Comprehensive Multi-compartment Sampling for Quantification of Long-Term Accumulation of PAHs in Soils

Abstract

Long-term accumulation in the soils of ubiquitous organic pollutants such as many polycyclic aromatic hydrocarbons (PAHs) depends on deposition from the atmosphere, revolatilization, leaching, and degradation processes such as photolysis and biodegradation. Quantifying the phase distribution and fluxes of these compounds across environmental compartments is thus crucial to understand the long-term contaminant fate. The gasphase exchange between soil and atmosphere follows chemical fugacity gradients that can be approximated by gas-phase concentrations, yet which are difficult to measure directly. Thus, passive sampling, measured sorption isotherms, or empirical relationships to estimate sorption distribution have been combined in this study to determine aqueous (or gas) phase concentrations from measured bulk concentrations in soil solids. All these methods have their strengths and weaknesses but agree within 1 order of magnitude except for ex situ passive samplers employed in soil slurries, which estimated much lower concentrations in soil water and gas likely due to experimental artifacts. In field measurements, PAH concentrations determined in the atmosphere show a pronounced seasonality with some revolatilization during summer and gaseous deposition during winter, but overall dry deposition dominates annual mean fluxes. The characteristic patterns of PAHs in the different phases (gas phase, atmospheric passive samplers, bulk deposition, and soil solids) confirm the expected compound-specific distribution pattern and behavior. Since revolatilization fluxes in summer are only minor and wet and dry deposition is ongoing, our results clearly show that the PAH loads in topsoils will continue to increase.

Water Column Organic Carbon Composition as Driver for Water-Sediment Fluxes of Hazardous Pollutants in a Coastal Environment

“…Higher PAH air concentrations during autumn are likely a consequence of higher emissions from combustion during the cold seasons. Higher gaseous and air bulk deposition of PAHs during cold periods were also observed in Germany as a result of higher emission rates and higher load of particles containing higher air concentrations of PAHs in winter compared to summer [44]. The seasonal concentration pattern of PAHs has been previously described also in the Baltic Sea, where PAH concentrations in surface water [45] and air [46] were higher during cold periods.…”

“…S2 SI). Meierdierks et al [44] found that PAHs accumulated in soils were deposited from air almost exclusively during cold periods (> 80% of the annual deposition rates) [44]. In the current study, bulk deposition from air was not measured.…”