Tracing Pharmaceuticals in the Unsaturated Zone (10 pp)

Background, Aim and Scope   One of the first occurrences of pharmaceutically active compounds in groundwater was reported from the sewage irrigation farms south of Berlin. At these sewage irrigation farms treated sewage effluent passed the soil and unsaturated zone before reaching the aquifer. Clofibric acid was detected in pore water from soils of those sewage irrigation farms in concentrations between 65 ng/L and 1430 ng/L. The aim of this study was to investigate the transport behavior of regularly detected clofibric acid, diclofenac, ibuprofen, and propyphenazone under conditions comparable to those at the sewage irrigation farms in a multiple compound sand column laboratory experiment. Materials and Methods   Sediment column experiments were conducted to study the transport of pharmaceuticals in the unsaturated zone. The migration was measured in fine to medium grained sand and leaching solution containing 1 mg/L of pharmaceutically active compounds and 61 mg/L of the tracer lithium chloride (LiCl). For the analysis of the pharmaceutical compounds the water samples were adjusted to a pH value of 2 and then extracted by solid-phase extraction (SPE). Before extraction, the samples were spiked with a surrogate standard for analytical quality control. The sample extracts were analyzed by capillary gas chromatography-mass spectrometry (GC-MS) with selected ion monitoring (SIM). Depending on the sample volume (100 to 200 mL) and the matrix, the limits of detection were between 1 and 10 ng/L, and the limits of quantitation were between 5 and 25 ng/L. Analysis for calcium, magnesium and lithium were carried out using a 'Trace Scan' ICP-AES from Thermo Jarrel Ash. Sodium, potassium, iron and manganese were analyzed using a Philips PU 9400 flame AAS. Analysis of anions was performed on a Dionex ion chromatograph DX 120. Results   At the sewage irrigation farms the average concentrations of clofibric acid in the unsaturated zone declined from higher values near ground surface (480 ng/L) to lower values near the groundwater table (65 ng/L). From the pharmaceuticals analyzed only clofibric acid, primidone and propyphenazone could be analyzed in the first (upper) aquifer at the sewage irrigation farms. All other pharmaceuticals could neither be detected in the first aquifer nor in the deeper aquifers. Breakthrough curves from soil column experiments revealed no transformation and no retardation for clofibric acid, whereas transformation of diclofenac was so high (79%) that no retardation factor could be calculated. Ibuprofen was significantly transformed (37%), transformation of propyphenazone (17%) was quite low and retardation (Rf = 2.05) was in the range of previously conducted column experiments. Discussion   The results confirm previously conducted experiments with clofibric acid where this compound was identified as highly mobile and persistent. The results that diclofenac and ibuprofen are significantly transformed where unexpected as other studies exhibited much lower transformation under saturated conditions at least for diclofenac. However, lower pH values and higher oxygen contents in the unsaturated zone compared to the aquifer may explain this observed high transformation of these compounds at the column experiments. Conclusions   We conclude that irrigation with sewage effluent containing the compounds used in our experiments will lead to an input into groundwater of clofibric acid, whereas diclofenac and ibuprofen will most likely be transformed during the passage. Propyphenazone will be retarded but will most likely occur in groundwater. These results from the column experiments coincide very well with the occurrence of the pharmaceuticals clofibric acid, primidone, and propyphenazone in the first aquifer. Recommendations and Perspective  : The results underline the need to study the sorption of pharmaceuticals on various materials. e.g. organic matter, surfaces at pH values occurring in the unsaturated zone. Future field studies will also include the investigation of desorption behavior in the unsaturated zone.