The processes affecting oxytetracycline contamination of groundwater in a phreatic aquifer underlying industrial fish ponds in Israel

Oxytetracycline (OTC) is an antibiotic that is regularly added to fish ponds used in industrial- scale fish-farming along the Mediterranean coast of Israel. It is not found in unpolluted water. The ponds are constructed upon porous sands that are also the host rock of the local aquifer. These ponds leak. Monitoring for OTC was carried out in a fish pond and three surrounding water wells that exploit the local aquifer. The local groundwater is composed of the native groundwater and the leakage additions. Two wells, P-204 P-205 are used to insure that the water levels in the ponds are maintained. A frequently pumping well, M-2, is located closest to the main source of OTC input at pond B. It is used to supply drinking water and OTC was found in it. This contaminant is related to leakage from the nearby fish pond. OTC is generally assumed to be immobile and effectively removed by soil and sediments. In this case, continuous leakage of the pond has created preferential saturated flow paths that bring the contaminants directly to groundwater, bypassing the immobilizing sorption pro cesses that usually take place in the unsaturated zone. In the absence of such conduits OTC is effectively excluded from reaching other producing wells.