Application of water pollution and heavy metal pollution indices to evaluate the water quality in St. Sebastian Canal, Colombo, Sri Lanka.

Abstract

Anthropogenic pollution plays an important role in deteriorating the water quality of canals worldwide, espe- cially in developing countries like Sri Lanka. The St. Sebastian Canal is one of the main canals in Sri Lanka, which runs through Colombo city that collects massive quantities of domestic, municipal, and industrial waste products. The aim of the present study is to develop water pollution and heavy metal pollution indices to assess the water pollution status of the St. Sebastian canal, Colombo by comparing water quality parameters with ambient water quality standards for aquatic life in Sri Lanka. Water samples were analyzed for physical and chemical param- eters and heavy metals. Ultimately, Water Pollution Index (WPI) and Heavy Metal Pollution Index (HPI) were developed for several sites along the canal. WPI ranged from 0.64 to 1.93 with a mean value of 1.12, indicating water of St. Sebastian canal is highly polluted. The mean value of HPI was found to be 50, which is higher than the critical HPI value of 30, thus indicating that water of the canal is critically polluted with heavy metals. Further, sites 1, 5, 6, 7, 8 and 9 and sites 1, 4, 5, 6, 7, 8 and 9 were found to be highly polluted as per the WPI and HPI, respectively. This shows the importance of having both WPI and HPI to assess the level of water pollution as site 4 is being categorized as a highly polluted site by HPI and as a good water quality site by WPI. Therefore, the site-specific assessment of water pollution by WPI and HPI will help the relevant authorities to implement remediation methods with respective to the critical pollutants in a particular location, to identify the polluters and to take measures to prevent the discharges to the water body from different sources.