Steven C. McCutcheon

Phytoremediation: An ecological solution to organic chemical contamination

Abstract Phytoremediation is a promising new technology that uses plants to degrade, assimilate, metabolize, or detoxify metals, hydrocarbons, pesticides, and chlorinated solvents. In this review, in situ, in vivo and in vitro methods of application are described for remediation of these compounds. Phytoaccumulation, phytoextraction, phytostabilization, phytotransformation, phytovolatilization and rhizodegradation are discussed and the role of enzymes in transforming organic chemicals in plants is presented. The advantages and constraints of phytoremediation are provided. Our conclusions is that phytoremediation prescriptions must be site-specific; however, these applications have the potential for providing the most cost-effective and resource-conservative approach for remediating sites contaminated with a variety of hazardous chemicals.

Runoff Curve Numbers for 10 Small Forested Watersheds in the Mountains of the Eastern United States

AbstractEngineers and hydrologists use the curve number method to estimate runoff from rainfall for different land use and soil conditions; however, large uncertainties occur for estimates from forested watersheds. This investigation evaluates the accuracy and consistency of the method using rainfall-runoff series from 10 small forested-mountainous watersheds in the eastern United States, eight annual maximum series from New Hampshire, West Virginia, and North Carolina, and two partial duration series from Georgia. These series are the basis to compare tabulated curve numbers with values estimated using five methods. For nine of 10 watersheds, tabulated curve numbers do not accurately estimate runoff. One source of the large uncertainty is a consistent decrease in storm-event curve numbers with increasing rainfall. A calibrated constant curve number is suitable for only two of 10 watersheds; the others require a variable watershed curve number associated with different magnitude rainfalls or probabilities...

Phytotreatment of TNT-Contaminated Groundwater

Phytoremediation is a viable technique for treating nitroaromatic compounds, particularly munitions. Continuous flow phyto-reactor studies were conducted at the following three influent concentrations of 2,4,6-trinitrotoluene (TNT): 1, 5, and 10 ppm. A control was also prepared with an influent TNT concentration of 5 ppm. Flow rates were systematically reduced to increase hydraulic retention times (HRT) which ranged from 12 to 76 days. Initially, the control reactor removed TNT as efficiently as the plant reactors. With time, however, the efficiency of the control became less than that of the plant reactors, suggesting that adsorption was initially the mechanism for removal. Up to 100% of the TNT was removed. Aminodinitrotoluene (ADNT) effluent concentration was higher for higher TNT influent concentrations. Increasing the retention time reduced ADNT concentration in the effluent. Supplementary batch studies confirmed that ADNT and diaminonitrotoluene (DANT) were phytodegraded. Preliminary batch studies w...

Phytotransformation of Perchlorate and Identification of Metabolic Products in Myriophyllum aquaticum

ABSTRACT The uptake and transformation of perchlorate in the presence of Myriophyllum aquaticum (parrot-feather) were examined in sand and aqueous treatments with concentrations between 0.2 to 20 ppm. Controls were included without plants to confirm the uptake of perchlorate by parrot-feather. The kinetic data followed a first-order reaction mechanism with rate constants ranging from 0.004 to 0.090, resulting in half-lives between 7 to 173 days. Uptake rates were five times higher in aqueous treatments than in sand treatments. The intermediates detected in the plant tissue suggest that perchlorate transformed in a step-wise fashion to form chloride. Accumulation of perchlorate in the plant tissues (1.2 g/kg) suggests that parrot-feather has a high capacity for accumulating this contaminant.

Use of Aquatic Plants and Algae for Decontamination of Waters Polluted with Chlorinated Alkanes

ABSTRACT The transformation of carbon tetrachloride (CT) and hexachloroethane (HCA) by aquatic plants and freshwater algae was investigated. Stressed, axenic, and physiologically healthy freshwater plants all transformed the two chlorinated alkanes, yielding similar breakdown products. Experiments conducted with dead plants were used to indirectly test the hypothesis that dead aquatic plants maintain and possibly contribute to the dehalogenase activity observed in organic-rich sediments. After exposure of the aquatic plants and algae to HCA- and CT-dosed solutions, a rapid sorption (or sequestration) step followed by a slow transformation lasting several hours thereafter was observed. The kinetics data were adequately described by two first-order rate equations; pseudo-first-order sorption rate coefficients were calculated for the initial rapid adsorption and transformation steps. The identified metabolites extracted from plants indicated that more than one pathway, possibly requiring different reactants,...

Modeling Reservoir Density Underflow And Interflow From A Chemical Spill

An integral simulation model has been developed for understanding and simulating the process of a density current and the transport of spilled chemicals in a stratified reservoir. The model is capable of describing flow behavior and mixing mechanisms in different flow regimes (plunging flow, underflow, and interflow). It computes flow rate, velocity, flow thickness, mixing parameterized by entrainment and dilution, depths of plunging, separation and intrusion, and time of travel. The model was applied to the Shasta Reservoir in northern California during the July 1991 Sacramento River chemical spill. The simulations were used to assist in the emergency response, confirm remediation measures, and guide data collection. Spill data that were available after the emergency response are used to conduct a postaudit of the model results. Predicted flow parameters are presented and compared with observed interflow intrusion depth, travel time, and measured concentrations of spilled chemicals. In the reservoir, temperature difference between incoming river flow and ambient lake water played a dominant role during the processes of flow plunging, separation, and intrusion. With the integral approach, the gross flow behavior can be adequately described and information useful in the analysis of contaminated flow in a reservoir after a spill is provided.

PHYTOREMEDIATION: STATE OF THE SCIENCE CONFERENCE AND OTHER DEVELOPMENTS

It is a pleasure to present six papers in this issue, selected from presentations at the U.S. Environmental Protection Agency (EPA) conference, Phytoremediation: State of the Science held May 1 to 2, 2000, in Boston, MA. These papers highlight some of the many advances reported in representative areas of phytoremediation. In addition to introducing the six papers that have undergone the standard International Journal of Phytoremediation (IJP) review, this special commentary also (1) briefly reviews the beginnings of phytoremediation to put the need for the 2000 EPS Conference venue into context, (2) reviews other advances presented at the conference, (3) notes where additional review and synthesis is necessary in context with the reports from other phytoremediation meetings and future developments.

Uptake and transformation of perchlorate by vascular plants

Phytoremediation is a promising new method that uses green plants to cleanse soil and water contaminated with organic or inorganic pollutants. In this study, the uptake and transformation of sodium perchlorate (NaClO4) using four vascular plant species were examined in batch experiments. The species include two trees, cabbage gum (Eucalyptus amplifolia) and eastern cottonwood (Populus deltoides), a herbaceous wetland plant, perennial glasswort (Salicornia virginica), and a herbaceous aquatic plant, waterweed (Elodea canadensis). Perchlorate was depleted from solution in the presence of all but one species (waterweed). Depletion was calculated as a first‐order kinetics reaction with k values in the range of 0–0.013 per day and accumulation of perchlorate was between 3.2 and 3138 mg/kg. Perchlorate and transformation metabolites (chlorate, chlorite, chloride) were observed in all plant tissues (e.g., roots, stems, leaves) analyzed. Results suggest that significant influences on perchlorate uptake include: (1) plant species present, (2) concentration of perchlorate, (3) sand versus hydroponic treatments, (4) the presence or absence of plant nutrients or competing ions, (5) stage of plant maturity.

Curve Number Approaches to Estimate Drainage from a Yard Waste Windrow Composting Pad

Abstract. Estimation of runoff from windrow compost pads is a challenge due to the different hydrologic properties of the compost and pad, and moisture storage in the compost, both of which change with time. The surface of a compost pad is usually crushed rock on top of a compacted layer of clay. The curve number method is widely used for estimating runoff from rainfall, but because the porous layer of gravel promotes greater infiltration and subsurface drainage, this study investigated the effectiveness of this standard approach. Four curve number based methods are assessed for their utility in estimating drainage from a 7284-m 2 windrow compost pad in Athens, Georgia, using 16 storm events. The methods estimate drainage using (1) a tabulated curve number, (2) a quasi-dynamic curve number based on the magnitude of the rainfall, antecedent rainfall, and areal coverage of the compost piles, (3) an asymptotic curve number, and (4) an average event-based curve number. Using the tabulated curve number, event runoff (r 2 = 0.92) was consistently underestimated. A quasi-dynamic curve number improved the runoff estimation (r 2 = 0.98). The asymptotic (r 2 = 0.90) and event-based averaged (r 2 = 0.92) curve number methods performed comparable to the tabulated curve number method. Although curve numbers for maturing compost decreased from approximately 95 to 75 over time, this study recommends use of a conservative curve number = 95 for containment of design storms, while curve numbers of 70 to 75 may be appropriate for estimating average annual runoff from mature compost and the area necessary for land application of the pad runoff.

Curve Numbers for Nine Mountainous Eastern United States Watersheds: Seasonal Variation and Forest Cutting

Many engineers and hydrologists use the curve number method to estimate runoff from ungaged watersheds; however, the method does not explicitly account for the influence of season or forest cutting on runoff. This study of observed rainfall and runoff for small, forested watersheds that span the Appalachian Mountains of the eastern United States showed that curve numbers calibrated for the growing season tended to be smaller than for the dormant season. Forest cutting tended to increase curve numbers. However, the increase in water yield following forest cutting on these watersheds only lasted 1 year to 11 years, thereby limiting the precision of the curve numbers estimated for these brief hydrologic effect periods. This study highlights the need to account for seasonal and forest cutting when estimating runoff from some forested watersheds.