Vegetation/Soil Distribution of Semivolatile Organic Compounds in Relation to Their Physicochemical Properties

Abstract

The concentrations (C) of several semivolatile organic compounds (SOCs) in Norway spruce needles (N) and in the local humus horizon (O) of 25 remote Austrian forest sites were used to calculate an ecosystem-oriented partition coefficient needles/humus horizon (CN/CO). Between 66 and 78% of the compounds' variation of this quotient could be explained by each of the following physicochemical parameters: vapor pressure (pS) and the partition coefficients n-octanol/water (KOW), n-octanol/air (KOA), and adsorbed/dissolved in soil (KOC) of the compounds. This result further underlines the usefulness of these parameters for predicting the behavior of SOCs in terrestrial ecosystems. Compounds with low pS and high KOW, KOA, and KOC show a very low CN/CO quotient, which implies a higher accumulation of these compounds in the O horizon than in the needles. The role of forest soils as sink for these SOCs is demonstrated. Alternatively, CN/CO > 1, due to higher concentrations in the needles than in the O horizon, have been shown for SOCs with comparably high pS and low KOW, KOA, and KOC. In this respect, the possible role of revolatilization of the more volatile SOCs from soils to needles is discussed. In the mineral soil layers below the O horizon, SOCs with lower KOC and better water solubility tend to be less accumulated. However, if all investigated compounds are taken into consideration, accumulation in the mineral soil layers showed no general trend in relation to the selected physicochemical parameters.