Grantee Research Project Results
Final Report: Molecular Tracers of Contaminant Sources to Surface Water Drinking Supplies
EPA Grant Number: R828159Title: Molecular Tracers of Contaminant Sources to Surface Water Drinking Supplies
Investigators: Standley, Laurel J. , Kaplan, Louis A. , Newbold, J. Denis
Institution: Stroud Water Research Center, Inc
EPA Project Officer: Aja, Hayley
Project Period: July 1, 2000 through December 31, 2001 (Extended to December 31, 2002)
Project Amount: $220,000
RFA: Exploratory Research - Engineering, Chemistry, and Physics) (1999) RFA Text | Recipients Lists
Research Category: Safer Chemicals , Water , Land and Waste Management , Air
Objective:
Nonpoint and point sources of contaminants currently contribute substantially to water quality degradation yet are difficult to assess in a defensible regulatory manner. These sources include septic systems and sewage treatment plants, agricultural runoff, urban/suburban runoff, and wildlife contribute nutrients, pesticides, pharmaceuticals, personal care products, heavy metals, and pathogens to freshwater ecosystems.
The use of molecular tracers to identify sources of contaminants is an emerging technique that links the presence of components unique to these sources with contaminants of concern. This quantitative link is essential for developing budgets for use in regulatory assessments of the predominant contributors to water quality degradation. We investigated the fate of molecular tracers in surface waters to improve their utility in quantitative source apportionment. Tracers studied included fecal steroids (to track fecal matter sources such as human, agricultural manures, and wildlife), caffeine and fragrances (used to assist in separating human from agricultural and wildlife sources of fecal matter), and polycyclic aromatic hydrocarbons (PAHs) (used to track road runoff [RR]).
Four general experiments were conducted to track fate of molecular tracers in freshwater ecosystems (see summary of findings for additional information). Tracers were extracted from water samples using Empore disks and from sediments and solid phase materials using an accelerated solvent extraction system and analyzed as silyl ethers via gas chromatography (DB 1701)/electron impact mass spectrometry (selected ion monitoring).
Summary/Accomplishments (Outputs/Outcomes):
Molecular Tracer Fate Results
Molecular tracers were spiked to filtered stream water in quartz tubes and placed in third order streams at half depth to determine degradation rates of key molecular tracers. Experiments lasted 14 days, with replicate tubes removed from exposure during the experiment to determine loss rates. Most fecal steroids were not investigated due to their predominance on the particle phase.
Overall loss rates for fragrances HHCB and AHTN were -0.013 and -0.019 hour-1, respectively, which is equivalent to half lives of 54 and 37 hours. Degradation of caffeine was insignificant in the time of the experiment (> 800 hr). Loss rates for dissolved fecal sterones bONE and aONE were -0.002 and -0.003, respectively. Since these compounds are also primarily associated with the particle phase, dissolved-phase degradation does not appear to be relevant. PAHs had loss rates comparable to the fragrances, which ranged from -0.005 to -0.038 hour-1. These degradation rates are sufficiently long to allow tracking of contaminant sources in small streams. For example, the White Clay Creek (WCC) drains to the bay within 24 hours. However, their utility in tracking contaminants such as nutrients will depend on relative loss rates for the contaminant of concern.
Source Materials
Levels of molecular tracers in contaminant sources were determined. Three wastewater treatment plants (WWTPs) were studied and determined to have 3 to 13 μg/L ∑ n-alkanes, 0.4 to 1.8 μg/L ∑ PAH, 1.7 to 5.2 μg/L ∑ fragrances, and 9.1 to 40 μg/L ∑ fecal steroids. Poultry and cow manure contained (poultry/cow) 0.9/0.9 μg/g ∑ PAH, 0.11/0.7 μg/g ∑ fragrances, and 130/107 μg/g ∑ fecal steroids. Caffeine was below detection limits in the WWTP effluent, possibly due to matrix interferences and the higher detection limit possible with the method used.
Ratios of the fecal steroids, often used to track sources of human sewage, were unique for WWTP and animal sources of fecal matter. The ratio of coprostanol to other stanols was 0.91 (s.d. 0.03) for WWTPs and 0.61 (s.d. 0.07) for other manures. The ratio of epicoprostanol to coprostanol, used to further separate human from other mammalian sources, was also different at 0.06 (s.d. 0.03) for WWTP effluent and 0.23 (s.d. 0.04) for manures. As seen in previous work, cholesterol was elevated in poultry manure.
Field Collections
Stream water and sediments were collected in four streams, which varied in sources of contamination but were predominantly selected to focus on WWTP effluent sources. Each stream was sampled at one upstream site and three downstream sites (up to several km downstream of contaminant sources). Losses of fragrances and caffeine below WWTPs were greater than rates measured in quartz tube experiments and that could be explained through dilution. Since the quartz tube exposures focused on dissolved phase processes, it is probable that sorption to and reaction with particle/sediment phases played a role in the fate of molecular tracers. Further analysis of stream results is underway.
Particle Fate Studies
Particles in two size categories (very fine 15-52 μm and fine 50-100 μm) were collected from RR, agricultural fields treated with liquefied cattle manure (AF/LCM), source LCM, stream seston from the WCC, forest soils (FS), and secondary sewage treatment plant effluent (WWTP). Deposition velocities (Vdep) were determined in a model stream, which receives WCC stream water. These values were compared with expected quiescent fall velocities calculated using Stoke’s Law. Organic matter content of particles was as follows (fine/very fine particles): RR – 3/4 percent, AF/LCM – 14/14 percent, WCC – 15/13 percent, LCM – 18/13 percent, FS – 46/44 percent, and WWTP – 69/65 percent.
Vdep for fine and very fine particles were as follows (fine/very fine): Both fine and very fine particles decreased in deposition velocity with increasing organic matter content, as expected; however, Vdep for WWTP particles was higher than those of particles with less organic matter, indicating a stickiness to the benthic surface. This effect was most pronounced for the fine particle fraction, where Vdep for WWTP was nearly as high as that for RR, at 0.97 and 1.2 mm/s, respectively. Conversely, FS, which are also high in organic matter, had a Vdep of 0.35 mm/s. Vdep was 0.2 to 5 times higher than calculated fall velocities in the fine particle category and 5 – 10 times higher for very fine particles, indicating a limitation for Stoke’s Law predictions of the behavior of fine organic matter particles. The deviation was greatest for WWTP particles. Microscopic examination of the particles indicated a strong presence of fungal material in the filtered WWTP particles and soot in the RR.
Quality Assurance/Quality Control
Information was collected on matrix spike recoveries, relative percent difference (RPDs) for laboratory duplicates and matrix spike duplicates (instrument replication) for at least 5 percent of total samples. Matrix spike recoveries for n-alkanes, PAHs, fragrances, caffeine, and fecal steroids averaged 65 percent (range 42 to 100%), 88 percent (range 62 to 105%), 95 percent (range 90 to 100%), 67 percent, and 62 percent (range 23 to 137%), respectively. Laboratory duplicate RPDs for n-alkanes, PAHs, fragrances, caffeine, and fecal steroids averaged 60 percent, 90 percent, 93 percent, 25 percent, and 49 percent, respectively. Concentrations in samples were very low, which explained this high variance between samples. Absolute variances ranged in the low ng/L. Matrix spike duplicates for n-alkanes, PAHs, fragrances, caffeine, and fecal steroids averaged 4.2 percent (range 1.9 to 24%), 4.8 percent (range 1.7 to 15%), 2.2 percent (range 1.9 to 2.5%), 1.9 percent, and 8.7 percent (range 5.7 to 19%), respectively. Laboratory blanks for n-alkanes were very high and after several unsuccessful attempts to track the contamination in procedures, these compounds were eliminated from the list of molecular tracers.
Conclusions:
Degradation of molecular tracers in the dissolved phase was sufficiently slow to allow tracking of contaminant sources in small streams. Interactions with solid phase particles and sediments appeared to greatly enhance removal. These loss rates require comparison with loss mechanisms of target contaminants in order to improve utility of molecular markers in tracking contaminants such as nutrients. Deviations in particle transport from Stoke’s Law are critical with respect to modeling dispersion of particle-associated contaminants, particularly with respect to WWTP effluent particles.
Journal Articles:
No journal articles submitted with this report: View all 3 publications for this projectSupplemental Keywords:
organic particles, deposition velocity,, RFA, Scientific Discipline, Air, Waste, Water, Hydrology, Contaminated Sediments, Remediation, Environmental Chemistry, Wet Weather Flows, Drinking Water, Engineering, Chemistry, & Physics, monitoring, fate and transport, wastewater treatment, transport containment, contaminant transport, quantitative method, nonpoint source runoff, contaminated sediment, surface water, treatment, point source effluents, agriculture, water quality, non-point sources, threshold values, drinking water contaminants, other - risk management, molecular tracerProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.