Potential for Phytoextraction of Cobalt by Tomato

Abstract

Cobalt (Co) is a common metal contaminant in soils. Certain plant species have the ability to extract metals (such as Co) from soils thus cleaning the environment. Patterns of cobalt accumulation and storage were determined in greenhouse-grown tomatoes (Lycopersicon esculentum Mill. cv. Supersonic). In addition, the effect of elevated Co plant accumulation of other metal concentrations in this species was evaluated. Tomato plants were treated once a week for 4 months with 10 mL of 5, 10, or 20 mM Co solutions or with 10 mL of 5 mM each of Co and nickel (Ni), Co and copper (Cu), or Co and zinc (Zn) in combination. Nickel, Cu, and Zn were included in treatments to test for the possibility that their uptake competes with Co. Cobalt, Ni, Cu, Zn, iron (Fe), and manganese (Mn) in homogenized and nitric acid-liquefied samples of dried roots, stems, leaves, and fruit–flowers of Co-treated plants were measured by inductively coupled plasma optical emission spectrometric analyses. Total Co accumulation in tomatoes was as high as 873 μg g⁻¹ in roots, 124 μg g⁻¹ in stems, 167 μg g⁻¹ in leaves and 21 μg g⁻¹ in fruit–flowers. Cobalt was detected in all parts of the tomatoes, though not in fruit–flowers at lower treatment conditions. The ratio of Co concentration in shoots (stems, leaves, and fruit–flowers) compared to roots was 1:2.8. Cobalt served as a synergist or antagonist to Fe and Zn accumulation in separate plant parts. Although not demonstrating hyperaccumulating characteristics, these data suggest that under some toxic soil conditions it may be possible to utilize the tomato plant in phytoextractive soil cleansing of Co.

Keywords:

• Phytoextraction
• Cobalt
• Tomato

Acknowledgments

Funding of this research was provided in part by a Merck Undergraduate Grant to Trevor L. Woodard at Bates College. Additional funding was provided by the Department of Biology and Program of Biochemistry at Bates College, Lewiston, ME.