Submitted to: International Journal of Phytoremediation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 15, 2001
Publication Date: March 1, 2002
Interpretive Summary: NTERPRETIVE SUMMARY: This paper reports research on using cover crops to aid in biodegradation of toxic organic compounds in soil. In the past, soils were often left bare so they could be repeatedly tilled to speed biodegradation, but bare soil may allow erosion, and plants may actively aid in biodegradation. Because plants secrete and leak nutrients into the soil around the roots (rhizosphere soil), plants can stimulate growth of soil microbes and increase diversity of soil microbes, which can speed up biodegradation of soil contaminants. The tests compared biodegradation of added trinitrotolune (TNT) and pyrene (a polycyclic hydrocarbon), in two soils, with a number of legumes and grasses. The outcome of the extent of biodegradation in each soil-crop-contaminant combination varied indicating that soil properties and crop species have different effects on degradation nof specific contaminant chemicals. Plants played little role in degradatio of pyrene, but had a strong effect on TNT. The forage grasses with extensive rooting systems offered much promise for phytoremediation (plant stimulated biodegradation of soil organic contaminants) compared to unplanted soils. If these kinds of semi-persistent organic contaminants need to be remediated, phytoremediation can achieve the needed biodegradation at low cost while the plant cover prevents erosion. All aspects of the use of plants in biodegradation of soil organic contaminants are aided by planting certain legumes and grasses rather than leaving the soil bare. Interestingly, high soil organic matter inhibited biodegradation by binding the contaminants even though high organic matter usually stimulates growth of soil microbes.
Technical ABSTRACT: The objective of this study was evaluation of seven forage and conservation crop species for phytoremediation of trinitrotoluene (TNT) and pyrene contaminated soils. TNT and pyrene were added to soil at 100 mg/kg. Crop species screening studies were conducted in a greenhouse and growth chambers on two soil types with different organic matter contents. Under high soil organic matter conditions, adsorption or covalent binding to the soil organic matter appeared to be a dominant force of removal limiting TNT and pyrene availability. In both soil types, pyrene dissipation could not be attributed to the presence of plants. However, in soils with lower organic matter content, all of the plant species treatments showed a significantly higher degree of TNT transformation compared to the unplanted control. Statistically significant differences in TNT transformation were observed among the crop species grown in the low OM soil. Reed canarygrass (Phalaris arundinacea L.) and switchgrass (Panicum virgatum L.) were the most effective species in enhancing TNT transformation. Our data indicated that use of plants was effective for phytoremediation of TNT contaminated low OM content soils, but did not have any significant effect on pyrene dissipation. Based on these observations, it appears that plant-soil-contaminant interactions are very specific and this specificity determines the effectiveness of phytoremediation schemes.