Soil is the primary sink of semivolatile organic compounds (SOCs) in the terrestrial environment, while the atmosphere is the primary vector of these substances to humans via the agricultural food chain. Hence, the exchange of SOCs between soil and air is of paramount importance to their environmental fate and potential risk to humans. In this paper, a method is developed to determine soil/air partition coefficients (K SA) of SOCs. On the basis of the solid-phase fugacity meter developed for plants, the method was initially tested using a soil contaminated in the laboratory with chlorinated benzenes, polychlorinated biphenyls, and polycyclic aromatic hydrocarbons. A systematic validation exercise demonstrated that the method is not subject to a wide range of potential artifacts. It was then shown that K SA in moist soil (relative humidity = 100%) is independent of the water content of the soil. The method was then extended to the measurement of K SA in the original soil, which contained background levels of the SOCs. Good agreement was found between the K SA values measured with the original soil and with the labora tory contaminated soil, confirming that the studies with contaminated soil can be extrapolated to environmental conditions and demonstrating that it is possible to directly measure K SA at current background levels of soil contamina tion. The K SA values of the compounds studied ranged over almost 4 orders of magnitude. There was an excellent linear relationship between K SA and the quotient of the octanol/water and air/water partition coefficients (K OW/K AW), indicating that the Karickhoff model commonly applied to soil/water partitioning can be extended to the soil/air system. An equally good regression was obtained between K SA and measured octanol/air partition coefficients (K OA).

The influence of temperature and relative humidity (RH) on the equilibrium partitioning of polychlorinated biphenyls (PCBs), pentachlorobenzene, and hexachlorobenzene between a sandy loam soil and air was investigated. The measurements were conducted at 6 temperatures from 5 to 60 °C at each of 5 different relative humidities from 29 to 93% in a solid-phase fugacity meter. The soil/air equilibrium partition coefficient (K SA) was very sensitive to temperature and humidity. For instance, K SA for PCB 52 was 46,000 times higher at T = 5 °C, RH = 29% than at T = 60 °C, RH = 93%. For a given RH, a linear relationship between ln K SA and 1/T was observed. The heats of phase change were similar for the di- through octachlorinated PCB congeners but varied with RH, increasing from 103 kJ/mol at RH = 29% to 116 kJ/mol at RH = 66% and then decreasing to 98 kJ/mol at RH = 93%. At a given temperature, an inverse linear relationship between ln K SA and RH was observed. The slopes of these lines were similar for all compounds studied at all temperatures. The increase in K SA with diminishing RH was much greater than could be explained by adsorption to soil minerals. This suggests that sorption in organic material also increases with diminishing RH. A simple predictive equation was developed to calculate K SA as a function of soil properties, physical chemical properties, soil temperature and soil relative humidity. The correlation coefficient for the 1131 data points predicted and the measured K SA was 0.97, with a root-mean-square residual of 0.24 log units. This equation provides an initial basis for exploring the influence of the high sensitivity of K SA to temperature and relative humidity on the environmental fate of SOCs.

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During a monitoring campaign concentrations of volatile organic compounds (VOCs) were measured in indoor air of 79 dwellings where occupants had not complained about health problems or unpleasant odour. Parameters monitored were the individual concentration of 68 VOCs and the total concentration of all VOCs inside the room. VOCs adsorbed by Tenax TA were then analysed by means of thermal desorption, gas chromatography and mass spectrometry. The analytical procedure and quantification was done according to the recommendation of the ECA-IAQ Working Group 13 which gave a definition of the total volatile organic compound (TVOC) concentration. Using this recommendation TVOC-concentrations ranged between 33 and 1600 microg m(-3) with a median of 289 microg m(-3). Compounds found in every sample and with the highest concentrations were 2-propanol, alpha-pinene and toluene. Save for a few samples, all concentrations measured have been a factor 2 to 10 lower, compared to data from similar studies. Only a few terpenes and aldehydes were found exceeding published reference data or odour threshold concentrations. However, it has been found that sampling and analysing methods do have a considerable impact on the results, making direct comparisons of studies somewhat questionable. 47% of all samples revealed concentrations exceeding the threshold value of 300 microg TVOC m(-3) set by the German Federal Environmental Agency as a target for indoor air quality. Using the TVOC concentration as defined in the ECA-IAQ methodology is instrumental in assessing exposure to VOCs and identifying sources of VOCs. The background concentrations determined in this study can be used to discuss and interpret target values for individual and total volatile organic compounds in indoor air.

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