149-Leaching Assessment of Pathogen Indicators in the Tropical Soils of Hawaii

Abstract

Ground water contamination from human pathogens is a concern in tropical islands where ground water is the source of drinking water. Understanding the processes of pathogen behavior, especially in unsaturated tropical soils, is important in preventing groundwater contamination. Laboratory column experiments (100 to 150 mm long columns) were conducted to study the effects of an anionic polyacrylamide (PAM) polymer on the movement of Escherichia coil and the FRNA phage MS-2 under unsaturated conditions. The study was designed to evaluate if PAM would enhance the mobility of human pathogens in tropical soils under unsaturated conditions. Soil in the columns was kept under unsaturated conditions by applying a small vacuum at the bottom of the columns. E. coil or MS-2 phage in the feed solution was pumped into the top of the columns. In addition, the surfactant, Linear Alkylbenzene Sulfonate (LAS), was used in low amounts to simulate a concentration that is present in sewage. The soil used for the column experiment was an Oxisol from the island of Oahu, Hawaii. No breakthrough of phage was observed in a 100 mm column after passing 100 pore volumes of solution containing 1 x 108 plaque-forming units (PFU)/rnL. In later experiments, after passing 10 to 20 pore volumes of solution containing 1 x 10 viral particles or bacterial cells per milliliter through 150 mm columns, the soil columns were sliced and the organisms eluted from the soil. Neither phage nor E. coil breakthrough occurred at the bottom of the columns with either PAM or PAM + LAS. Phage progressed slightly further in the polymer-treated column than in the control column. There was no measurable difference in the movement of E. coil in either polymer-treated or control columns. The properties of the soil (high amounts of metal oxides, kaolinitic clay), unsaturated flow conditions during the leaching experiments, and relatively high ionic strengths of the leaching solution contributed to significant retention of the indicators. The impact of PAM and LAS on the mobility of E. coil or MS-2 phage in the chosen soils was not significant under the conditions of the study. Additional studies were conducted for two other soils to evaluate the mobility of MS-2 under conditions of variable pH and solution salinity.