Soil memory in mineral surface coatings: Environmental processes recorded at the nanoscale

Abstract

This study shows that mineral surface coatings in upper soil horizons can preserve products of past abiotic and biotic soil processes and are thus able to record environmental changes on the nanoscale. Contrary to studies involving paleosols, the soil memory of coatings can only be deciphered with high-resolution transmission electron microscopy (HRTEM) on samples prepared using focused ion beam technology. To demonstrate this method, mineral grains were collected in the shallow soils of the Greater Sudbury area, Ontario, Canada, where large fluctuations in the soil pH have occurred during emissions of vast amounts of sulfuric acid and particulate matter (a result of decades of smelter activity in the Sudbury mining district) and subsequent reclamation efforts using lime and phosphates. Observations with HRTEM indicate that limited diffusion of elements in silicified Fe-hydroxide coatings has been the key to the preservation of a rarely observed mineralogy and chemistry. The most intriguing features include petrified cocci in proximity to a structural analogue of green rust (formed prior to the peak of smelter emissions), pockets of jarosite encapsulated by amorphous silica (peak of the smelter emissions), chains of biogenic magnetite, and Fe-(hydr)oxides with high amounts of adsorbed phosphate species (during and after reclamation). These observations indicate that chemical processes in confined pore and interface spaces are commonly in disequilibrium with the surrounding soil, and that Fe-silica-bearing coatings can be excellent tracking tools for the evolution of the chemistry of soils and sediments.

Natural, incidental, and engineered nanomaterials and their impacts on the Earth system

“…The formation and nature of incidental nanomaterials in the subsurface in lands affected by mining and ore benefaction and smelting has been a field of growing research interest (28,29). In some cases, incidental nanoparticles can preserve or record complex biogeochemical histories as they persist or evolve through changing environmental conditions.…”

“…These materials range from complex aggregates of inorganic and organic compounds, some with crystalline structures (26), to carbonaceous "tar balls" and organic droplets (31,32). Exhaust from gasoline and diesel engines contains graphitized carbon nanomaterials that are associated with metal and metal-oxide nanomaterials, polycyclic aromatic hydrocarbons (PAHs), nitrated PAHs, and heterocyclic aromatic compounds formed from vaporization and partial combustion of lubricants and fuel additives (29). Furthermore, nanomaterials form in the atmosphere as a result of the anthropogenic and natural emission of precursors, such as sulfuric acid and other compounds that form molecular clusters, which then grow into stable nanomaterials through Earth has not only water and rock cycles, and many chemical cycles, but also a nanomaterial cycle.…”

Nanoscale Observations Support the Importance of Chemical Processes in Rock Decay and Rock Coating Development in Cold Climates

“…Nanoscale earth science methods [49][50][51], including studies of mineral and rock decay processes [52][53][54][55][56][57][58][59][60], by and large, have not yet reached cold climate rock decay research-with the prominent exception of explorations by Schindler and collaborators of anthropogenic interactions with rock surfaces [61][62][63][64][65][66]. D.H. Krinsley has been the leading pioneer in the use of nanoscale electron microscopy in the field of rock coating research [67][68][69][70][71], and followed by others [72][73][74].…”

The formation of spinel-group minerals in contaminated soils: the sequestration of metal(loid)s by unexpected incidental nanoparticles

“…1 wt% Ni) occur in different shapes and of different origins in a mineral surface coating of a Fe-rich pyroxene (Fig. 5a–f) [32, 33]. Trevorite forms a linear array of nano-domains at the interface between two zones of the mineral surface coating (Fig.…”