Introduction

Pharmaceuticals and personal care products (PPCPs) comprise a wide suite of prescription and over-the-counter (non-prescription medications) compounds intended for human and veterinary use, including animal production (e.g., livestock production and poultry processing), that are widely detected in aquatic and terrestrial environments (Ebele et al., 2017; Jaffrézic et al., 2017). Pharmaceutical products generally consist of biologically active organic compounds including but not limited to antibiotics, antidepressants, stimulants, X-ray contrast media drugs, anti-inflammatory, lipid regulators, β-blockers, antihypertensive compounds, and illicit/recreational drugs (Richmond et al., 2017; Yang, et al.,

Methods

Study area

The Laurentian Great Lakes constitutes the largest freshwater system in the world, containing an estimated 21% of the Earth’s surface freshwater (~ 90% of US freshwater; Fields, 2005; Sponberg, 2009). The Great Lakes Basin covers a total area of 244,000 km2 (94,000 mi2) and is home to over 35 million people (Breffle et al., 2013; Danz et al., 2007). The region watersheds which drain almost 518,000 km2 (200,000 mi2) support numerous economic industries, including manufacturing, agriculture, and commercial fisheries, with areas of intense urbanization and industrialization occurring along its coastal zone (Breffle et al., 2013; Wolter et al., 2006). Land-use and land cover differ between eco-regions and eco-provinces, with predominantly forested areas in the northern and southeastern sections, and agricultural activities more pronounced in the western and central sections of the Basin (Morrice et al., 2008). Increased anthropogenic and environmental stressors, including rapid urban growth and municipal and industrial wastewater discharge, have led to increased water quality impairment within the Great Lakes Basin and adjacent sub-watersheds (Danz et al., 2007; Elliot et al., 2017; Kiesling et al., 2022). Specifically, the continuous loading of organic pollutants from point and diffuse/fugitive sources has been identified as an environmental driver behind coastal water quality and ecosystem impairment within the Great Lakes (Baldwin et al., 2016; Cornwell et al., 2015; Kiesling et al., 2019).

Site designation and categorization

A total of 131 sites, representing inshore and offshore locations in the Great Lakes Basin, were sampled between 2013 and 2018 (Fig. 1). A detailed description of the Great Lakes MWP study site locations including designated reference sites is provided in Table S1 (Supplementary Information) and described elsewhere (Edwards et al., 2016; Kimbrough et al., 2018, 2021). Additional information on MWP sampling locations is also provided in Table S10. Collectively, 14 sites were sampled in 2013, 29 sites were sampled in 2014, 15 sites were sampled in 2015, 12 sites were sampled in 2016, 19 sites were sampled in 2017, and 42 sites were sampled in 2018. Overall, CEC data from dreissenid mussel tissue were generated from multiple contamination assessment studies conducted under the expanded Great Lakes MWP basin-wide contaminant monitoring objectives. These objectives included addressing the Great Lakes Restoration Initiative (GLRI) Action Plan I (2010–2014) and GLRI Action Plan II (2015–2019; Kimbrough et al., 2018). To increase the likelihood of finding PPCPs, sites were preferentially selected based on the following: (1) riverine systems and tributaries known for higher contamination based on previous MWP studies, and (2) pollution gradients influenced by urban and sub-urban centers that receive high volume of pollutants from point source discharge and urban/storm-water runoff. MWP sites established in the Great Lakes Areas of Concern (AOC; areas designated for restoration due in part to historical environmental contamination; Hartig et al., 2020) and priority urban areas, including Milwaukee, Niagara, Toledo, Cleveland, and Detroit, were targeted with the objective of providing a more robust measure of bioavailable contaminants that would be generated from municipal, industrial, and fugitive sources, including urban storm water runoff (Kimbrough et al., 2021).

Fig. 1
figure 1

Great Lakes Mussel Watch Program (MWP) inshore (rivers, harbors, embayment, and tributaries) and offshore (nearshore lake and deep-water lake) dreissenid mussel 2013–2018 sampling locations. Some sampling locations have multiple sites. Most sampling locations have 1–3 sites, except Maumee River (8 sites), Muskegon (9 temporal sites), Milwaukee Estuary (13 sites), and Niagara River (20 sites). Additional information on MWP sampling locations description is provided in Table S1 and Table S10 (Supplementary Information)

Multiple techniques including monitoring studies and place-based/caged mussel deployment were used to conduct contamination assessments and contaminant source tracking at inshore riverine and nearshore sites (Kimbrough et al., 2021). Mussels sampled at designated offshore locations included all lake sites (nearshore lake and deep-water lake sites), as well as sites sampled in the Great Lakes connecting channels. Inshore sampling locations include sites sampled at harbor, river, embayment, and tributary locations. Overall, most sampling locations have 1–3 sites, except for sampling locations in the Maumee River, Detroit River, Muskegon, Milwaukee Estuary, and Niagara River.

Sampling procedures

Information on MWP sampling procedures is presented elsewhere (Kimbrough et al., 2018, 2021), as sampling methods and procedures were slightly different for various MWP basin-wide contaminant monitoring objectives. Sampling procedures conducted in this study utilized both in situ and caged dreissenid mussels for basin-wide surveillance monitoring and place-based contaminant assessment studies. When available, divers harvested in situ dreissenid mussels from established populations in open lake, near-shore lake zone, or from outer harbor stone breakwaters (Kimbrough et al., 2018). For sampling locations and place-based contaminant assessment sites where in situ mussels were unavailable, mussels were harvested by divers from nearshore harbor and stone breakwaters, placed in cages (e.g., minnow traps; approximately 300–500 mussels per cage), and deployed at selected sites for 28–55 days. For temporal studies, mussels were caged for up to 55 days.

The use of caged mussels in biomonitoring studies is well established. For example, studies have shown that caged mussels can be strategically deployed along known or suspected pollutant gradients to track and measure source contaminant exposure over time (de Solla et al., 2016; Guerlet et al., 2007; James et al., 2020; Salazar & Salazar, 1995). Additional studies have shown that caging mussels for 28–30 days (4 weeks) avoids bias relating to physiological and reproductive status that might influence organic pollutant uptake and bioaccumulation over the period of exposure (Tsangaris et al., 2010; Viarengo et al., 2007). Dreissenid mussels collected from in situ and place-based/caged deployment was rinsed with site water to remove debris, placed in labeled freezer bags, packed in ice containers, and shipped to contract laboratories within 2 days for analysis. Homogenates with more than 100 individuals were used for chemical analysis. Tissue sample collection and processing were consistent with NOAA methods and procedures for bivalve tissue assessment.

Chemical analysis

Mussel tissue samples were analyzed at SGS AXYS Analytical Services (Sidney, British Columbia, Canada). A total of 141 contaminants were analyzed in mussel tissue samples (Table S2). Tissue samples were analyzed using a series of high-performance liquid chromatography reversed phase C18 or HILIC columns, combined with tandem mass spectrometry (HPLC/MS/MS) platform extraction, including gas chromatography coupled with high-resolution mass spectrometry (GC-HRMS) extraction. Individual PPCP analytes measured by positive or negative mode electrospray ionization (+ / − ESI) liquid chromatography tandem mass spectrometry (LC/MS/MS), or electron impact (EI) or electron capture negative chemical ionization (ECNI) mode gas chromatography mass spectrometry (GC/MS), were analyzed from modified methods described in EPA Method 1694 and 1698 (Dodder et al., 2014; U.S. EPA 2007). SGS AXYS quality assurance criteria used for method MLA-075 Rev 06.01 and method MLA-075 Rev 07 included analyses of laboratory blanks, duplicate samples, labeled quantification standard recovery, and blind field sample duplicates.

Quality assurance and quality control

Standard SGS AXYS laboratory quality control measures used for mussel tissue analyses are described elsewhere (James et al., 2020). Briefly, mussel tissue analyses were performed in batches. Each batch consisted of test samples and additional QC samples, with ultrapure water used as the blank matrix. Procedural blanks were extracted and analyzed using the same procedures as the test samples in the analysis batch. Standard SGS AXYS laboratory quality control measures, which included matrix blanks and matrix spikes, were also used for mussel tissue analysis. Only blank corrected concentrations above the method detection limit were recorded as present. In addition, all PPCPs quantified in mussel tissue were prioritized and grouped into 27 classes, based on their primary therapeutic class, with concentration for each compound class summed to provide a cumulative total PPCP concentration measured at each MW site.

Data analysis

Land-use and point source data

The land-use and land cover (LULC) assessment conducted in this study is described elsewhere (Edwards et al., 2014, 2016; Kimbrough et al., 2021; Freitag et al., 2021). A brief overview is provided here to describe additional techniques used to develop and determine LULC estimates for each Great Lakes MWP study site. Site LULC estimates were mainly created from the USGS Multi-Resolution Land Characteristics (MRLC) (https://www.mrlc.gov/data/nlcd-2016-land-cover-conus) and 2016 National Land Cover Database (NLCD) raster layer (Homer et al., https://open.canada.ca/data/en/dataset/4e615eae-b90c-420b-adee-2ca35896caf6), based on the Anderson LULC values (Anderson et al., 1976; Choy et al., 2017; Yang et al., 2). Additional information on study sites that overlap clusters and fall within the 95% confidence interval is provided in Table S10

Fig. 6
figure 6

Box and whisker plots showing PPCP concentration (log ng/g (wet weight)) profile for compounds observed in individual clusters derived from unsupervised random forest (RF) classification. PPCP compounds are ordered by lowest to highest concentration in each RF cluster. Cluster 3 represents the group with the most predominant PPCP mixtures and contained the greatest chemical load and composition observed between clusters. Additional information is provided in Table S5

Table 1 Summary of dreissenid mussel tissue PPCP concentrations (ng/g (wet weight)) detected in RF clusters (1–3). Additional information is provided in Fig. 6 and Table S3 (Supplementary Information)

Additional analysis revealed differences in mussels sampled at inshore (river-tributary-harbor complexes) and offshore sampling locations. On average, overall PPCP concentrations varied across inshore and offshore sampling locations, with the highest mean concentrations observed in mussels from tributary sites sampled in cluster 1 (58.6 ng/g wet weight; Table 2). However, differences in inshore and offshore sampling locations PPCP concentrations were not statistically significant (Kruskal–Wallis; p > 0.05). Overall mean concentrations measured in mussels from harbor (30.1 ng/g wet weight) and offshore sites (32 ng/g wet weight) in cluster 1 were 1 to 2 orders of magnitude higher than mussels from cluster 2 and cluster 3, indicating active/fresh PPCP inputs (primary source), as well as pseudo-persistence occurring at these sampling locations. Likewise, additional comparison revealed elevated mean concentration in mussels from river sites (17.2 ng/g wet weight) in cluster 2, and mussels from river, harbor, and offshore sites sampled in cluster 3 (range: 9.84–10.3 ng/g wet weight; Table 2 and Fig. S2). Overall, measured concentration for 9 PPCPs (1,7-dimethylxanthine, 2-hydroxy-ibuprofen, theophylline, ciprofloxacin, clonidine, iopamidol, sertraline, triclocarban, and melphalan) was higher in mussels across all examined inshore and offshore sampling locations (Table S5). However, with the exception of iopamidol, the magnitude for 7 compounds (melphalan, 1,7-dimethylxanthine, 2-hydroxy-ibuprofen, ciprofloxacin, clonidine, sertraline, and triclocarban) was higher in mussels from inshore (i.e., harbor and river sites) and offshore sites in cluster 3, compared to cluster 2 and cluster 1.

Table 2 Summary of the PPCP concentrations (ng/g (wet weight)) detected in dreissenid mussel tissue sampled at inshore (harbor, river, tributaries) and offshore sampling locations between 2013 and 2018

With the exception of cluster 2, measured concentrations for 2-hydroxy-ibuprofen (range: 32.9–269 ng/g wet weight), clonidine (range: 3.6–332 ng/g wet weight), and melphalan (range: 67.8–475 ng/g wet weight) were highest across cluster 1 and cluster 3, spanning several orders of magnitude when compared to other PPCP compounds assessed in this study (Table S5). Additional examination revealed 2-hydroxy-ibuprofen (anti-inflammatory), clonidine (antihypertensives), and melphalan (chemotherapy) elevated concentrations across cluster 1 and cluster 3 are indicative of their incomplete breakdown and release from wastewater treatment processes and medical discharges, since these pharmaceuticals are used extensively to treat cancer, hypertension (e.g., regulate blood pressure), and other related ailments (Ebele et al., 2017; Godoy et al., 2015; Yadav et al., 2021). Overall, this study confirms PPCPs detected in mussels from inshore and offshore sites are similar in complexity and occurrence to other comparative studies that have examined PPCPs throughout the Great Lakes (Baker et al., 2022; Banda et al., 2020b; Choy et al., 2017; Custer et al., 2020). Equally important, this study further provides evidence of emerging contaminant concentrations and composition strong variations that can occur between inshore and offshore (i.e., open/deep lake) sampling locations.

PPCP basin-wide and reference site assessment

Basin-wide, we detected significant differences for the majority of PPCP compounds measured in this study, although more sites were sampled in Lakes Michigan (67 sites) and Erie (29 sites), compared to other lakes (Lake Huron and Lake Ontario) and connecting channels (inclusive of all sites in the Detroit River and Niagara River), due in part to PPCP sampling objectives. For example, PPCP concentration and composition varied among lakes, connecting channels, and reference sites, with relatively higher mean concentration detected in mussels from Lake Huron (39.8 ng/g wet weight), compared to Lakes Erie (11.7 ng/g wet weight), Michigan (14.0 ng/g wet weight), Ontario (21.0 ng/g wet weight), the Niagara (5.10 ng/g wet weight), and Detroit River (5.95 ng/g wet weight) connecting channels, respectively (Table 3 and Fig. S3). Overall, PPCPs were mainly detected as complex mixtures basin-wide, with 4 (reference site; NRNF-1–7.14) to 28 (LMMB-01-INMU-6.18) compounds detected in mussels at one or more sampling location. These results indicate that PPCP chemical composition generally differed among MWP sites basin-wide, with some sites experiencing elevated contaminant exposure during the 2013–2018 study period. In addition to this study, several comparative studies have shown PPCPs are also occurring as complex mixtures in surface water (Baker et al., 2022; Baldwin et al., 2016; Blair et al., 2013; Ferguson et al., 2013; Pronschinske et al., 2022) and tissue samples (i.e., mussels, fish, and tree swallows [Tachycineta bicolor]; Banda et al., 2020; Cipoletti et al., 2019; Custer et al., 2020; Deere et al., 2020; de Solla et al., 2016; Woolnough et al., 2020) in the Great Lakes region. As shown in a previous study, the detection of these compounds as complex mixtures in the Great Lakes is of concern, due to their constituents, which were formulated to act on specific molecular targets in humans (Maloney et al., 2022).

Table 3 Summary of the PPCP concentrations (ng/g (wet weight)) detected in dreissenid mussel tissue sampled at Lake Michigan, Lake Huron, Lake Erie, Lake Ontario, Detroit, and Niagara River connecting channels (*), and designated MW reference sites between 2013 and 2018. Additional information is provided in Table S5

A lake-lake comparison revealed antihypertensives, antidepressants, anti-histamine (diphenhydramine), insect repellant (DEET), chemotherapy (Etoposide), and antibacterial (triclocarban) were among the classes of pharmaceuticals most frequently detected in mussel’s basin-wide. PPCPs frequently detected in mussels represent a wide variety of therapeutic uses, with most previously reported in comparative surface water (Baker et al., 2022; Blair et al., 2013; Ferguson et al., 2013; Pronschinske et al., 2022) and tissue studies (Banda et al., 2020; Custer et al., 2020; Deere et al., 2020; de Solla et al., 2016; Woolnough et al., 2020) in the Great Lakes region. Overall, cumulative tissue concentrations (sum of detected PPCPs) ranged by several orders of magnitude (range: 3.6–674.9 ng/g ng/g wet weight) per site, with the highest total concentrations (> 350 ng/g wet weight) measured in mussels from sites sampled in Lake Michigan (MUS-6.26.18 and LMMB-01-INMU-6.18; Fig. S5 and Table S7). This finding is consistent with results from previous studies that reported elevated PPCP levels in fish (Banda et al., 2020) and surface water (Elliott et al., 2017; Ferguson et al., 2013; Pronschinske et al., 2022) were highest in Lake Michigan.

A broader assessment of PPCPs detected in mussels from designated offshore reference sites revealed significant variation in PPCP frequency, composition, and concentration. Of the 70 PPCPs quantified in this study, 37 (53%) compounds were detected in mussels from offshore reference sites (Fig. S4 and Table S6). Etoposide (68%), diphenhydramine (79%), citalopram (79%), DEET (89%), amitriptyline (89%), and sertraline (100%) were among the PPCPs most frequently detected in mussels from designated reference sites. Overall PPCP concentrations ranged from 0.067 to 236 ng/g (wet weight), with the highest total concentrations measured in mussels from reference sites in the Milwaukee Estuary (LMMB-5-S5-8.17) and western Lake Erie basin (Maumee Lighthouse: LEMR-3–6.15; Fig. S5 and Table S7). On average, approximately 78% (29/37) of the PPCPs measured in mussels from designated reference sites were measured at relatively low concentrations (< 5 ng/g wet weight). The detection of PPCPs at environmentally low concentrations, and also as complex mixtures in non-target lower trophic organisms including dreissenid mussels, especially in offshore zones of large water bodies such as the Great Lakes remains poorly understood (Blair et al., 2013). Thus, the toxicological effects and endpoints resulting from PPCPs long-term (i.e., chronic exposure), and low-level exposures in dreissenid mussels and other aquatic biota, may warrant additional consideration and future assessments of these emerging contaminants in the Great Lakes.

In general, several compounds including 1,7-dimethylxanthine, sertraline, metformin, clonidine, and iopamidol were measured at the highest mean concentration in mussels across all designated reference sites (> 10 ng/g wet weight; Fig. S4 and Table S6). Interestingly, clonidine, 1,7-dimethylxanthine, and iopamidol concentrations measured in mussels from offshore reference sites were similar or equal to chemical signatures observed at some inshore sites. Elevated concentrations detected at offshore reference sites, which are well beyond major pollution sources (e.g., Maumee Lighthouse-3, ~ 10 km away from nearest WWTP and storm-water outfall), are indicative of some PPCPs pseudo-persistence, recalcitrance to degradation (e.g., abiotic and biotic transformations), and active offshore contaminant transport in the Great Lakes Basin (Blair et al., 2013; Helm et al., 2012; Kimbrough et al., 2018; Patel et al., 2019). This further highlights the importance of bio-monitoring programs such as the MWP, and studies such as this in sampling emerging contaminants on a larger spatial scale, even at offshore lake complexes to better understand the magnitude and distribution of these organic contaminants in large freshwater systems.

PPCP discharge type assessment

The concentration profile for PPCPs measured in dreissenid mussels at major discharge types, including sites proximate to WWTPs only, sites proximate to both WWTP and CSO point source discharge, sites downstream and along gradients of wastewater discharge, and sites not influenced by either WWTP or CSO discharge (i.e., non-WWTPs), is presented in Fig. 7 and Table S8. Overall, PPCP concentrations varied among the major discharge types assessed in this study, with relatively higher mean concentration observed in mussels from non-WWTP sites (13.4 ng/g wet weight; Table 4). However, differences in discharge type mean concentrations were not statistically significant (Kruskal–Wallis; p > 0.05). Compared to the other major discharge types, PPCP loading and composition were also higher in mussels from non-WWTP sites (62/70; Table S8), thus demonstrating non-point/diffuse sources might also be important pollution pathways and routes of exposure for PPCPs detected within the Great Lakes Basin. Equally important, the highest total PPCP concentrations (summed by their respective compound class) were measured at non-WWTP sites (11,899.1 ng/g wet weight), compared to sites sampled proximate to WWTPs (1883.4 ng/g wet weight), sites downstream and along wastewater gradients (2149.1 ng/g wet weight), and sites sampled proximate to WWTPs/CSOs (2547.0 ng/g wet weight), respectively.

Fig. 7
figure 7

Box and whisker plots depicting detected concentrations (log ng/g (wet weight)) for individual PPCPs detected in dreissenid mussels sampled at sites proximate to point source discharge (WWTPs and WWTPs/CSOs), sites downstream and along gradients of wastewater discharge (WWTP Gradient), and non-WWTP sites (sites not influenced by WWTPs or CSOs) during 2013–2018. PPCP compounds are ordered by lowest to highest concentration in each discharge category. Additional information is provided in Table S8

Table 4 Summary of dreissenid mussel PPCP concentration (ng/g (wet weight)) measured at major discharge types including sites sampled proximate to point source discharge (i.e., WWTPs and CSOs), sites downstream and along gradients of wastewater discharge, and sites without wastewater influence (non-WWTPs). Additional information is provided in Table S8

While PPCPs relative concentration and composition are expected to be higher at sites in proximity to point sources (Apeti et al., 2018), comparative studies have shown fugitive release from leaking septic systems, landfills/landfill leachate, urban runoff, agricultural runoff following the land-applied of manure and/or biosolids, runoff from CAFO facilities, and overland flow of contaminants can contribute to elevated PPCP composition and concentration detected at non-WWTP zones (Adams et al., 2014; Baldwin et al., 2016; Elliott et al., 2017; Fairbairn et al., 2016; Ferrey et al., 2015; Pronschinske et al., 2022). In a follow-up study, Deere et al. (2021) demonstrated that a large percentage of high priority pharmaceuticals was detected at remote regions (e.g., non-WWTP zones) due to factors such as atmospheric wet deposition and the persistence of these organic pollutants. On average, the highest PPCP loading and concentration were measured in mussels from non-WTTP sites in Lake Michigan (MUS-6.26.18 and LMMB-01-INMU-6.18). As shown in prior studies conducted by Blair et al. (2013) and Li et al. (2017), elevated PPCP composition and concentration detected in Milwaukee Estuary, Lake Michigan, are not uncommon, as urban runoff and river discharge from the Menomonee River, Kinnickinnic River, and Milwaukee River confluence is viewed as potential sources of elevated PPCP composition and concentration.

Overall, a total of 29 PPCPs were found recurring in mussels across all site discharge types, which further highlight the ubiquity and persistence of these contaminants across all sampling types and locations in the Great Lakes Basin. In addition, 9 PPCPs (atenolol, benztropine, cyclophosphamide, flumequine, penicillin G, prednisolone, promethazine, thiabendazole, and zidovudine) were only detected in mussels from non-WWTP sites, which were not detected at any other discharge type assessed in this study (Table S8). In general, 5 PPCPs (1,7-dimethylxanthine, 2-hydroxy-ibuprofen, iopamidol, clonidine, and melphalan) were consistently measured at relatively high mean concentrations (> 30 ng/g wet weight; Fig. 7) in mussels across all site discharge types. Similar to studies conducted by de Solla et al. (2016) and Deere et al. (2020), this study detected iopamidol (range: 77.7–254 ng/g [wet weight]), melphalan (range: 172–217 ng/g [wet weight]), and 2-hydroxy-ibuprofen (range: 47.9–269 ng/g [wet weight]) concentrations relatively higher at sites sampled in proximity to WWTP/CSO point discharge.

Based on a prior study of 1448 municipal WWTPs found within the US and Canadian portion of the Great Lakes Basin coastal zone that discharge treated effluent to the Great Lakes Basin International Joint Commission (2009), most of the secondary and conventionally designed WWTPs are capable of achieving reductions for some emerging contaminants. Thus, the above finding suggests the type of wastewater treatment system, incomplete elimination during conventional wastewater treatment processes, low in-stream dilution, and hydrodynamic flushing and residence time are important drivers for various pharmaceuticals including 2-hydroxy-ibuprofen, melphalan, and iopamidol detected at mussel sampling locations (Baker et al., 2022; Castellano‐Hinojosa et al., 2023; Deere et al., 2021; de Solla et al., 2016; Ribbers et al., 2019). Additional correlation analysis revealed strong positive association between several classes of pharmaceuticals and point source parameters (i.e., WWTPs, WWTP effluent flow, and CSOs). Specifically, strong correlations were observed between 11 classes of pharmaceuticals (antacids, anti-histamines, antihypertensives, chemotherapy, diuretics, insect repellant, metabolites and transformation products (TPs), opioids, stimulants, X-ray contrast media, and antibacterial) and site point source/wastewater parameters (Spearman’s rho (ρ) = 0.5007–0.9341; Table S12).

Similar to results presented in Fairbairn et al. (2016) and Deere et al. (2020), four mixed-use pharmaceuticals (hydrocortisone, prednisone, sulfadimethoxine, and tylosin) were only detected in mussels from WWTP/CSO sites in this study (Table S8). The presence of macrolide and sulfonamide antibiotic residue, such as tylosin and sulfadimethoxine, in freshwater environments is more related to agricultural/non-urban activities, which includes extensive use in cattle, swine, and beef confined animal feeding operations (CAFO; De Liguoro et al., 2007; Fairbairn et al., 2016; Kaczala and Blum, 2016). However, tylosin (brand name, Tylan) and sulfadimethoxine (brand name, Albon) detection in mussels from WWTP/CSO discharge sites in the lower Maumee (LEMR-1–6.16) and the Detroit riverine system (River Rouge-2–6.16) is indicative of their mixed-use in both non-urban and urban/residential settings (Grześkowiak et al., 2015; Papich., 2020).

Interestingly, among the classes of pharmaceuticals examined in this study, antifungal, anti-histamine, beta-blockers, diuretics, metabolites, and opioids displayed similar chemical profile across all major discharge types (Fig. S6 and Table S9), which is likely indicative of the environmental fate and attenuation dynamics (e.g., abiotic transformation, photodegradation, and biodegradation processes) occurring across these discharge types. Similar to our findings at wastewater impacted sites (Custer et al., 2020; de Solla et al., 2016; Elliott et al., 2018), sites downstream and along wastewater gradients (Cipoletti et al., 2020; Jorgenson et al., 2018; Thomas et al., 2017), and non-WWTP sites (Deere et al., 2020), the detection of these contaminants across major discharge types in this study highlights the acute and sublethal risk posed by these classes of emerging contaminants on non-targeted organisms in the Great Lakes Basin.

Comparable to studies conducted in the Great Lakes (Baker et al., 2022; de Solla et al., 2016; Muir et al., 2017; Woolnough et al., 2020), across North America (Bradley et al., 2017; James et al., 2020), and Europe (Álvarez-Muñoz et al., 2015), this study detected similar patterns in PPCP concentrations for antibacterial (i.e., triclocarban wastewater indicator compound), stimulant (i.e., 1,7-dimethylxanthine, amphetamine, and cocaine), and chemotherapy pharmaceuticals at sites in proximity to WWTP and CSO discharges (Fig. S6 and Table S9). Thus, input from WWTP and CSO discharge is considered an important anthropogenic driver for these organic pollutants elevated concentration measured in mussels across these major discharge types. In addition, Spearman’s correlation results further revealed antibacterial, as well as anti-histamine, beta-blockers, diuretics, and PPCP transformation products (TP), were strongly correlated to site population estimates (Spearman’s rho (ρ) = 0.707–0.799; Table S12), suggesting local usage, pharmaceutical consumption patterns (e.g., seasonal usage patterns; Boogaerts et al., 2021), and wastewater treatment loading capacity are drivers for to the widespread detection of these contaminants (Khasawneh and Palaniandy., 2021). Although PPCP chemical interactions across major discharge types were not addressed in the current study, the sublethal effects for most contaminants detected in mussels across the major discharge types in this study are unknown. As such, follow-up investigations should be conducted to address potential environmental exposure and effects on non-targeted and lower trophic aquatic organisms.

PPCP relationship to land-use gradients

Detailed information on mussel sampling locations land-use/land cover estimates are presented in Table S10. Additional information on PPCP magnitude and environmental occurrence at predominant developed and open-water sites are presented in Table S11. The overall pattern in PPCP distribution remained heterogeneous among land-use categories assessed in this study (Fig. S7 and Table S10). In addition, developed and open-water were among the dominant site land-use categories, as well as land-use groups depicting the highest correlation among the classes of pharmaceuticals examined in this study (Table S12). Planted/cultivated (agricultural) land cover category was dominant (> 32%) at one study site (NRYT-INMU-CH-10.18; Fig. 2 and Table S10). This site was not included in the final assessment of PPCPs detected at mussel study sites, since there were not enough planted/cultivated sites available for comparison and subsequent discussion in this study.

The magnitude for PPCPs examined at predominant developed (range: 0.147–332 ng/g wet weight) and open-water sites (range: 0.098–475 ng/g wet weight) sites varied, with several mixed-use and human-specific pharmaceuticals including azithromycin, etoposide, diphenhydramine, clonidine, verapamil, triclocarban, DEET, fluoxetine, citalopram, sertraline, and amitriptyline, among the compounds most frequently detected (> 50%) in mussels across developed and open-water sampling locations. However, PPCPs were detected at higher frequency in mussels from developed sites, compared to open-water sites. Relatively higher mean concentrations were observed in mussels from open-water sites (14.2 ng/g wet weight), compared to developed sites (9.72 ng/g wet weight; Fig. S8 and Table 5). However, differences in developed and open-water sites mean concentration were not statistically significant (Kruskal–Wallis; p > 0.05). Eight pharmaceuticals (triclocarban, theophylline, 1,7-dimethylxanthine, sertraline, iopamidol, 2-hydroxy-ibuprofen, clonidine, and melphalan) were among the compounds measured at relatively higher concentrations (> 40 ng/g wet weight; Fig. 8; Table S11) in mussels across developed and open-water sites. Interestingly, the magnitude for several compounds (clonidine, azithromycin, verapamil, etoposide, citalopram, triclocarban, sertraline, diphenhydramine, amitriptyline, and DEET) frequently detected (> 50%) in mussels from developed and open-water sites were similar or higher, compared to results and findings for mussels, fish, and bird tissue in other reported studies (Cipoletti et al., 2020; Custer et al., 2020; Deere et al., 2020; James et al., 2020; Meador et al., 2017; Muir et al., 2017).

Table 5 Summary of the PPCP concentrations (ng/g (wet weight)) detected in dreissenid mussel tissue sampled at predominant developed and open-water sites between 2013 and 2018. Additional information is provided in Table S9
Fig. 8
figure 8

Box and whisker plots showing PPCP concentration (log ng/g (wet weight)) measured in dreissenid mussels from designated A developed (combined developed medium intensity; developed high intensity; developed, open space; developed, low intensity categories) and B open-water sites. PPCP concentrations summarized by compounds in descending order based on highest to lowest mean concentration. The x axis (log scaled) represents several orders of magnitude difference between PPCP concentrations quantified in dreissenid mussel tissue sampled at developed and open-water sites. Additional information is provided in Table S11

The highest total PPCP concentrations (> 400 ng/g wet weight) were detected in mussels from open-water and developed sites in Lakes Ontario and Michigan (Fig. S5 and Table S7). Large urban clusters and higher residential/population density is likely related to the high variability and elevated PPCP concentrations detected in mussels from developed sites sampled in this study (Ferguson et al., 2013). As discussed in a previous study (Bai et al., 2018), developed/urban land cover types such as golf courses, dog parks, and recreation parks are likely major sources and environmental pathways for pharmaceuticals, due to increased surface runoff which introduces contaminants to urban surface waters, resulting in higher PPCP concentrations. Likewise, increased urban population density/residents often result in higher pharmaceutical consumption and usage, thus resulting in increased surface runoff and overland flow of contaminants to surface water (Wu et al., 2009). Similar to MacLeod and Wong (2010), this study detected positive relationship between higher PPCP concentrations and site population estimates (Table S7). Moreover, strong positive correlations were observed between several classes of pharmaceutical concentrations (chemotherapy, anticoagulant, x-ray contrast media, stimulants, insect repellant, beta-blockers diuretics, metabolites, anti-histamine, opioids, antacids, antihypertensives, and antibacterial) and developed and open-water land-use categories (Spearman’s rho (ρ) = 0.6386–0.913; Table S12), suggesting surrounding developed/urban and open-water land-use gradients are likely sinks and hotspots for these contaminants (Baldwin et al., 2016; Deere et al., 2021; Fairbairn et al., 2016).

Compared to other studies (Cipoletti et al., 2019; Custer et al., 2020), similar spatial patterns and chemical signatures were observed for some classes of pharmaceuticals examined at developed and open-water sites (Fig. S9 and Table S11). For example, antihistamine, antifungal, beta-blockers, diuretics, stimulants, metabolites/transformation products (TPs), and antidepressants were detected at similar or higher mean concentrations in mussels examined across developed and open-water sites, highlighting the complexity of PPCP source and anthropogenic pressures within the Great Lakes. Of interest, chemotherapeutic pharmaceuticals were detected at significantly higher mean concentrations in mussels at open-water sites, compared to developed sites. However, no statistically significant difference (Kruskal–Wallis p > 0.05) was observed between open-water and developed sites for melphalan concentrations. The highest concentrations of melphalan were found at developed and open-water sites in Lake Michigan/Black River (LMBR-0–5.18) and Lake Ontario/Cape Vincent (LOCV-INMU-10.18), respectively. Chemotherapeutic pharmaceuticals including melphalan body burden in tissue samples (i.e., fish and Bay mussels [Mytilus trossulus]) are documented for developed and open-water sites in the Great Lakes (Banda et al., 2020; Deere et al., 2020) and the Puget Sound (WA, USA; James et al., 2020). However, reported levels in the above studies are well below chemotherapeutic pharmaceuticals bivalve body burden values measured in this study (475 ng/g wet weight).

Similar patterns were observed for antihypertensive (range: 0.061–332 ng/g wet weight), and X-ray contrast media compounds (range: 49.2–261 ng/g wet weight), with mussels sampled at developed sites representing the highest concentrations detected in this study (Table S11). Compared to other developed sites examined in this study, X-ray contrast media concentrations were not statistically different across developed sampling locations (Kruskal–Wallis p > 0.05). However, higher concentrations were detected in mussels from sites sampled in the Maumee (Toledo WWTP/LEMR-1–6.15) and Ottawa (LEOT-2–6.15) riverine systems. Overall, X-ray contrast media magnitude detected in this study agrees with results reported in other studies conducted in the western Lake Erie basin (Cipoletti et al., 2020; Custer et al., 2020), northeastern Minnesota (Deere et al., 2020), and the Grand River watershed in southern Ontario (de Solla et al., 2016). Similarly, clonidine concentrations were not statistically different across developed sampling locations (Kruskal–Wallis p > 0.05). However, the highest average concentrations were observed in mussels from developed sites in Lake Huron, Thunder Bay (TBRD-INMU-CH-6.18), and Lake Michigan, Milwaukee Bay (LMMB-01-INMU-6.18). While most PPCP compounds quantified in this study were detected at relatively low concentrations (< 10 ng/g wet weight) in mussels from open-water (61%, 43/70) and developed sites (56%, 39/70), their detection as complex mixtures in this study might warrant additional assessment and prioritization, since information regarding their toxicity, fate, potential bioaccumulation, and endpoint is lacking and at times not fully understood. However, the potential adverse bio-effects and risks posed to aquatic organisms, directly associated with individual PPCPs quantified in dreissenid mussels, are beyond the scope of this study and are addressed in further detail in Fuller et al., (2023; in press).