**4. Discussion**

The average total footprint for each of the households that participated in the citizen science study was 113–184 g (Table 4). This is such a small mass that it can be challenging to interpret the potential for this footprint to inadvertently impact aquatic ecosystems. Therefore, the footprint calculator was programmed to provide the user with perspective for the interpretation of their results by scaling up the per capita footprint (i.e., total household EDC footprint divided by the number of people in the household) and multiplying by the total population of the United States. For example, the average two-person household's footprint of 151 g would estimate that the total EDC footprint for the United States (330 M people) if everyone had the same per capita footprint as the user would be approximately 24,915 metric tonnes, which is the equivalent of approximately 82 commercial airplanes (each plane is approximately 300 tonnes).

In the context of the specific citizen science study conducted here, a more regional context would be the potential impacts of these EDC footprints on the presence of emerging contaminants in the Chesapeake Bay watershed. Given the population in the watershed (18 M people) and an average per capita EDC footprint, the total EDC footprint across the Bay watershed would be 1287 metric tonnes. If this entire footprint reached the Chesapeake Bay, which has a volume of approximately 81.8 km3, the EDC concentration in the Bay would be 15.7 g/L. Although some of these EDCs can be treated by wastewater treatment plants or septic tanks before ultimately reaching the Bay, mitigation in the treatment facilities may not be effective enough to remove potential ecological risks.

These estimated footprints are significant given the potential impact of the presence of these contaminants in the environment even at trace concentrations (μg–ng/L). For example, triclosan has been shown to affect hindlimb development in amphibians at concentrations as low as 0.15 μg/L [19]. Musks, which are significant contributors to the fragrances commonly found in perfume and cologne [29], have been shown to exhibit estrogenic effects [31,32]. BPA is also known to exhibit estrogenic potential and has been documented to cause gender skewing in flathead minnows at exposure concentrations as low as 0.32 ng/L [33]. Additionally, EDCs have been shown to exhibit synergistic behavior when multiple compounds are present together, such that the total endocrinedisrupting potential of the "cocktail" is greater than simply adding the potential of each individual compound [34]. Although the potential harm to human health is unclear, there is a significant need to understand synergistic interactions and the risks to humans and the environment.

While these results clearly have implications for both human and environmental health, Dodson et al. [27] found that various compounds detected in tested personal care products were not present on the products' labels. This makes decision making more challenging for consumers, as even someone who wants to be an informed consumer may be unable to make satisfying decisions about product selection, especially in real time while shopping. Additionally, the study found that some product labels can be misleading due to labeling standards, with some products advertising to be "fragrance-free" when they indeed contained synthetic fragrances to mask an undesirable chemical odor. Rather than the product being "free" of fragrances, the product has a neutral smell due to a combination of various fragrances ultimately canceling each other out. Therefore, this EDC calculator tool can serve as a mechanism to increase awareness of EDCs and their potential effects on environmental quality, as well as engage the public about the role everyone plays in contributing to the presence of EDCs in the environment.

The rhetoric surrounding the presence of EDCs in the aquatic environment is often filled with fear and uncertainty, particularly because of the near-ubiquitous presence of synthetic chemicals in the environment and because of the lack of water quality standards for EDCs. Here, we sought to provide a tool that could shift the public perception from one of fear to one of empowerment by providing consumers with the knowledge they need to make more informed choices. The results of the tool may help to reduce the consumption of EDC-containing products and ultimately reduce EDC presence in the environment.

**Author Contributions:** Conceptualization, H.P. and R.T.; methodology, H.P., R.T., K.H., M.G. and L.G.; software, H.P., R.T., M.G., L.G. and S.G.; validation, H.P., R.T. and K.H.; formal analysis, R.T. and K.H.; investigation, H.P., R.T., K.H. and B.S.; resources, H.P. and B.S.; data curation, R.T. and K.H.; writing—original draft preparation, H.P. and R.T.; writing—review and editing, K.H.; visualization, R.T., K.H., M.G. and L.G.; supervision, H.P. and B.S.; project administration, H.P. and B.S.; funding acquisition, H.P. and B.S. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the National Science Foundation (Grant Number 1743981). Rachel Taylor was supported by Penn State's College of Engineering Summer Research Experience for Undergraduates (REU) program in 2014 and is currently supported by the Penn State Department of Agricultural and Biological Engineering. Kathryn Hayden is currently supported by a cooperative agreement from the United States Department of Agriculture's Agricultural Research Service (USDA-ARS). Marc Gluberman was funded by Penn State's College of Agricultural Sciences Summer Undergraduate Research Program in 2015. Laura Garcia was selected to participate in the Summer Research Opportunities Program in 2015 and was supported at Penn State through support from the College of Agricultural Sciences diversity program and from the Department of Agricultural and Biological Engineering. Serap Gorucu was funded, in part, by a grant from the Penn State Office of Physical Plant. Heather Preisendanz is supported, in part, by the USDA National Institute of Food and Agriculture Federal Appropriations under Project PEN04574 and Accession Number 1004448.

**Institutional Review Board Statement:** The Pennsylvania State University Office of Research Protections determined that this research met the criteria for exempt research according to the policies of the institution and the provisions of applicable federal regulations.

**Informed Consent Statement:** Informed consent was obtained from all citizen scientists who volunteered to participate in this study.

**Data Availability Statement:** The calculator tools can be accessed at: https://sites.psu.edu/edccal culator/ (Created on 10 February 2017; accessed on 25 February 2022).

**Acknowledgments:** The authors wish to thank Jamie Shallenberger from the Susquehanna River Basin Commission for his help in recruiting citizen scientists to participate in this project.

**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.
