dc.description.abstract
Even some 50 years after the ban of DDT in Europe and North America, DDT and its metabolites are still posing a severe problem due to the environmental persistence. According to the Stockholm Convention DDT is one of the “Dirty Dozen”, supposed to be phasing out in 2020. Industrial production sites and their surroundings still exhibit a high risk of contamination in recent years.
During the mid-1990´s a survey of different aquatic ecosystems revealed background information about the degree of contamination in North-East (NE) Germany, including the Arkona Basin in the Baltic Sea. The applied analytical approach provided basic data on trace metals and organic contaminants such as PCDD/F´s, PAH´s, PCB´s, DDX and HCH´s. The optimising of the analytical tool and extension to include non-extractable residues into the assessment led in combination with a non-target screening approach to the identification of the point source (Berlin-Chemie) at the Teltow Canal. Recent research activities have focused on this area contaminated by the effluents from this point source. Surface sediments, sediment cores, surface and ground water samples were extensively analysed and identified more than 30 different metabolites of DDT, among other pesticides and various industrial compounds.
As a result, in the 1990´s about 135,000 m-3 of contaminated sediment (approximately 180,000 t) were removed by dredging. The remaining sediment has been investigated with regard to the contamination state. Due to the improved water solubility of DDA through the polar carboxyl group, it is one of the best water-soluble DDT metabolites. The assessment of the maximum contamination potential in relation to DDX (in particular DDA and its precursor metabolites) was considered. Furthermore, the incorporation of metabolites into sediment was investigated by applying a five-step degradation procedure. Free available (Extractable Fraction) as well as easily (Easily Releasable) and hardly available fractions of DDA and precursor metabolites were obtained and a maximum of 48 kg in the EF fraction (32 - 82 kg) and 1,360 kg in the ER fraction (11 – 4,010 kg) were estimated by application of a trapezoid model. Calculation using a column model resulted in 278 kg in the EF fraction (214 - 354 kg) and 9,800 kg in the ER fraction (250 - 29,000 kg). In both cases the mean values are applied and the variation is high, resulting in a very rough calculation. The comprehensive analysis scheme provides information on free accessible and potentially metabolised precursors also in the non-extractable residues (NER). This allows a quantitative assessment of the DDA contamination potential derived from DDT residues in the canal sediments close to the source. The remobilisation of sedimentary DDA under dynamic conditions such as dredging or shipping activities has been investigated. Hence, a high remobilisation and release potential of DDA was observed. The vast majority of the available DDA content has been released immediately resulting in a direct contamination potential for the aquatic environment.
Several precursor metabolites of DDA, e.g. DDD and DDMS, extractable from the sediment organic matter (SOM), revealed a high potential for a long-term formation of DDA, especially in the easily releasable fraction (via hydrolysis) with a mean concentration of up to 11,000 μg g-1 dry sediment. The resulting DDA-contamination potential represents a significant contamination risk for the groundwater from a downstream waterworks area and by remobilisation into the whole ecosystem and adjacent rivers.
The application of the presented methods provides a tool for a quantitative assessment of the long-term release potential of DDA and similar compounds under different scenarios by a comprehensive analysis of contaminated sediments (and soils). This approach can be transferred to contaminants that are also characterised by a complex metabolism accompanied by NER-formation and, in combination with toxicological data and bioavailability tests, represents a more advanced and detailed evaluation approach.
This thesis should demonstrate the necessity to investigate not only extractable residues of sedimentary contamination but to consider the incorporation of contaminants and metabolites in particulate matter as well. Non-extractable residues in sediments can represent a long-term contamination potential for the environment. In most studies, the remobilisation of NER and their transformation reactions were widely neglected. In addition, released compounds can be transported to distant locations due to sorption on particles and colloids. The transport of released sedimentary compounds to the aquatic environment is neglected in literature as well.
An analytical approach resulting from the experience of the work is presented, where a distinction is made between the water phase and various particulate phases, including humic substances. The applied degradation scheme is integrated in the scheme. These separate extracts can be used for bioassays.
Differences in the analytical approaches and degradation techniques lead to further scientific questions about the formation of NER and the constituents involved. Combined analytical approaches with classes of SOM components (such as lipids, humic substances) are possible and the kinetics and dynamics of the NER formation and release process can be studied.
Natural attenuation is underway. To complete the evaluation potential of the instrument, desorption and bio-accumulation experiments can provide insights into the actual and potential contamination by the accumulated sediments.
Comparable contamination data were obtained in comparison to previous studies, indicating a still high contamination level and, by calculating the maximum contamination range, a continuous release potential into the water phase and the canal ecosystem.
Besides natural particulate sorbents such as humic substances and natural organic matter, synthetic polymers and plastic particles are an additional particulate sorbent in aquatic ecosystems. Plastic is a general term for a class of materials that is composed of different types of (synthetic) polymers. Such materials own beside the polymer often different additives at a low content, which optimise or adjust the properties during processing and application.
Plastic particles including micro plastic are widely detected in the environment today. Micro contaminants, especially very persistent organic compounds, are also detected in large parts in the (aquatic) environment resulting in many recent papers, dealing with interactions between organic contaminants and (micro) plastic particles in the environment, hypothesizing the function of plastic particles as a vector for bio-magnification, resulting in negative ecosystem effects.
In the present work such interactions between polymers (polyethylene (LD-PE) and hard polyvinyl chloride (H-PVC) and organic, persistent compounds (here: DDT, methoxychlor and dicofol) were investigated. A new and innovative experimental approach based on a static system similar to a burial in deeper sediment layers was investigated.
With the presented sorption test, it was possible to demonstrate the adsorption/incorporation of contaminants into the two polymers. The recovery of the three target compounds ranged between 2.0 - 2.4 % of the initial concentration for PE and 0.2 – 1.9 % for PVC, respectively. Differences between the two polymers are addressed. In the sorption experiments all the target compounds were detected in alignment with their hydrophobicity, resulting in a relative order of DDT > DMDT > Dicofol.
In the desorption experiments, diffusion of the contaminants out of a contaminated sediment on the polymers could be verified. In maximum 22 μg Ʃ DDX (DDD/DDE/DBP and DDMS) could be desorbed within one month in the PE-experiment. Relative to published data of the International Pellet Watch project (IPW) 180-460 ng Ʃ DDX/g PE-polymer were analysed. These are in the range of other more contaminated sites, except for a few very highly sites.
Differences in polymers are analysed and explained mainly by the glassy transition temperature with subsequent flexibility at room temperature. All three aspects differentiating LD-PE and H-PVC in polymer structure, polarity and properties, free volume and contaminant behaviour are obvious.
The rapid formation of a biofilm on the polymer surface limits the sorption capacity, even with highly contaminated material and compared to pellets and fragments. The ATR-FTIR analysis of the surface layers of the 3-month containers led to the identification of a water-rich surface layer consisting of hydroxy and aromatic structures. The differences between the two plastic polymers meet expectations, based upon the different glass transition temperatures (Tg).
The new experimental desorption approach shows an easy to handle alternative means for sorption and desorption experiments with (plastic) polymers as well as kinetic experiments. The limited capacity of pure polymers is demonstrated in the sorption experiments, including antagonistic effects due to differences in hydrophobicity. These complex issues are routinely not addressed in simple kinetic lab-experiments with a single substance approach.
The rapid formation of diffusion barriers at the polymer surface limits the sorption capacity, even for the highly contaminated material, demonstrating a more realistic approach for naturally contaminated systems with a huge number of different compounds and possible antagonistic effects on sorption.
The very low sorption capacity means that the possibility of remediation by plastic polymer material is very low and, together with the natural organic matrix, it has no function as a transport vehicle in natural ecosystems. Further investigations are urgently needed to verify the postulated effect as a vector.
A monitoring programme is strongly recommended, especially in the heavily contaminated area near the point source, considering the use of the Johannisthal waterworks as a protective well for the incoming bank filtrate from the Teltow Canal. The analysis of micro plastic in the Teltow Canal ecosystem is currently underway and the relative proportion of anthropogenic contaminants in these analyses can provide information about the relative proportion of micro plastic as a transport vehicle.
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