TOXICITY OF ZINC AND COPPER TO BRASSICA SPECIES - IMPLICATIONS FOR PHYTOREMEDIATION

The toxicity of Zn and Cu in three species from the genus Brassica was examined to determine if these plants showed sufficient tolerance and metal accumulation to be used to phytoremediate a site contaminated w ith these two heavy metals. Hydroponically grown 12-d-old plants of Br assica juncea, B. rapa, and B. napus were grown for an additional 14 d in the presence of either elevated Zn (6.5 mg L-1), Cu (0.32 mg L-1), or Zn+Cu to quantify the toxic effects of these metals on several dif ferent growth parameters. With few exceptions, both root and shoot dry weight for all three species decreased significantly in the presence of heavy metals. Cu inhibited lateral root elongation in B. rapa, B. n apus, and, to a lesser extent, B. juncea, while Zn tended to decrease only lateral root diameter. Both metals reduced shoot Fe and Mn concen trations in all three Brassica spp. to levels associated with Fe and M n deficiencies. These deficiencies, however, did not correlate with ob served patterns of leaf chlorosis. Nonetheless, heavy metal-induced in hibition of Fe and Mn accumulation may have been a significant factor in reducing plant growth. In terms of heavy metal removal, the Brassic a spp. were more effective at removing Zn from the nutrient solution t han Cu. The extent of Zn and Cu removal was reduced in the presence of both metals, as compared to the single heavy metal treatments. The im plications of these results for phytoremediation are discussed.