Chronic effects assessment and plasma concentrations of the β-blocker propranolol in fathead minnows (Pimephales promelas)
Introduction
Pharmaceuticals in the environment has become a growing concern after the realisation that ethinyl estradiol could be found in the aquatic environment at concentrations exceeding 0.5 ng/L, the concentration at which vitellogenin induction can occur in male fish (Purdom et al., 1994). Since then, advancement of analytical techniques has shown that there are in fact many pharmaceuticals in our rivers and surface waters, including human beta adrenoreceptor blockers (β-blockers) (Fent et al., 2006, Ternes et al., 2001). The question that follows therefore, is are the concentrations of pharmaceuticals found in the aquatic environment high enough to cause harm to the wildlife that are exposed to them?
Propranolol and other human and animal pharmaceuticals reach the aquatic environment through a variety of routes. However, the majority of pharmaceuticals are present in the aquatic environment due to incomplete removal at sewage treatment works (STWs). In Germany it was found that 96% of propranolol was removed from the influent compared to the effluent, yet the 4% remaining is largely why propranolol has been found ubiquitously in rivers and streams in America and Europe at concentrations in the ng/L range, with maximum and median concentrations reaching 590 and 12 ng/L, respectively (Ashton et al., 2004, Huggett et al., 2003b, Ternes, 1998).
There are many different classes of pharmaceuticals in the environment but this study and a companion study (Winter et al., 2008) focus solely on one group, the β-blockers. This is so that a comprehensive picture around one class of pharmaceuticals can be built up in order to try to establish some general principles that might be applicable to other classes of pharmaceuticals. A feature of the study was to apply the ‘fish plasma model’ as hypothesised by Huggett et al., 2003a, Huggett et al., 2003b, which compares estimated or actual drug concentrations in fish plasma with human therapeutic plasma concentrations, in order to assess whether it is likely that environmental or experimental concentrations of a drug would produce therapeutic levels in fish. If the fish plasma model is found to be successful when applied to β-blockers, it might also be applicable to other groups of pharmaceuticals.
The physiology, pharmacology and toxicology of β-blockers, in both humans and fish, has recently been reviewed (Owen et al., 2007). This class of human pharmaceuticals targets the beta-adrenergic receptors (β-ARs). There are three of these in both mammals and fish, namely β1-, β2-, and β3-ARs, which have different tissue distributions and different specificities for the various β-blockers in therapeutic use, and they regulate different physiological processes (see Owen et al., 2007, for details). Although there may be some cross-species differences in the pharmacology and toxicology of β-blockers, such as different rates of metabolism (e.g. Jackson and Fishbein, 1986), the similarities between fish and mammals in all aspects of β-blocker physiology and pharmacology appear very much more pronounced compared to any differences that might exist (Owen et al., 2007).
Published data shows propranolol, out of all the β-blockers investigated, to be the most toxic to aquatic organisms. For example, invertebrate LC50 values for metoprolol and propranolol range from 64 to >100 mg/L and 0.8 to 29.8 mg/L, respectively, showing that propranolol is harmful to invertebrates at much lower concentrations than metoprolol (Cleuvers, 2003, Huggett et al., 2002, Villegas-Navarro et al., 2003). In fish studies, the published data on propranolol are limited. However, a report by Huggett et al. (2002) showed propranolol to be relatively toxic with LOEChatchability and egg production values of 0.0005 mg/L. Hence the message is mixed, with most studies suggesting that propranolol is not particularly toxic to aquatic organisms, but some suggesting this is not the case.
Section snippets
Test substance
The test substance, pharmaceutical grade propranolol (dl-propranolol hydrochloride, 1-isopropylamino-3-(1-naphthyloxy) proprano-2-ol hydrochloride, 99% pure, racemic mixture, CAS 318-98-9, to be referred to as propranolol), was obtained from AstraZeneca, Brixham (UK). In the first experiment, five concentrations of propranolol, namely 0.001, 0.01, 0.1, 1.0 and 10 mg/L, were used, together with a dilution water control (DWC). In the second experiment this was reduced to 4 concentrations of
Water concentrations of propranolol
Concentrations of propranolol were in the expected range for all treatments, except for the 10 mg/L tanks in experiment 1 (Table 1). There was no contamination of control tanks with propranolol. At a nominal concentration of 10 mg/L, only 34% of the nominal concentration was recovered from water. This may have been due to solubility issues, and/or uptake of the drug by fish in the tanks. In all other treatments, the mean concentrations of propranolol in experiments 1 and 2 ranged from 53 to 112%
Discussion
The toxicity data for propranolol obtained from the 21-day adult reproduction study reported here differed by at least 10-fold from the comparable data obtained for another β-blocker, atenolol (Winter et al., 2008). Fathead minnows were able to tolerate higher concentrations of atenolol (LOECsurvival > 10 mg/L) than in this study, in which propranolol caused acute toxicity at lower concentrations (acute LOECsurvival 3.4 mg/L). This could be the result of differences in lipophilicity between the two
Acknowledgements
The authors would like to thank the European Union for funding this work as part of the ERAPharm project, contract no. 511135 (Knacker et al., 2005), and to NERC for providing studentship funding to PDE.
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2021, Science of the Total EnvironmentCitation Excerpt :EC50-48h was 5 and 27 mg/L of D. magna and D. crassicaudis, respectively, in propranolol treatment (Di Lorenzo et al., 2019). Propranolol and atenolol reduced the survival rate of fathead minnows P. promelas, and propranolol was significantly more toxic than atenolol with LOECmalesurvival > 1.0 mg/L (Giltrow et al., 2009). Plasma levels of steroids in both male and female O. mykiss changed in 1 μg/L propranolol, and heart rate in rainbow trout was a sensitive indicator of the effects of short-term exposure (Larsson et al., 2006), also the plasma yolk erythropoietin concentration increased of Japanese medaka (Oryias latipes) in 1.91 mM and 0.5 μg/L propranolol, respectively (Huggett et al., 2002).