R6 AM Plant Uptake of Organic Pollutants - Processes and Modeling|
Thursday, 17 November 2005: 8:00 AM - 11:40 AM in 324-326
646 (SCH-1117-579851) Accumulation of PAHs in Plant Tissue During Phytoremediation of Contaminated Soils.
Start time: 8:00 AM
Schwab, A1, Banks, M1, Cofield, N1, 1 Purdue University, West Lafayette, IN, USA
A recurring concern in the phytoremediation of contaminated soil is whether the pollutants will be introduced in the food chain through plant uptake and subsequent consumption by grazers. For hyperaccumulators of metals, uptake of the target metal into plant tissues is part of the phytoremediation process. This is also the case for the use of plants to remove nitrate and atrazine from water with rapidly respiring trees. In these cases, the concentrations of contaminants in plant tissues must be monitored carefully, and exclusion of grazers may be necessary. Plant accumulation of hydrophobic contaminants such as PAHs is not a part of the remediation process, and the chemistry of PAHs in soils and roots is highly unfavorable for plant accumulation. Nevertheless, the question of PAH uptake is always asked, and our research group has investigated this issue on several occasions. We have found that accumulation of PAHs in contaminated soils seldom exceeds concentrations found in plants growing in unimpacted areas. Plants will accumulate or transpire the 14C from radiolabeled PAHs, but only after the parent compound has been altered in the rhizosphere. In agreement with predictive models, PAH assimilation from soils by higher plants is negligible.
647 (DET-1117-734891) Fate of 14C Nonylphenol (NP), Nonylphenol Tetraethoxylate (NPE4), and Nonylphenol Nonylethoxylate (NPE9) in Biosolids/Soil Systems Planted with Crested Wheatgrass.
Start time: 8:20 AM
Dettenmaier, E1, Doucette, W1, 1 Utah State University, Logan, Utah, USA
Microcosm experiments, 150 days in duration, were conducted to evaluate the fate of 14C-labeled nonylphenol (NP), nonylphenol tetraethoxylate (NPE4), and nonylphenol nonylethoxylate (NPE9) in a soil/biosolids (99.5:0.5% w/w) environment planted with crested wheatgrass (Agropyron cristatum). Three concentrations 6, 24, and 47 mg/kg dry wt of NP, NPE4 and NPE9 were examined along with unplanted and unplanted poisoned controls. A single concentration of phenol 22 mg/kg was also evaluated as a more degradable reference compound. The biosolids were obtained from a municipal wastewater treatment plant receiving industrial, commercial and domestic wastewater. The loamy sand soil (1.6 %OC) was collected from a former agricultural field. Mineralization was quantified by collecting the 14CO2 produced during the course of the study. Roots and foliar tissue were analyzed for 14C and parent compound. The extent of mineralization at the end of the study ranged from 7% for NP to 53% for phenol. No enhancement of mineralization was observed in the planted systems. 14C concentrations in the foliar tissues were proportional to the exposure concentration but were 10 times lower than concentration in the roots and 2-3 times lower than the soil.
648 (WIL-1117-821971) A novel approach to understand the uptake and storage compartments of organic chemicals in vegetation: implications for our current state of knowledge.
Start time: 8:40 AM
Wild, E1, Dent, J1, Thomas, G1, Jones, K1, 1 Lancaster University, Lancaster, UK
Vegetation plays an important role in the environmental fate of many organic chemicals. It is well know that atmospheric organic chemicals uptake to plant surfaces, and soil bound xenobiotics become associated with roots ; however there is significant uncertainty as to the fates of these chemicals, including uptake, storage, transport and degradation processes once sorbed to vegetation. New approaches to tackle these uncertainties; through the use of two photon excitation microscopy (TPEM), and chemical and plant autofluorescence have provided a method for visualising exactly where these chemicals are residing within the plant. This has been achieved for both air uptake to leaves and soil uptake to roots. These findings are casting significant doubt upon many of our common assumptions with regards to air/vegetation and soil/root uptake.
649 (BUR-1117-833900) Modeling the Uptake of Organic Contaminants from Soil into Plant Foliage.
Start time: 9:00 AM
Burris, J. 1, Sample, B.2, Hoff, D. 3, Ells, S. 4, 1 Syracuse Research Corporation, Denver, CO, USA2 USEPA, Washington, DC, USA3 USEPA Region 8, Denver, CO4
As part of EPAs effort to establish ecological soil screening values (Eco–SSLs), models were developed to estimate the uptake of non–ionic organic contaminants from soil into plant tissue. A limited literature search was completed and data were compiled from this as well as citations used in the Travis and Arms (1988) model. All data were extracted from published literature and studies were deemed acceptable if they presented measured analyte concentrations in soil and tissues of plants grown in that soil (paired data) and provided details concerning expsoure duration, sample collection and handling and analytical methods. Studies based on uptake from solution or by excised plants parts were excluded as were bioaccumulation data summarized in review papers. Rinsed and unrinsed data were segregated. Estimation of chemical concentrations in plant foliage was accomplished by either chemical–specific linear regressions relating the concentration in soil to the concentration in plant or by estimation using a predictive model based on the log Kow. For DDT and metabolites, ten separate polynuclear aromatic hydrocarbons (PAHs) and for PAHs as a group, chemical specific regression equations were identified. For other non-ionic organic contaminants, a regression model was developed relating the Kow of the chemical to the bioaccumulation factor (BAF). These models were added to the Eco–SSL guidance in March of 2005. Data will also be presented concerning uptake of non-ionic organics into roots and seeds.
Start time: 9:20 AM
650 (MAD-1117-841277) Background air component of vegetation/soil bioconcentration ratios.
Start time: 10:00 AM
Maddalena, R1, Kulakow, P2, 1 Lawrence Berkeley National Laboratory, Berkeley, CA, USA2 Kansas State University, Manhattan, KS, USA
Soil-to-plant biotransfer plays a critical role in assessing both human and ecological risks at phytoremediation sites and in establishing risk-based screening levels (RBSLs) at hydrocarbon impacted exploration and production sites. The plant/soil bioconcentration ratios (BCRs) that are used to estimate exposure concentrations are based on empirical relationships developed from measured chemical concentrations in plants and soil. However, these relationships do not explicitly account for the contribution of background air to measured concentrations in vegetation. As a result, measured plant/soil BCRs (and the resulting empirical models) likely overstate the contribution of soil to contaminant concentrations in vegetation. To explore this issue we combine two separate but related studies of Polycyclic Aromatic Hydrocarbon uptake into vegetation. Results from a controlled exposure chamber study using spiked soils provide details on direct (soil-plant) and indirect (soil-air-plant) uptake pathways while results from a cooperative phytoremediation field study yield relevant field measurements. Air-to-plant exchange is faster than soil-to-plant exchange such that air concentrations are the primary factor controlling the maximum attainable concentrations in the aboveground vegetation. The air-to-plant pathway also sets a limit on the concentrations in soil below which soil-to-plant transfers can no longer be reliably measured. We find that even low background atmospheric concentrations can affect our ability to reliably measure soil-to-plant BCRs, particularly for chemicals with high Koa. The contribution from air varies significantly across chemicals, which provides an opportunity to identify the primary factors that influence the fraction of chemical in vegetation that is attributable to air and subsequently that which is attributable to soil.
651 (MCK-1117-845931) Plant uptake of organic pollutants: Model performance evaluation.
Start time: 10:20 AM
McKone, T.1, 2, Maddalena, R.2, 1 University of California, Berkeley, CA, United States2 Lawrence Berkeley National Laboratory, Berkeley, CA, United States
In spite of continuing field and laboratory studies, the role of terrestrial vegetation in transferring chemicals from soil and air into specific plant tissues (stems, leaves, roots, etc.) is still not well understood. This has led to a reliance on models to explain and predict the fate of chemicals in air/plant/soil systems. But models of plant uptake have a number of uncertainties that have not been fully characterized. Here we illustrate performance evaluation of plant uptake models by considering three key sources of uncertainty (1) uncertainties in the conceptual/theoretical formulation of the model, (2) uncertainties in formulating the mathematical algorithm and (3) parameter uncertainty and variability. For the conceptual vegetation mass-balance model, we evaluate the theoretical basis for the model and consider the appropriate level of modeling complexity. We next consider alternate modeling strategies and the associated changes in the reliability, fidelity, and transparency of the model. Here we confront such issues as the how many compartments to include, how to establish mass transfer rates among compartments and whether to build process-based or empirical partition and mass-transfer coefficients. Finally there is the issue of parameter uncertainty and variability. For this we evaluate both the magnitude and primary sources of parameter variability/uncertainty in plant uptake parameters and compare these uncertainties to conceptual uncertainty and model formulation uncertainty. For plant uptake models that must address competing soil-root-leaf and soil-air-leaf pathways, we find that conceptual uncertainties remain a dominant source of overall uncertainty. We also find that variability in plant-species and soil characteristics are large contributors relative to parameter uncertainty when predicting the fate of chemicals in terrestrial vegetation.
652 (NEW-1117-834461) Uptake and Fate of Trichloroethylene in Plants.
Start time: 10:40 AM
Newman, L1, 3, Strycharz, S1, Muiznieks, I2, Kim, R3, 1 University of South Carolina, Columbia, sc, USC3 Savannah River Ecology Laboratory, Aiken, SC, USA2 University of Washington, Seattle, WA, USA
Plant uptake of trichloroethylene has been accepted for several years, and many sites have already been planted with high water uptake trees such as poplar and willow for the remediation of contaminated groundwater. However, we are still trying to understand the fate of trichloroethylene in plants. Several chlorinated metabolites are known to be present in plants exposed to trichloroethylene, but the fate after dechlorination is not understood. The mechanisms, or enzymatic pathways, for degradation in plants is not well understood. The relative importance of multiple pathways within the plant, degradation, accumulation, leaf transpiration, trunk and stem volatilization are still being debated and studied. And finally, the role of microbes, both in the rhizosphere and those that have formed endophytic relationships within the plant tissues, is not yet understood. However, it is almost certain that all of these pathways do play and role, and understanding them and being able to predict which pathway is most likely to dominate in a given situation will be critical to successful application of the technology. We will present information on the multiply pathways that can lead to remediation of trichloroethylene in plants, and genes involved in degradation within the plant, and methods that have been developed in our labs, in conjunction with colleagues, and by others in the field to monitor the fate of trichloroethylene when the technology has been applied to remediation site.
653 (GEN-1117-225643) Plant species differ in movement of hydrophobic organic chemicals: Measurements and modeling.
Start time: 11:00 AM
Gent, M1, White, J1, Eitzer, B1, Mattina, M1, 1 Connecticut Agricultural Experiment Station, New Haven, CT, USA
The pathway for uptake of organic chemicals into plants is important when considering the risks associated with soil contamination. The pathway is likely to differ, depending on the molecular weight and hydrophobicity of the contaminant. We conducted studies under controlled conditions in which DDE, a very hydrophobic chemical, was supplied to plants at a constant concentration over two weeks in hydroponics solution. The concentration and amount of DDE were assayed at various times in solution and in various tissues of cucumber and zucchini plants. These studies were designed to test quantitatively a model of the uptake and movement of hydrophobic chemicals into plants. Simulations using a discrete-compartment model based on fugacity indicated that the primary route of movement of DDE was in the transpiration stream, rather than through the air. However, the apparent fugacity, or tendency of DDE to partition to xylem water, appeared to be more than 10 fold greater in zucchini than in cucumber. Thus, plant species may vary dramatically in this aspect of the transpiration pathway. Further work is needed to characterize this behaviour in other plant species, as it has a fundamental effect on the rate of movement of organic contaminants from soil into the aerial parts of plants.
654 (COL-1117-797910) Plant uptake of organic chemicals - the soil-air-plant pathway.
Start time: 11:20 AM
Finnegan, E1, Collins, C1, 1 Imperial College, London, UK
The understanding of plant uptake of organic contaminants has expanded in recent years. Most notably there has been improvements in our understanding of the aerial deposition pathway and the influence of the soil-air-plant pathway. This paper will review and quantify the soil-air-plant pathway of plant contamination from soils polluted with organic chemicals. Relationships to describe the pathways will be presented to help those wishing to model this process. Finally the contribution of this process to the overall contamination of plants from polluted soils using a number of established models, some updated based on our findings, will be presented.