Progress 06/01/02 to 05/09/06
Outputs
Field experiments were conducted to assess the impact of inoculation with mycorrhizal fungi on the accumulation of weathered DDE from soil by zucchini (Cucurbita pepo spp pepo). Three commercially available mycorrhizal products (BioVam, Myco-VamTM, INVAM) were inoculated into the root system of the zucchini seedlings at planting. The effect of fungal inoculation on contaminant uptake appeared to vary at the cultivar level. For one zucchini cultivar, fungal inoculation generally decreased DDE accumulation but because of slightly larger biomass, did not significantly impact the percent contaminant phytoextracted. Alternatively, for another cultivar, fungi enhanced DDE accumulation by up to 34%. The data show that fungal inoculation may significantly increase the remedial potential of C. pepo ssp pepo. The apparent cultivar specific response to mycorrhizal inoculation is unexpected and a subject for future investigation. For the project summary, this prooject had the goal
of identifying the role of plant root exudates in the mobilization and remediation of hydrophobic weathered organic pollutants in soil. Specifically, the objectives included quantifying the degree to which exudates could promote bioavailability and then to subsequently characterize that mechanism. Through the 5-peer reviewed publications that resulted from this work, I have shown that this process is indeed far more complex than originally thought. Through the work conducted as part of this project, I have learned that the root exudate mediated release of contaminants from soil does indeed occur and varies dramatically among plants even to the subspecies level. In addition, nutrient status of the plant is highly relevant and inoculation with organisms such as fungi that may promote soil structure alteration/destruction will also enhance contaminant release/desorption. But perhaps most importantly, I have learned that the release of the pollutant from soil is only the first part of the
highly complicated multi-step process. Where C. pepo ssp pepo truly excels and what clearly differentiates it from other plants is its ability to take that highly hydrophobic pollutant that has accumulated in its root system and to translocate the contaminant to aerial tissues. Other plants can be induced to accumulate contaminants in their roots after the addition of soil amendments (such as fungi) but only zucchini has the ability to move the pollutant to the stems and leaves. The work conducted within this project has been instrumental in elucidating these processes and will serve as the basis for future research investigating techniques to optimize this remedial system.
Impacts
Weathered persistent organic pollutants have very low bioavailability in soil, making remediation extremely difficult and costly. Research in this Hatch project over the last 4 years, as well as the project that preceded it (CONH00766), has convincingly shown that one subspecies of Cucurbita pepo (zucchini) can extract significant amounts of these pollutants from soil and translocate the contaminants to aboveground tissues. Elucidating the mechanism driving that phenomenon is not only an academic question of scientific interest but may lead to a novel and invaluable tool for the remediation of POP-contaminated soils. It is now clear that the ability to move hydrophobic pollutants from roots to shoots is the most critical and unique aspect of this plant system; understanding the mechanisms governing that transport will be critical in maximizing remedial potential. As stated in previous years, potential long-term benefits could include growers removing historical
contamination from their fields, more rapid development of Brownfield sites, and on site remediation of areas previously not thought to be amenable to restoration.
Publications
- White, J.C.; Ross, D.R.; Gent, M.P.N.; Eitzer, B.D.; Mattina, M.I. 2006. Effect of mycorrhizal fungi on the phytoextraction of weathered p,p-DDE by Cucurbita pepo. J. Hazard. Mat. B137:1750-1757.
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Progress 01/01/05 to 12/31/05
Outputs
This project continues my investigation of the phytoremediation of weathered persistent organic pollutants (POPs) in soil. We have discovered that Cucurbita pepo ssp pepo (zucchini, pumpkin) accumulates POPs such as DDE and chlordane from soil through a process of phytoremediation. Investigations this year have focused on maximizing the remedial potential, as well as gaining indirect evidence for the mechanisms governing the process. Field experiments assessed the effects of nutrient amendments on the phytoextraction of field-weathered DDE by 8 cucurbits cultivars, as well as 8 other plant species (rye, mustard, canola, vetch, pigeonpea, clover, peanut, white lupin) known to accumulate inorganic elements from soil. Four cultivars of zucchini (accumulators) have been shown to extract percent level quantities of POPs whereas summer squash, cucumber, and the other non-cucurbits are non-accumulators and have little impact on the fate of the weathered contaminants in soil.
For the cucurbits, the zucchini phytoextracted 1.0% of the DDE and had a translocation factor (contaminant concentration ratio of stems to roots, TF) of 0.44 while the non-accumulators removed 0.16% of the contaminant with a TF of 0.09. Each cultivar received nutrient amendments of phosphorus (P), nitrogen (N), or nitrogen/phosphorus (N/P). The accumulator and non-accumulator cucurbits responded differently to the nutrients. When normalized to control values, the root and stem DDE content of the accumulators were significantly greater than that of the non-accumulators under most nutrient regimes. The total biomass of accumulators tended to decrease with nutrients and resulted in mixed effects on the amount of DDE extracted from the soil. Treatments with N and P resulted in significantly greater biomass for the non-accumulators, and increased the amount of DDE extracted from soil by 75%. The 8 non-cucurbit species varied widely in their ability to phytoextract and translocate weathered
DDE. The percentage of contaminant phytoextracted ranged from 0.06% (white lupin) to 0.22% (clover, vetch), and an inverse relationship existed between the amount of contaminant in the root and the TF. The effect of nutrient amendments on biomass, DDE uptake, and inorganic element content varied greatly among the 8 plant species. For some species (rye, vetch, pigeonpea, clover, white lupin), reductions or non-significant changes in DDE uptake were observed with nutrient treatment and were not correlated with plant biomass effects. For mustard, canola, and peanut, the amount of DDE phytoextracted in the nutrient treatments was doubled and was correlated with a two-fold increase in total plant biomass. Although it is generally assumed that fertilizer amendments to vegetation will enhance phytoremedial potential, as evidenced here by the non-accumulator cucurbits and certain other species, additions of certain macronutrients may reduce the phytoextraction of weathered POPs by Cucurbita
pepo ssp pepo. These findings support our hypothesis that C. pepo ssp pepos unique ability to remove sequestered organic contaminants is governed by evolved nutrient acquisition mechanisms.
Impacts
It has been widely accepted in the scientific literature that hydrophobic organic chemicals such as POPs have very low bioavailability once they become weathered in soil. This feature makes remediation of these types of compounds extremely difficult and costly. Research in this Hatch proposal over the last 4 years, as well as the project that preceded it, has convincingly shown that one subspecies of C. pepo can accumulate significant amounts of these pollutants in its aboveground tissues. Elucidating the mechanism driving that phenomenon is not only an academic question of scientific interest but may lead to a novel and invaluable tool for the remediation of POP-contaminated soils. This years findings were particularly interesting in that fertlization, the most common practice in phytoremediation systems, actually depressed remedial potential of the plants. Again, these findings have scientific value as they help in the elucidation of the governing processes for this
plant but the obvious practical implications are also significant. As stated in previous years, potential long-term benefits could include growers removing historical contamination from their fields, more rapid development of Brownfield sites, and on site remediation of areas previously not thought to be amenable to restoration.
Publications
- White, J.C.; Parrish, Z.D.; Iseleyen, M.; Gent, M.P.N.; Iannucci-Berger, W.; Eitzer, B.D.; Mattina, M.I. 2005. Uptake of weathered p,p-DDE by plant species effective at accumulating soil elements. Microchem. J. 81:148-155.
- White, J.C.; Parrish, Z.D; Iseleyen, M.; Gent, M.P.N.; Iannucci-Berger, W.; Eitzer, B.D.; Mattina, M.I. 2005. Influence of nutrient amendments on the phytoextraction of weathered p,p-DDE by cucurbits. Environ. Toxicol. Chem. 24:987-994.
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Progress 01/01/04 to 12/31/04
Outputs
This project is essentially a continuation of a previous Hatch project (CONH00766) that began investigations on the uptake and translocation of highly weathered persistent organic pollutants (POPs) in soil. We have discovered that Cucurbita pepo ssp pepo (zucchini and pumpkin) has a very unique ability to removed DDE and chlordane (both are POPs) from soil through a process termed phytoremediation. Our investigations are focused on elucidating the mechanisms driving that behavior. A range of studies was initiated this project period, producing four publications. However, 3 of those publications are still in press and thus, discussion of those findings will be reserved for next year's report. The findings of the published study follow. Previous studies have shown that zucchini (Cucurbita pepo) and cucumber (Cucumis sativus) under field conditions are good and poor accumulators, respectively, of persistent organic pollutants from soil. Here, each species was grown under
three cultivation regimes: dense (5 plants in 5 kg soil), non-dense (1 plant in 80 kg soil), and field conditions (2-3 plants in approximately 789 kg soil). DDE and inorganic element content in roots, stems, leaves, and fruit were determined. Under field conditions, zucchini phytoextracted 1.3% of the weathered DDE with 98% of the contaminant in the aerial tissues. Conversely, cucumber removed 0.09% of the DDE under field conditions with 83% in the aerial tissues. Under dense cultivation, cucumber produced a fine and fibrous root system not observed in our previous experiments and phytoextracted 0.78% of the contaminant, whereas zucchini under similar conditions removed only 0.59%. However, cucumber roots translocated only 5.7% of the pollutant to the shoot system, while in zucchini 48% of the DDE in the plant was present in the aerial tissue. To enable direct comparison across cultivation regimes, total in planta DDE and inorganic elements were mass normalized or multiplied by the
ratio of plant mass to soil mass. For cucumber, differences in total DDE and inorganic element content among the cultivation regimes largely disappear upon mass normalization, indicating that greater uptake of both types of constituents in the dense condition is due to greater plant biomass per unit soil. Conversely, for zucchini the mass normalized content of DDE and inorganic elements is up to 2 orders of magnitude greater under field conditions than under dense cultivation, indicating a unique physiological response of C. pepo in the field. The role of cultivation conditions and nutrient availability in controlling root morphology, organic acid exudation, and contaminant uptake are the topics of ongoing studies.
Impacts
Several types of highly weathered and hydrophobic contaminants have been shown to be nonavailable to a variety of receptors and not-amenable to a variety of on site remediation technologies. The fact that a very narrow group of plant species have the ability to extract significant quantities of these residues is suprising and of great interest both scientifically and practically. This project is designed to elucidate the mechanism by which the contaminant uptake occurs and that information could prove invaluable in designing future phytoremediation strategies for this group of recalcitrant compounds. Potential long-term benefits could include growers removing historical contamination from their fields, more rapid development of brownfield sites, and on site remediation of contaminated areas not thought amenable to such approaches.
Publications
- Wang, X.; White, J.C.; Gent, M.P.N.; Iannucci-Berger, W.; Eitzer, B.D; Mattina, M.I. 2004. Phytoextraction of weathered DDE by zucchini (Cucurbita pepo) and cucumber (Cucumis sativus) under different cultivation conditions. Int. J. Phytoremed. 6(4):289-297.
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Progress 01/01/03 to 12/31/03
Outputs
This project is essentially a continuation of a previous Hatch project (CONH00766) that began investigations on the uptake and translocation of highly weathered persistent organic pollutants (POPs) in soil. We have discovered that Cucurbita pepo (zucchini and pumpkin) has a very unique ability to remove DDE and chlordane (both are POPs) from soil through a process termed phytoremediation. Our investigations are focused on elucidating the mechanisms driving that behavior. Two studies have been completed this year. First, experiments were conducted to assess the effect of seven organic acids (succinic, tartaric, malic, malonic, oxalic, citric, EDTA) over a concentration range of 2 orders of magnitude (0.001-0.10 M) on the release of weathered DDE and the extraction of polyvalent inorganic ions from soil. At 0.05 M, all organic acids significantly increased contaminant release by 19-80%. Organic acids also increased the aqueous concentration of 8 inorganic constituents
extracted from soil, with at least a six-fold increase in the release of Al, Fe, Mn, and P at 0.001 M. Zucchini seedlings grown for 28 d in soil containing weathered DDE were periodically amended with distilled water, citric or oxalic acids (0.01 M). Plants receiving water removed 1.7% of the DDE from the soil. Seedlings amended with citric or oxalic acids removed 2.1 and 1.9% of the contaminant, respectively, and contained up to 66% more contaminant in the shoot system than unamended vegetation. The data indicate that the addition of low molecular weight organic acids causes the partial dissolution of the soil structure through the chelation of inorganic structural ions, potentially enhancing bioavailability and having implications for the phytoremediation of persistent organic pollutants in soil. A second study was undertaken to investigate intraspecific variability in uptake potential of weathered DDE by 21 cultivar varieties of summer squash from 2 distinct subspecies, C. pepo ssp
texana and C. pepo ssp pepo. Significant differences existed between the 2 subspecies, with average root and stem to soil bioconcentration factors (BCF, dry weight ratio of contaminant concentration in the vegetation to that in the soil) of 7.22 and 5.40 for ssp pepo and of 2.37 and 0.454 for spp texana, respectively. The amounts of weathered DDE removed from the soil by ssp pepo and ssp texana were 0.301 and 0.065%, respectively, with maximum values within each subspecies of 0.780 and 0.182%, respectively. The quantities of 14 inorganic elements were determined in both the soil and tissues (roots, stems, leaves, and fruit) of all 21 cultivar varieties. Phosphorus concentrations in the tissues of ssp pepo were 14 (fruit)-73% (stems) greater than those of ssp texana. These data support our hypothesis that the unique ability of certain cultivars of C. pepo to phytoextract highly weathered POPs from soil is the result of low molecular weight organic acid exudation as a unique phosphorus
acquisition mechanism.
Impacts
Several types of highly weathered and hydrophobic contaminants have been shown to be nonavailable to a variety of receptors and not-amenable to a variety of on site remediation technologies. The fact that a very narrow group of plant species have the ability to extract significant quantities of these residues is suprising and of great interest both scientifically and practically. This project is designed to elucidate the mechanism by which the contaminant uptake occurs and that information could prove invaluable in designing future phytoremediation strategies for this group of recalcitrant compounds. Potential long-term benefits could include growers removing historical contamination from their fields, more rapid development of brownfield sites, and on site remediation of contaminated areas not thought amenable to such approaches.
Publications
- White, J.C.; Mattina, M.J.I.; Lee, W-Y; Eitzer, B.D.; Iannucci-Berger, W. 2003. Role of organic acids in enhancing the uptake of weathered p,p'-DDE by plants. Environ. Poll. 124:71-80.
- White, J.C., Wang, X., Gent, M.P.N., Ianucci-Berger, W., Eitzer, B.D., Schultes, N.P., Arienzo, M., Mattina, M.I. 2003. Subspecies-level Variation in the Phytoextraction of Weathered p,p'-DDE by Cucurbita pepo. Environ. Sci. Technol. 37:4368-4373.
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Progress 01/01/02 to 12/31/02
Outputs
This project is essentially a continuation of a previous hatch project (CONH00766), which investigated the uptake and translocation of persistent organic pollutants (POPs) from soil. POPs are of concern due to their toxicity, longevity in natural systems, potential for bioaccumulation, and recalcitrance to remediation. We have been focusing on two organochlorine insecticides that were banned in the US decades ago, DDE and chlordane. The long-held assumption in the scientific and regulatory community has been that the longer an organic compound sits in soil, the less and less available it becomes due to sequestration within the soil organic matter. In fact, there is much data to support those assumptions with plants and many other species. However, in CONH00766 we observed that certain plant species (specifically certain cultivar varieties of Cucurbita pepo) may accumulate much higher that expected levels of these weathered organic pollutants. This project has just
begun but will seek to define the mechanism by which this narrow range of plant species accumulates contaminants from soil that seemingly most other plants cannot. The focus is on the exudation of low molecular weight organic acids and their resulting localized destruction of the soil matrix through routine nutrient acquisition activities. This project will also involve field studies at real hazardous waste sites to assess the liklihood of practically applying the observed pattern of uptake in a remediation scenario.
Impacts
The potential significance of this project is 2-fold. It will first supply useful information to those wishing to estimate bioavailability and risk of contaminated soils through these use of a narrow range of assays. The data will likely show that under specific conditions and with specific biological receptors, availability and thus risk could vary dramatically. Secondly, the project will investigate the possibility of utilizing a low-cost in situ remediation technology for a class of contaminants that are extremely difficult to remove from soil.
Publications
- No publications reported this period
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