Response of sorption properties to long-term soil management

For many pollutants soil acts as the main sink in the terrestrial environment. Interaction of pollutants with mineral and organic soil constituents, microbes and plant roots determine their medium- and long-term behaviour. Soil organic matter (SOM) governs many soil properties and processes. SOM quantity and quality shows a considerable site variation caused by levels of OM input, related biological activity, overall nutrient status of the soil, vegetation, climate and soil minerals. SOM has a major influence on the adsorption properties of soils both by providing ample sites for adsorption and complexation of cations and anions and by altering the general chemical properties of soils. The only way to investigate the SOM effect isolated and possible concrete interactions with the unaltered mineral soil constituents is to use soils from long-term experiments, in which the SOM was altered, but the mineral phase was considerably less influenced by the long-term management. Sorption of a pesticide, which was used as first model substance (MCPA) was significantly altered by SOM levels. It is suggested to examine the impact of different management (fertilization, manures,...) of arable land and different landuse (permanent pasture vs. arable land) on the sorption properties for: -selected organic compounds (pesticides, polar and apolar substances) -heavy metals -radionuclides (Cs, Sr) A possible correlation of SOM turnover/buildup and sorption sites should be evaluated during the project by various methods. The outcome of the experiments will determine the effect of different treatments on the sorption behavior. Analysis of the experimental data and comparison of the sorption and leaching behavior to mineral and organic soil properties, structure and properties of the organic compounds and properties of the heavy metals and radionuclides should reveal the effect to long term treatments on arable soil systems. Thus, such sorption experiments allows to generate a set of data which can be used both to (i) improve our recent knowledge regarding sorption behavior of the investigated analytes and (ii) to assess the influence of certain long term treatments on the migration behavior of selected pollutants. Comparison of our calculated data with experimental data will shows how far a quantitative structural adsorption relationship can be applied to our system. Results from our QSAR (Quantitative Structure Activity Relation) model will be related to other existing soil sorption models, which obtained their input data from experimental data (e.g. log Pow) or quantum chemical descriptors.

For many pollutants soil acts as the main sink within our environment. Organic compounds and heavy metals interact with clay minerals, soil organic matter, microbes and plant roots, which influence their medium- and long- term behaviour in the ecosystem. Soil also represents a potential source of pollutants entering the food chain via plant root uptake or by leaching and subsequent groundwater contamination. Predictions of sorption properties of soils are not easy due to their highly heterogeneous nature both in mineral constituents and soil organic matter. The origin, composition and content of the organic matter have an important impact on the sorption behaviour of the soil for organic compounds and heavy metals. The content and quality of organic matter of agricultural soils is related to farming practices including manuring. Thus, changes in farming practices over time will change soil organic matter, which consequently will also influence the adsorption behaviour for pollutants. Within this project we investigated the sorption mechanisms of organic compounds and heavy metals onto soils and soil fractions from two long-term field experiments and model soils, respectively. On the other hand, organic molecules like pesticides show a huge complexity making it difficult to predict the responsible moiety driving the adsorption process. We decided to use 8 naphthalene derivatives differing in their functional groups for our adsorption studies. This combination of molecules with a relative simple structure and soils from two long-term fertilizing experiments has proven the impact of both soil management and the characteristics of organic molecules or heavy metals on adsorption in soil. Soil management alone - e.g. bare fallow versus mineral fertilizer and animal manure -resulted in differences in adsorption of up to a factor of 6. In case of heavy metals (Cd, Cu, Zn) the adsorption properties could be well described by changes of soil-pH, soil organic matter content and/or cation exchange capacity. In case of the organic model compounds their properties had a larger impact on adsorption processes than the soil characteristics. An interesting property to characterize the sorption behaviour in this respect were negative electrostatic potential moieties. The results obtained during this project reached a noticeable response from the soil science community. We clearly demonstrated deeper insights in adsorption mechanisms what opens new perspectives for further investigations in this field.