Roy F. Spalding

Analysis of oxytetracycline, tetracycline, and chlortetracycline in water using solid-phase extraction and liquid chromatography–tandem mass spectrometry

A method using liquid chromatography-tandem mass spectrometry has been developed for determination of trace levels of tetracycline antibiotics in ground water and confined animal feeding operation waste water. Oxytetracycline (OTC), tetracycline (TC), and chlortetracycline (CTC) were extracted from water samples using both polymeric and C18 extraction cartridges. The addition of a buffer containing potassium phosphate and citric acid improved tetracycline recoveries in lagoon water. Method detection limits determined in reagent water fortified with 1 microg l(-1) OTC, TC, and CTC were 0.21, 0.20, and 0.28 microg l(-1). Method detection limits in lagoon water samples fortified at 20 microg l(-1) for OTC, TC, and CTC were 3.6, 3.1, and 3.8 microg l(-1). Variability in recovery from laboratory fortified blanks ranged from 86 to 110% during routine analysis.

Groundwater munition residues and nitrate near Grand Island, Nebraska, U.S.A.

Abstract Munition residues from waste disposal on ordnance property have resulted in a defined plume of RDX contaminated groundwater stretching 6.5 km and underlying an area of 6.5 km 2 . A smaller plume of TNT was detected near the plants boundary. The relative positions of the plumes combined with an historical review of total plant output of RDX and TNT indicates that RDX is much more persistent than TNT. The estimated RDX transport velocity of 0.5 m day −1 closely approximates the calculated Darcian velocity. The RDX plume sinks with recharge at a rate of about 0.5 m yr −1 . Nitrate is associated primarily with adjacent upgradient landuse and is not related to plant manufacture of ammonium nitrate. The average δ 15 N of the Nitrate was about + 10% and strongly suggests that animal wastes are the predominant source.

Investigation of sources of groundwater nitrate contamination in the Burbank-Wallula area of Washington, U.S.A.

During the fall and early winter of 1980, groundwater samples were collected from 38 public supply and domestic wells in the Burbank-Wallula area of Washington. Groundwater nitrate-nitrogen (NO3-N) concentrations ranged from 3.9 to 32 mg l−1 and averaged 10.5 mg l−1. Nitrogen isotope composition (δ15N) of the NO3-N ranged from +1.3 to +16.0‰ and averaged +4.1‰. The preponderance of low δ15N-values suggests that agricultural leachates (from oxidation of soil humus or use of nitrogen fertilizers) are the primary source of contamination for the area. Fourteen of the 38 wells were sampled at least twice in a four-month period. The relative invariability in NO3-N levels and δ15N in these wells suggests little or no temporal change in either the source or the magnitude of the source. Two additional samples collected in May 1981 from monitoring wells on the perimeter of a cropped field spray-irrigated with cattle waste from an anaerobic lagoon had δ15N-values for the NO3-N of +12.0 and +18.7‰, respectively. The high δ15N-values in these wells indicate that the NO3-N is predominantly derived from animal waste.

Shallow groundwater denitrification

Abstract In domestic and irrigation wells in a 324-square kilometer area, nitrate concentrations greater than the maximum contaminant Level (MCL) for potable water almost always were associated with relatively oxidizing groundwater (measured Eh > +0.28 ± 0.02 volts). Removal of nitrate, most probably via bacterial reduction (denitrification), occurred below +0.28 rmv. The observed Eh for this reduction is in reasonable agreement with thermodynamics. In these wells the variability in areal nitrate concentrations is strongly influenced by location with respect to the sharp redox front although there is a significant negative association between nitrite-N concentrations and well depth. This purification process removes an estimated 46 metric tons N/year from the groundwater at this reducing front. On a global scale similar redox fronts could remove thousands of tons of nitrate from groundwater annually. In specially installed nested wells in the vicinity of the redox front, groundwater nitrous oxide (N 2 O) concentrations were highest at or near the water table and decreased with depth indicating that most of the N 2 O loading was derived from nitrification and denitrification processes in the vadose zone and transported via recharge to the water table. The vertical stratification of both nitrate and N 2 O indicates that denitrification was removing both compounds. Nitrous oxide concentrations is shallow groundwater were as much as three orders of magnitude higher than those expected in water at equilibrium with the atmosphere.

Evidence for Holocene environmental change from C/N ratios, and δ13C and δ15N values in Swan Lake sediments, western Sand Hills, Nebraska

Profiles of percent carbon and nitrogen, carbon/nitrogen (C/N) ratios and stable carbon (δ13C), and nitrogen (δ15N) isotopic ratios in organic matter from an 11.6 m core were used to reconstruct environments of deposition in the Swan Lake basin during the past 5300 YBP. The upper 6.5 m consisted of gyttja containing variable amounts of reddish brown-colored fine organic matter and calcium carbonate. It was followed by a 0.5 m sandy silt, which was followed by a 3.6 m reduced layer characterized by large quantities of black organic plant remains, sapropel, and then by another sapropel layer consisting mainly of well-sorted sapropelic sand with relatively low organic matter content. The C- and N-contents in the organic matter in the sediment profile ranged from 0.5 to 23% and from 0.02 to 2%, respectively. Carbon content were positively correlated to both N and clay content while carbon content was negatively correlated to sand content. Two major environmental phases in Swan Lake were apparent from large differences in the C and N data of the sediment organic matter. These include the sapropel (marsh) stage that stretched from approximately 5330 to 3930 YBP, and the following gyttja (open water stage). During the sapropel marsh plants identified in a previous pollen study as cattails and sedges proliferated and produced copious amounts of well-preserved organic matter. C/N ratios, δ13C values, and δ15N values in the sapropel were significantly different from those that characterized organic matter in the gyttja. During the gyttja δ13C values indicated that deep primary producers have dominated lake biomass. By utilizing bicarbonate as their C-source, the accumulating biomass became relatively enriched δ13C values. The presence of high sediment CaCO3 contents indicated more alkaline and deeper water conditions prevailed during the gyttja. Further refinement of the data suggested that each major phase initially contained an identifiable transition stage. During the sapropelic (initial marsh stage) which occurred before 5330 YBP, sand content gradually decreased as organic matter increased. As reflected by high C/N ratios and slightly enriched δ13C values, these sands appear to have contained sufficient permeability to promote partial mineralization of accumulated organic-N containing compounds. A short initial gyttja transition period from about 3930–3830 YBP occurred in which the sediment silt content was anomalously high relative that measured in the surrounding layers. The silt content suggests that this turbid transition layer can not be completely explained by sediment mixing via bioturbation. The silts appeared to have been associated with the sharp climate change that resulted in higher water-table conditions during the gyttja stage.

Determination of atrazine, deethylatrazine and deisopropylatrazine in water and sediment by isotope dilution gas chromatography—mass spectrometry

Methods for the trace analyses of atrazine, deethylatrazine (DEA), and deisopropylatrazine (DIA) in water and sediment have been developed by using stable-isotope dilution with gas chromatography-mass spectrometry detection. Water samples are spiked with known amounts of 13C3-atrazine, 13C3-DEA and 13C3-DIA and submitted to solid-phase extraction with C18 bonded silica. Pesticides are eluted from the solid phase with ethyl acetate. Sediment samples are spiked and equilibrated with a known amount of each labeled standard before supercritical fluid extraction (SFE) using a 4% (v/v) methanol-CO2 mobile phase at 43°C and 10 MPa with off-line collection in methanol. A gas chromatograph coupled with a quadrupole mass spectrometer operated in the selected ion monitoring (SIM) mode was used to analyze the concentrated sample extracts. When compared to conventional liquid—liquid extraction methods, these methods decrease extraction time, labor, and solvent volume required. Quantification of the triazines by using isotope dilution compensates for differences in physical recovery for atrazine and its metabolites, especially when large ( > 100 ml) water volumes are extracted. Method detection limits for atrazine, DEA and DIA are 0.02, 0.02 and 0.10 μ g 1−1, respectively, in water. In sediment, the method detection limits are 0.10, 0.20 and 0.50 ng g−1 for atrazine, DEA and DIA, respectively. More than 4000 water and 800 sediment samples have been analyzed by these methods for more than two years. The average accuracy (bias) for atrazine-fortified water samples is +6.4% (n = 200) and the precision from duplicate analyses is ±6.0%. Precision of the SFE method for atrazine is ±11% at the 2 ng g−1 level whereas accuracy is −3.2% (n = 8) for recovery of 13C3-atrazine standard at the 5 ng g−1 level.

Streamlevels of agrichemicals during a spring discharge event

Abstract Levels of agrichemicals were monitored during a spring runoff event in Shell Creek, an eastern tributary of the Platte River, which drains a 700 km 2 watershed of predominantly row-cropped corn. Discharge during the runoff event ranged from 19 to 781 cfs. Maximum levels of atrazine, cyanazine, and alachlor of 89, 76, and 46 μg/L, respectively, occurred prior to the peak in stream discharge. Other residues detected at low concentrations during the peak in stream discharge include the herbicides- butylate, EPTC, metolachlor, metribuzin, propachlor, and trifluralin, and one insecticide- disulfoton. Suspended sediment levels (max = 19.7 g/L) correlated with pesticide levels, while nitrate-N concentrations (max = 6.3 mg/L) did not.

Effects of sludge disposal on groundwater nitrate concentrations

More than 100 groundwater samples were collectd and analyzed for nitrate-nitrogen, δ15N of the nitrate, dissolved organic carbon (DOC), and chloride. Multilevel samplers and nested monitoring wells were located beneath and down-gradient from an irrigated cornfield on which human waste sludge was injected. The sampling delineated a 1.3km× 0.3km plume of nitrate contamination. Both the nitrate-nitrogen concentrations and the δ15N values within the plumes centroid were homogeneous. The levels were 34 ± 3mg1−1 and + 13.4 ± 1.2%, respectively. A retarding zone of clayey silt split the plume and separated the oxic water from the deeper anoxic water. Nitrate levels were lower in the anoxic water and declined rapidly with depth. The significant association (r = − 0.91) between increasing δ15N values and decreasing nitrate concentrations indicated that the nitrate was denitrified. High chloride concentrations in the anoxic zone beneath the retarding layer are thought to originate from the sludge storage lagoon and/or the sludge compost piles. Tritium and atrazine levels confirm that this is recent recharge water. Denitrification has utilized most of the original nitrate and DOC in the plume.

N-15 Identification of nonpoint sources of nitrate contamination beneath cropland in the Nebraska Panhandle: two case studies

Abstract Monitoring of municipal wells near the town of Sidney and domestic wells near Oshkosh in Nebraskas Panhandle indicated the nitrate-nitrogen (NO3-N) levels were increasing and exceeded the maximum contaminant level of 10 mg/l NO3-N in several wells. Both areas are located in narrow stream valleys that are characterized by well-drained soils, highly permeable intermediate vadose zones, shallow depths to groundwater, and intensive irrigated corn production. Both areas also have a large confined cattle feeding operation near the suspected contamination and potentially could be contaminated by more than on nitrate source. At Sidney NO3-N concentrations were measured in 13 monitoring wells installed along an east-west transect im the direction of groundwater flow, 26 private wells, and eight municipal wells. Nitrate-nitrogen concentrations were homogeneous beneath a 5 km by 1.2 km area and averaged 11.3 ± 1.8 mg/l NO3-N. The δ15N-NO3 values in the monitoring and municipal wells had a narrow range from +5.8 to +8.8%. The isotopic ratios are indicative of a mixed source of nitrate contamination, which originates from agronomic (commercial fertilizer N and mineralized N) N and animal waste. Both commercial fertilizer N and animal wastes are applied to the irrigated fields. Nitrate-nitrogen concentrations in two multilevel samplers installed downgradient from irrigated cornfields at the Oshkosh site averaged 20.1 ± 13.3 mg/l NO3-N and 37.3 ± 8.2 mg/l NO3-N. The δ15N-NO3 values spanned a narrow range from +3.5 to +5.9% and averaged +4.0 ± 0.5% and +5.0 ± 0.6%. These low values are indicative of leachates from commercial fertilizer applied to the irrigated fields.

Long-Term Response of Groundwater Nitrate Concentrations to Management Regulations in Nebraska's Central Platte Valley

The impact of 16 years (1988–2003) of management practices on high groundwater nitrate concentrations in Nebraskas central Platte River valley was assessed in a 58,812-ha (145,215-ac) groundwater quality management area intensively cropped to irrigated corn (Zea mays L.). Crop production and groundwater nitrate data were obtained from ~23,800 producer reports. The terrace, comprising ~56% of the study area, is much more intensively cropped to irrigated corn than the bottomland. From 1987 to 2003, average groundwater nitrate concentrations in the primary aquifer beneath the bottomland remained static at ~8 mg N/l. During the same period, average groundwater nitrate concentrations in the primary aquifer beneath the terrace decreased from 26.4 to 22.0 mg N/l at a slow, but significant (p < 0.0001), rate of 0.26 mg N/l/year. Approximately 20% of the decrease in nitrate concentrations can be attributed to increases in the amount of N removed from fields as a consequence of small annual increases in yield. During the study, producers converted ~15% of the ~28,300 furrow-irrigated terrace hectares (~69,800 ac) to sprinkler irrigation. The conversion is associated with about an additional 50% of the decline in the nitrate concentration, and demonstrates the importance of both improved water and N management. Average N fertilizer application rates on the terrace were essentially unchanged during the study. The data indicate that groundwater nitrate concentrations have responded to improved management practices instituted by the Central Platte Natural Resources District.