Norfluoxetine Is the Only Metabolite of Fluoxetine in Zebrafish (Danio rerio) Embryos That Accumulates at Environmentally Relevant Exposure Scenarios

Visible-light-induced N-alkylation of anilines with 4-hydroxybutan-2-one

The synthesis of amines through N-alkylation is particularly attractive. Herein, a strategy for visible-light-induced N-alkylation of anilines with 4-hydroxybutan-2-one was developed in the presence of NH4Br, which avoid the use of metals, bases and ligands. In addition, gram-scale experiments proved that the system has the potential to be scaled.

Synthesis of novel rapanone derivatives via organocatalytic reductive C-alkylation: biological evaluation of antioxidant properties, in vivo zebrafish embryo toxicity, and docking studies

A biologically crucial natural product rapanone 1 was isolated from Embelia ribes at the gram scale with excellent purity. Semi-synthetic analogs of 1 semi-synthesized through reductive C-alkylation could increase the therapeutic value of the compounds. Herein, a new synthetic methodology was developed as a single-step reductive C-alkylation protocol using a metal-free, room-temperature-based reaction condition that can be scaled up to gram-scale synthesis with an excellent yield of up to 93%. A straightforward purification protocol was employed for the product obtained by this method. The derivatives of 1 showed antioxidant activity, which was evaluated using DPPH and ABTS scavenging assays. Compounds 5a-5ze showed an IC50 value of 2.48-3.37 μM and 1.81-3.12 μM. Substitution by electron-donating groups on the quinone moiety seems to play an essential role in the increased antioxidant activity of compounds 5a-5i, 5v, 5w, 5zc, and 5z. Further, the in vivo embryotoxicity of 1 and its derivatives was analyzed in a zebrafish-based aquatic toxicology model. Zebrafish embryos were exposed to 1 and 5a-5ze at 20 to 160 μM concentrations. They showed reduced toxicity and a survival rate of 90-98% after 96 hpf of treatment; similarly, the compounds 5a-5i, 5v, 5w, 5zc, and 5zd did not significantly affect the hatching rates of 75.66-85.33% or developmental abnormalities of the embryos after 48 hpf of treatment. In silico molecular docking studies for the parent compound, along with its derivatives 5a-5i, 5v-5w, 5zc-5zd, and standard l-ascorbic acid (l-Aa) indicated favorable interactions with the active site of the crystal structure, coupled with the assay protein PDB:1ZB6, which was responsible for the observed biological understanding and potential.

Neurotoxic pesticides change respiratory parameters in early gill-breathing, but not in skin-breathing life-stages of zebrafish (Danio rerio)

Neurotoxic compounds can interfere with active gill ventilation in fish, which might lead to premature death in adult fish, but not in skin-breathing embryos of zebrafish, since these exclusively rely on passive diffusion across the skin. Regarding lethality, this respiratory failure syndrome (RFS) has been discussed as one of the main reasons for the higher sensitivity of adult fish in the acute fish toxicity test (AFT), if compared to embryos in the fish embryo toxicity test (FET). To further elucidate the relationship between the onset of gill respiration and death by a neurotoxic mode of action, a comparative study into oxygen consumption (MO2), breathing frequency (fv) and amplitude (fampl) was performed with 4 d old skin-breathing and 12 d old early gill-breathing zebrafish. Neurotoxic model substances with an LC50 FET/AFT ratio of > 10 were used: chlorpyrifos, permethrin, aldicarb, ziram, and fluoxetine. Exposure to hypoxia served as a positive control, whereas aniline was tested as an example of a narcotic substance interfering non-specifically with gill membranes. In 12 d old larvae, all substances caused an increase in MO2, fv and partly fampl, whereas effects were minor in 4 d old embryos. An increase of fv in 4 d old embryos following exposure to chlorpyrifos, aldicarb and hypoxia could not be correlated with an increased MO2 and might be attributed either to (1) to the successfully postponed decrease of arterial partial pressure of oxygen (PO2) through support of skin respiration by increased fv, (2) to an unspecific stimulation of the sphincter muscles at the base of the gill filaments, or (3) to the establishment of oxygen sensing for later stages. In gill-breathing 12 d old zebrafish, a concentration-dependent increase of fv was detected for aniline and chlorpyrifos, whereas for aldicarb, fluoxetine and permethrin, a decline of fv at higher substance concentrations was measured, most likely due to the onset of paralysis and/or fatigue of the gill filament sphincter muscles. Since alterations of fv serve to postpone the decrease in arterial PO2 and MO2 increased with decreasing fv, the respiratory failure syndrome could clearly be demonstrated in 12 d old zebrafish larvae. Passive respiration across the skin in zebrafish embryos could thus be confirmed as a probable reason for the lower sensitivity of early life-stages to neurotoxicants. Integration of respiratory markers into existing testing protocols with non-protected developmental stages such as embryos might help to not underestimate the toxicity of early life-stages of fish.

A comprehensive insight into the transformation pathways and products of fluoxetine and venlafaxine in wastewater based on molecular networking nontarget screening

Fluoxetine (FLX) and venlafaxine (VEN) are widely used antidepressant pharmaceuticals and were frequently detected in wastewater. Despite incomplete mineralization during biological wastewater treatment processes has been revealed, little is known about their transformation products (TPs) formed in the biological systems. To fill this gap, batch reactors and molecular networking nontarget screening were employed to identify the TPs and explore the transformation pathways of FLX and VEN in wastewater. On the basis, the concentrations of the TPs in wastewater treatment plants (WWTPs) were determined and their toxicity was predicted. The removal rate constants per unit of biomass of FLX and VEN were up to 0.3192 and 0.1644 L/(gMLSS*d) in batch experiments, respectively. Subsequently, 11 TPs of VEN and 11 TPs of FLX were tentatively identified, among which 9 TPs of FLX and 5 TPs of VEN were newly reported in this study. The proposed transformation pathways provided new insights into the transformation reactions including dehydrogenation, N-formylation and hydroxylation for FLX, and formylation, epoxidation and methylation for VEN. Particularly, N-succinylation and demethylation were the dominant transformation pathways for FLX and VEN during transformation processes. The results of sampling campaigns revealed that the accumulated concentration of TPs were higher than the concentrations of VEN in effluent of WWTPs. In silico prediction results suggested that certain TPs have higher toxicity, persistence and biodegradability than their corresponding parent compounds of FLX and VEN. In addition, VEN-TP264(a) showed higher ecological risks than VEN. This study revealed the transformation processes and fate of FLX and VEN in wastewater, indicating that greater concerns should be exerted on the toxicity detection and control of the TPs of FLX and VEN in the treated wastewater.

Water, Water Everywhere, but Every Drop Unique: Challenges in the Science to Understand the Role of Contaminants of Emerging Concern in the Management of Drinking Water Supplies

The protection and management of water resources continues to be challenged by multiple and ongoing factors such as shifts in demographic, social, economic, and public health requirements. Physical limitations placed on access to potable supplies include natural and human-caused factors such as aquifer depletion, aging infrastructure, saltwater intrusion, floods, and drought. These factors, although varying in magnitude, spatial extent, and timing, can exacerbate the potential for contaminants of concern (CECs) to be present in sources of drinking water, infrastructure, premise plumbing and associated tap water. This monograph examines how current and emerging scientific efforts and technologies increase our understanding of the range of CECs and drinking water issues facing current and future populations. It is not intended to be read in one sitting, but is instead a starting point for scientists wanting to learn more about the issues surrounding CECs. This text discusses the topical evolution CECs over time (Section 1), improvements in measuring chemical and microbial CECs, through both analysis of concentration and toxicity (Section 2) and modeling CEC exposure and fate (Section 3), forms of treatment effective at removing chemical and microbial CECs (Section 4), and potential for human health impacts from exposure to CECs (Section 5). The paper concludes with how changes to water quantity, both scarcity and surpluses, could affect water quality (Section 6). Taken together, these sections document the past 25 years of CEC research and the regulatory response to these contaminants, the current work to identify and monitor CECs and mitigate exposure, and the challenges facing the future.

The occurrence of typical psychotropic drugs in the aquatic environments and their potential toxicity to aquatic organisms - A review

Psychotropic drugs (PDs) and their bioactive metabolites often persist in aquatic environments due to their typical physical properties, which made them resistant to removal by traditional wastewater treatment plants (WWTPs). Consequently, such drugs and/or their metabolites are frequently detected in both aquatic environments and organisms. Even at low concentrations, these drugs can exhibit toxic effects on non-target organisms including bony fish (zebrafish (Danio rerio) and fathead minnows) and bivalves (freshwater mussels and clams). This narrative review focuses on the quintessential representatives of three different categories of PDs-antiepileptics, antidepressants, and antipsychotics. The data regarding their concentrations occurring in the environment, patterns of distribution, the degree of enrichment in various tissues of aquatic organisms, and the toxicological effects on them are summarized. The toxicological assessments of these drugs included the evaluation of their effects on the reproductive, embryonic development, oxidative stress-related, neurobehavioral, and genetic functions in various experimental models. However, the mechanisms underlying the toxicity of PDs to aquatic organisms and their potential health risks to humans remain unclear. Most studies have focused on the effects caused by acute short-term exposure due to limitations in the experimental conditions, thus making it necessary to investigate the chronic toxic effects at concentrations that are in coherence with those occurring in the environment. Additionally, this review aims to raise awareness and stimulate further research efforts by highlighting the gaps in the understanding of the mechanisms behind PD-induced toxicity and potential health risks. Ultimately, the study underscores the importance of developing advanced remediation methods for the removal of PDs in WWTPs and encourages a broader discussion on mitigating their environmental impacts.

The sensitivity of the zebrafish embryo coiling assay for the detection of neurotoxicity by compounds with diverse modes of action

In the aim to determine neurotoxicity, new methods are being validated, including tests and test batteries comprising in vitro and in vivo approaches. Alternative test models such as the zebrafish (Danio rerio) embryo have received increasing attention, with minor modifications of the fish embryo toxicity test (FET; OECD TG 236) as a tool to assess behavioral endpoints related to neurotoxicity during early developmental stages. The spontaneous tail movement assay, also known as coiling assay, assesses the development of random movement into complex behavioral patterns and has proven sensitive to acetylcholine esterase inhibitors at sublethal concentrations. The present study explored the sensitivity of the assay to neurotoxicants with other modes of action (MoAs). Here, five compounds with diverse MoAs were tested at sublethal concentrations: acrylamide, carbaryl, hexachlorophene, ibuprofen, and rotenone. While carbaryl, hexachlorophene, and rotenone consistently induced severe behavioral alterations by ~ 30 h post fertilization (hpf), acrylamide and ibuprofen expressed time- and/or concentration-dependent effects. At 37-38 hpf, additional observations revealed behavioral changes during dark phases with a strict concentration-dependency. The study documented the applicability of the coiling assay to MoA-dependent behavioral alterations at sublethal concentrations, underlining its potential as a component of a neurotoxicity test battery.

The metabolites could not be ignored: A comparative study of the metabolite norfluoxetine with its parent fluoxetine on zebrafish (Danio rerio)

The ubiquitous pharmaceuticals in aquatic environments have attracted huge attention due to their significant risks to humans and ecosystems. However, even though the knowledge of the negative effects induced by the parent pharmaceuticals is quite extensive, little is known about their metabolites for a long time. This study provides systematical knowledge about the potential toxicity of metabolite norfluoxetine and its parent fluoxetine on zebrafish (Danio rerio) at the early life stage. The results showed that the metabolite norfluoxetine had similar acute toxicity in fish with the parent fluoxetine. For the altered fish development, there was no significant difference in most cases between the two pharmaceuticals. Compared to the control, the metabolite markedly inhibited the locomotor behavior under light-to-dark transitions, which was comparable to the parent. Norfluoxetine could easily accumulate but hardly eliminate from fish, relative to fluoxetine. In addition, the accumulated fluoxetine in zebrafish may rapidly metabolize to norfluoxetine and then be eliminated through different metabolic pathways. The functional genes related to serotonergic process (5-ht1aa, 5-ht2c, slc6a4b, and vmat), early growth (egr4), and circadian rhythm (per2) were downregulated by both the norfluoxetine and fluoxetine, indicative of the same mode-of-action of norfluoxetine with its parent in these functions. Meanwhile, the alterations caused by norfluoxetine were more pronounced than that of fluoxetine in the genes of 5-ht2c, slc6a4b, vmat, and per2. The molecular docking also confirmed that norfluoxetine could bind with serotonin transporter protein in the same as fluoxetine with a lower binding free energy. Overall, the metabolite norfluoxetine could induce similar and even more toxic effects on zebrafish with the same mode of action. The different and binding energy of the metabolite norfluoxetine and its parent fluoxetine on zebrafish may be responsible for the differentiated effects. It highlights the risks of the metabolite norfluoxetine in the aquatic environment could not be ignored.

Bioaccumulation and Biotransformation of BDE-47 Using Zebrafish Eleutheroembryos (Danio rerio)

Polybrominated diphenyl ethers (PBDEs) are well-known endocrine disrupting chemicals identified as organic persistent pollutants. Their metabolites OH-BDE and MeO-BDE have been reported to be potentially more toxic than the postulated precursor PBDEs. One of the most predominant congeners of PBDEs in the environment is BDE-47, due to its high presence in industrially used mixtures. In the present study, the bioaccumulation and biotransformation of BDE-47 into its major metabolites is evaluated using zebrafish (Danio rerio) eleutheroembryos adapting a previously developed alternative method to bioconcentration official guideline Organisation for Economic Co-ordination and Development 305, which reduces the animal suffering, time, and cost. For the simultaneous determination of BDE-47 and its metabolites in larvae and exposure medium, and considering the polarity difference of the analytes and the small sample size, the development of a validated analytical method is a step to ensure quality results. In the present study, an ultrasound-assisted extraction followed by a solid phase extraction dispersive clean-up step and gas chromatography-mass spectrometry-microelectron capture detector (GC-MS-μECD) with a previous derivatization process was optimized and validated. Bioconcentration factors (BCFs) were calculated using a first-order one-compartment toxicokinetic model. The profiles found show rapid absorption in the first hours of larval development and great bioaccumulative capacity, finding BCFs of 7294 ± 899 and 36 363 ± 5702 at nominal concentrations of 10 and 1 μg L^-1 , respectively. Metabolization studies show increasing concentrations of the metabolites BDE-28, 2'-OH-BDE-28, and 5-MeO-BDE-47 throughout the exposure time. The results obtained show the feasibility of the method for bioaccumulation and open up the possibility of metabolic studies with zebrafish eleutheroembryos, which is a very underdeveloped field without official testing or regulation. Environ Toxicol Chem 2023;42:835-845. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Environmental risk caused by drug waste in the city of Rio de Janeiro, Brazil, during the SARS-Cov19 pandemic

Abstract The relationship between the distribution of medicines used in the Pandemic by SARS-COV-19 in the municipality of Rio de Janeiro and the estimated level of environmental risk caused by their residues was evaluated. The amount of medicines distributed by primary health care (PHC) units between 2019 and 2021 were collected. The risk quotient (RQ) corresponded to the ratio between the estimated predictive environmental concentration (PECest) obtained by the consumption and excretion of each drug and its non-effective predictive concentration (PNEC). Between 2019 and 2020, the PECest of azithromycin (AZI) and ivermectin (IVE) increased between 2019 and 2020, with a decrease in 2021 probably due to shortages. Dexchlorpheniramine (DEX) and fluoxetine (FLU) fell, returning to growth in 2021. While the PECest of diazepam (DIA) increased over these 3 years, ethinylestradiol (EE2) decreased possibly due to the prioritization of PHC in the treatment of COVID-19. The largest QR were from FLU, EE2 and AZI. The consumption pattern of these drugs did not reflect their environmental risk because the most consumed ones have low toxicity. It is worth noting that some data may be underestimated due to the incentive given during the pandemic to the consumption of certain groups of drugs.

Environmental risk caused by drug waste in the city of Rio de Janeiro, Brazil, during the SARS-Cov19 pandemic

The relationship between the distribution of medicines used in the Pandemic by SARS-COV-19 in the municipality of Rio de Janeiro and the estimated level of environmental risk caused by their residues was evaluated. The amount of medicines distributed by primary health care (PHC) units between 2019 and 2021 were collected. The risk quotient (RQ) corresponded to the ratio between the estimated predictive environmental concentration (PECest) obtained by the consumption and excretion of each drug and its non-effective predictive concentration (PNEC). Between 2019 and 2020, the PECest of azithromycin (AZI) and ivermectin (IVE) increased between 2019 and 2020, with a decrease in 2021 probably due to shortages. Dexchlorpheniramine (DEX) and fluoxetine (FLU) fell, returning to growth in 2021. While the PECest of diazepam (DIA) increased over these 3 years, ethinylestradiol (EE2) decreased possibly due to the prioritization of PHC in the treatment of COVID-19. The largest QR were from FLU, EE2 and AZI. The consumption pattern of these drugs did not reflect their environmental risk because the most consumed ones have low toxicity. It is worth noting that some data may be underestimated due to the incentive given during the pandemic to the consumption of certain groups of drugs.

Adapting classic paradigms to analyze alterations of shoal-wide behavior in early-life stages of zebrafish (Danio rerio) - A case study with fluoxetine

Given the strong increase in prescription of neuroactive pharmaceuticals, neurotoxicity has received growing concern in science and the public. Regulatory requirements stimulated the development of new methods to evaluate the risk of neurotoxic substances for humans and the environment, and, with respect to potential damage to aquatic ecosystems, a variety of behavior-based assays have been proposed for neurotoxicity testing, most of which, however, are restricted to changes in the behavior of individual fish. Since many fish species form shoals under natural conditions, this may cause important aspects of behavior to be overlooked and there is a need for behavior assays integrating individual behavior with behavior of the entire swarm. In order to combine more environmentally realistic sub-chronic exposure scenarios with undistorted social behavior and animal welfare considerations, two behavioral assays are proposed that might be integrated into early-life stage toxicity studies according to OECD TG 210, which are commonly run for a multitude of regulations: To this end, protocols for a novel tank test and a predator response assay were adapted to also record the behavior of free-swimming zebrafish (Danio rerio) juveniles within shoals. Comparisons of the diving response (novel tank) or the shoal's coherence and position relative to the stimulus (predator) with control groups allow conclusions about the anxiety state of the fish, which might well have an impact on survival chances in the wild. As a model substance, the antidepressant fluoxetine ((RS)-N-Methyl-3-phenyl-3-(4-trifluoromethylphenoxy)propylamine) produced adverse effects down to concentrations three orders of magnitude below the EC₁₀ from acute fish embryo toxicity tests according to OECD TG 236. With the integration of such behavior tests into OECD TG 210, important population-relevant information on potential neurotoxicity can be collected without increasing the number of experimental animals.

Ecotoxicological effects of the antidepressant fluoxetine and its removal by the typical freshwater microalgae Chlorella pyrenoidosa

The antidepressant fluoxetine (FLX) has gained increasing attention due to its frequent detection in aquatic environments and negative effects on non-target organisms. However, knowledge on the ecotoxicological effects of FLX and its removal by microalgae is still limited. In this study, the ecotoxicological effects of FLX (10 -1000 μg/L) were assessed using batch cultures of the freshwater microalgae Chlorella pyrenoidosa for 10 days based on changes in growth, antioxidant response, and photosynthetic process. The removal efficiency, removal mechanism, and degradation pathway of FLX by C. pyrenoidosa were also investigated. The results showed that the growth of C. pyrenoidosa was inhibited by FLX with a 4 d EC₅₀ of 0.464 mg/L. Additionally, FLX significantly inhibited photosynthesis and caused oxidative stress on day 4. However, C. pyrenoidosa can produce resistance and acclimatize to FLX, as reflected by the declining growth inhibition rate, recovered photosynthetic efficiency, and disappearance of oxidative stress on day 10. Despite the toxicity of FLX, C. pyrenoidosa showed 41.2%- 100% removal of FLX after 10 days of exposure. Biodegradation was the primary removal mechanism, accounting for 88.2%- 92.8% of the total removal of FLX. A total of five metabolites were found in the degradation processes of FLX, which showed less toxicity than FLX. The main degradation pathways were proposed as demethylation, O-dealkylation, hydroxylation, and N-acylation. Our results not only highlight the potential application of microalgae in FLX purification, but also provide insight into the fate and ecological risk of FLX in aquatic environments.

Fluoxetine-induced neurotoxicity at environmentally relevant concentrations in adult zebrafish Danio rerio

Fluoxetine (FLX) exerts its therapeutic effect by inhibiting the presynaptic reuptake of the neurotransmitter serotonin. Nonetheless, at high concentrations of this drug, adverse effects occur in the brain of exposed organisms. Bearing this into account, the objective of this study was to evaluate the neurotoxic effects of the fluoxetine through the evaluation of behavior (Novel tank test), determination of oxidative stress, and determination of acetylcholinesterase (AChE) activity in adult zebrafish Danio rerio. For this purpose, Danio rerio adults were exposed to three environmentally relevant concentrations (5, 10, 16ngL^-1) of FLX for 96h. Our results demonstrate fish presented a significant disruption in their behavior, as they remained long-lasting time frozen at the top of the tank. Since we observed a significant reduction of AChE activity in the brain of fish, we believe the above described anxiety-like state is the result of this enzyme impairment. Moreover, as FLX-exposed fish showed a significant increase in the levels of oxidative damage biomarkers, we suggest this AChE disruption is associated with the oxidative stress response fish exhibited. Based on our findings, we believe the environmentally relevant concentration of FLX alters the redox status of the brain, impairing this way the behavior of fish and making them more vulnerable to predation.

Specificity of time- and dose-dependent morphological endpoints in the fish embryo acute toxicity (FET) test for substances with diverse modes of action: the search for a "fingerprint"

The fish embryo acute toxicity (FET) test with the zebrafish (Danio rerio) embryo according to OECD TG 236 was originally developed as an alternative test method for acute fish toxicity testing according to, e.g., OECD TG 203. Given the versatility of the protocol, however, the FET test has found application beyond acute toxicity testing as a common tool in environmental hazard and risk assessment. Whereas the standard OECD guideline is restricted to four core endpoints (coagulation as well as lack of somite formation, heartbeat, and tail detachment) for simple, rapid assessment of acute toxicity, further endpoints can easily be integrated into the FET test protocol. This has led to the hypothesis that an extended FET test might allow for the identification of different classes of toxicants via a "fingerprint" of morphological observations. To test this hypothesis, the present study investigated a set of 18 compounds with highly diverse modes of action with respect to acute and sublethal endpoints. Especially at higher concentrations, most observations proved toxicant-unspecific. With decreasing concentrations, however, observations declined in number, but gained in specificity. Specific observations may at best be made at test concentrations ≤ EC₁₀. The existence of a "fingerprint" based on morphological observations in the FET is, therefore, highly unlikely in the range of acute toxicity, but cannot be excluded for experiments at sublethal concentrations.

Differential Molecular Responses of Zebrafish Larvae to Fluoxetine and Norfluoxetine

The occurrence of psychopharmaceuticals in aquatic ecosystems is a growing problem. Fluoxetine (FL) and its metabolite norfluoxetine (NF) are selective serotonin reuptake inhibitors. Although they may be potentially harmful to non-target species, available knowledge on the effects of NF is sparse, relative to FL. This study aimed at contributing to the body of knowledge about the modes-of-action (MoA) of these compounds and their underlying mechanisms eliciting hazardous effects during the early development of the teleost model zebrafish (Danio rerio). One hour post-fertilisation (hpf), embryos were exposed up to 80 hpf to these compounds at levels found in surface waters and higher (FL, 0.0015 and 0.05 µM; NF, 0.00006 and 0.0014 µM). Developmental anomalies were observed at 8, 32 and 80 hpf. Larvae were collected at 80 hpf to assess the expression of 34 genes related to FL and NF MoA and metabolism, using qPCR (quantitative reverse transcription PCR). Results showed that both compounds elicited an increased frequency of embryos exhibiting abnormal pigmentation, relative to controls. Gene expression alterations were more pronounced in FL- than in NF-exposed larvae. Cluster Analysis revealed two groups of genes discriminating between the drugs. for their marked opposing responses. Globally, downregulation of gene expression was typical of FL, whilst upregulation or no alteration was found for NF. These clusters identified were linked to the adrenergic pathway and to the retinoid and peroxisome proliferator-activated nuclear receptors. Overall, our data contradict the prevailing notion that NF is more toxic than FL and unveiled the expression levels of genes drd2b, 5-ht2c and abcc2 as possible markers of exposure to FL.

Transformation products of pharmaceuticals in the environment: Their fate, (eco)toxicity and bioaccumulation potential

Nowadays, a huge scientific attention is being paid to the chemicals of emerging concern, which may pose a significant risk to the human and whole ecosystems. Among them, residues of pharmaceuticals are a widely investigated group of chemicals. In recent years it has been repeatedly demonstrated that pharmaceuticals are present in the environment and that some of them can be toxic to organisms as well as accumulate in their tissues. However, even though the knowledge of the presence, fate and possible threats posed by the parent forms of pharmaceuticals is quite extensive, their transformation products (TPs) have been disregarded for long time. Since last few years, this aspect has gained more scientific attention and recently published papers proved their common presence in the environment. Also the interest in terms of their toxicity, bioconcentration and stability in the environment has increased. Therefore, the aim of our paper was to revise and assess the current state of knowledge on the fate and effects resulting from the presence of the pharmaceuticals' transformation drugs in the environment. This review discusses the metabolites of compounds belonging to six major pharmaceutical groups: SSRIs, anticancer drugs, antibiotics, antihistamines, NSAIDs and opioids, additionally discussing other individual compounds for which literature data exist. The data presented in this paper prove that some TPs may be as harmful as their native forms, however for many groups of drugs this data is still insufficient to assess the risk posed by their presence in the environment.

Near future ocean acidification modulates the physiological impact of fluoxetine at environmental concentration on larval urchins

Pharmaceuticals found in human wastes are emergent pollutants that are continuously released into aquatic systems. While exposure to pharmaceuticals alone could adversely impact aquatic organisms, few studies have considered the interactive effects of pharmaceuticals and the future environmental conditions, such as decreasing pH due to ocean acidification. Given the bioavailability of many pharmaceuticals is dependent on these physical conditions, we investigated the effect of environmentally-relevant concentrations of fluoxetine (10 and 100 ng L^-1) under ambient (pH 8.0) and reduced pH conditions (pH 7.7) on physiology, behavior, and DNA integrity of larval sea urchins (Heliocidaris crassispina). Notably, the negative impacts of fluoxetine exposure were attenuated by reduced pH. Larvae exposed to both reduced pH and fluoxetine exhibited lower levels of DNA damage compared to those exposed to only one of the stressors. Similar antagonistic interactions were observed at the organismal level: for example, fluoxetine exposure at 10 ng L^-1 under ambient pH increased the percentage of embryos at later developmental stages, but such effects of fluoxetine were absent at pH 7.7. However, despite the modulation of fluoxetine impacts under ocean acidification, control larvae performed better than those exposed to either stressor, alone or in combination. We also observed that pH alone impacted organismal behaviors, as larvae swam slower at reduced pH regardless of fluoxetine exposure. Our findings highlight the need to consider multi-stressor interactions when determining future organismal performance and that multiple metrics are needed to paint a fuller picture of ecological risks.

Uptake, elimination, and toxicokinetics of selected pharmaceuticals in multiple tissues of Nile tilapia (Oreochromis niloticus) exposed to environmentally relevant concentrations

Pharmaceuticals in aquatic environment displayed adverse effects to fish. The effects are usually related to the internal levels of pharmaceuticals accumulated in specific fish tissues. In this study, we investigated the uptake, elimination, and toxicokinetics of six pharmaceuticals, e.g. naproxen (NAX), diclofenac (DCF), ibuprofen (IBU), carbamazepine (CBZ), fluoxetine (FLX), and sertraline (SER), in 11 fish tissues of Nile tilapia. The experiments were conducted in a flow-through system with an 8-day uptake/8-day elimination periods. The fish exposure groups involved the control, single FLX, and mixture of six pharmaceuticals at environmentally relevant concentration of 4 μg/L. FLX and SER showed the maximum concentrations of 145 and 201 ng/g wet weight, respectively, in fish spleen tissue, while NAX and IBU were not detected in any tissue. The mean concentrations for the pharmaceuticals in Nile tilapia tissues generally followed the order: bile> kidney, gut, stomach, liver> brain, gill, spleen> plasma, skin, muscle. The steady-state bioconcentration factors in various tissues generally range at 0.74-437.58 L/kg. The uptake and elimination toxicokinetics illustrated the rapid accumulation and depuration of pharmaceuticals in fish tissues. The results help to understand the internal bioconcentration, tissue distribution, and toxicokinetics of pharmaceuticals in multiple fish biological compartments.

Exposure via biotransformation: Oxazepam reaches predicted pharmacological effect levels in European perch after exposure to temazepam

It is generally expected that biotransformation and excretion of pharmaceuticals occurs similarly in fish and mammals, despite significant physiological differences. Here, we exposed European perch (Perca fluviatilis) to the benzodiazepine drug temazepam at a nominal concentration of 2 µg L^-1 for 10 days. We collected samples of blood plasma, muscle, and brain in a time-dependent manner to assess its bioconcentration, biotransformation, and elimination over another 10 days of depuration in clean water. We observed rapid pharmacokinetics of temazepam during both the exposure and depuration periods. The steady state was reached within 24 h of exposure in most individuals, as was complete elimination of temazepam from tissues during depuration. Further, the biologically active metabolite oxazepam was produced via fish biotransformation, and accumulated significantly throughout the exposure period. In contrast to human patients, where a negligible amount of oxazepam is created by temazepam biotransformation, we observed a continuous increase of oxazepam concentrations in all fish tissues throughout exposure. Indeed, oxazepam accumulated more than its parent compound, did not reach a steady state during the exposure period, and was not completely eliminated even after 10 days of depuration, highlighting the importance of considering environmental hazards posed by pharmaceutical metabolites.

Development of a method for assessing the accumulation and metabolization of antidepressant drugs in zebrafish (Danio rerio) eleutheroembryos

Antidepressant drugs are widely used for the treatment of common mental or other psychiatric disorders such as depression, which affect about 121 million people worldwide. This widespread use has contributed to the input of these pharmaceuticals and their metabolites into the environment. The aim of this work was to develop an analytical method to quantify the most widely used antidepressant drugs, selective serotonin reuptake inhibitors (SSRI), and their main metabolites in the environment. For this, a new and reliable miniaturized extraction method based on dispersive SPE cleanup procedure for extraction of SSRI followed by derivatization with n-heptafluorobutyrylimidazole, and detection by GC-MS was developed. The methodology, including a first-order one-compartment model, was then applied to a bioconcentration study in zebrafish (Danio rerio) eleutheroembryos. The results showed low bioaccumulation of these compounds; however, a biotransformation evidence of the parent compounds into their metabolites was observed after 6 h of exposure. These results indicate the need to integrate metabolic transformation rates to fully model and understand the bioaccumulation patterns of SSRI and their metabolites.

Cytochrome P450-dependent biotransformation capacities in embryonic, juvenile and adult stages of zebrafish (Danio rerio)-a state-of-the-art review

Given the strong trend to implement zebrafish (Danio rerio) embryos as translational model not only in ecotoxicological, but also toxicological testing strategies, there is an increasing need for a better understanding of their capacity for xenobiotic biotransformation. With respect to the extrapolation of toxicological data from zebrafish embryos to other life stages or even other organisms, qualitative and quantitative differences in biotransformation pathways, above all in cytochrome P450-dependent (CYP) phase I biotransformation, may lead to over- or underestimation of the hazard and risk certain xenobiotic compounds may pose to later developmental stages or other species. This review provides a comprehensive state-of-the-art overview of the scientific knowledge on the development of the CYP1-4 families and corresponding phase I biotransformation and bioactivation capacities in zebrafish. A total of 68 publications dealing with spatiotemporal CYP mRNA expression patterns, activities towards mammalian CYP-probe substrates, bioactivation and detoxification activities, as well as metabolite profiling were analyzed and included in this review. The main results allow for the following conclusions: (1) Extensive work has been done to document mRNA expression of CYP isoforms from earliest embryonic stages of zebrafish, but juvenile and adult zebrafish have been largely neglected so far. (2) There is insufficient understanding of how sex- and developmental stage-related differences in expression levels of certain CYP isoforms may impact biotransformation and bioactivation capacities in the respective sexes and in different developmental stages of zebrafish. (3) Albeit qualitatively often identical, many studies revealed quantitative differences in metabolic activities of zebrafish embryos and later developmental stages. However, the actual relevance of age-related differences on the outcome of toxicological studies still needs to be clarified. (4) With respect to current remaining gaps, there is still an urgent need for further studies systematically assessing metabolic profiles and capacities of CYP isoforms in zebrafish. Given the increasing importance of Adverse Outcome Pathway (AOP) concepts, an improved understanding of CYP capacities appears essential for the interpretation and outcome of (eco)toxicological studies.

Toxicological Study on Chiral Fluoxetine Exposure to Adult Zebrafish (Danio rerio): Enantioselective and Sexual Mechanism on Disruption of the Brain Serotonergic System

The increasing number of people with depression worldwide has led to concerns regarding antidepressant contamination in aquatic environments, which could have the risk of negative effects on aquatic organisms. Chirality increases its toxicity potentials. Accordingly, we investigated the negative effects of racemic (rac-), R-, and S-FX at environmental levels (100 ng/L) on the brain serotonergic system in zebrafish (Danio rerio) for 42 days. Additionally, we measured the whole-body concentrations of FX and norfluoxetine (NFX). We found that S-FX exposure disrupted the brain serotonergic system more severely than rac- and R-FX exposure. The mechanism underlying this disruption induced by S-FX was sex-specific, with female zebrafish showing disruption of the serotonin (5-HT) release process but male zebrafish showing disruption of the 5-HT synthesis process. In addition, enantioselective enrichment and biotransformation (R-FX to R-NFX and S-FX to S-NFX) occurred in zebrafish. Sex-specific accumulation was also observed, with higher concentrations in females. Our study provides evidence for enantiomer- and sex-specific effects of FX exposure at biologically relevant concentrations. More broadly, our study demonstrated that SSRI antidepressants, such as FX, can affect aquatic life by causing important shifts in not only their active sites of the serotonin transporter.

New insights into cardiotoxicity induced by chiral fluoxetine at environmental-level: Enantioselective arrhythmia in developmental zebrafish (Danio rerio)

Fluoxetine is frequently detected in aquatic environment, and chronic FLX exposure exhibits adverse effects on aquatic communities. Its chirality makes the adverse effects more complicated. This study aimed at the enantioselective cardiotoxicity in developmental zebrafish induced by racemic (rac-)/S-/R-fluoxetine. The accumulation profiles demonstrated that biotransformation of fluoxetine to norfluoxetine occurred during rac-fluoxetine exposure, with a higher enrichment of S-norfluoxetine than R-norfluoxetine. Heart malformations including pericardial edema, circulation abnormalities, and thrombosis were observed, and enantioselective changes also occurred. According to H&E staining and Masson's trichrome staining, the loose severity of cardiac structure and cardiac fibrosis in rac-norfluoxetine treated group was worse than that in fluoxetine treated groups. Results of toxicity-associated parameters in our homochiral enantiomers' exposure also indicated that the toxicity induced by S-fluoxetine was more severe than R-fluoxetine. Enantioselective arrhythmia in developmental zebrafish after chiral fluoxetine exposure could be caused by myocardial fibrosis, abnormal developmental processes, and the biotransformation of fluoxetine to norfluoxetine could make that worse. Our findings can be used to assess the environmental risk of the two enantiomers of fluoxetine that induce cardiotoxicity in aquatic organisms.

Tissue-specific expression and activity of cytochrome P450 1A and 3A in rainbow trout (Oncorhynchus mykiss)

Piscine cytochrome P450 (CYP) enzymes play an important role in the metabolism of xenobiotics. Xenobiotics often act as inducers of CYP1A1 and CYP3A expression and activity in fish. We compared constitutive mRNA expression of CYP1A1, CYP3A27, and CYP3A45 and catalytic activity of CYP1A (7-ethoxyresorufin-O-deethylation, EROD) and CYP3A-like (benzyloxy-4-trifluoromethylcoumarin-O-debenzyloxylation, BFCOD) enzymes in the following six rainbow trout tissues: liver, gill, heart, brain, intestine, and gonad. mRNA expression and activity were present in all investigated tissues. The CYP1A1 mRNA expression was higher in the liver, gill, heart, and brain compared to gonad and intestine. The intestine was the main site of CYP3A27 and CYP3A45 expression. The highest EROD and BFCOD activity was observed in liver tissue followed in descending order by heart, brain, gill, intestine, and gonad. Such differences might be related to the role of CYP physiological functions in the specific tissue. Rainbow trout exposure to 50 mg/kg of β-naphthoflavone for 48 h resulted in a 7.5- and 5.9-fold increase in liver EROD and BFCOD activity, respectively. In vitro EROD activity inhibition with ellipticine showed tissue-specific inhibition, while ketoconazole decreased BFCOD activity by 50-98 % in all tissues. Further studies are needed to identify all CYP isoforms that are responsible for these activities and modes of regulation.

Do environmentally relevant concentrations of fluoxetine and citalopram impair stress-related behavior in zebrafish (Danio rerio) embryos?

Selective serotonin reuptake inhibitors (SSRIs) have been shown to interfere with various physiological functions of aquatic organisms, yet the neuroactive potential of low concentrations of SSRIs in the aquatic environment is unclear. The current study investigated the effects of fluoxetine and citalopram on the visual motor response (VMR) of 107 h old zebrafish (Danio rerio) embryos. Results document a reduction in stress-related swimming activity of zebrafish embryos at environmentally relevant concentration levels, with fluoxetine being more effective than citalopram. Further experiments were designed to elucidate (1) if the lower neuroactive potential of citalopram is due to differences in uptake kinetics, (2) if the metabolite of fluoxetine, norfluoxetine, contributes to the neuroactive potential of fluoxetine, (3) and how SSRIs and their metabolites interact in equimolar mixtures. At the stage of 120 h, zebrafish embryos accumulate citalopram at significantly lower rates (up to 127 times) than fluoxetine. Moreover, it was demonstrated that norfluoxetine reduces the embryonic VMR similarly to fluoxetine resulting in additive effects of these substances on stress-related behavior in zebrafish embryos. In contrast, the interaction of fluoxetine, norfluoxetine and citalopram varied with test concentrations of the equimolar mixtures. Findings provide evidence that environmentally relevant concentrations of fluoxetine reduce stress-related behavior of zebrafish embryos, while these effects may be enhanced by the interaction of multiple SSRIs and their metabolites in environmental exposure scenarios.

First record of emerging contaminants in sponges of an inhabited island in the Maldives

In the Maldivian islands, the lack of sewage wastewater treatment and an improper landfill enhance the potential hazard of emerging contaminants, including pharmaceuticals and personal care products. In order to analyze the occurrence of emerging contaminants in the marine biota, sponges were collected in two coral reef areas of Magoodhoo island (Faafu), one near the landfill and the other furthest from the island. Caffeine, fluoxetine and norfluoxetine were detected only in the proximity of the landfill, with caffeine showing the highest concentration (28.4 ng/g d.w.), followed by fluoxetine (6.00 ng/g d.w.). Norfluoxetine was below the limit of quantification of 10 ng/g d.w. Nitro xylene, N,N-Diethyl-meta-toluamide and galaxolide were found in both areas, with concentrations of 3.51/6.11/8.54 and <LOQ/1.14/0.62 ng/g d.w., respectively. Due to the vital role of the coral reef for the livelihood and economy of the Maldivian people, attention should be paid to this class of contaminant.