George, IA, United States
George, IA, United States

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Mechtensimer S.,Soil Quality Laboratory | Toor G.S.,Soil Quality Laboratory
PLoS ONE | Year: 2017

Septic systems can be a potential source of phosphorus (P) in groundwater and contribute to eutrophication in aquatic systems. Our objective was to investigate P transport from two conventional septic systems (drip dispersal and gravel trench) to shallow groundwater. Two new in-situdrainfields (6.1 m long by 0.61 m wide) with a 3.72 m2 infiltrative surface were constructed. The drip dispersal drainfield was constructed by placing 30.5 cm commercial sand on top of natural soil and the gravel trench drainfield was constructed by placing 30.5 cm of gravel on top of 30.5 cm commercial sand and natural soil. Suction cup lysimeters were installed in the drainfields (at 30.5, 61,106.7 cm below infiltrative surface) and piezometers were installed in the groundwater (>300 cm below infiltrative surface) to capture P dynamics from the continuum of unsaturated to saturated zones in the septic systems. Septic tank effluent (STE), soil-water, and groundwater samples were collected for 64 events (May 2012-Dec 2013) at 2 to 3 days (n = 13), weekly (n = 29), biweekly (n = 17), and monthly (n = 5) intervals. One piezometer was installed up-gradient of the drainfields to monitor background groundwater (n = 15). Samples were analyzed for total P (TP), ortho-phosphate-P (PO4-P), and other-P (TP-PO4-P). The gravel trench drainfield removed significantly (p<0.0001) greater TP (∼20%) than the drip dispersal in the first 30.5 cm of the drainfield. However, when STE reached >300 cm in the groundwater, both systems had similar TP reductions of >97%. After 18 months of STE application, there was no significant increase in groundwater TP concentrations in both systems. We conclude that both drain-field designs are effective at reducing P transport to shallow groundwater. © 2017 Mechtensimer, Toor. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.


Yang Y.-Y.,Soil Quality Laboratory | Toor G.S.,Soil Quality Laboratory
Water Research | Year: 2017

Nutrients export from residential catchments contributes to water quality impairment in urban water bodies. We investigated the concentrations, transport mechanisms, and sources of nitrate-nitrogen (NO3–N) and orthophosphate-phosphorus (PO4–P) in urban stormwater runoff generated in residential catchments in Tampa Bay, Florida, United States. Street runoff samples, collected over 21 storm events, were supplemented with rainfall and roof runoff samples from six representative residential catchments. Samples were analyzed for N and P forms, N and oxygen (O) isotopes of nitrate (δ18O–NO3 − and δ15N–NO3 −), and δ18O and hydrogen (δD) isotopes of water (H2O). We found that the main NO3–N source in street runoff was atmospheric deposition (range: 35–64%), followed by chemical N fertilizers (range: 1–39%), and soil and organic N (range: 7–33%), whereas PO4–P in the street runoff likely originated from erosion of soil particles and mineralization from organic materials (leaves, grass clippings). The variability in the sources and concentrations of NO3–N and PO4–P across catchments is attributed to different development designs and patterns, use of various fill materials during land development, and landscaping practices. This data can be useful to develop strategies to offset the impacts of urban development (e.g., designs and patterns resulting in variable impervious areas) and management (e.g., fertilizer use, landscaping practices) on NO3–N and PO4–P transport in urban residential catchments. © 2017 Elsevier Ltd


Lusk M.G.,Soil Quality Laboratory | Toor G.S.,Soil Quality Laboratory
Water Research | Year: 2016

A portion of the dissolved organic nitrogen (DON) is biodegradable in water bodies, yet our knowledge of the molecular composition and controls on biological reactivity of DON is limited. Our objective was to investigate the biodegradability and molecular composition of DON in streams that drain a gradient of 19-83% urban land use. Weekly sampling over 21 weeks suggested no significant relationship between urban land use and DON concentration. We then selected two streams that drain 28% and 83% urban land use to determine the biodegradability and molecular composition of the DON by coupling 5-day bioassay experiments with high resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). Both urban streams contained a wide range of N-bearing biomolecular formulas and had >80% DON in lignin-like compounds, with only 5-7% labile DON. The labile DON consisted mostly of lipid-and protein-like structures with high H/C and low O/C values. Comparison of reactive formulas and formed counterparts during the bioassay experiments indicated a shift toward more oxygenated and less saturated N-bearing DON formulas due to the microbial degradation. Although there was a little net removal (5-7%) of organic-bound N over the 5-day bioassay, there was some change to the carbon skeleton of DON compounds. These results suggest that DON in urban streams contains a complex mixture of compounds such as lipids, proteins, and lignins of variable chemical structures and biodegradability. © 2016 Elsevier Ltd.


Mechtensimer S.,Soil Quality Laboratory | Toor G.S.,Soil Quality Laboratory
Chemosphere | Year: 2016

Septic systems can be a potential source of phosphorus (P) in shallow groundwater. Our objective was to investigate the fate, mass balance, and transport of P in the drainfield of a drip-dispersal septic system. Drainfields were replicated in lysimeters (152.4 cm long, 91.4 cm wide, and 91.4 cm high). Leachate and effluent samples were collected over 67 events (n = 15 daily; n = 52 weekly flow-weighted) and analyzed for total P (TP), orthophosphate (PO4P), and other P (TP - PO4P). Mean TP was 15 mg L-1 (84% PO4P; 16% other P) in the effluent and 0.16 mg L-1 (47% PO4P, 53% other P) in the leachate. After one year, 46.8 g of TP was added with effluent and rainfall to each drainfield, of which, <1% leached, 3.8% was taken up by St. Augustine grass, leaving >95% in the drainfield. Effluent dispersal increased water extractable P (WEP) in the drainfield from <5 to >10 mg kg-1. Using the P sorption maxima of sand (118 mg kg-1) and soil (260 mg kg-1), we estimated that ~18% of the drainfield P sorption capacity was saturated after one year of effluent dispersal. We conclude that despite the low leaching potential of P dispersed with effluent in the first year of drainfield operation, a growing WEP pool in the drainfield and low P sorption capacity of Florida's sandy soils may have the potential to transport P to shallow groundwater in long-running septic systems. © 2016 Elsevier Ltd.


Pannu M.W.,University of Florida | Toor G.S.,Soil Quality Laboratory | O'Connor G.A.,University of Florida | Wilson P.C.,University of Florida
Environmental Toxicology and Chemistry | Year: 2012

Triclosan (TCS) is an antimicrobial compound commonly found in biosolids. Thus, plants grown in biosolids-amended soil may be exposed to TCS. We evaluated the plant toxicity and accumulation potential of biosolids-borne TCS in two vegetables (lettuce and radish) and a pasture grass (bahia grass). Vegetables were grown in growth chambers and grass in a greenhouse. Biosolids-amended soil had TCS concentrations of 0.99, 5.9, and 11mg/kg amended soil. These TCS concentrations represent typical biosolids containing concentrations of 16mg TCS/kg applied at agronomic rates for 6 to 70 consecutive years, assuming no TCS loss. Plant yields (dry wt) were not reduced at any TCS concentration and the no observed effect concentration was 11mg TCS/kg soil for all plants. Significantly greater TCS accumulated in the below-ground biomass than in the above-ground biomass. The average bioaccumulation factors (BAFs) were 0.43±0.38 in radish root, 0.04±0.04 in lettuce leaves, 0.004±0.002 in radish leaves, and <0.001 in bahia grass. Soybean (grain) and corn (leaves) grown in our previous field study where soil TCS concentrations were lower (0.04-0.1mg/kg) had BAF values of 0.06 to 0.16. Based on the data, we suggest a conservative first approximate BAF value of 0.4 for risk assessment in plants. © 2012 SETAC.


Lusk M.G.,Soil Quality Laboratory | Toor G.S.,Soil Quality Laboratory
Environmental Science and Technology | Year: 2016

Dissolved organic nitrogen (DON) can be a significant part of the reactive N in aquatic ecosystems and can accelerate eutrophication and harmful algal blooms. A bioassay method was coupled with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) to determine the biodegradability and molecular composition of DON in the urban stormwater runoff and outflow water from an urban stormwater retention pond. The biodegradability of DON increased from 10% in the stormwater runoff to 40% in the pond outflow water and DON was less aromatic and had lower overall molecular weight in the pond outflow water than in the stormwater runoff. More than 1227 N-bearing organic formulas were identified with FT-ICR-MS in the stormwater runoff and pond outflow water, which were only 13% different in runoff and outflow water. These molecular formulas represented a wide range of biomolecules such as lipids, proteins, amino sugars, lignins, and tannins in DON from runoff and pond outflow water. This work implies that the urban infrastructure (i.e., stormwater retention ponds) has the potential to influence biogeochemical processes in downstream water bodies because retention ponds are often a junction between the natural and the built environment. (Figure Presented). © 2016 American Chemical Society.


Waria M.,University of Florida | O'Connor G.A.,University of Florida | Toor G.S.,Soil Quality Laboratory
Environmental Toxicology and Chemistry | Year: 2011

Land application of biosolids can constitute an important source of triclosan (TCS) input to soils, with uncertain effects. Several studies have investigated the degradation potential of TCS in biosolids-amended soils, but the results vary widely. We conducted a laboratory degradation study by mixing biosolids spiked with [ 14C]-TCS (final concentration=40mg/kg) with Immokalee fine sand and Ashkum silty clay loam soils at an agronomic application rate (22 Mg/ha). Biosolids-amended soils were aerobically incubated in biotic and inhibited conditions for 18 weeks. Subsamples removed at 0, 2, 4, 6, 9, 12, 15, and 18 weeks were sequentially extracted with an operationally defined extraction scheme to determine labile and nonlabile TCS fractions. Over the 18-week incubation, the proportion of [ 14C] in the nonlabile fraction increased and the labile fraction decreased, suggesting decreasing availability to biota. Partitioning of TCS into labile and nonlabile fractions depended on soil characteristics. Less than 0.5% of [ 14C]-TCS was mineralized to carbon dioxide ( 14CO 2) in both soils and all treatments. A degradation metabolite, methyl triclosan (Me-TCS), was identified in both soils only in the biotic treatment, and increased in concentration over time. Even under biotic conditions, biosolids-borne TCS is persistent, with a primary degradation (TCS to Me-TCS) half-life of 78d in the silty clay loam and 421d in the fine sand. A half-life of approximately 100d would be a conservative first approximation of TCS half-life in biosolids-amended soils for risk estimation. © 2011 SETAC.


Pannu M.W.,University of Florida | O'Connor G.A.,University of Florida | Toor G.S.,Soil Quality Laboratory
Environmental Toxicology and Chemistry | Year: 2012

Triclosan (TCS) is a common constituent of personal care products and is frequently present in biosolids. Application of biosolids to land transfers significant amounts of TCS to soils. Because TCS is an antimicrobial and is toxic to some aquatic organisms, concern has arisen that TCS may adversely affect soil organisms. The objective of the present study was to investigate the toxicity and bioaccumulation potential of biosolids-borne TCS in terrestrial micro- and macro-organisms (earthworms). Studies were conducted in two biosolids-amended soils (sand, silty clay loam), following U.S. Environmental Protection Agency (U.S. EPA) guidelines. At the concentrations tested herein, microbial toxicity tests suggested no adverse effects of TCS on microbial respiration, ammonification, and nitrification. The no observed effect concentration for TCS for microbial processes was 10mg/kg soil. Earthworm subchronic toxicity tests showed that biosolids-borne TCS was not toxic to earthworms at the concentrations tested herein. The estimated TCS earthworm lethal concentration (LC50) was greater than 1mg/kg soil. Greater TCS accumulation was observed in earthworms incubated in a silty clay loam soil (bioaccumulation factor [BAF]=12±3.1) than in a sand (BAF=6.5±0.84). Field-collected earthworms had a significantly smaller BAF value (4.3±0.7) than our laboratory values (6.5-12.0). The BAF values varied significantly with exposure conditions (e.g., soil characteristics, laboratory vs field conditions); however, a value of 10 represents a reasonable first approximation for risk assessment purposes. © 2011 SETAC.


Toor G.S.,Soil Quality Laboratory | Han L.,Soil Quality Laboratory | Stanley C.D.,Soil Quality Laboratory
Environmental Monitoring and Assessment | Year: 2013

Our objective was to evaluate changes in water quality parameters during 1983-2007 in a subtropical drinking water reservoir (area: 7 km2) located in Lake Manatee Watershed (area: 338 km2) in Florida, USA. Most water quality parameters (color, turbidity, Secchi depth, pH, EC, dissolved oxygen, total alkalinity, cations, anions, and lead) were below the Florida potable water standards. Concentrations of copper exceeded the potable water standard of <30 μg l-1 in about half of the samples. About 75 % of total N in lake was organic N (0.93 mg l-1) with the remainder (25 %) as inorganic N (NH3-N: 0.19, NO3-N: 0.17 mg l -1), while 86 % of total P was orthophosphate. Mean total N/P was <6:1 indicating N limitation in the lake. Mean monthly concentration of chlorophyll-a was much lower than the EPA water quality threshold of 20 μg l-1. Concentrations of total N showed significant increase from 1983 to 1994 and a decrease from 1997 to 2007. Total P showed significant increase during 1983-2007. Mean concentrations of total N (n=215; 1.24 mg l-1) were lower, and total P (n=286; 0.26 mg l-1) was much higher than the EPA numeric criteria of 1.27 mg total N l-1 and 0.05 mg total P l-1 for Florida's colored lakes, respectively. Seasonal trends were observed for many water quality parameters where concentrations were typically elevated during wet months (June-September). Results suggest that reducing transport of organic N may be one potential option to protect water quality in this drinking water reservoir. © 2012 Springer Science+Business Media B.V.


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