Evaluation of Veterinary Pharmaceuticals and Iodine for Use as a Groundwater Tracer in Hydrologic Investigation of Contamination Related to Dairy Cattle Operations

Standard groundwater tracers such as Rhodamine WT, Fluorescein, Eosin and Tinopal CBX effectively provide a snapshot of hydrological conditions over a brief period of time and in a tightly controlled setting. However, in complex environmental situations with multiple potential sources, groundwater hydrologists are often seeking groundwater tracers that have extended longevity in the natural environment and the ability to directly pinpoint source locations. After reviewing operations of the nearby dairy it was determined that emerging contaminants, specifically two bovine veterinary pharmaceuticals (antibiotics), cephapirin sodium (CEPNa) and cephapirin benzathine (CEPB), and a sanitation agent, elemental Iodine (I) may have potential as extended longevity groundwater tracers if analytical methodology could be established. Initially, sample analysis indicated that cephapirin is undetectable in unconcentrated samples of lagoon wastewater at parts per billion (ppb) concentration; pre-concentrated samples which utilized solid phase extraction allowed for better detection at part per trillion level. Concentrated samples from one of the two lagoon cells sampled (cell #3), detected cephapirin at 13.14 ppt level, while cell #1 failed to detect any cephapirin present. Controlled laboratory testing later indicated that in a wastewater environment cephapirin degrades to approximately 20% of initial concentrations within 4 days, with complete degradation within 6 days. Degradation patterns in surface water and groundwater samples were less dramatic and at slower rates. Degradation curves of the surface and groundwater samples indicate that concentrations of cephapirin are still detectable for approximately 25 days. Unconcentrated Iodine samples collected in lagoon cells ranged from 50.896 ppb and 1,704.55 ppb with variations determined to be a result of the primary inflow of the lagoon. Cephapirin’s use as a long term groundwater tracer does not seem to be an immediate option. Further research may reveal that its degradation products are potentially useful as a tracer. In some instances, such as catastrophic discharges of large volumes of milk when samples can be collected and analyzed quickly, the use of cephapirin as an environmental tracer may prove possible. The validity of pharmaceutical iodine as a groundwater tracer appears to be much greater than that of cephapirin. Iodine was detected in all of the environmental samples including the highly organic and anaerobic environment of the dairy wastewater lagoon. This study concludes that iodine is capable of surviving the hostile wastewater environment. If sufficient data is collected to determine natural background levels, iodine may prove useful in determining hydrological connections between iodine laden dairy effluent and the underlying groundwater.