Approximately 70% of the initial Cr was recovered in the plant materials. More than 90% of the applied Cr(3+) was removed from the aqueous solution by willows at concentrations up to 7.5 mg Cr/L.
Results from the Cr uptake study showed that significant removal of Cr from hydroponic solution was observed in the presence of hybrid willows without showing detectable phytotoxicity, even at high does of Cr. The correlation between the concentration of Cr and CAT activity in leaf cells was the highest of all toxicity assays (R ( 2 ) = 0.9096), indicating that CAT activity was most sensitive to the change in Cr(3+) doses compared with the other selected parameters. Superoxide dismutase activity (SOD) in leaves between the treated and untreated willows did not show any significant difference, but activities of both catalase (CAT) and peroxidase (POD) in leaf cells of all treated plants were higher than those in the untreated willows.
The contents of chlorophyll in leaves of willows exposed to > or =7.5 mg Cr/L were higher than that of the untreated plants but lower at 30.0 mg Cr/L.
The measured chlorophyll contents in leaves of treated plants varied with the dose of Cr, but a linear correlation could not be established. Removal rates of Cr (III) decreased linearly with the strength of nutrient solutions with or without N addition (p or =20%) of soluble protein in young leaves of willows was detected in the treatment group with > or =7.5 mg Cr/L. Substantial difference existed in the distribution of Cr in different parts of plant tissues due to the nitrogen in nutrient solutions (p0.05). Although faster removal of Cr (VI) than Cr (III) was observed, translocation of Cr (III) within plant materials was more efficient than Cr (VI). The results revealed that higher removal of Cr by plants was achieved from the hydroponic solutions without any nitrogen than those containing nitrogen. Pre-rooted hankow willows ( Salix matsudana Koidz) were grown in a hydroponic solution system with or without nitrogen, and amended with hexavalent chromium or trivalent chromium at 25.0+/-0.5 degrees C for 192 h. The effect of available nitrogen in nutrient solution on removal of two chemical forms of chromium (Cr) by plants was investigated. Effect of available nitrogen on phytoavailability and bioaccumulation of hexavalent and trivalent chromium in hankow willows ( Salix matsudana Koidz).
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