Abstract
Pharmaceutical residues impose a new and emerging threat to aquatic environments and its biota. One of the most commonly prescribed pharmaceuticals is the antidepressant fluoxetine, a selective serotonin re-uptake inhibitor that has been frequently detected, in concentrations up to 40 μg L–1, in aquatic ecosystems. The present study aims to investigate the ecotoxicity of fluoxetine at environmentally relevant concentrations (0.3, 0.6, 20, 40, and 80 μg L–1) on cell energy and lipid metabolism, as well as oxidative stress biomarkers in the model diatom Phaeodactylum tricornutum. Exposure to higher concentrations of fluoxetine negatively affected cell density and photosynthesis through a decrease in the active PSII reaction centers. Stress response mechanisms, like β-carotene (β-car) production and antioxidant enzymes [superoxide dismutase (SOD) and ascorbate peroxidase (APX)] up-regulation were triggered, likely as a positive feedback mechanism toward formation of fluoxetine-induced reactive oxygen species. Lipid peroxidation products increased greatly at the highest fluoxetine concentration whereas no variation in the relative amounts of long chain polyunsaturated fatty acids (LC-PUFAs) was observed. However, monogalactosyldiacylglycerol-characteristic fatty acids such as C16:2 and C16:3 increased, suggesting an interaction between light harvesting pigments, lipid environment, and photosynthesis stabilization. Using a canonical multivariate analysis, it was possible to evaluate the efficiency of the application of bio-optical and biochemical techniques as potential fluoxetine exposure biomarkers in P. tricornutum. An overall classification efficiency to the different levels of fluoxetine exposure of 61.1 and 88.9% were obtained for bio-optical and fatty acids profiles, respectively, with different resolution degrees highlighting these parameters as potential efficient biomarkers. Additionally, the negative impact of this pharmaceutical molecule on the primary productivity is also evident alongside with an increase in respiratory oxygen consumption. From the ecological point of view, reduction in diatom biomass due to continued exposure to fluoxetine may severely impact estuarine and coastal trophic webs, by both a reduction in oxygen primary productivity and reduced availability of key fatty acids to the dependent heterotrophic upper levels.
Highlights
Pharmaceuticals and personal care products (PPCPs) are a group of substances that include cosmetics, hormones, antibiotics, antimicrobial agents, and other organic substances (Daughton and Ternes, 1999; Liu and Wong, 2013)
This experiment lasted for 96 and 48 h after cell inoculation, which corresponds to a lag phase or adaptation period, cells were exposed to different concentrations of fluoxetine as they entered the exponential phase
Some replicates seem to grow slower than the control samples during the first 48 h, it is important to notice that each replicate started with the same amount of cells and small variations in cell density during this lag phase can be related to minor variations in aeration, manual sampling or counting and even the microenvironment inside each flask
Summary
Pharmaceuticals and personal care products (PPCPs) are a group of substances that include cosmetics, hormones, antibiotics, antimicrobial agents, and other organic substances (Daughton and Ternes, 1999; Liu and Wong, 2013). It is not surprising that fluoxetine has been frequently detected in aquatic environments worldwide (Vasskog et al, 2008; Mezzelani et al, 2018; Reis-Santos et al, 2018), in concentrations that reach up to 40 μg L−1 (aus der Beek et al, 2016), where it seems to be more persistent than most SSRIs (Johnson et al, 2005; Neuwoehner et al, 2009). Since pharmaceuticals are intended to produce effects at low concentrations in humans (Ebele et al, 2017; Duarte I.A. et al, 2019), and fluoxetine has been reported to be toxic to various groups of organisms (Fent et al, 2006; Corcoran et al, 2010), its presence in marine ecosystems is of emerging concern. To evaluate the impacts of fluoxetine on invertebrates and vertebrates, it is paramount that we understand its effects in microorganisms and autotrophs at the base of the marine food webs
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