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Open dumping and burning of solid waste are widely practiced in underserved communities lacking access to solid waste management facilities. The generation of microplastics from these sites has been overlooked. 

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 abundance of particles found at the three sites (35,000 to 69,200 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. 

The fish intestine is an important barrier for environmental toxicants, including metals and metal nanoparticles. Tracking chemical transformation at the interface between the intestinal epithelium and the intestinal lumen can inform us about chemicals' bio-reactivity and toxicity but is challenging due to the lack of appropriate models. To allow for such investigations, a model of the fish intestine derived from rainbow trout ( Oncorhynchus mykiss ), the RTgutGC cell line, was used. Cells were exposed to silver nitrate (AgNO 3 ) or citrate coated silver nanoparticles (cit-AgNPs) in Leibovitz's L-15 medium without amino acids and vitamins (L-15/ex), which allowed the determination of the extracellular silver species using a chemical equilibrium model. X-ray absorption spectroscopy (XAS) was used to track intracellular silver speciation. Cellular toxicity, silver accumulation, and metallothionein (MT) mRNA levels were also measured. Cells accumulated the same concentrations of silver when exposed to equimolar amounts ( i.e. 1, 5 and 10 μM) of AgNO 3 or cit-AgNPs. However, AgNO 3 was shown to be more toxic than cit-AgNPs. Intracellular silver speciation changed over time in both exposure series. After 1 hour, intracellular silver speciation was dominated by chloride complexation in both exposures. After 24 and 72 hours of exposure to cit-AgNPs, ∼7% of silver was complexed to cysteine, whereas the remaining silver was AgNPs. In cells exposed to AgNO 3 for 72 hours, 97% of Ag was complexed to cysteine. A significant increase, compared to controls, in metallothionein mRNA levels at 24 and 72 hours of exposure to AgNO 3 and cit-AgNPs can explain the formation of Ag–cysteine complexes. In summary, these data show that silver chloride species are bioavailable and that complexation to cysteine scavenges intracellular dissolved silver ions, thus preventing toxicity. Silver nanoparticles present a similar but attenuated toxic response to AgNO 3 . Thus, at least in acute exposures, existing risk assessment for dissolved silver species could be protective for nanosilver.