Final Report: The Effect of Plants on the Bioavailability and Toxicity of Contaminants in Soil

EPA Grant Number: R825413
Title: The Effect of Plants on the Bioavailability and Toxicity of Contaminants in Soil
Investigators: Banks, M. Katherine , Schwab, Arthur Paul , Smith, J. Scott
Institution: Kansas State University , Purdue University
EPA Project Officer: Lasat, Mitch
Project Period: January 1, 1997 through December 31, 2000
Project Amount: $499,941
RFA: DOE/EPA/NSF/ONR Joint Program on Bioremediation (1996) RFA Text |  Recipients Lists
Research Category: Hazardous Waste/Remediation , Land and Waste Management


The overall objective of this project was to evaluate the effect of plants on the bioavailability and toxicity of soil contaminants. This objective was accomplished with three concurrent studies. In the first study, the fate of representative petroleum contaminants in planted systems was evaluated using closed plant chambers and 14C radiolabeled compounds with an aggressive grass species. This study allowed us to trace the contaminant as it became incorporated into soil organic material. The second study was designed to evaluate the effect of weathering on petroleum contaminant bioavailability in unvegetated and vegetated soil. This two-phase study consisted of an outdoor weathering phase followed by an extensive greenhouse phase with a suitable grass species. Contaminants and toxicity were evaluated over time. The third study was a field project at the U.S. Naval Port in Hueneme, CA. Vegetated plots were established in petroleum contaminated soil, and contaminants and toxicity of the soil were evaluated over a 2-year period. In support of these three studies, a soil extraction method was developed to predict bioavailability of soil contaminants.

Summary/Accomplishments (Outputs/Outcomes):

In the plant chamber study, 7.6 percent and 8.7 percent of the parent compound, pyrene, were recovered from the switchgrass and tall fescue treated soil, respectively, but the unplanted control contained 31.5 percent of the initially added pyrene. Pyrene concentrations in all organic fractions were significantly reduced in planted soil when compared to the unplanted control.

In the weathering study, for nearly every detectable contaminant with no aging, the presence of fescue and red clover resulted in lower contaminant concentrations than when plants were absent. Switchgrass was ineffective in the silty loam soil but superior to the unvegetated treatments in the sandy loam. These trends were not as apparent in the silty loam soil for the contaminants aged 6, 12, and 18 months in which treatment effects were absent or inconsistent. Aging did not affect the trends in the effect of vegetative treatment for the sandy loam soil. However, the concentrations in the sandy loam were much higher than in the silty loam. These interactions are likely the result of higher microbial activities in the finer textured silty loam soil, resulting in higher rates of degradation. Higher amounts of available water and higher total irreversible adsorption may have contributed as well.

In the field trial, the plant mixtures chosen for the field trial were not negatively affected by the presence of the contaminants after 9 months of aging. Root development was extensive in the second year of the project. Bacterial numbers, petroleum degraders, and plant biomass increased with time, and a strong relationship exists between the presence of plants and the degradation of total petroleum hydrocarbons in these plots. Also, more petroleum degraders were present in the rhizosphere of the test species than in the unvegetated soil.

The field soil samples were subjected to analysis by toxicity tests, including earthworm growth and mortality, Microtox, and lettuce germination. Some initial toxicity was observed for all tests (particularly the unvegetated soil using the earthworm test), but by the end of the test period no differences in toxicity existed among the vegetation treatments.

The octanol extraction method developed in this research marks a significant deviation away from the use of cosolvent extraction, which only reflects a specific point of bioavailability to a certain bioreceptor by a certain volume fraction of cosolvent. The method is flexible and provides release rates instead of mass of contaminants extracted from soil to water and to solvent. The octanol extraction technique more closely mimics the mass transfer mechanisms that govern the bioavailability of organic contaminants in soil.

The results from this research project support the hypothesis that aging decreases bioavailability and impedes phytoremediation, particularly in silty loam soil. Twelve months of phytoremediation are not long enough for plant treatments to reduce weathered petroleum contaminants to an acceptable regulatory level. Although plants accelerated detoxification of the soils, the same results eventually were achieved in the absence of plants. The modest changes in toxicity, particularly in light of the significant reduction in petroleum concentrations, reflect the fact that the aged contaminated material used for this research was fairly nontoxic from the outset. Also, the extraction technique developed in this project may provide a reliable means to determine the bioavailable fraction of a range of soil-associated organic contaminants and be applicable in the assessment of risk.

Journal Articles on this Report : 3 Displayed | Download in RIS Format

Other project views: All 22 publications 6 publications in selected types All 3 journal articles
Type Citation Project Document Sources
Journal Article Banks MK, Schwab AP, Liu B, Kulakow P, Smith JS, Kim R. The effect of plants on the degradation and toxicity of petroleum contaminants in soil: a field assessment. In: Tsao D., ed. Advances in Biochemical Engineering/Biotechnology, Special Volume: Phytoremediation. Springer-Verlag, 2001. R825413 (Final)
not available
Journal Article Kulakow PA, Schwab AP, Banks MK. Screening plant species for growth on weathered, petroleum hydrocarbon-contaminated sediments. International Journal of Phytoremediation 2000;2(4):297-318. R825413 (Final)
not available
Journal Article Silciliano SD, Fortin N, Mihoc A, Wisse G, Labelle S, Beaumier D, Ouellette RR, Whyte LG, Banks MK, Schwab P, Lee K, Greer CW, Roy R. Selection of specific endophytic bacterial genotypes by plants in response to soil contamination. Applied and Environmental Microbiology 2001; 67(6):2469-2475. R825413 (Final)
not available

Supplemental Keywords:

phytoremediation, toxicity, risk assessment, accumulation, uptake, degradation, pollution., Scientific Discipline, Geographic Area, Waste, Water, Ecosystem Protection/Environmental Exposure & Risk, Bioavailability, Contaminated Sediments, Environmental Chemistry, State, Bioremediation, Biology, fate and transport, petroleum, contaminated sediment, plants, greenhouse phase, contaminants in soil, toxicity, bioremediation of soils, grass species, phytoremediation, vadose zone, California (CA), diesel fuel, shrimp, earthworm

Relevant Websites: Exit EPA icon Exit EPA icon Exit EPA icon

Progress and Final Reports:

Original Abstract
  • 1997 Progress Report
  • 1998
  • 1999 Progress Report