Rajiv Bhadra, Colorado State University and Kristin O’Neill, University of Dayton

A large category of chemical pollutants that has received very little attention is the active ingredients of pharmaceuticals. These are diverse in structure and chemical and biochemical activity, are used in large quantities throughout the world, and are continually discharged into wastewater streams via industrial and domestic effluents. Reports of detection of intact pharmaceuticals and their metabolites in effluents of wastewater treatment plants, and in surface waters and groundwater in Europe and the U. S. A., are on the increase. Since their behavior in the environment has not been investigated and is poorly understood, the early identification and investigation of their potential impact is critical to protecting ecological health. In this paper we present our studies on the response of plants to pharmaceutical exposure in aquatic phytoremediation systems. Several high-volume pharmaceuticals or their common metabolites were investigated: acetaminophen, ibuprofen, salicylic acid and clofibric acid. Acetaminophen and ibuprofen are employed as non-steroidal analgesics and anti-inflammatories. Salicylic acid is the primary hydrolytic metabolite of acetylsalicylic acid, a common analgesic, and clofibric acid is a common active metabolite of several blood lipid regulators. The aquatic macrophyte Myriophyllum aquaticum was exposed separately to each of these pharmaceutical compounds for a period of 7-14 days at an initial concentration of 8-10 mg/L. At this exposure level, acetaminophen and salicylic acid disappeared rapidly, while ibuprofen and clofibric acid proved recalcitrant. Dose-response analysis with a range of exposure levels – 10 to 65 mg/L – delineate further differences in plant response. The rate and extent of uptake of salicylic acid remains consistently high at several exposure levels, while that of acetaminophen exhibits a plateau. These and other fate analyses based on ¹⁴C-label will be presented, and implications to the emerging issue of pharmaceutical pollution of waters and its biotreatment design will be discussed.

Kijune Sung, M. Yavuz Corapcioglu, Malcolm C. Drew, and Clyde L. Munster, Texas A&M University

Phytoremediation is the technique that uses plants to enhance bioremediation either through stimulation of soil microbial activity and/or by plant accumulation of contaminants. Even when the principal mechanism is by stimulation of bacteria, any resultant plant contamination cannot be overlooked. For the purpose of phytoremediation, a two-compartment plant model has been developed. The model divides the plant into herbage (which can be harvested) and the root compartment in which contaminants can accumulate. Numerical experiments were conducted to investigate the model behavior and to determine important parameters affecting plant contamination. To investigate the behavior of the model under field conditions, real irrigation, weather, and plant data are used. Johnsongrass (Sorghum halepense) was used to evaluate the model behavior. Contaminants (TNT and chrysene) were selected on the basis of their contrasting aqueous phase solubilities. The results indicate that plant contamination and soil remediation by plants depend on soil properties such as soil organic carbon content, the physicochemical properties of the contaminants such as octanol:water partition coefficient, and plant properties. An important factor affecting plant contamination is bioavailability, i.e. defined as contaminant mass in the water phase/total mass in the soil. As bioavailability increased, the concentrations in root and herbage compartment were predicted to increase as well. Additionally, increase microbial activity in soils was predicted to decrease plant contamination by these organic pollutants. This suggests that plants and microorganisms can have complementary roles in phytoremediation. To apply this approach to a practical situation, the model was also used to investigate the effect of planting time, planting method, and plant type. Johnsongrass (Sorghum halepense) and TNT were selected for model application. Although planting time and methods are important factors affecting plant contamination, bioavailability is shown to be the most influential consideration for plant contamination in phytoremediation.

Petroleum hydrocarbons degrade soil quality, making bioremediation difficult. Restoration of soil quality is a prerequisite for successful bioremediation. Soil with percent levels of total petroleum hydrocarbons (TPHs) is difficult to wet, has degraded structure and consistence, poor aeration, and reduced pH and nutrient buffering capacity. Soil limitations adversely affecting bioremediation should be identified and corrected prior to implementing full-scale treatment. Plants are adversely affected by petroleum even when phytotoxic hydrocarbons are absent. Plant-specific inhibitory effects of TPHs include reduced root respiration and water and nutrient uptake due to thin oily films on root hairs. Plants must also compete with soil microorganisms for available nitrogen (N), phosphorus (P) and other plant nutrients. Adding large quantities of fertilizer N can increase soil salinity beyond plant tolerance thresholds. Soil from four petroleum contaminated sites was evaluated for soil quality in both bench- and field-scale studies. Soil was tested from two inactive refineries, a Superfund site, and an abandoned oil well field. Soil TPH ranged from 0.4 to 24%. Soil quality improvement measures included liming, blending with organic and inorganic bulking agents, adding commercial fertilizer or composts to restore soil fertility, and blending with uncontaminated soil. A multi-phase soil quality improvement (SQI) process was implemented at one of the refinery sites to improve soil consistence, permeability and aeration, reduce soil subgrade compaction to improve internal drainage, and lower soil salinity. The SQI program had limited success. Phased bioremediation was implemented which included plant-mediated treatment. Phase I provided pretreatment with either conventional or plant-mediated bioremediation using TPH-tolerant agronomic plants. Plants were evaluated for TPH tolerance in the growth chamber and in the field. For Phase I treatment, we recommend an upper limit of 3 to 5% soil TPHs and a soil depth of 15 to 20 cm. Phase II combined plant-mediated treatment with final revegetation using native grasses. Native grasses were less tolerant of soil TPHs than agronomic species, and their use may require pretreatment to about 1% soil TPH.

Lori S. Siegel and Akram N. Alshawabkeh, Northeastern University, Melinda A. Hamilton, Idaho National Engineering and Environmental Laboratory (INEEL)

Radiocesium (Cs) is one of the most common contaminants found at Department of Energy (DOE) sites. Remediation of Cs-contaminated soil is challenging because Cs binds strongly within the soil matrix and its release may require breakdown of the soil minerals. It is hypothesized that complex biological, geochemical, and physical processes in the rhizosphere, the zone where soil and plant roots interface, can solubilize bound Cs. Proper understanding of the partitioning of Cs between the bound, aqueous, and phytoextracted phases requires comprehensive modeling of the rhizosphere as an ecological packet. A conceptual model is being developed that categorizes the processes into six sub-models: geochemistry, physical factors, root density, microorganisms, nutrients, and root exudates. A seventh sub-model (Cs fate) describes Cs movement between the three phases. Functional relationships and parametric values within and between the sub-models are being developed based on literature, field characterization, and on-going laboratory experiments. This approach allows for expertise in defining each sub-model, while simultaneously promoting the comprehensive nature of the system. Currently, this research focuses primarily on the specific effects of root exudates on Cs partitioning. The model provides a framework for better understanding the fundamental processes that control Cs fate in the rhizosphere. Modeling results will generate hypotheses for additional investigations to further elucidate these mechanisms. The ability to better understand, predict, and control Cs solubilization could be applied to other metals in the future. Ultimately, the model will be used as a tool for enhancing field implementation of in situ solubilization of metals for a variety of remedial activities. The model formulation, solution procedure, parameter estimation, and results will be presented.

Peter A. Kulakow and Larry E. Erickson, Kansas State University.

Ten field trials are in progress to test the ability of plants to enhance the degradation of weathered petroleum contaminated soils. The USEPA has sponsored the Remediation Technologies Development Forum or RTDF to provide a mechanism for industry, government, and university participants to cooperate in developing and testing innovative technologies, sharing results and discussing lessons learned. The RTDF Phytoremediation Action Team, TPH Subgroup, developed a standard experimental protocol to test phytoremediation of petroleum-contaminated soils that vary in contaminant conditions and test environments. Test locations include refinery sites, former manufactured gas plants, spill sites, motor vehicle wastes, and an oil production site. The protocol specifies a standard experimental design for use at each location. Three or four vegetation treatments are compared in a randomized complete block experimental design with four replications. The treatments include 1) a standard cool-season grass/legume mixture composed of a combination of fescue, ryegrass, and a legume; 2) one or two locally optimized treatment that may include grasses or species mixtures, including trees; and 3) an unplanted and unfertilized control. The unplanted treatments are to be kept free of vegetation. Soils are sampled annually at two depths within each plot and submitted to common contracting laboratories for analysis. Estimates of petroleum hydrocarbon concentration include total petroleum hydrocarbons, polycyclic aromatic hydrocarbons, biomarkers such as hopane, and petroleum fractions by the TPH Criteria Working Group Method. Each site is also monitored for vegetation condition and rooting density. All trial sites will be sampled for three growing seasons. In 2001, a second annual report will be completed highlighting results in progress, issues encountered, and lessons learned. Analytical results covering the second growing season for six locations and the first growing season for one location will be completed in 2001.

Victor F. Medina, Washington State University Tri-Cities, Cynthia Teeter, Steven L. Larson², United States Army Corp of Engineers

Phytoremediation is a useful technology for the removal of metals from soils. Metals removal from water is very rapid. However, metals removal from soils is much slower and less complete because the metals are bound to the soil. Therefore, desorption governs the rate of treatment.

Enhancing the rate of desorption, therefore, might increase treatment rates. Processes have been developed using chemical chelating agents, such as EDTA, to enhance desorption and improve phyto-uptake of metals from soils. These techniques have had successes. However, there are concerns. First, these chelating agents can be potential contaminants themselves, if misapplied. And, there is concern that these chelating agents might essentially wash away the metals, spreading contamination.

Our studies will investigate an alternative, the use of natural occurring phyto-chelating agents. These agents may be produced by the plants themselves, or by associated microorganisms. We will measure complexing of lead in hydroponic systems with plant exudates and will attempt relate exudate and complexing measurements to simple measurements, such as total dissolved solids. We will, then, catagorize and identify the complexing agents. And, we will test the exudates in various soil matrices to determine if significant increases of lead solubility occur.

Cary T. Chiou, U.S. Geological survey, Guang Sheng, University of Arkansas

In dealing with the passive transport of organic contaminants from soils to plants (including crops), a partition-limited model is proposed in which (i) the maximum (equilibrium) concentration of a contaminant in any location in the plant is determined by partition equilibrium with its concentration in the soil interstitial water, which in turn is determined essentially by the concentration in the soil organic matter (SOM); and (ii) the extent of approach to partition equilibrium, as measured by the ratio of the contaminant concentrations in plant water and soil interstitial water, a _pt (≤ 1), depends on the transport rate of the contaminant in soil water into the plant and the volume of soil water solution that is required for the plant contaminant level to reach equilibrium with the external soil-water phase. Through reasonable estimates of plant organic-water compositions and of contaminant partition coefficients with various plant components, the model accounts for calculated values of a _pt in several published crop-contamination studies, including near-equilibrium values (i.e., a _pt @ 1) for relatively water-soluble contaminants and lower values for much less soluble contaminants; the differences are attributed to the much higher partition coefficients of the less soluble compounds between plant lipids and plant water, which necessitates much larger volumes of the plant water transport for achieving the equilibrium capacities. The model analysis indicates that for plants with high water contents the plant-water phase acts as the major reservoir for highly water-soluble contaminants. By contrast, the lipid in a plant, even at small amounts, is usually the major reservoir for highly water-insoluble contaminants.