1. Introduction
Pharmaceuticals, pharmaceutical metabolites, and other personal care products are found in surface and ground waters throughout the world, including the streams and rivers in the United States [
1,
2]. The ecotoxicological effects of these pharmaceutical pollutants on aquatic organisms are of concern due to the increasing usage of pharmaceuticals in human and veterinary medicine. Pharmaceuticals are a unique pollutant, because they are specifically designed to target specific physiological processes and persist for some time within the body. Another issue of concern specific to aquatic organisms is that they can be exposed to these pollutants for their entire lives, and multiple generations will most likely be exposed as well. Acute toxicity exposure in the wild is highly unlikely and only applicable following a large accidental discharge. Thus, chronic toxicity studies are more relevant in assessing potential impacts to aquatic organisms [
1,
3]. The literature surrounding the acute toxicity of specific pharmaceuticals far outweighs the literature regarding their chronic or lifelong toxicity [
4]. For the reasons outlined above, a brief review of known chronic toxicity effects regarding statins and beta-blockers on aquatic organisms is likely to be relative to scenarios found in most areas of interest.
Statins are lipid lowering agents that inhibit cholesterol synthesis by inhibiting the 3-hydroxymethlglutaril coenzyme A reductase (HMGR) enzyme. Statins are HMGR inhibitors in both vertebrates and in arthropods, but arthropods synthesize cholesterol via a slightly different mechanism [
5,
6]. A key concern regarding statins is their low log Kow values, indicating that they are likely to bioaccumulate, which can have wide ranging effects [
7]. Chronic toxicity studies of statins are rare in general and almost non-existent regarding freshwater systems, with most current chronic toxicity studies having focused on marine organisms and arthropods. Based on the limited studies available, simvastatin has been shown to impact the reproduction and growth of crustaceans as well as several other invertebrates [
6,
8,
9,
10]. To the best of our knowledge, atorvastatin has few chronic toxicity studies with only one aquatic organism paper published by Santos et al. [
7] hypothesizing that metazoans could be at risk to statins. There are currently no published studies regarding long-term or chronic exposure in fish species. Fish conditions relative to environmental concentrations within a controlled environment or within an observational study framework has not been published, to the best of our knowledge.
Beta-blockers are antihypertensive medications that inhibit beta-adrenergic receptors to control blood pressure, heart rate, and airway strength reactivity, depending on the location of the targeted beta-adrenergic receptors [
11]. Just like mammals, fish also possess beta-adrenergic receptors in the heart, liver, and reproductive system, and are potentially susceptible to their effects [
4,
12,
13]. Several studies have investigated the effects of beta-blockers on fish and found that fish are less susceptible than other aquatic organisms such as macroinvertebrates, plants, and algae [
4]. However, a study by Triebskorn et al. [
14] showed that chronic exposure to metoprolol at environmentally relevant levels can lead to ultrastructural changes in the gills, kidneys, and liver. Another study showed that prolonged exposure to beta-blockers can negatively impact fish growth, as well as decrease egg production [
13]. Invertebrates do not possess beta-receptors like fish and mammals, but are still susceptible to their impacts via different mechanisms, such as membrane disruption [
15]. Massarky et al. [
16] hypothesized the potential for beta-blockers to be endocrine disruptors and that beta-blockers would affect the stress response of aquatic organisms, especially fish. The ecotoxicological impacts from carvedilol are not documented at all as of this time and need significant research. Chronic toxicity testing on macroinvertebrates and aquatic plants are still lacking, and multi-generational testing for beta-blockers is also quite scarce for all aquatic organisms. Congruently, bioaccumulation and field studies for the detection of beta-blockers in aquatic biota are also scarce.
There is a well-established understanding of the point sources for pharmaceutical waste [
17] and the primary mechanism of action for both statins and beta-blockers within aquatic organisms are thought to be similar to mammals [
18,
19]. However, there is insufficient information regarding their long-term impacts or even the most effective approach for investigating these impacts. Previous studies have thoroughly investigated the acute toxicity of isolated pharmaceuticals in laboratory environments. In contrast, the number of chronic toxicity studies pales in comparison, and is an area of study that requires more attention going forward. In addition, mixture studies are sparse at best and provide the best possibility of simulating real-world exposure scenarios for aquatic organisms. We know that these pharmaceuticals pseudo-persist in the environment as a complex mixture, and initial mixture studies have shown that they can interact with one another leading to greater toxic effects on aquatic organisms [
9,
20,
21]. Additional mixture studies and the various environmental factors that contribute to variations in pharmaceutical waste toxicity are still required. At the same time, most impact studies involving aquatic organisms take place in laboratory environments, and there is a lack of field studies using real world systems to investigate the ecological impacts of pharmaceuticals (
Table 1). Furthermore, information is lacking regarding the potential sublethal impacts pharmaceuticals have on growth, reproduction, and survival across multiple species and organisms over multiple generations. While direct impacts to a single species may not be harmful, impacts to multiple organisms or species throughout the food web at various trophic levels could potentially lead to ripple effects that are harder to predict and thus require further investigation. To gain a better understanding of the potential effects from these pharmaceuticals, it is essential that studies include multiple species simultaneously. By filling in these knowledge gaps, more accurate and effective risk assessments can be created, thereby giving managers better tools for assessing, reducing, and/or preventing severe ecological damage from pharmaceutical and personal care product wastes.
Herein, we report the correlations between several fish condition metrics from multiple fish species along with environmental surface water concentrations of statins and beta-blockers. We collected multiple species of fish at locations upstream, downstream, and near two West Virginia wastewater treatment plants (WWTPs). Using the surface water concentration data, we created a Bayesian linear mixed effects model capable of accounting for the spatial, physiological, and individual pharmaceutical differences between sampling locations and fish genera. The objective of this study was to investigate whether relevant surface water concentrations are negatively correlated to fish health and, if so, at what concentration level.
4. Discussion
We observed differences in liver, gonad, and relative weight based on species/genus and sex in riverine waters around two WWTP within the Tygart Valley River and West Fork River, but none of these were consistently related to the selected pharmaceutical levels. Lepomis spp. displayed nearly significant differences in liver condition (assessed via HSI) based on individual species and sex, with no differences observed based on sampling section. In addition, Lepomis spp. displayed differences in gonad condition (via GSI) based on sex, but not species or sampling section. Significant differences in relative weight were identified based on seven genera and the interaction of genera within a given section, but section by itself was not significant. Further analysis of relative weight revealed that section and genus were significant random effects; however, all four pharmaceuticals (atorvastatin, simvastatin, metoprolol, and carvedilol) did not appear to have a significant effect on relative weight at any of the observed concentrations. Furthermore, the marginal effects from the mixed linear effects model were a mixed bag of positive (atorvastatin and metoprolol) and negative effects (simvastatin and carvedilol).
Differences in HSI between species and sex near WWTP’s could be the result of several factors, including phylogenetic differences, pollution tolerance, and indirect dietary factors. Phylogenetic differences among the species we observed could lead to significant variation in the HSI scores even if these species belong to the same genus [
52]. Similarly, different species of
Lepomis have varying degrees of pollution tolerance, which could explain some of the observed differences in HSI [
53]. Several studies have demonstrated how WWTP plant effluent negatively impacts certain species to a greater extent, compared to more tolerant species [
54,
55,
56]. In addition to chemical contaminants, thermal pollution can also impact liver physiology by disrupting the physiological processes associated with temperature acclimation [
57], and during November, the water exiting the WWTP is likely warmer than the native river temperature. The differences in effluent temperatures and native temperatures are likely to implore stress on all fish, with some species acclimating more efficiently than others [
58,
59]. The observed differences in HSI scores based on sex of the individual fish is likely linked to vitellogenesis in the liver which causes the liver of female fish to increase in size [
60]. Vitellogenesis occurs leading up to a fish’s spawning window and, in some cases, will occur leading up to winter, but is seasonal in nature and is dependent upon a species spawning period. There is the possibility that endocrine-disrupting compounds from the WWTP were stimulating vitellogenesis in the female fish, leading to the increase in liver size compared to the males [
61]. Further testing would be required to prove this hypothesis for the samples used in this study, but it should also be considered for future studies. Based on the receiving waters and the treatment processes of both WWTP, it is reasonable to assume that endocrine disrupting compounds have not been removed and are entering the river systems. However, no differences in HSI were observed based on sample section, which could indicate that the difference in pharmaceutical concentrations provided by the nearby WWTP did not have a noticeable effect on the livers of the fish. It is worth noting that there is the distinct possibility that since fish are mobile organisms, they do not spend their whole lives in any single section for 4 months, let alone an entire year. The mobility of the fish could explain why we did not observe differences in HSI based on section.
Like the HSI scores, differences in the GSI scores were detected based on the sex of the fish and are likely tied to inherent differences in mature male and female GSI values and influential factors stemming from nearby WWTP effluent.
Lepomis spp. are typically summer spawners and, since the specimens were collected in November, both male and female specimens were likely focused on somatic growth and not gonadic growth [
62]. However, as adults,
Lepomis gonads possess inherent size proportion differences even during periods of primarily somatic focused growth [
63]. To account for this, we included a sex and section interaction term, but it was not significant. Previous research has shown, however, that differences in GSI are easier to detect right before or during spawning season, which could account for the lack of a significant difference between sampling sections [
64].
Differences in relative weight were observed between genera and the interaction between genera and sample section, indicating that certain groups of fish are experiencing varying degrees of impacts to their growth based on their genus and their location. Previous research has established that pollution tolerance varies by genus and species, and the variation in pollution levels upstream and downstream from the WWTP likely explain some of these differences [
65,
66,
67]. More specifically, fish near the discharge and downstream are exposed to a variety of pollutants, which can cause endocrine disrupting effects, genotoxicity effects, immunotoxicity effects, and behavioral changes, to name a few [
54,
55,
66,
68]. There is also the consideration of indirect effects on fish health through changes in food availability/quality. Macroinvertebrates and microscopic organisms inhabiting the same area experience the same pollution levels, but with a greater sensitivity which, in turn, may affect their growth and abundance, therefore leading to changes in available food and food quality for fish. [
8,
21,
69]. Furthermore, the marginal effects produced from the linear mixed effects model for atorvastatin, simvastatin, metoprolol, and carvedilol were not statistically significant, but the overall relative weight based on the mixed effect model showed that fish within both study sites were likely stressed upstream and downstream of the WWTPs. We observed pharmaceutical concentrations for all four pharmaceuticals upstream of the WWTPs, indicating the widespread prevalence of these pharmaceuticals. In turn, that meant that non-exposed fish were never observed or compared to fish that were exposed to these compounds. Based on the known pharmacology of the cardiovascular medicines of interest and the marginal effect sizes, it is likely that there was some type of effect, but it is difficult to tell if it was beneficial or harmful based on the relative weight metrics.
While the information provided in this study is valuable, it is not without its limitations, and areas for either improvement or expansion are available. One of the biggest limitations encountered in this study was that the experimental design is purely observational, which can lead to bias and difficulty sourcing unknown variance in the dataset [
70]. In the same vein, it was difficult to account for either fish immigration or emigration due to physical constraints within the rivers themselves, as well as any type of survivorship biases within our samples [
71,
72]. Other contaminants present within the WWTP effluent could also be responsible for some of the negative impacts we observed [
54,
65,
73]. Finally, the last issue was that the metrics chosen to assess fish health are a small set of metrics used to assess fish, and that other metrics might be more effective for future studies. A list of exhaustive alternatives can be found in Murphy et al. [
74].
Future work on cardiovascular medicine wastes will need to incorporate laboratory studies and field studies to capture seasonal changes, as well as community-wide impact assessments. Controlled lab experiments will allow for testing complex mixtures of pharmaceuticals at different environmental concentrations while minimizing outside factors. Uncertainty analyses should also be included with lab experiments to better highlight the contribution of error in future experiments. Furthermore, seasonal variation, as it relates to spawning times for different species, can be studied more efficiently in a laboratory setting to determine if these cardiovascular pharmaceuticals impact reproductive systems. Applying the principles of ecotoxicology, the use of community-wide assessments that include fish, macroinvertebrates, and lower-level lifeforms can also help elucidate if exposure to environmentally relative concentrations of cardiovascular medicines leads to significant changes in aquatic communities [
75]. Alternative methods of identifying sublethal responses in fish species should include genetic response testing, as well as testing for mechanistic effects of chemicals at the cellular and molecular level, which can then be extrapolated to the wider community [
75]. Detailed histology and tissue analyses combined with these tests will assist managers in determining the scale of impact from cardiovascular medicinal waste. Ideally, the results and measurements from these future works in conjunction with more accurate loading assessments could be applied to comprehensive life cycle assessments (LCA) for the various statins and beta-blockers currently in circulation [
76]. However, the uncertainty observed within our study will need to be reduced prior to inclusion in an LCA due to the sensitivity of LCAs to uncertainty [
77].
Within the limitations of this study at the current environmental concentrations, there is a limited effect from atorvastatin, simvastatin, metoprolol, and carvedilol on fish liver, gonads, and overall condition. Streams and rivers not dominated by WWTP discharge still contain detectable and quantifiable concentrations of these pharmaceuticals, indicating widespread distribution and potentially ubiquitous impacts at various levels. However, streams that are predominantly made up of WWTP effluent discharge will contain greater concentrations, and thus be at greater risk for sublethal impacts. The methods from this study can be applied to any river or stream system to assess fish assemblage conditions relative to pharmaceutical inputs, but care must be taken to assess the pharmaceutical mixture in the surface waters before drawing any conclusions. Managers of effluent-dominated systems can use this methodology in conjunction with other methods to better define and understand the extent of statins, beta-blockers, or other pharmaceutical impacts on their fisheries. Further refinements in this methodology will include the addition of tissue concentration testing and comparing tissue concentrations to various metrics, such as those in this study to further understand potential impacts to fish growth, condition, and survival. Additional considerations should also include surrounding land use that may cause alterations to flow regimes or other anthropogenic impacts [
78]. Pharmaceutical wastes by themselves may be unlikely to cause fish kills, but pharmaceutical wastes impacts compounded with other anthropogenic impacts can potentially cause substantial damage to fisheries and aquatic communities.