The Pedosphere as a Sink, Source, and Record of Anthropogenic and Natural Arsenic Atmospheric Deposition

Abstract

The Anthropocene has led to global-scale contamination of the biosphere through diffuse atmospheric dispersal of arsenic. This review considers the sources arsenic to soils and its subsequent fate, identifying key knowledge gaps. There is a particular focus on soil classification and stratigraphy, as this is central to the topic under consideration. For Europe and North America, peat core chrono-sequences record massive enhancement of arsenic depositional flux from the onset of the Industrial Revolution to the late 20th century, while modern mitigation efforts have led to a sharp decline in emissions. Recent arsenic wet and dry depositional flux measurements and modern ice core records suggest that it is South America and East Asia that are now primary global-scale polluters. Natural sources of arsenic to the atmosphere are primarily from volcanic emissions, aeolian soil dust entrainment, and microbial biomethylation. However, quantifying these natural inputs to the atmosphere, and subsequent redeposition to soils, is only starting to become better defined. The pedosphere acts as both a sink and source of deposited arsenic. Soil is highly heterogeneous in the natural arsenic already present, in the chemical and biological regulation of its mobility within soil horizons, and in interaction with climatic and geomorphological settings. Mineral soils tend to be an arsenic sink, while organic soils act as both a sink and a source. It is identified here that peatlands hold a considerable amount of Anthropocene released arsenic, and that this store can be potentially remobilized under climate change scenarios. Also, increased ambient temperature seems to cause enhanced arsine release from soils, and potentially also from the oceans, leading to enhanced rates of arsenic biogeochemical cycling through the atmosphere. With respect to agriculture, rice cultivation was identified as a particular concern in Southeast Asia due to the current high arsenic deposition rates to soil, the efficiency of arsenic assimilation by rice grain, and grain yield reduction through toxicity.

The Global Biogeochemical Cycle of Arsenic

“…The resulting global flux is 0.07 × 10 9 g As/yr. This flux is about 20% of that calculated by Meharg and Meharg (2021: 0.34 × 10 9 g As/yr), who used a much larger global surface area of peatlands (4,000 × 10 9 m 2 ). Rice paddies add little to the global flux of arsines from wetlands, owing to their lower emissions (Table 3), despite covering a large area (1,475 × 10 9 m 2 ; Matthews et al., 1991).…”

“…In developed countries, airborne As emissions, primarily from the production of glass and copper, have been curtailed by strict emissions standards (e.g., USEPA, 1986). Longitudinal studies show declining As deposition from the atmosphere in North America (Wiklund et al., 2020) and Europe (Kyllönen et al., 2009), and lower concentrations in recent deposits in peatbogs and mosses in these areas (Meharg & Meharg, 2021). Spatial heterogeneity in As deposition persists (Jovan et al., 2022), with high concentrations of As in drinking water associated with low‐income communities (Nigra et al., 2022).…”

“…Based on the measurements of Savage et al. (2018), Meharg and Meharg (2021) estimate the global volatilization of arsines from seawater as 0.70 × 10 9 g As/yr. Calculating a mean annual rate of volatilization from Savage et al.…”

Interactions with Arsenic: Mechanisms of Toxicity and Cellular Resistance in Eukaryotic Microorganisms

“…Natural inputs of As to the atmosphere come mainly from volcanic activity, biovolatilisation, wind erosion of soils and salt dissolutions [7,18,40]. However, the main sources of As in the atmosphere are anthropogenic.…”

“…However, the main sources of As in the atmosphere are anthropogenic. The Anthropocene period has been proposed to have caused global-scale contamination of the biosphere through atmospheric dispersion of As [40]. Metal smelting (copper, zinc, and lead) and coal combustion are the main anthropogenic sources of As [41].…”