Suspect screening and prioritization of chemicals of concern (COCs) in a forest-water reuse system watershed

https://doi.org/10.1016/j.scitotenv.2019.07.184Get rights and content

Highlights

  • Suspect screening of waste-, ground-, surface water in a forest-water reuse system

  • Wastewater often contributed more chemical features to water on site vs. off site.

  • Numbers of chemicals impacted by precipitation, irrigation, & soil drainage

  • Results suggest low off-site surface water export of wastewater-derived chemicals.

  • Chemicals prioritized based on abundance, prevalence, and toxicity (ToxPi scores)

Abstract

Much research has assessed organic chemicals of concern (COCs) in municipal wastewater and receiving waters, but few studies have examined COCs in land treatment systems. Many prior studies have implemented targeted methods that quantify a relatively small fraction of COCs present in wastewater and receiving waters. This study used suspect screening to assess chemical features in ground- and surface waters from a watershed where secondary-treated wastewater is irrigated onto 900 ha of temperate forest, offering a more holistic view of chemicals that contribute to the exposome. Chemical features were prioritized by abundance and ToxPi scoring across seasonal sampling events to determine if the forest-water reuse system contributed to the chemical exposome of ground- and surface waters. The number of chemical features detected in wastewater was usually higher than on- and off-site ground- and surface waters; in wastewater, chemical features trended with precipitation in which greater numbers of features were detected in months with low precipitation. The number of chemical features detected in off- and on-site waters was similar. The lower overlap between chemical features found in wastewater and downstream surface waters, along with the similar numbers of features being detected in upstream and downstream surface waters, suggests that though wastewater may be a source of chemicals to ground and surface waters on-site, dissipation of wastewater-derived features (in number and peak area abundance) likely occurs with limited off-site surface water export by the forested land treatment system. Further, the numbers of features detected on site and the overlap between wastewater and surface waters did not increase during periods of low rainfall, counter to our initial expectations. The chemical features tentatively identified in this watershed appear common to features identified in other studies, warranting further examination on the potential for resulting impacts of these on humans and the environment.

Introduction

Forested land application systems, also known as forest-water reuse systems, involve the application of municipal wastewater (untreated or treated) to forested lands. This results in slow-rate soil infiltration to groundwater recharge and finally surface water discharge, serving as an active component of water treatment and management (Crites, 1984). When appropriately managed, these systems can offer a favorable means of delivering sustainable water while preserving forested habitats and the ecosystem services therein (Bastian, 2005; Crohn, 1995; Magesan and Wang, 2003; Nichols, 2016).

While much is known about the functioning of these systems in terms of nutrient and micronutrient removal (Nichols, 2016 and references therein), fewer studies have assessed the environmental fate of organic chemical contaminants of concern (“COCs”) in these particular wastewater treatment systems. COCs are a growing concern for managing for sustainable public water and waste/sanitation hygiene systems (Benson et al., 2017; Clarke and Smith, 2011; Pereira et al., 2015). Organic COCs consist of legacy contaminants (e.g. polycyclic aromatic hydrocarbons “PAHs”, polychlorinated biphenyls “PCBs”, legacy pesticides including DDT, etc.) and contaminants of emerging concern, or “CECs.” A CEC is defined by Diamond et al. (2011) as one of over 40,000 organic contaminants for which “there are increasing concerns regarding its potential risks to humans and ecological systems,” and include pharmaceuticals, disinfection by-products, endocrine disrupting compounds, plasticizers, surfactants, flame retardants, pesticides, high production volume chemicals, and their degradates. COCs are commonly detected in wastewater and subsequently, in receiving waters and soils of wastewater effluent (Cincinelli et al., 2012; Harrison et al., 2006; Hedgespeth et al., 2012; Köck-schulmeyer et al., 2013; Lampard et al., 2010; Sedlak et al., 2008).

Previously, researchers have called for field-scale studies on the environmental impacts of land application due to increased pressures for water reuse (O'Connor et al., 2004). Studies to date, however, have primarily focused on the fate of COCs in biosolids and reclaimed water application to agricultural lands, as well as COC uptake by food crops (Gushit et al., 2013; Kipopoulou et al., 1999; Riemenschneider et al., 2016; Wu et al., 2015). A few studies have assessed COCs within land application systems and found that land applied wastewater contributed to the presence of chemicals in ground- and surface waters (Karnjanapiboonwong et al., 2011; Kibuye et al., 2019; Lesser et al., 2018; McEachran et al., 2016, McEachran et al., 2017a).

Most studies assess the presence of COCs in wastewater and environmental samples using targeted approaches wherein specific chemical/s are identified a priori and quantified with authentic analytical standards (Cahill et al., 2004; Cincinelli et al., 2012; Köck-schulmeyer et al., 2013; Lesser et al., 2018; Scheurer et al., 2011). “Non-targeted” or “untargeted” analytical approaches, such as suspect screening and non-targeted analyses, screen for a broader range of chemicals not decided upon a priori and are increasingly used to screen for COCs in environmental samples (Gosetti et al., 2016; Hollender et al., 2017). Both approaches involve the use of high-resolution mass spectrometry (HRMS) for the chemical analysis of environmental samples. The spectral output of suspect screening analysis is compared with compound-specific parameters available in chemical databases as a means to tentatively identify chemicals present in the samples. In non-targeted analysis, no a priori information is available. Chemical identities can subsequently be confirmed and quantified using suspect screening and non-targeted approaches if reference standards are available. These approaches have been used for the analysis of pharmaceutical metabolites in wastewater influent (Gago-Ferrero et al., 2015), detection of novel micropollutants in wastewater effluent (Hug et al., 2014), and assessment of chemical removal at different stages of the wastewater treatment process (Nürenberg et al., 2015). Non-targeted approaches have also been used to examine samples taken from rivers (Ruff et al., 2015; Strynar et al., 2015) and groundwater (Soulier et al., 2016) impacted by municipal wastewater, industrial wastewater, and/or agricultural land use. To date, there are no comprehensive studies utilizing non-targeted approaches to analyze COCs that may be present in forested land application systems for water reuse.

This study utilized a suspect screening approach to assess organic COCs in a watershed where secondary-treated municipal wastewater is irrigated onto 900 ha of temperate forestland. Quarterly grab samples from irrigated and non-irrigated areas in the watershed were used to evaluate the chemicals that contribute to the “exposome” (Wild, 2005, Wild, 2012) in waters impacted by wastewater irrigation to waters off site. Prior research at this specific site focused primarily on targeted analysis of a subwatershed comprising about 60% of the total forest area and did not extensively evaluate the unknown chemical exposome of groundwater or surface water across the watershed on- and off-site of the facility (Birch et al., 2016; McEachran et al., 2016, McEachran et al., 2017a, McEachran et al., 2018). A hydrological evaluation of the irrigated subwatershed found that groundwater was 50–76% derived from wastewater and that the wastewater fraction in exported surface waters contained 23 to 60% wastewater under normal rainfall and drought conditions, respectively (Birch et al., 2016). Prior targeted studies quantified selected pharmaceuticals and personal care products in waste-, ground-, and surface waters in the same subwatershed (McEachran et al., 2016, McEachran et al., 2017a) and have demonstrated that chemicals were detected at similar or lower concentrations in the surface water outlet of this forested land application system than in receiving surface waters from conventional wastewater treatment (McEachran et al., 2016). Additionally, a limited suspect screening study compared upstream and downstream surface waters from a subwatershed of the forested land treatment site to the surface waters collected at a conventional wastewater treatment plant (McEachran et al., 2018). For the forested site, only 30% of the total number of chemical features in wastewater effluent was detected in the downstream surface water sample.

Therefore, our study provides a more spatially and temporally extensive evaluation using a stratified sampling approach by soil type and catchments and suspect screening analysis of waste-, ground-, and surface waters at the scale of the entire watershed. The use of suspect screening allows for a broader assessment of the chemical exposome across different water types, time points, and spatial locations (on-site irrigation versus off-site, adjacent lands). We expected that wastewater would contribute more chemical features to the chemical exposomes of groundwater and surface water on site than from waters off site. We also expected the number and overlap of chemical features in wastewater to increase in groundwater and surface waters on site during periods of low rainfall. Results of suspect-screening were used to prioritize tentatively identified features to more holistically evaluate potential COC toxicity and exposure to humans and wildlife over time and space, an important aspect of the exposome (Wild, 2005, Wild, 2012). This approach not only addresses unrealized and unknown COCs in the present but supports future studies on chemical features/groups of interest via retrospective analyses.

Section snippets

Sample site and collection

The City of Jacksonville's Land Treatment Site (LTS) is a forest-water reuse system that serves approximately 70,000 customers and treats roughly 19 million L municipal wastewater/day; this system has previously been described by Birch et al. (2016) and McEachran et al. (2016). The LTS utilizes secondary treatment and disinfects of the effluent via chlorination prior to irrigation. The site relies on infiltration of water through soil before release to receiving waters, i.e. groundwater and

Chemical features linked to rainfall, irrigation, and soil types

The Jacksonville LTS demonstrates a general northwestern to southeastern hydraulic gradient for both ground and surface waters in the watershed (Fig. 1). Therefore, off-site surface waters were sampled upstream (north) and downstream (south) of the site, and off-site groundwater was sampled from the northwestern region of the site. Our primary hypotheses were as follows: 1.) wastewater would contribute more chemical features to the chemical signature of groundwater and surface water on site

Conclusion

This study represents the first comprehensive, watershed-scale study of COCs in a forested land application/water reuse site using a suspect screening approach to assess chemicals in wastewater effluent and ground- and surface waters. Wastewater typically contributed more chemical features to the chemical exposome of groundwater and surface water on site than from off-site waters. The input and subsequent fates of chemicals in receiving ground- and surface waters appear to be impacted by both

Acknowledgements & disclaimers

The authors would like to thank the Jacksonville Land Treatment Site and the City of Jacksonville for their assistance. This study was funded by the United States Department of Agriculture National Institute of Food and Agriculture [grant number 2016-68007-25069].

This article was reviewed in accordance with the policy of the National Exposure Research Laboratory, U.S. Environmental Protection Agency, and approved for publication. Approval does not signify that the contents necessarily reflect

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