Estimating the Influence of Forests on the Overall Fate of Semivolatile Organic Compounds Using a Multimedia Fate Model

Abstract

On the basis of recently reported measurements of semivolatile organic compound (SOC) uptake in forest canopies, simple expressions are derived that allow the inclusion of a canopy compartment into existing non-steady-state multimedia fate models based on the fugacity approach. One such model is used to assess how the inclusion of the canopy compartment in the model affects the calculated overall behavior of SOCs with specific physical−chemical properties. The primary effect of the forest is an increase in the net atmospheric deposition to the terrestrial environment, reducing atmospheric concentrations and accordingly the extent of deposition to the agricultural and aquatic environments. This effect was most pronounced for chemicals with log K OA around 9−10 and log K AW −2 to −3; their average air concentrations during the growing season decreased by a factor of 5 when the canopy compartment was included. Concentration levels in virtually all compartments are decreased at the expense of increased concentrations in the forest soil. The effect of the forest lies not in a large capacity for these chemicals but in the efficiency of pumping the chemicals from the atmosphere to the forest soil, a storage reservoir with high capacity from which the chemicals can return to the atmosphere only with difficulty. Because of seasonal variability of canopy size and atmospheric stability, uptake into forests is higher during spring and summer than in winter. The model suggests that this may dampen temperature-driven seasonal fluctuations of air concentrations and in regions with large deciduous forests may lead to a temporary, yet notable dip in air concentrations during leaf development in spring. A sensitivity analysis revealed a strong effect of forest cover, forest composition, and degradation half-lives. A high degradation loss on the plant surface has the effect of preventing the saturation of the small plant reservoir and can cause very significant reductions in atmospheric concentrations of those SOCs for which uptake in the canopy is limited by the size of the reservoir.

Dechlorane Plus (DP) in air and plants at an electronic waste (e-waste) site in South China

“…At the e-waste site, however, DP may penetrate into the interior through leaf cuticles or stomata due to the long-term exposure of leaves to high air DP concentrations. The observation also suggests that uptake can efficiently reduce air DP concentration, in agreement with previous model calculations, which indicate that the forest filter effect can notably decrease SOC concentrations in the air, particularly for those with higher octanolair partition coefficients (log K OA ) McLachlan and Horstmann, 1998;Wania and McLachlan, 2001).…”

Distribution of PCBs and PBDEs in soils along the altitudinal gradients of Balang Mountain, the east edge of the Tibetan Plateau

“…The concentrations were comparable to those of the alpine meadow sampling sites and also similar to our previous result on OCPs in this area (Zheng et al, 2009). Forests can accumulate organic pollutants by gaseous uptake and atmospheric deposition, and eventually transfer them to forest soil (McLachlan, 1999;Wania and McLachlan, 2001;Nizzetto et al, 2006). A model estimated that the concentrations of SVOCs in soils could increase by 28% for areas with forest than without forest (Wania and McLachlan, 2001).…”

“…Forests can accumulate organic pollutants by gaseous uptake and atmospheric deposition, and eventually transfer them to forest soil (McLachlan, 1999;Wania and McLachlan, 2001;Nizzetto et al, 2006). A model estimated that the concentrations of SVOCs in soils could increase by 28% for areas with forest than without forest (Wania and McLachlan, 2001). Considering the uniform air concentrations of chemicals along the transect (Liu et al, 2010), the forest filter effect could be responsible for the higher levels in the below-treeline soils in Balang Mountain.…”

A GIS model-based assessment of the environmental distribution of γ-hexachlorocyclohexane in European soils and waters

“…Moreover, as in 2005 y-HCH emissions are supposed to come from non-agricultural usages, and they are assumed to be proportional to human population density, higher valúes are predicted in the most densely populated áreas for 2005, while for 1995 the hot spots followed agricultural intensity. At a finer scale, the model reflects the importance of organic carbón content of soils for the sorption of y-HCH (Wania and McLachlan, 2001), with higher valúes of mass in soils in organic-rich terrestrial áreas such as forested regions or peats. Median valúes are in the order of magnitude of 0.001 ng/g, or 100 times less than in 1995.…”