The effect of Cr 6+ on Allium cepa root length was studied using both clean and polluted river waters. Seven series of Cr 6+-doped polluted and non-polluted river waters were used to grow onions. Chromium concentration (Cr 6+) of 4.2 mg L -1(EC 50 value), doped in clean river water caused a 50% reduction of root length, while in organically polluted samples similar root growth inhibition occurred at 12.0 mg Cr 6+ L -1. The results suggested that there was a dislocation to higher values in toxic chromium concentration in polluted river water due to the eutrophization level of river water. © 2009 Springer Science+Business Media, LLC.