An investigation on heavy metal (cadmium, chromium, zinc) concentration changes in water and sediment, and assessing the biological value index (Z) in Karaj River

Karaj River, as one of main source of drinking and agriculture water for Tehran and Alborz provinces, has biological potentials, and is one of the protected rivers in Iran. The main purpose of this study was to investigate the concentrations of heavy metals: cadmium, chromium and zinc in the water and sediment samples of Karaj River in order to evaluate the quality of water, using biological value index (Z). Sampling of water, benthos and sediments was carried out from January 2018 to July 2018 from 7 point stations along the river. Preparation of water and sediment samples was performed by evaporation and the studied metals concentrations were measured by ICP device. The obtained results demonstrated that both in water and sediment samples, studied metals showed significant differences from upstream to downstream stations. Also, the concentration of all metals in water and sediment was lower in January than in July. The results of the Z biological value index revealed a significant difference in both seasons between the sampling stations, and the highest value of in both seasons belonged to the downstream stations. Contamination by heavy metals, especially in downstream, is due to human interventions such as agricultural, urban and industrial wastewaters. In the cold season, because of declining population density in the river vicinity area, pollution levels have been decreased. Also, in terms of quality, in general, Karaj River can be classified in saprobe class II and III.