A Dynamic Model of the Fate of Organic Chemicals in a Multilayered Air/Soil System: Development and Illustrative Application

Abstract

A new site-specific, dynamic model (SoilPlus) was developed to simulate the fate of nonionized organic chemicals in the air/litter/soil system; key features of the model are the double-layered air compartment interacting dynamically with multilayered litter and soil compartments, with seasonal dissolved organic carbon (DOC) fluxes. The model describes the soil environment calculating separate mass balances for water, chemical, and organic matter. SoilPlus underwent a process of benchmarking and evaluation in order to reach a satisfying confirmation of its predictive capability. Several simulations were performed to estimate the role of litter and DOC in affecting the fate of a model contaminant for POPs (hexachlorobenzene). The model shows that litter can behave as a buffer in the process of transferring hexachlorobenzene from air to the mineral soil and as a trap when hexachlorobenzene tends to move from a contaminated field toward clean air. DOC seems to behave as a leaching-enhancer in certain climatic conditions (heavy rainfall, high DOC concentrations), but it does not appear to move significant amounts of HCB in a year calculation.

Environmental fate and exposure models: advances and challenges in 21st century chemical risk assessment

“…[61][62][63][64][65] Multimedia models of the 1990s included bulk compartments for air, water, soil, and sediment. Several additional environmental compartments, sub-compartments and processes have been incorporated into fate and exposure models, including terrestrial and aquatic vegetation, [66][67][68][69][70][71][72][73][74][75][76][77][78][79] DOC in terrestrial and aquatic systems, 76,80,81 ice and snow, [82][83][84] different types of aerosols, 85 mountainous regions, 86,87 and the effect of intermittent rain. [88][89][90] The fundamental concept underlying all fate and exposure models is the integration of chemical transport, transfer and degradation processes into mass balance equations for the chemical investigated.…”

“…Bioavailability of chemicals to terrestrial and aquatic environments and more generally the ecological realism of scenario descriptions has been pointed out as a critical issue to evaluate the exposure and therefore the toxicity of hydrophobic chemicals in the environment. 7,129,130 Some models were recently published and have incorporated additional compartments and subcompartments (such as dissolved organic carbon, macrophytes, algae) to account for their inuence on dynamically changing bioavailable concentrations, 76,81,131,132 as well as compartment variability in scenarios. 78,132,133…”

“…121 Mountainous regions are characterized by rapid land response to precipitation, resulting in quick runoff chemical peaks and consequent potentially high peak exposure concentrations in aquatic ecosystems receiving such runoff. The model consisted of a dynamic water network model (built upon the Dyna model 136 ) and a spatially explicit terrestrial multimedia model 81,120 parametrized using specic scenario and emission data provided by the local authorities. The model incorporated an improved algorithm to calculate water runoff in steep slopes (average 30%, up to 80%) which allowed to more accurately calculate chemical runoff in these conditions.…”

Shallow Water 1D Model for Pollution River Study

“…Chemical half-lives in water (33.3, 0.05 and 68 days, respectively) were used to update concentrations according to decay, as expressed by (16). Hourly chemical loading at the inflow deriving from water runoff in the Novella watershed were calculated for the three chemicals using SoilPlus [11], a dynamic multimedia model based on the fugacity concept developed to investigate the fate organic chemicals in the air/litter/soil system at the local scale. A 10 cm loamy soil compartment divided in 20 sub-layers (thickness: 0.5 cm) and starting from field-capacity conditions was simulated.…”

Guidance on the Selection of Efficient Computational Methods for Multimedia Fate Models

“…layered soil compartments) in order to gain a more accurate description of chemical movement. [10][11][12][13] Spatial variability of emissions and environmental scenarios was later introduced and handled in a variety of ways, from site specific models, to GIS/spatially explicit approaches. [14][15][16] More recently, a lot of effort was devoted to incorporating the influence of environmental scenario and chemical changes in the models: 17 from seasonal changes, such as vegetation cycles, to monthly/daily/hourly 18 variations of compartment properties, meteorological conditions, and physical-chemical properties.…”