2.6.1. Pollution load index (PLI) and contamination factor (CF)
To assess the sediment quality, an integrated approach of pollution load index of the six metals is calculated according to Suresh et al. (2011). The PLI is defined as the nth root of the multiplications of the contamination factor of metals (CF).
1/n
PLI(CF1 × CF2 × CF3 × . . . × CFn) (1) where CFmetals is the ratio between the content of each metal to the background values (background value from the preindustrial samples of the study area in Bangladesh) in sediment,
CFmetals = Cmetal/Cbackground. Therefore, PLI value of zero indicates perfection, a value of one indicates the presence of only baseline level of pollutants and values above one would indicate progressive deterioration of the site and estuarine quality (Tomilson et al., 1980). The PLI gave an assessment of the overall toxicity status of the sample and also it is a result of the contribution of the six metals. The ratio of the measured concentration to natural abundance of a given metal had been proposed as the index contamination factor (CF) being classified into four grades for