Eco-Toxicological Risk Assessment of Heavy Metals and Polycyclic Aromatic Hydrocarbons in Sediments of Tigris River, Iraq

Abstract

The Tigris River is an important source for domestic, agricultural, industrial, fisheries, and ‎even recreational activities. Therefore, environmental assessment of river sediments is vital, as sediments can be considered ‎reservoirs of pollutants that are re-released into the water during floods or human activities. ‎This research aimed to assess Tigris river sediments‎ ‎ from Al ‎Qayyarah to Al Tarmiyah.‎ Nine samples of sediment were collected for analysing seven heavy metals and a metalloid (i.e. Cu, Cd, Cr, Pb, Zn, Ni, and As) and sixteen PAHs compounds. The concentrations of heavy metals Cd, Pb, As, Cr, and Ni in some locations have exceeded ‎their background concentrations in the earth's crust. For assessing the contamination of sediments by metals, three indices, viz, SPI, TRI, and MERMQ were used. According to the results of the three indices, Al ‎Qayyarah‎ and Baiji sites were more contaminated than other sites. This may be attributed to anthropogenic activities represented by the petroleum industry which enriches sediments with metals. Also, three indices for evaluating the environmental risk of PAHs, i.e., MERMQ, ‎SQGQ‎, and RQ, were used. Based on Mean ERM Quotient values, the toxicity probability of PAHs in sediments ranged from 49% at Al ‎Qayyarah and Baiji to 21% and 9% at other sites. The SQGS index values showed that Al ‎Qayyarah‎ and Baiji sites‎ were highly affected by PAHs contaminants.‎ ‎According to the Risk Quotient (RQ) values of the sum PAHs, the environmental risk of river sediments ranged from low to moderate.