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Abstract

Mbuya, O., W. Mwegoha, A. Jain, T. Tsegaye and N. Jaja. 2008. Effect of perchlorate concentration on phytoremediation and phytotoxicity. JEMREST 5:30-40.

The effect of perchlorate concentration on rhizodegradation, plant uptake, phytoaccumulation and phytotoxicity was studied using hydroponic and soil bioreactors planted with willows (Salix babylonica) under greenhouse conditions. All bioreactors were amended with approximately 300 mg L-1 dissolved organic carbon (DOC) in the form of cow manure extract. Planted and non-planted hydroponic experiments were conducted at three perchlorate concentration ranges namely; low (50-200 mg L-1), high (300-700 mg L-1) and very high (2,000-6,000 mg L-1). Planted soil bioreactors filled with sandy loam soil were evaluated at perchlorate concentration range of 1,000-10,000 mg L-1. Complete perchlorate removal was reached within 5-9 days for both the planted and non-planted bioreactors at the low concentration range. The planted hydroponic bioreactors with high perchlorate concentrations exhibited total perchlorate removal within 6-10 days, whereas non-planted bioreactors had substantial amount of perchlorate remaining in solution when the experiment was terminated in day 10 (9.68%, 17.89% and 61.07% of the initial concentrations of 300, 500 and 700 mg L-1, respectively). Planted hydroponic bioreactors treated with very high concentration of perchlorate were not able to completely remove perchlorate in the 15 experimental days despite the abundance of external DOC. All plants in the very high perchlorate concentrations suffered phytotoxic effects from day 2 and totally dried up by day 8. Solution samples taken 7 days after leaf fall indicated that approximately 40.02%, 66.24% and 55.99% of the initial perchlorate doses were still in solution, for the 2,000; 4,000 and 6,000 mg L-1 perchlorate treatments, respectively. Results from soil bioreactors dosed with 1,000; 5,000 and 10,000 mg L-1 perchlorate were consistent with hydroponics experiment at very high concentrations. Perchlorate concentration in leaf tissue samples increased with increasing perchlorate concentration in solution. Perchlorate dose of e” 1,000 mg L-1 in both hydroponic and soil bioreactors significantly curtailed the performance removal of perchlorate from solution and resulted into high phytoaccumulation in plant leaves.