Development of a new aggregative index to assess potential effect of metals pollution in aquatic sediments

•A new aggregative index (mRAC) based on metal toxicity and risk of release was developed to assess potential adverse effect of metals.•Sediments of Anzali wetland are categorized as high or very high potential adverse effect of metals.•Application of mRAC may provide deeper insight in the assessment of potential risk of metals pollution.

A new aggregative index called modified risk assessment code (mRAC) was developed based on heavy metal toxicity and fractionation in aquatic sediment. Results of the application of mRAC to assess metal pollution in surface sediment samples of Anzali international wetland revealed that the new index led to more precise results than those of other prevalent aggregative indexes, such as modified degree of contamination (mCd) and ecological risk index (RI). Based on assessment by mRAC, sediments of the study area were at high or very high potential adverse effect levels, compared to using mCd and RI where sediments were at a moderate or low potential adverse effect level. This is due to mRAC taking both metal toxicity and fractionation into account.