Risky pollution index: an integrated approach towards determination of metallic pollution risk in sediments

In all three types of metallic pollution indices (accumulative or comparative, enrichment and ecological risk indices) the bulk concentration of metals in the sediment sample is considered. Such point of view indicates that all chemical forms of a given metal have an equal impact on the environment which may not be regarded reasonable. In order to include the effect of metal fractionation in sediments for estimating the pollution risk to the biota, developing a risky pollution index (IR) has been considered in this study. In contrast with Mobility Factor (MF) and Risk Assessment Code (RAC) indices, IR attributes a risk share to metal species bound to reducible and oxidizable phases which are totally neglected in both two above-mentioned indices. In other words, besides the absolutely mobile fractions, the potentially mobile ones are also regarded in risk evaluation process elaborated by IR. The different structure of the newly-developed index may prevent risk level underestimation especially in case where a remarkable percent of bulk concentration is accumulated within reducible and oxidizable phases. The independency of the index value to the bulk concentration makes it possible to discuss the potential risk in different levels of bulk concentration. Furthermore, the index capability in indication of risky pollution regardless of the pollution source type may prevent the probable misleading caused by distinct separation of bulk concentration into geopogenic and anthropogenic portion.