Background: Sediments in the aquatic ecosystems can be used as suitable indicators for monitoring contaminants. Then, objectives of this study were to evaluate the concentration of heavy metals in the surface sediments of the Mohammad Abad River, to determine the degree of pollution of heavy metals in sediments using some major contamination indices; to identify the major sources (anthropogenic or natural sources) of the studied metals; and to evaluate the “reference river” of the river under study for ecotoxicology studies.

Methods: Samples of sediment were taken from six sites of the river. The present study, eleven heavy metals (chromium, manganese, iron, cobalt, nickel, zinc, selenium, magnesium, silver, aluminum and arsenic) were studied.

Results: Comparison of metal concentrations with those of Sediment Quality Guidelines (SQGs) showed no association with harmful biological effects for the heavy metals studied except for Se and As. The results of the contamination factor index showed low pollution levels for most metals (Cr, Mn, Fe, Co, Ni, Zn and Al), moderate pollution levels for As, and very high pollution levels for Se. The degree of contamination (Cd) and modified degree of contamination (mCd), showing the total contamination of elements, demonstrated very high degree contamination status in the study area. According to the index of quantification of contamination, the values of Cr, Mn, Fe, Ni, Zn and Al were derived mainly from geogenic sources of enrichment, while the values for Se and As were enriched by anthropogenic source of enrichment.

Conclusion: These findings suggest that continuous monitoring of Se and As in sediment and organisms of the Mohammad Abad River should be directed to evaluate the threat of these elements to the public health and to the ecology of the river under study.