Submitted to: International Journal of Phytoremediation
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/25/2014
Publication Date: 8/25/2013
Citation: Broadhurst, C.L., Chaney, R.L., Davis, A.P., Cox, A., Kumar, K., Green, C.E. 2013. Growth and cadmium uptake of Swiss chard, Thlaspi caerulescens and corn in pH adjusted biosolids amended soils. International Journal of Phytoremediation. DOI:10.1080/15226514.2013.828015. Interpretive Summary: Excessive cadmium in farm soils comprises a risk to food safety and a strong limit on land use. Before modern regulations were established for beneficial use of biosolids, some fields received applications of high cadmium biosolids materials which raised soil cadmium to levels which limit value of the land. Phytoextraction of cadmium from such soils might remove land use restrictions and increase land value. Control and biosolids amended soils from a site in Illinois were collected and adjusted to varied soil pH. Because more acidic soils promote cadmium accumulation by plants, the soil pH was adjusted across a range to learn maximal crop cadmium levels without phytotoxicity from the other metals in the amended soil. Swiss chard was grown to test the present potential impact on cadmium accumulation by leafy vegetables; chard is an cadmium “accumulator” crop, but not hyperaccumulator. Several ecotypes of alpine pennycress (Thlaspi caerulescens) were grown, as was corn inbred B37 previously shown to be a cadmium accumulator on such soils. For each crop, lower soil pH promoted cadmium accumulation in plant shoots. Chard reached levels unsafe for regular human consumption confirming the need for remediation of cadmium risks of these soils. Alpine pennycress accumulated up to 400mg Cd/kg dry shoots, and the corn inbred up to 25 and 900mg Cd/kg dry shoots. Comparison of potential cadmium annual removal with different reported cadmium phytoextraction technologies was summarized, including the present data. Taking into account normal crop yields, both alpine pennycress and the corn inbred may remove enough cadmium to support economic phytoextraction of the excessive soil cadmium at these fields. Double cropping the corn inbred to forage harvest at low soil pH could increase annual Cd removals, as could using fungicide to aid alpine pennycress growth during warm seasons as a perennial crop. Phytoextraction appears to be a valid alternative for cadmium contaminated agricultural soils.
Technical Abstract: Before regulations were established, some biosolids applications added higher Cd levels than presently permitted. Cadmium phytoextraction from such soils would alleviate constraints on land use. Unamended farm soil, and biosolids amended farm soil and mine soil were obtained from Fulton County, Illinois. Soils contained 0.16, 22.8, 45.3mg Cd/kg and 43.1, 482, 812mg Zn/kg respectively with initial pH 6.14, 6.10, 6.35. In greenhouse studies, Swiss chard was grown to assess potential Cd accumulation by leafy vegetables and as a potential Cd accumulator, while a well known Cd hyperaccumulating southern France ecotype of Thlaspi caerulescens and a Cd accumulator corn (Zea mays L.) inbred (B37) were tested for phytoextraction. Soil pH was adjusted from ~5.5 to 7. Chard suffered phytotoxicity at low pH and accumulated up to 90mg Cd/kg on the biosolids amended mine soil. T. caerulescens did not show phytotoxicity even in the acidic pH levels, and accumulated up to 235mg Cd/kg. Harvested plants regrew in many of the treatments, and with continued growth in cooler conditions accumulated up to 900mg Cd/kg. The corn inbred was grown at the range of soil pH and accumulated up to 20-45mg Cd/kg with moderate phytotoxicity symptoms at the lowest pH. Both T. caerulescens and Cd-accumulator B37 corn show promise for effective Cd phytoextraction and require field evaluation. Use of fungicides may improve Thlaspi growth in the field enough to allow practical Cd phytoextraction. Other corn inbreds may offer higher Cd phytoextraction at lower pH, and mono-cross hybrids higher yields; further, corn grown only for biomass Cd maximum removal could be double-cropped.