Sequestration of Pb–Zn–Sb- and As-bearing incidental nanoparticles by mineral surface coatings and mineralized organic matter in soils

Nanoparticles (NPs) often play significant roles in dictating the transport, distribution, bioavailability and toxicity of contaminants in the environment. Incidental NPs (i.e. NPs of anthropogenic origin but not purposely engineered) are often overlooked in contaminant transport and fate studies; yet in many systems they dominate contaminant transport processes. Using surficial contaminated regosols from Trail, British Columbia, Canada, a metal smelting and refining area along the banks of the Columbia River, we show that sequestration of Pb-, Zn-, Sb-, and As-bearing incidental NPs is strongly influenced by their aggregation, crystal growth, and/or particle attachment to mineral surface coatings (MSC) and in mineralized organic matter (MOM). Transmission electron microscopy shows the occurrence of NPs of anglesite (PbSO4), Fe–As-phosphate, kintoreite (Pb[(Fe,Al)3(P(As)O4)(PO3(OH))(OH)6]), and franklinite (ZnFe2O4) in matrices of amorphous silica which retain different stages of their agglomeration and aggregation. Other identified nano-size phases in the MSC and MOM indicate a complex and previously unrecognized mineralogy of Pb-, Zn-, Sb-, and As-phase in surficial soils. Mineralogical complexity and the various sequestration processes observed in this study indicate a new dimension of nano-scale processes on mineral surfaces and organic matter that have been previously overlooked when studying the fate of contaminants with bulk-analytical tools such as micro-X-ray diffraction or synchrotron-based spectroscopic methods.