Bestimmung des Ferntransports von persistenten organischen Spurenstoffen und der Umweltexposition mittels Modelluntersuchungen

Background, Aim and Scope

Many environmental pollutants are slowly degrading (persistent) and very mobile. They are semivolatile, i.e. they are partitioned between the environmental media of soil, water and air, and undergo long-range transport. The combined action of climate and substance properties determines the distributions and fate of these substances, among them as the persistent organic pollutants (POPs), other pesticides and industrial chemicals.

Main Features

Multicompartment chemistry-transport models are under development in order to study environmental exposure models.

Results

The investigation of transport and fate of some POPs on the global scale has emphasized the significance of historically explicit and geo-referenced simulations for substance distributions, persistence and long-range transport potential. Apart from the substance properties, it is the regional climate which is most important. This was illustrated by studies into the regional cycling of DDT and γ-HCH in selected tropical and extra-tropical regions.

Discussion

The isolation of individual steps of subsequent cycles of emission, transport and deposition (a so-called grasshopper effect) in model experiments shows the potential to elucidate the complex superposition of substance properties and environmental conditions, variable in time and space.

Conclusions

The results suggest that the grasshopper effect enhances the long-range transport potential, but is not required to explain an accumulation in polar regions (at least for γ-HCH).

Perspectives

A number of relevant scientific questions should be addressed by exposure modelling.     

Sources of organochlorine pesticides in air in an urban Mediterranean environment: volatilisation from soil

Organochlorine pesticide (OCP) cycling was studied in the area of Banja Luka, Bosnia and Herzegovina, over 3 days in summer with high temporal (4 h-means) and spatial (3 sites distanced 3-6 km) resolutions. Elevated levels of DDX compounds (i.e. o,p'- and p,p'-isomers of DDT, DDE and DDD, 44-74 pg m(-3) at the urban sites and 27 pg m(-3) as a background level), HCH (α-, β- and γ-isomers, 52-70 vs. 147 pg m(-3)), HCB (34-48 vs. <0.1 pg m(-3)) and pentachlorobenzene (6.8-9.9 vs. 6.0 pg m(-3)) were found. The variation of OCP levels at the two urban sites was not in phase, except for most DDX compounds. This was related to background levels, which for HCH were higher than in the urban area. Vertical profiles between samples collected from 1.1 and 2.3 m (part of the time 0.6 and 2.3 m) above a soil, which was only moderately contaminated by OCPs (0.12 ng g(-1) HCH, 0.11 ng g(-1) DDX, 0.44 ng g(-1) HCB) were analysed. Volatilisation from the ground caused negative vertical concentration gradients of HCH isomers (day and night), but not for HCB (except for 1 day-time sample) and DDX compounds (except p,p'-DDD, day-time, sporadically). The concentration in air and the vertical concentration gradient of the HCH isomers varied with air temperature (day-time maxima), while the variation of the HCB concentration was inversely related to air temperature and was determined by mixing (night-time maxima). α- and β-HCH were volatilised from soil throughout the three days, even during periods of cooling. Fugacity calculations, based on the absorption in soil organic matter as the process determining retention in soil, underestimated the volatilisation of β-HCH and p,p'-DDD. It is concluded that the representativeness of point measurements of OCPs in urban areas is limited by the spatial variability of soil contamination.     

Quantification of sources of PCBs to the atmosphere in urban areas: A comparison of cities in North America, Western Europe and former Yugoslavia

We present estimated emission source strengths of seven polychlorinated biphenyl (PCB) congeners for Banja Luka, a city that was affected by the civil war in Bosnia and Hercegovina (former Yugoslavia) in the 1990s. These emission estimates are compared to PCB emission rates estimated for the cities of Zurich, Switzerland, and Chicago, USA using an approach that combines multimedia mass balance modeling and measurement data. Our modeled per-capita emission estimates for Banja Luka are lower by a factor of ten than those for Zurich and Chicago, which are similar. This indicates that the sources of PCB emissions in Banja Luka are likely to be weaker than in the Western European and North American cities which show relatively high PCB emissions. Our emission rates from the three cities agree within a factor of ten with emission estimates from a global PCB emission inventory derived from production and usage estimates and emission factors.     

Determination of malic acid and other C4 dicarboxylic acids in atmospheric aerosol samples

An ion chromatographic method was developed which is able to separate five unsubstituted and hydroxy C4 dicarboxylic acids, succinic, malic, tartaric, maleic and fumaric acid, besides the other unsubstituted C2-C5 dicarboxylic acids, oxalic, malonic and glutaric acids, as well as inorganic ions in samples extracted from atmospheric particulate matter. By the application of this method it was found for both rural and urban sites and for various types of air masses that in the summer-time malic acid is the most prominent C4 diacid (64 ng m(-3) by average), exceeding succinic acid concentration (28 ng m(-3) by average) considerably. In winter-time considerably less, a factor of 4-15, C4 acids occurred and succinic acid was more concentrated than malic acid. Tartaric, fumaric and maleic acids were less concentrated (5.1, 5.0 and 4.5 ng m(-3) by average, respectively). Tartaric acid was observed for the first time in ambient air. The results indicate that in particular anthropogenic sources are important for the precursors of succinic, maleic and fumaric acids. Biogenic sources seem to influence the occurrence of malic acid significantly.