The application of adsorptive processes for an estimation of ecological risk at soil pollution by organic compounds

Contaminated sites recovery is time consuming and involves increasingly high costs, despite in presence of limited economic resources availability. The existing legislation or guidelines currently stand on the total soil content of pollutants. Feature of soil pollution is that components of ground (organic mass, clay minerals) are capable to adsorb organic compounds and a part from them are kept irreversibly. At an identical total level of pollution the soil of various structures represent a various level of ecological risk. Therefore it should be possible to assess ecologically the risk of soil, evaluating the mobile fraction of pollutants by means of diffusive gradient technique in thin film (DGT) [1]. Principles of an estimation of ecological risk with DTG- device have been confirmed for the heavy metals determination [2]. In the given research there was a task to carry out tests of the above mentioned unit in conditions of soil pollution by organic compounds. The heavy metals DTG-device uses a cation-exchangeable resin and a diffusive gel. The resin mimics the metals uptake of plant from soil, lowering soil solution metal concentration. The metal concentration at the interface between soil and diffusion layer is calculate by applying the first Fick’s law . In the case of hydrocarbon absorption it is necessary to replace the resin with an opportune adsorbent and to realize a diffusion layer transparent for organic pollutants. The new device, realized by authors, consists of an assembly containing a layer of water-saturated adsorbent and a chamber of deionized water, confined between glass fiber filters, as diffusion layer. Such design allows diffusion of hydrocarbons from soil through soil solution to adsorbent. Thus there is a displacement of equilibrium and begins desorption from solid phase to soil solution. In the case of correct selection of the adsorbent it is possible to estimate the quantity of pollutant, capable to resupply in soil solution. Values of the parameters, describing transport of hydrocarbons in a solution from soil solid phase, were received experimentally. The trend in time variation of these parameter show a law similar to that obtained in soil pollution by heavy metals ions. Hence, the principle of DGT-technique can be also extended for an estimation of the ecological risk on soil pollution by organic compounds.