In the initial phase of the project "Organic Trace Substances Relevant for Drinking Water – Assessing their Elimination through Bank Filtration (TRACE)" the total herbicide glyphosate was classified as highly relevant for further investigations [Chorus & Wessel 2007]. Glyphosate is one of the most widely used and distributed herbicides in the world. Even though it has been on the market since 1974 its use increased with the expiry of the patent at the beginning of the 1990s, in the context of “soil conserving” agriculture (no ploughing) and with the introduction of glyphosate resistant, genetically manipulated cultures like corn, soy beans and cotton wool in 1997. To estimate the occurrence of glyphosate and its main metabolite AMPA in the surroundings of Berlin samples from 22 surface water sites were analysed within this study. In 5 samples the glyphosate concentration was above the European threshold for herbicides of 0.1 µg/L in drinking water. Up to 70 % of Berlin’s drinking water is produced via bank filtration and aquifer recharge characterized by comparatively low flow velocities (< 1 m/d), long contact times (3-6 months) and mainly anoxic redox conditions. To evaluate the potential of bank filtration to protect the drinking water from glyphosate contaminations an experimental study was conducted in the second phase of the TRACE project. Three enclosures at the UBA’s center for aquatic simulations were dosed with three different concentration levels (average concentration: 0.7, 3.5 and 11.6 µg/L) over a time period of 14 days. The effluent was sampled daily for 34 days. Glyphosate and AMPA were analysed applying the HPLC method according to the German Standard DIN 38407-22/2001. In parallel the applicability of the ELISA kit of the company Abraxis was tested without adequate results. The one-dimensional substance transport model VisualCXTFit was applied to obtain substance specific parameters of glyphosate and hydrodynamic parameters of the filter substrate from observed and measured breakthrough curves. The obtained results show that the breakthrough of glyphosate was retarded remarkably (retardation coefficient (R): 18.3 to 25) despite of the initially postulated low adsorption potential of the sandy filter substrate. Also a significant reduction, probably due to degradation was observed (1st order decay-rate (alpha): 0.069 to 0.092 d-1). In addition to the semi-technical scale enclosure experiments laboratory and lysemeter tests were carried out to investigate the processes responsible for glyphosate removal during subsurface passage. The laboratory experiments yielded a KF-value of 1.8998 mgLkg-1 and a Freundlich exponent of 0.4805, from which a retardation coefficient of 53.4 was calculated for a glyphosate concentration of 20 µg/L. Furthermore, delayed degradation under sub-oxic conditions could be observed. The lysemeter experiments ensured no glyphosate breakthrough in the effluent of a 2 m thick column of fine to medium sandy material within 7 months. The data obtained in this project prove that there is a potential of bank filtration to eliminate the herbicide glyphosate: Taking into account that glyphosate concentrations in surface water are highly variable a good protection of the drinking water source by bank filtration especially in respect to peak concentration is ensured. However, adsorption and degradation parameters obtained in the laboratory and semi-technical experiments vary significantly due to the difficulty to imitate natural conditions in the laboratory. Therefore the experimental study of the project TRACE emphasises the need to conduct semi-technical experiments in a near-natural environment to evaluate the risk of contamination.

The project “Organic Trace Substances Relevant for Drinking Water – Assessing their Elimination through Bank Filtration (TRACE)” aims at giving an up-to-date overview of the potential risk resulting from the occurrence of chelating agents, perfluorinated compounds (PFCs) and selected pesticides in surface waters and to show if there is a potential for the substances to persist during bank filtration and artificial recharge. During the first phase of the project which is subject of this paper, a literature study was conducted addressing their occurrence (in the Berlin region and elsewhere), amounts produced as well as data on their persistence in the subsurface. This was the basis for a decision on the substance applied in the field scale experiments at the UBAs experimental field during the following project phase. Using freely available databases (e.g. ULIDAT, DIMDI, Tiborder) 1148 references were screened for their relevance to these topics, and 450 of these were classified as relevant. Of these, so far the 223 most important references have been compiled in an ACCESS database which comprises data on the data origin as well as on specific values (e.g. measured concentrations, amounts produced, use, main metabolites, sources, pathways in the environment). The database links this information so that output forms (“fact sheets”) can be created that summarize all data for one specific substance. The regarded substances were subsequently classified according to the criteria: usage / production, occurrence in surface water (if possible also in groundwater and bank filtrate), degradation potential, biological degradability, production of relevant metabolites and toxicity. For the chelating agents three substance groups were examined closely: aminocarboxylates, hydrocarboxylates and phosphonates (all other substance groups were found to be irrelevant due to total biodegradability). The aminocarboxylates are produced in highest numbers and occur most frequently (especially EDTA, PDTA, NTA and DTPA). There are, however, already extensive investigations on this field so that few knowledge gaps were identified. Hydrocarboxylates are produced in lesser amounts and for some ready biological degradability has been shown. For these reasons further investigations were not seen as a priority. Phosphonates produce relevant metabolites (phosphates that enhance eutrophication) and are produced in high amounts (> 1000 t/a). This substance group was therefore recommended for further investigations. Currently a variety of research projects cover the field of perfluorinated compounds (PFCs) that occur in aquatic environments world wide and whose toxicity and persistence is not yet clearly determined. Most investigations aim at the main substances of this group: PFOA and PFOS. These are, however, currently being replaced by shorter chained PFCs on which investigations are lacking. This substance group is therefore also of interest for further investigations. For the pesticides glyphosate and isoproturone high production rates and frequent occurrence in surface and groundwater world wide were determined. Due to this fact and to the presence of relevant metabolites (e.g. AMPA) as well as to limited knowledge on their fate during underground passage these substances were classified as highly interesting for further investigations.