The study, published in the journal Environmental Geochemistry and Health, is described by its authors as the first city-wide assessment in the United States to systematically measure contamination by potentially toxic elements in soils at community-reported illegal dumping sites. Led by Erica D. Walker of Brown University’s School of Public Health, the team measured eight elements: the metalloid arsenic along with cadmium, chromium, copper, manganese, nickel, lead and zinc. Jackson made an urgent and instructive setting. The city has struggled for years to maintain reliable waste collection, and a 2023 breakdown in negotiations halted residential trash pickup across the city, during which illegal dumping rose sharply.

The methodological heart of the study is portable X-ray fluorescence, or pXRF, an instrument technique that bombards soil samples with X-rays and reads the characteristic fluorescent signatures of the elements they contain. At each of the 45 sites, the researchers collected soil from 20 locations, at two depths, and combined the samples into composite surface and subsurface specimens. The soils were dried, sieved to below 250 micrometers, and analyzed in triplicate. On a subset of 13 sites, the team also ran laboratory analysis by inductively coupled plasma optical emission spectrometry, or ICP-OES, following standard acid digestion, to provide an independent comparison.

The results revealed a clear hierarchy of contamination. Lead, copper and zinc dominated the enrichment, co-occurring across sites and reaching striking extremes: lead peaked at 2,910 milligrams per kilogram at depth, zinc at 1,630, and copper at 1,220. The distributions were strongly right-skewed, so a handful of extreme sites drove the averages. Surface lead, for example, averaged 226 milligrams per kilogram against a median of just 84.7. Cadmium, by contrast, was barely detectable by the field instrument, and the few pXRF readings that did appear proved to be spectral artifacts, contradicted by laboratory values 30 to 570 times lower.

Perhaps the most elegant result is the separation of two distinct geochemical fingerprints using field-portable screening alone. Principal component analysis and hierarchical clustering, applied to the depth-specific measurements, independently grouped chromium, nickel and iron together, while placing lead, zinc, arsenic and copper in a separate cluster. The iron association points to a lithogenic origin, elements present because of the local geology, since Jackson’s soils sit on deep silt deposits of Peoria Loess. The lead-zinc-arsenic-copper group, by contrast, is consistent with waste inputs from tires, wiring, plumbing, electronics, painted debris and treated wood. Partial-extraction recoveries from the laboratory subset corroborated the split: chromium was recovered at roughly a tenth of its total concentration by nitric acid extraction, as expected for chromium locked in silicate phases, while lead and copper were recovered at about half, consistent with more readily extractable, waste-derived forms.

The depth data carry the study’s central practical warning. For every element measured, surface and 15-centimeter concentrations were significantly correlated, and for lead the correlation was nearly perfect, at r = 0.982. In the cluster analysis, every element paired with its own counterpart at the other depth before joining any other element, a structural signature of vertical coherence. The researchers are careful to note that they sampled sites as found, with waste present, so the depth data describe contamination already in the ground beneath active dumping sites. But the inference for cleanup policy is the same: clearing surface waste, or even removing the uppermost soil layer, would not eliminate the elemental burden at these locations.

To translate concentrations into health-relevant terms, the team ran a screening-level risk assessment following United States Environmental Protection Agency guidance, evaluating incidental soil ingestion, dermal contact and inhalation of resuspended particles for a hypothetical child and adult resident. For a child, the hazard index exceeded unity at 21 of the 45 sites, with a maximum of 2.98. For adults, it stayed below unity everywhere. But the drivers of that calculated hazard are largely natural: arsenic and manganese, both geogenic in this setting, dominated the index, and the EPA’s arsenic screening level of 0.68 milligrams per kilogram actually sits below the local background of 6.9. Remove arsenic from the calculation, and only one site remains above unity. The honest reading, the authors argue, is that the elements driving computed hazard are mostly natural, while the element driving regulatory exceedance is the one attributable to dumping.

That element is lead. Because the EPA assigns lead no reference dose, evaluating it instead through blood-lead modeling, the researchers compared depth-averaged lead concentrations against absolute regulatory thresholds. Lead exceeded the residential soil screening level of 200 milligrams per kilogram at 11 of the 45 sites, roughly a quarter, and exceeded the 600 milligram per kilogram removal management level at four sites. Exceedances appeared in five of the six wards containing sites, most often in Ward 5. Since lead is also the element that the component, cluster and extraction evidence identifies most clearly as waste-derived, the authors describe this combination of regulatory exceedance and unambiguous anthropogenic attribution as the study’s principal public health finding.

The study is equally candid about its own limits, and those limits carry lessons for how such screening should be used. The contamination factor and degree of contamination indices the team calculated are useful for ranking and prioritizing sites, but they depend entirely on the chosen background values, and the researchers show that classifications derived from total pXRF measurements and from partial-extraction laboratory measurements agreed for only one of 13 paired sites. Chromium hazard remains unresolved, because the field instrument measures total chromium and cannot distinguish the relatively benign Cr(III) form from the toxic Cr(VI); under a worst-case assumption the child hazard quotient for chromium would jump from 0.001 to 1.42. No conclusions about mobility or bioavailability were drawn, since leaching tests and organic carbon measurements were not performed.

What emerges is a practical blueprint for resource-limited cities. Portable XRF screening, embedded in a public repository where residents and field teams document dumping locations, waste composition and exposure observations, makes city-wide assessment affordable and repeatable, while costlier laboratory analysis is reserved for high-priority sites. The spatial pattern in Jackson argues for site-by-site triage rather than uniform cleanup standards, because contamination is decentralized and scattered across individual locations that differ in size and contents. The authors’ closing message is blunt: a former dumping site converted into a community garden or playground may look fully restored while still carrying lead, arsenic and other elements that a visible cleanup did nothing to remove. A site is not recovered when it merely looks clean; it is recovered when a city can show that the land is safer for the people who live, work, garden or play on it.

Subject of Research: Soil contamination by potentially toxic elements at illegal dumping sites in Jackson, Mississippi

Article Title: Hidden toxicities: assessing city-wide contamination by potentially toxic elements from illegal dumping in Jackson, Mississippi

Article References: Walker, E. D., Klevan, C., Mathews, K., Mandalapu, S. V., Nica, C., & Ibrahim, N. (2026). Hidden toxicities: assessing city-wide contamination by potentially toxic elements from illegal dumping in Jackson, Mississippi. Environmental Geochemistry and Health, 48(15), Article 603. https://doi.org/10.1007/s10653-026-03450-y

Image Credits: AI Generated

DOI: 10.1007/s10653-026-03450-y

Keywords: illegal dumping, soil contamination, potentially toxic elements, lead, portable X-ray fluorescence, Jackson Mississippi, environmental geochemistry, public health, risk assessment, urban soil, ICP-OES, environmental justice