Emerging investigator series: open dumping and burning: an overlooked source of terrestrial microplastics in underserved communities

Abstract

Open dumping and burning of solid waste are widely practiced in underserved communities lacking access to solid waste management facilities; however, the generation of microplastics from these sites has been overlooked. We report elevated concentrations of microplastics (MPs) in soil of three solid waste open dump and burn sites: a single-family site in Tuttle, Oklahoma, USA, and two community-wide sites in Crow Agency and Lodge Grass, Montana, USA. We extracted, quantified, and characterized MPs from two soil depths (0-9 cm and 9-18 cm). The average of abundance of particles found at community-wide sites three sites (18, 460 particles kg^-1 soil) equals or exceeds reported concentrations from currently understood sources of MPs including biosolids application and other agricultural practices. Attenuated total reflectance Fourier transformed infrared (ATR-FTIR) identified polyethylene as the dominant polymer across all sites (46.2-84.8%). We also detected rayon (≤11.5%), polystyrene (up to 11.5%), polyethylene terephthalate (≤5.1), polyvinyl chloride (≤4.4%), polyester (≤3.1), and acrylic (≤2.2%). Burned MPs accounted for 76.3 to 96.9% of the MPs found in both community wide dumping sites. These results indicate that solid waste dumping and burning activities are a major source of thermally oxidized MPs for the surrounding terrestrial environment with potential to negatively affect underserved communities.

Fig. 1. Abundance of particles (particles kg⁻¹ soil) at each soil depth at Lodge Grass dump site (A), Crow Agency burn site (B), and Tuttle burn site (C) and size distribution of all particles detected with Nile Red at Lodge Grass dump site (D), Crow Agency burn site (E), and Tuttle burn site (F). All analyses were performed in analytical triplicate.

Fig. 2. Stratification ratio of particle abundance (particle concentration at 0–9 cm/particle concentration at 9–18 cm) plotted against percentage of clay in all quadrants of each site.

Fig. 3. Comparison of representative FTIR spectra of selected MPs found open dumping and burning sites respect to the plastic reference of polyethylene-containing MPs (A–C) and other prevalent types of MPs (D–F). Particles shown in panel A are CABS-NW-Shallow-1 (LLDPE), CABS-NE-Shallow-5 (PE), CABS-NW-Deep- 3 (LDPE). Particles shown in panel B: LG-NW-Shallow-1 (HDPE), LG-NW-Deep-4 (LLDPE), LG-W-Deep-5 (PE), LG-SW-Deep-2 (LDPE). Particles shown in panel C: Tuttle OK-West-Shallow-1 (HDPE), Tuttle OK North- Shallow-3 (PE), Tuttle OK-West-Deep-3 (LDPE). Particles shown in panel D: CABS-NE-Shallow-3 (PP), CABS-SE-Deep-1. Particles shown in panel E: LG-SW-Shallow-1 (PS). Particles shown in panel F are Tuttle OK-East-Shallow-2 (PS), Tuttle OK-East-Deep-3 (PP). The information for the rest of the particles is available in the ESI File.

Fig. 4. Effects of thermal and UV oxidation on the functional chemistry of PE and PS microplastics.

Fig. 5. Microplastics found in the sites sampled. (A) Relative abundance. (B) Representative microplastics found in the sites of Tuttle OK (top to bottom): Tuttle OK-West-Shallow-1, Tuttle OK-W-Deep-1 Tuttle OKW- Shallow-2, Tuttle OK-W-Deep-7; microplastics found in Crow Agency (top to bottom): CABS-NW Shallow-2, CABS-NW-Shallow-12 CABS-SE-Deep-4; and microplastics found in Lodge Grass: LG-SW-Deep-12; LG-SW-Shallow-13; LG-SW-Shallow-7. CABS: Crow Agency burn site; LG: Lodge Grass. N, S, W, E indicate cardinal directions.

Fig. 6. Soil plastic concentration (mg g⁻¹) measured by py-GC/MS for the Crow Agency burn site, Lodge Grass dump site, and Tuttle, Oklahoma burn site 0–9 and 9–18 cm samples. Plastic types are indicated as polyethylene (PE), polyethylene terephthalate (PET), polycarbonate (PC), nylon 6 (N6), nylon 66 (N66), polyvinyl chloride (PVC), and polystyrene (PS).