A Simple and Rapid Method to Assess the Quality of River Water: Correlation Between Electrical Conductivity and Fecal Coliform Density in Hyogo Prefecture, Japan

Abstract

This is a report regarding the development of a simple survey method for monitoring water pollution in the Toga River in Kobe City, Japan. This river is popular with local citizens as a water park, and especially in the summer, various activities are introduced to encourage children to play in the river. However, in recent years, contamination by fecal coliforms, probably caused by the accidental influx of domestic wastewater, often limits children from playing in the water. From May to October 2019, water samples were collected from five locations in the Toga River and the concentration of fecal coliforms was measured, along with the electrical conductivity and the chloride ion concentration of the river water, to establish a method for estimating the fecal coliform density (FCD) as a quicker alternative to a culture test. By comparing these parameters with the actual density of fecal coliforms, a high correlation was found between the electrical conductivity and FCD. On the other hand, there was almost no correlation between FCD and the chloride concentration. Receiver operating characteristic (ROC) analysis was used to evaluate the method that uses the electrical conductivity as an estimating parameter. The area under the curve (AUC) was used to determine the performance of the ROC curve algorithm. The calculated AUC value stayed high, above 0.95, over a wide range of threshold values of FCD, suggesting that this rapid method is appropriate for assessing the quantity of contaminating fecal coliforms in the range of 300–2,000/100 mL.