass Inc.) for 12 hours. ICP-OES analysis (ICP-OES S800, Agilent Technologies, USA); recovery standards indium and neodymium; internal standard ytterbium. Spatial analysis used a 7.5 km radius cutoff determined by visual inspection of scatterplots.

Evidence fitness

Toenails reflect cumulative metal exposure over approximately 7-12 months preceding collection. This paper provides evidence that the nearby OB/OD facility elevated Ni, Pb, and Mo body burden in community members, and that cessation reduced those levels. The study does not measure metals in food, cosmetics, or consumer products; it measures metals as biomarkers of environmental exposure. The paper is relevant to the wiki as a demonstration of toenail biomonitoring methodology and as evidence of community-level heavy metal exposure from a point source. It does not provide contamination data for any food or personal care product category.

Limitations

Small sample size (n=52 original, n=36 repeat). Non-random community recruitment via social media and poster announcements may introduce selection bias. As and Cd were below detection limits in both sampling periods, limiting conclusions about these analytes. The facility also burned Superfund site waste and fireworks; attribution of specific metals to specific waste streams is not possible. No dietary assessment was conducted, so contributions from food sources cannot be separated from airborne/soil/water pathways.

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