Pamela J. Rice

Phytoremediation—An Overview

The use of plants (directly or indirectly) to remediate contaminated soil or water is known as phytoremediation. This technology has emerged as a more cost effective, noninvasive, and publicly acceptable way to address the removal of environmental contaminants. Plants can be used to accumulate inorganic and organic contaminants, metabolize organic contaminants, and encourage microbial degradation of organic contaminants in the root zone. Widespread utilization of phytoremediation can be limited by the small habitat range or size of plants expressing remediation potential, and insufficient abilities of native plants to tolerate, detoxify, and accumulate contaminants. A better understanding and appreciation of the potential mechanisms for removing contaminants from the root zone and the interaction between plants, microorganisms, and contaminants will be useful in extending the application of phytoremediation to additional contaminated sites.

Sources and transport of contaminants of emerging concern: A two-year study of occurrence and spatiotemporal variation in a mixed land use watershed

The occurrence and spatiotemporal variation of 26 contaminants of emerging concern (CECs) were evaluated in 68 water samples in 2011-2012 in the Zumbro River watershed, Minnesota, U.S.A. Samples were collected across a range of seasonal/hydrological conditions from four stream sites that varied in associated land use and presence of an upstream wastewater treatment plant (WWTP). Selected CECs included human/veterinary pharmaceuticals, personal care products, pesticides, phytoestrogens, and commercial/industrial compounds. Detection frequencies and concentrations varied, with atrazine, metolachlor, acetaminophen, caffeine, DEET, and trimethoprim detected in more than 70% of samples, acetochlor, mecoprop, carbamazepine, and daidzein detected in 30%-50% of samples, and 4-nonylphenol, cotinine, sulfamethoxazole, erythromycin, tylosin, and carbaryl detected in 10%-30% of samples. The remaining target CECs were not detected in water samples. Three land use-associated trends were observed for the detected CECs. Carbamazepine, 4-nonylphenol, erythromycin, sulfamethoxazole, tylosin, and carbaryl profiles were WWTP-dominated, as demonstrated by more consistent loading and significantly greater concentrations downstream of the WWTP and during low-flow seasons. In contrast, acetaminophen, trimethoprim, DEET, caffeine, cotinine, and mecoprop patterns demonstrated both seasonally-variable non-WWTP-associated and continual WWTP-associated influences. Surface water studies of CECs often target areas near WWTPs. This study suggests that several CECs often characterized as effluent-associated have additional important sources such as septic systems or land-applied biosolids. Finally, agricultural herbicide (atrazine, acetochlor, and metolachlor) profiles were strongly influenced by agricultural land use and seasonal application-runoff, evident by significantly greater concentrations and loadings at upstream sites and in early summer when application and precipitation rates are greatest. Our results indicate that CEC monitoring studies should consider a range of land uses, seasonality, and transport pathways in relation to concentrations and loadings. This knowledge can augment CEC monitoring programs to result in more accurate source, occurrence, and ecological risk characterizations, more precisely targeted mitigation initiatives, and ultimately, enhanced environmental decision-making.

Sediment-water distribution of contaminants of emerging concern in a mixed use watershed.

This study evaluated the occurrence and distribution of 15 contaminants of emerging concern (CECs) in stream water and sediments in the Zumbro River watershed in Minnesota and compared these with sub-watershed land uses. Sixty pairs of sediment and water samples were collected across all seasons from four stream sites for over two years and analyzed for selected personal care products, pesticides, human and veterinary medications, and phytoestrogens. Spatial and temporal analyses indicate that pharmaceuticals and personal care products (urban/residential CECs) are significantly elevated in water and/or sediment at sites with greater population density (>100 people/km(2)) and percentage of developed land use (>8% of subwatershed area) than those with less population density and land area under development. Significant spatial variations of agricultural pesticides in water and sediment were detectable, even though all sites had a high percentage of agricultural land use. Seasonality in CEC concentration was observed in water but not in sediment, although sediment concentrations of three CECs did vary between years. Average measured non-equilibrium distribution coefficients exceeded equilibrium hydrophobic partitioning-based predictions for 5 of the 7 detected CECs by at least an order of magnitude. Agreement of measured and predicted distribution coefficients improved with increasing hydrophobicity and in-stream persistence. The more polar and degradable CECs showed greater variability in measured distributions across different sampling events. Our results confirm that CECs are present in urban and agricultural stream sediments, including those CECs that would typically be thought of as non-sorptive based on their log Kow values. These results and the observed patterns of sediment and water distributions augment existing information to improve prediction of CEC fate and transport, leading to more accurate assessments of exposure and risk to surface water ecosystems.

Sorption of isoxaflutole and DKN on organoclays

Sorption of the herbicide isoxaflutole and its main degradate, diketonitrile (DKN), to natural clays, SAz-1, SWy-2 and SHCa-1, and the organoclay derivatives (octadecylammonium (ODA) and hexadecyltrimethylammonium (HDTMA)) of these clays was investigated. Isoxaflutole hydrolysis to DKN was too rapid in aqueous solutions with organoclays to characterize sorption. No measurable DKN sorption was observed for the natural clays. Sorption of DKN was greater on organoclays with an interlayer paraffin-like complex that were prepared from the high-charge SAz-1 clay than on organoclays with a bilayer or monolayer interlayer complex prepared using lower-charge SWy-2 or SHCa-1 clays. Desorption isotherms indicated that sorption was irreversible. For SAz-1 with HDTMA at ∼100% of the clay CEC, the d001 values suggest that DKN enters the interlamellar space of the organoclay and dissociates into the anion. The DKN anion forms a very stable chelate complex with the residual cations and/or partially-coordinated structural cations. This strong interaction supports the irreversibility of the sorptive process.

Evaluation of core cultivation practices to reduce ecological risk of pesticides in runoff from Agrostis palustris

Pesticides associated with the turfgrass industry have been detected in storm runoff and surface waters of urban watersheds, invoking concern of their potential environmental effects and a desire to reduce their transport to nontarget locations. Quantities of chlorpyrifos, dicamba, dimethylamine salt of 2,4-dichlorophenoxyacetic acid (2,4-D), flutolanil, and mecoprop-p (MCPP) transported in runoff from bentgrass (Agrostis palustris) fairway turf managed with solid tine (ST) or hollow tine (HT) core cultivation were compared to determine which cultivation practice is more efficient at mitigating environmental risk. Plots receiving HT core cultivation showed a 10 and 55% reduction in runoff volume and a 15 to 57% reduction in pesticide transport with runoff at 63 d and 2 d following core cultivation. Estimated environmental concentrations of the pesticides in a surface water receiving runoff from turf managed with ST core cultivation exceeded the median lethal concentration (LC50) or median effective concentration (EC50) of nine aquatic organisms evaluated. Replacing ST core cultivation with HT core cultivation reduced surface water concentrations of the pesticides to levels below the LC50 and EC50 for most these aquatic organisms, lessening risk associated with pesticides in runoff from the fairway turf. Results of the present research provide quantitative information that will allow for informed decisions on cultural practices that can maximize pesticide retention at the site of application, improving pest control in turf while minimizing environmental contamination and adverse effects associated with the off-site transport of pesticides.

Pesticide transport with runoff from creeping bentgrass turf: Relationship of pesticide properties to mass transport

The off-site transport of pesticides with runoff is both an agronomic and environmental concern, resulting from reduced control of target pests in the area of application and contamination of surrounding ecosystems. Experiments were designed to measure the quantity of pesticides in runoff from creeping bentgrass (Agrostis palustris) turf managed as golf course fairway to gain a better understanding of factors that influence chemical availability and mass transport. Less than 1 to 23% of applied chloropyrifos, flutolanil, mecoprop-p (MCPP), dimethylamine salt of 2,4-dichlorophenoxyacetic acid (2,4-D), or dicamba was measured in edge-of-plot runoff when commercially available pesticide formulations were applied at label rates 23 +/- 9 h prior to simulated precipitation (62 +/- 13 mm). Time differential between hollow tine core cultivation and runoff did not significantly influence runoff volumes or the percentage of applied chemicals transported in the runoff. With the exception of chlorpyrifos, all chemicals of interest were detected in the initial runoff samples and throughout the runoff events. Chemographs of the five pesticides followed trends in agreement with mobility classifications associated with their soil organic carbon partition coefficient (K(OC).) Data collected from the present study provides information on the transport of chemicals with runoff from turf, which can be used in model simulations to predict nonpoint source pollution potentials and estimate ecological risks.

Nutrient loss with runoff from fairway turf: an evaluation of core cultivation practices and their environmental impact.

The presence of excess nutrients in surface waters can result in undesirable environmental and economic consequences, including nuisance algal blooms and eutrophication. Fertilizer use in highly managed turf systems has raised questions concerning the contribution of nutrients to surrounding surface waters. Experiments were designed to quantify phosphorus and nitrogen transport with runoff from turf plots maintained as a golf course fairway to identify which cultural practice, solid tine (ST) or hollow tine (HT) core cultivation, maximized phosphorus and nitrogen retention at the site of fertilizer application. Simulated precipitation and collection of resulting runoff were completed 26 ± 13 h following granular fertilizer application (18-3-18: N-P₂O₅-K₂O) and 63 d and 2 d following core cultivation. Runoff volumes were reduced in fairway turf plots aerated with HT relative to ST (63 d: 10%, 2 d: 55% reduction). Analysis of the runoff revealed a reduction in soluble phosphorus, ammonium nitrogen, and nitrate nitrogen losses with runoff from plots managed with HT; a 5 to 27% reduction after 63 d; and a 39 to 77% reduction at 2 d. Golf course runoff-to-surface water scenarios were used to calculate estimated environmental concentrations (EECs) of nitrogen and phosphorus in surface water receiving runoff from turf managed with ST or HT core cultivation. Surface water concentrations of phosphorus remained above the U.S. Environmental Protection Agencys water quality criteria to limit eutrophication, with the exception of concentrations associated with HT core cultivation at 2 d. Regardless of management practice (ST or HT) and time between core cultivation and runoff (63 d or 2 d), all EECs of nitrogen were below levels associated with increased algal growth. Understanding nutrient transport with runoff and identifying strategies that reduce off-site transport will increase their effectiveness at intended sites of application and minimize undesirable effects to surrounding surface water resources.

Evaluation of nitrogen and phosphorus transport with runoff from fairway turf managed with hollow tine core cultivation and verticutting

Enrichment of surface waters with excess nutrients is associated with increased algal blooms, euthrophication and hypoxic zones, as reported in the northern Gulf of Mexico. A source of nutrients to surface waters results from fertilizer runoff. Management strategies used to maintain turf on golf courses and recreational fields often include aerification and application of fertilizer. Although research exists on benefits of core cultivation and verticutting (VC) to reduce thatch and the transport of applied chemicals with runoff, there are no studies reporting the effect of coupling these management practices with the goal of further reduction of off-site transport of fertilizer with runoff. We hypothesized that the addition of VC to hollow tine core cultivation (HTCC) would enhance infiltration of precipitation, reduce runoff and nutrient transport with runoff and therefore influence concentrations of nutrients in surface waters receiving runoff from turf managed as a golf course fairway. Greater runoff and mass of soluble phosphorus and ammonium nitrogen transported with runoff were measured from plots managed with HTCC+VC than HTCC; however, the reverse was noted for nitrate nitrogen. Only a portion of the observed trends proved to be statistically significant. Our research showed no reduction or enhancement of risk associated with surface water concentrations of phosphorus or nitrogen, resulting from runoff from creeping bentgrass turf that was managed with HTCC+VC compared to HTCC. Data obtained in this research will be useful to grounds superintendents when selecting best management practices and to scientists seeking data relating runoff to land management for watershed-scale modeling.

Use of vegetative furrows to mitigate copper loads and soil loss in runoff from polyethylene (plastic) mulch vegetable production systems

The transport of runoff with high copper concentrations and sediment loads into adjacent surface waters can have adverse effects on nontarget organisms as a result of increased turbidity and degraded water quality. Runoff from vegetable production utilizing polyethylene mulch can contain up to 35% of applied copper, a widely used fungicide/bactericide that has adverse effects on aquatic organisms. Copper is primarily transported in runoff with suspended particulates; therefore, implementation of management practices that minimize soil erosion will reduce copper loads. Replacing bare-soil furrows with furrows planted in rye (Secale cereale) significantly improved the sustainability of vegetable production with polyethylene mulch and reduced the potential environmental impact of this management practice. Vegetative furrows decreased runoff volume by >40% and soil erosion by >80%. Copper loads with runoff were reduced by 72% in 2001, primarily as a result of reduced soil erosion since more than 88% of the total copper loads were transported in runoff with suspended soil particulates. Tomato yields in both years were similar between the polyethylene mulch plots containing either bare-soil or vegetative furrows. Replacing bare-soil furrows with vegetative furrows greatly reduces the effects of sediments and agrochemicals on sensitive ecosystems while maintaining crop yields.

Experimental Variability in Characterization of Cyfluthrin Sorption to Soil

To assess the risk of a pesticide to leach to groundwater or to run off to surface water after application, it is necessary to characterize the sorption of the pesticide to soil. For pyrethroids, their hydrophobicity, strong sorption to various materials, and low solubility make it difficult to accurately characterize sorption processes. The objective of this research was to evaluate the variability in cyfluthrin ((RS)-α -cyano-4-fluoro-3-phenoxybenzyl (1RS,3RS;1RS,3SR)-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropanecarboxylate) sorption to soil as affected by experiment conditions. To minimize cyfluthrin sorption on the walls of glass, silanized-glass, stainless steel, and PTFE centrifuge tubes, cyfluthrin solution was added to aqueous soil slurries or directly to soil, after which it was equilibrated with aqueous solution. Depending on the soil, variation in sorption coefficients, K oc, obtained using different experimental methodologies with one soil can be comparable to the variation in K oc values obtained for soils with different physical and chemical properties using one method. K oc values for cyfluthrin ranged from 56,000 to 300,000 L kg−1. Sorption methodology needs to be evaluated before sorption coefficients are used in predictive transport models.