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Contaminants of Emerging Concern: Mass Balance and Comparison of Wastewater Effluent and Upstream Sources in a Mixed-Use Watershed David J Fairbairn, William A. Arnold, Brian L. Barber, Elizabeth F. Kaufenberg, William C. Koskinen, Paige J Novak, Pamela J Rice, and Deborah L. Swackhamer Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.5b03109 • Publication Date (Web): 25 Nov 2015 Downloaded from http://pubs.acs.org on December 5, 2015

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Environmental Science & Technology

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Title: Contaminants of Emerging Concern: Mass Balance and Comparison of Wastewater

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Effluent and Upstream Sources in a Mixed-Use Watershed

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Fairbairn, David J.†,*; Arnold, William A. ‡; Barber, Brian L.§; Kaufenberg, Elizabeth F.†,a;

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Koskinen, William C.||; Novak, Paige J.‡; Rice, Pamela J.||; Swackhamer, Deborah L.†

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†

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United States

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‡

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Minneapolis, MN, 55455, United States

University of Minnesota, Water Resources Center, 1985 Buford Ave., St Paul, MN 55108,

University of Minnesota, Civil, Environmental, and Geo- Engineering, 500 Pillsbury Drive SE,

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§

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MN, 55108, United States

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||

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Circle, University of Minnesota, Saint Paul, MN, 55108

University of Minnesota, Department of Soil, Water, and Climate, 1902 Dudley Ave, Saint Paul,

United States Department of Agriculture, Agricultural Research Service, 1991 Upper Buford

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*

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USA, 55101. Tel: (651)-757-2659.

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a

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55101

Corresponding author: [email protected], 520 Lafayette Rd., St. Paul, MN,

Current address: Minnesota Pollution Control Agency, 520 Lafayette Rd., St. Paul, MN, USA,

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ACS Paragon Plus Environment


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TOC Art Figure

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Abstract

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Understanding the sources, transport, and spatiotemporal variability of contaminants of

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emerging concern (CECs) is important for understanding risks and developing monitoring and

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mitigation strategies. This study used mass balances to compare wastewater treatment plant

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(WWTP) and upstream sources of sixteen CECs to a mixed-use watershed in Minnesota, USA,

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under different seasonal and hydrological conditions. Three distinct CEC groups emerged with

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respect to their source proportionality and instream behavior. Agricultural herbicides and

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daidzein inputs were primarily via upstream routes with the greatest loadings and

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concentrations during high flows. Trimethoprim, mecoprop, non-prescription pharmaceuticals,

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and personal care products entered the system via balanced/mixed pathways with peak

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loadings and concentrations in high flows. Carbaryl, 4-nonylphenol, and the remaining

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prescription pharmaceuticals entered the system via WWTP effluent with relatively stable

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loadings across sampling events. Mass balance analysis based on multiple sampling events

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and sites facilitated CEC source comparisons and may therefore prove to be a powerful tool for

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apportioning sources and exploring mitigation strategies.

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Introduction Chemicals classified as contaminants of emerging concern (CECs) have been found in

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most environmental compartments, including polar ice caps, groundwater, treated drinking

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water, soil, the atmosphere, precipitation, animal tissues, breast milk, and the blood and urine of

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infants.1-4 This is problematic because CECs have been linked with numerous endocrine,

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reproductive, neurologic, and carcinogenic effects in biological systems.3,4 Despite numerous

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studies, significant gaps remain in our knowledge of CEC fate and transport,5-10 effects,6,11 and

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mitigation potential in complex environmental systems.4 The sheer numbers of CECs that have

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been identified, and their often similar modes of action, pose serious challenges to addressing

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these gaps.3,12,13



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Major CEC sources to surface waters include municipal wastewater treatment plants

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(WWTPs), industrial and commercial facilities, croplands, concentrated animal feeding

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operations (CAFOs), urban exterior landscapes, landfills, and septic systems.4,6,9,10,14,15

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Transport to surface waters occurs via point and nonpoint mechanisms including pipe

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discharges, surface runoff, atmospheric deposition, and baseflow.7 Instream studies often

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indicate the potential for long-range transport.6,17 Because fate and transport depend on the

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CEC and local environmental characteristics, however, these processes are not easily modeled

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or extrapolated across sites.2,5-8,14,16

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WWTP effluents often account for significant portions of discharge in rivers downstream

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of urban and mixed-use areas, especially during low-flow periods.2,5 Thus, WWTPs can act as

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point sources of CEC fractions that may persist through treatment.17 Accordingly, wastewater-

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associated CECs are often detected at greater frequencies and concentrations downstream

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than upstream of WWTPs and in low-flow versus high-flow conditions.2,18,19 Other studies,

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however, report poor source differentiation, variable associations with discharge, and/or

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significant non-WWTP sources of pharmaceuticals and other CECs.7,9-11,18,19 Although

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sometimes unexpected, these patterns may be explained by ubiquitous mixed sources that

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create a multitude of transport routes for CECs.

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Indeed, CEC transport to surface waters can occur via a number of additional routes. In

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urban or mixed-use areas, CEC occurrences have been linked to stormwater conveyances,

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leaking sewer pipes, managed aquifer recharge, and septic systems.1,2,20,21 Agricultural activities

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such as pesticide applications, livestock rearing, and land-spreading of manure, sewage, and

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other biosolids may contribute CECs to agricultural landscapes.6,22 Transport to surface waters

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then occurs via runoff, tile drainage, volatilization, baseflow, and other routes.22,23 Indeed, runoff

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of CECs associated with land-applied manure and biosolids has been proposed to explain

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unexpectedly greater concentrations and loads of pharmaceuticals and personal care products


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(PPCPs) in high-flow versus low-flow conditions in agricultural areas.9,24,25 Inputs from croplands

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and CAFOs remain less-studied than from WWTPs.6,9,10

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Given the multitude of compounds identified as CECs and their varied transport to

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surface waters, it is important to provide quantitative characterization and differentiation of these

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sources. Human health and ecological risk assessments and mitigation depend on

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understanding both the adverse effects of CECs and their spatiotemporal occurrence patterns.

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Spatiotemporal patterns depend on sources, fate, and transport. Retrofitting WWTPs and other

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pollution prevention strategies (e.g., reduced veterinary pharmaceutical use, changes to

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pesticide practices, consumer product changes) currently being considered to reduce CEC

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exposure risk may entail considerable expense.7,10,11 Thus, an understanding of proportional

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sources of CECs is critical to ensure that these efforts are applied wisely and effectively.

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Fingerprinting approaches use source-specific indicators to detect and differentiate

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particular contaminant sources in receiving waters.26 Various micropollutants have been

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proposed as suitable markers of different effluents (e.g., caffeine for untreated domestic

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wastewater,27,28 carbamazepine as a conservative wastewater marker,29-33 and micropollutant

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ratios to differentiate among septic systems, WWTP discharges, stormwater, and irrigation

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reuse34,35). Nonetheless, quantitative relationships between instream markers and contaminant

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burdens from different sources are often inconsistent due to marker sensitivity and specificity

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issues, variable effluent concentrations, and variable, compound-specific attenuation rates.36-38

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Further characterization of marker compounds and sources is needed.33-38

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Mass balance approaches have been used successfully for source apportionment of

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CECs such as caffeine and carbamazepine to receiving waters from untreated and treated

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wastewater in various conditions.28,39,40 If the major flows are accounted for, this approach may

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provide useful approximations of dominant sources even when flows are highly variable or only

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a few samples are collected.39 Repeated measurements in different seasonal/hydrologic



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conditions can elucidate temporal variations in sources and transport at coarse scales, though near-continuous sampling may be required to account for fine-scale variability.41 A principle component analysis of CEC concentrations in the study area targeted in this

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work attributed agricultural herbicide patterns to agricultural land use, and patterns of some

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PPCPs (e.g., carbamazepine, erythromycin, and DEET) to urban wastewater, but did not clarify

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the sources of acetaminophen or caffeine.42 Analysis of mass balances that include WWTP

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effluent samples over multiple events could build on this understanding of CEC sources and

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variability, resolve some of the source ambiguity, and indicate if the measured sources properly

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account for the total loading at a downstream location.

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Despite the need to characterize CEC sources, transport, and seasonal/hydrologic

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variability, relatively few studies have compared mass loadings from different sources under a

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range of conditions.7,10 The objectives of this field-based study were to use mass balances to

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compare loads, sources, and transport of different types of CECs in a mixed-use watershed

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under different seasonal and hydrologic conditions. We assessed the loadings of twenty-six

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CECs at downstream and upstream sites and in WWTP effluent across seven sampling events

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in the South Fork of the Zumbro River in Rochester, MN, U.S.A. We anticipated that mass

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balances would provide information on source proportionality and that patterns would emerge

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based on CEC use/class, land uses, and seasonal hydrology. This comparative characterization

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of CEC sources, loads, and transport provides enhanced information with which to assess risks,

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stressors, and impacts, and mitigate exposures related to human and aquatic health.

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Materials and Methods

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Study Area and CECs of Interest

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The study area is part of the Zumbro River Watershed (Figure 1), in southeastern

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Minnesota, and encompasses an area of approximately 786 km2. The South Fork of the Zumbro

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River (SFZR) is a second-order stream that is intersected by only a few other streams in this


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well-defined, mid-sized, mixed-use, and gently rolling drainage area. Agriculture, livestock, and

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septic systems are present in the upstream areas. An estimated 15,000 residents use septic

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systems. Agriculture accounts for approximately 64% of the study area. Corn and soybeans are

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the dominant crops. Approximately 212,000 livestock exist on 269 feedlots. The City of

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Rochester is situated in the downstream area. Near the catchment mouth, the Rochester Water

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Reclamation Plant uses activated sludge and chlorine disinfection to treat the wastewater of

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approximately 107,000 residents and other commercial/industrial entities, including a world-

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renowned medical complex with more than 2,100 beds and 225,000 annual outpatient visitors.

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The Supporting Information (SI) provides additional study area details.

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Figure 1. Map of land uses, major streams, and sampling sites in the South Fork of Zumbro River (SFZR) study area. The Rochester city limits are indicated by the red outline.

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Water samples were collected from four instream sites and a treated effluent sampling

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location within the WWTP. A detailed land use analysis was previously described.42 Sites with

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>50% associated agricultural area were categorized as “agricultural”, sites with >5% associated

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residential/urban area were categorized as “residential/urban”, and sites meeting both of these



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criteria were categorized as “mixed-use” (Table S1).1 Thus, SFZR-US2 was agricultural and

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Bear Creek, SFZR-US1, and SFZR-DS were mixed-use sites. SFZR-US1 and SFZR-DS have

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similar drainage areas but were just upstream and downstream of the WWTP discharge,

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respectively. The flow distances between sites were as follows: SFZR-US1 to SFZR-DS, 300m;

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BC to SFZR-US1, 5.8 km; and SFZR-US2 to SFZR-US1, 6.8 km.

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Twenty-six CECs (details in Table S2) were selected for analysis as previously

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described.42 These include CECs used primarily in agriculture (herbicides and veterinary

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pharmaceuticals), urban/residential applications (PPCPs and industrial/commercial ingredients),

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and mixed settings (pesticides, phytoestrogens, and pharmaceuticals).

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Sample Collection, Processing, and Analysis

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Grab water samples (2-L) were collected as previously described42 from effluent,

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upstream, and downstream sites on seven days from March-October 2012 representing

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different seasonal and hydrologic conditions. Governmental precipitation forecasts,43 streamflow

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data,44 and crop reports45 were used to target snowmelt (March), the first precipitation when at

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least 90% of corn cropland was planted (May), late summer baseflow conditions (September),

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and post-harvest fall conditions (October) for sampling. Equipment, equipment cleaning,

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chemical standards, and sample collection, handling, processing, and analysis were as

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previously described42,46 (summarized in the SI). Streamflow and WWTP discharge data were

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used to calculate loadings, develop mass balances, and provide context on the hydrologic

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conditions represented by the sampling events.

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Data Quality Assurance, Mass Balances, and Statistical Analysis

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Method reporting limits (MRL, Table S2) were determined using U.S. EPA methods.47

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Quantification of CECs concentrations and other quality assurance procedures were as

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previously described46 (summarized in the SI). Grab and composite sample data representing

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coincident time periods were compared as “proxy replicates” to assess short-term CEC


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concentration variability and concomitant effects on loading (Figure S3 and Table S3, discussed

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in SI).

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Mass balances were assessed to determine if measured CEC loadings at SFZR-DS

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were effectively explained by the WWTP effluent and SFZR-US1 loadings. The stream was

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modeled as a plug-flow reactor in which the loading into a cross-section equaled the loading out

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of the cross-section plus or minus mass transformation processes. To complete the mass

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balance for each CEC and event, the observed SFZR-DS loading (MSFZR-DS-Obs) was compared

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to the predicted SFZR-DS loading as calculated by: MSFZR-DS-Pred = MSFZR-US1 + MEffluent, where Mi

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(mass) = Ci (concentration)* Qi (discharge).

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Although loading of individual CECs is expected to change over time, if the mass

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balance is robust then MSFZR-DS-Obs should be equivalent to MSFZR-DS-Pred for the range of sampled

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events. Therefore, the relationship between MSFZR-DS-Pred and MSFZR-DS-Obs was analyzed by linear

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regression over all CECs and events to determine if significant sources or sinks to SFZR-DS

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had affected the mass balances over time. Also, for individual CECs, the agreement of all pairs

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of observed and predicted SFZR-DS loadings were compared with Wilcoxon signed-rank tests

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(α= 0.05).

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To compare source proportionality, upstream and effluent loadings were compared with

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one-way analysis of variance (ANOVA) on ranks and the Protected Least Significant Difference

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multiple comparison procedure (α=0.05).

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Statistical analysis was conducted using SPSS (IBM) and Stata (StataCorp). Data below

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the MRL were ranked lowest in the dataset for the respective CEC.

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Results and Discussion

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Sixteen of the twenty-six studied CECs were detected in water samples. Concentrations

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are presented in Table S4 and summarized in Figure 2. The most frequently detected CECs

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(>50% detection frequency) were the herbicides atrazine, acetochlor, metolachlor, and



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mecoprop, and the PPCPs caffeine, DEET, acetaminophen, trimethoprim, and carbamazepine.

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The greatest concentrations (median >100 ng/L) were detected for 4-nonylphenol and the

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prescription drugs erythromycin, sulfamethoxazole, and carbamazepine. The CEC-specific

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MRLs should be considered when comparing detection frequencies among CECs.

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WWTP effluent comprised 11%-43% (median: 23%) of SFZR-DS discharge over the

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sampling events (additional discharge data in Table S5). The distributions of sampled

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discharges were similar to those of the entire calendar period of the study for each site (Figure

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S2). Additionally, there was general agreement of coincident pairs of grab and composite

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samples in terms of concentration and loading (Figure S3 and Table S3, discussed in SI).

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Together, this indicates that the data effectively represented the various hydrological events of

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interest for spatiotemporal loading comparisons.


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Figure 2. Concentrations of contaminants of emerging concern (CEC) measured in 35 water samples in the South Fork of the Zumbro River (SFZR) study area. Boxes represent interquartile ranges (IQR) of concentrations of individual CECs by site. Lines within boxes represent median concentrations. Whiskers extend to minimum and maximum concentrations, up to 1.5 times the IQR from each box. Circles indicate values beyond that range. Data below the method reporting limit were ranked lowest for statistical comparisons and given a value of zero for boxplots. CECs labeled with an asterisk (*) had significant concentration variation across sites (results in Tables S4 and S6).



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Mass Balance The suitability of the mass balances was evident in the strong and nearly 1:1 agreement

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of a scatterplot of MSFZR-DS-Obs and MSFZR-DS-Pred for all CECs and sampling events (m=0.894,

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r2=0.881, p

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