Proximity to a hazardous waste thermal treatment facility alters human physiology: a community-driven pilot study

Abstract

Open burn/open detonation (OB/OD) disposes of explosive waste via uncontrolled combustion, releasing harmful pollutants like toxic gases and particulate matter. Colfax, Louisiana, houses the nation's only commercially OB/OD thermal treatment (TT) facility, raising concerns about environmental and public health impacts due to its emissions. In this exploratory pilot study, we investigated metabolic alterations indicative of potential health impacts from exposure to emissions from a TT facility through an untargeted metabolomics analysis of urine samples obtained from local residents. Urine samples were collected from 51 residents living within a 30-km radius of the facility, with proximity, race, and sex as key variables. Samples were analyzed using ultra-high-performance liquid chromatography coupled with high-resolution mass spectrometry (UHPLC-HRMS) to identify metabolic alterations and potential biomarkers of exposure. A total of 217 metabolites were identified, with significant differences in abundance based on proximity to the facility. Key metabolic pathways affected included energy metabolism, amino acid metabolism, and oxidative stress-related pathways. Metabolites associated with oxidative stress, such as glutathione sulfonamide (GSA), were elevated in individuals residing closer to the facility, indicating increased oxidative stress. Alterations in the glutathione/glutathione disulfide (GSH/GSSG) ratio further highlighted redox imbalances. Pathway enrichment analyses revealed perturbations in glycolysis, citric acid cycle, sulfur metabolism, and nucleotide metabolism, which are linked to critical biological functions like energy production and DNA repair. Notable differences in metabolite profiles were also observed between sexes and racial groups, pointing to the interplay of intrinsic biological and environmental factors. These findings demonstrate that exposure to emissions from the TT facility may have significant impacts on human health, including disruptions in cellular metabolism and increased oxidative stress. Further research is crucial to understand the long-term health implications of these metabolic alterations and to develop strategies to mitigate the environmental and health risks associated with this facility.

Keywords: environmental exposure; hazard waste remediation; metabolomics; open burn; oxidative stress.

FIGURE 1

A heatmap illustrating fold changes in metabolite abundance, organized by compound class, across sample groups stratified by sex, race, and proximity to the facility. The fold changes include Female/Male, Black/White, and Less than 5 km/Greater than 5 km (n = 51). Statistically significant differences are indicated by asterisks (*P < 0.1, **P < 0.05, ***P < 0.01). Metabolite abundance is represented using a color gradient, with red indicating a higher abundance and blue indicating lower abundance in female for sex-based comparison, Black individuals for race-based comparison, or individuals residing less than 5 km from the facility for proximity-based comparison.

FIGURE 2

Partial Least Squares-Discriminant Analysis (PLS-DA) plots illustrating metabolic profile separations with 95% confidence intervals, grouped by: (A) Sex (Female vs. Male), (B) Race (Black vs. White), and (C) Distance from the facility (Less than 5 km vs. Greater than 5 km) (n = 51).

FIGURE 3

Variable Importance in Projection (VIP) score plots highlighting metabolites with 15 highest VIP scores. All metabolites with a VIP score greater than 1 significantly contribute to the observed group separations. These metabolites drive the differences across (A) Sex (Female vs. Male), (B) Race (Black vs. White), and (C) Distance from the facility (Less than 5 km vs. Greater than 5 km) (n = 51).

FIGURE 4

Volcano plots illustrating the differentially abundant metabolites across groups: (A) Sex (Female vs. Male), (B) Race (Black vs. White), and (C) Distance from the facility (<5 km vs. >5 km). Metabolites with a fold change ≥2 and P-value <0.1 are highlighted with red spot, while those with a fold change ≤0.5 and P-value <0.1 are highlighted with blue spot.

FIGURE 5

(A) Venn diagram depicting the distribution of differentially abundant metabolites uniquely identified in each group—Sex (n = 16), Race (n = 26), and Distance (n = 33)—as well as the metabolites shared across all groups (n = 27). (B) Clustered bar graph illustrating the enriched metabolic pathways across the sample groups, with logarithmically transformed FDR values. Pathway significance was determined using P-values, with a false discovery rate (FDR) threshold of <0.05.

FIGURE 6

(A) Schematic representation of amino acid metabolism pathways enriched with metabolites that exhibit differential abundance between females and males. Metabolites highlighted in red are significantly more abundant in females, while those in blue are significantly less abundant (P < 0.1). (B–D) Illustrating the most impacted pathways for differentially abundant metabolites in the Less than 5 km vs. Greater than 5 km groups. Metabolites highlighted in red are significantly upregulated, while those in blue are significantly downregulated in the Less than 5 km group (P < 0.1) (B) Schematic representation of energy and sulfur compound metabolism pathways. (C) Schematic representation of energy and carbohydrate metabolism pathways. (D) Schematic representation of nucleotide and amino acid metabolism pathways.

FIGURE 7

(A) Relative abundances of glutathione sulfonamide (GSA) in Female vs. Male sample groups. (B) Relative abundances of GSA in Black vs. White sample groups. (C) Absolute abundances of GSA in Less than 5 km vs. Greater than 5 km sample groups (D) Relative abundances of glutathione (GSH) and glutathione disulfide (GSSG), along with their ratio, in Female vs. Male sample groups. (E) GSH/GSSG abundance ratio in Black vs. White sample groups. (F) GSH/GSSG abundance ratio in Less than 5 km vs. Greater than 5 km sample groups.

FIGURE 8

(A) Relative abundance of vanillin in Less than 5 km vs. Greater than 5 km sample group. (B) Relative abundance of leucine/isoleucine in Less than 5 km vs. Greater than 5 km sample group. (C) Relative abundance of tryptophan in Less than 5 km vs. Greater than 5 km sample group (D) Relative abundance of kynurenic acid in Less than 5 km vs. Greater than 5 km sample group (E) Relative abundance of methionine in Less than 5 km vs. Greater than 5 km sample group (F) Relative abundance of homocysteic acid in Less than 5 km vs. Greater than 5 km sample group. *p < 0.05, ***p < 0.001.