Dual effect of polyaromatic hydrocarbons on sarco(endo)plasmic reticulum calcium ATPase (SERCA) activity of a teleost fish (Oncorhynchus mykiss)

Polycyclic aromatic hydrocarbons (PAHs) are embryo- and cardiotoxic to fish that might be associated with improper intracellular Ca2+ management. Since sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) is a major regulator of intracellular Ca2+, the SERCA activity and the contractile properties of rainbow trout (Oncorhynchus mykiss) ventricle were measured in the presence of 3- and 4-cyclic PAHs. In unfractionated ventricular homogenates, acute exposure of SERCA to 0.1-1.0 μM phenanthrene (Phe), retene (Ret), fluoranthene (Flu), or pyrene (Pyr) resulted in concentration-dependent increase in SERCA activity, except for the Flu exposure, with maximal effects of 49.7-83 % at 1 μM. However, PAH mixture did not affect the contractile parameters of trout ventricular strips. Similarly, all PAHs, except Ret, increased the myotomal SERCA activity, but with lower effect (27.8-40.8 % at 1 μM). To investigate the putative chronic effects of PAHs on SERCA, the atp2a2a gene encoding trout cardiac SERCA was expressed in human embryonic kidney (HEK) cells. Culture of HEK cells in the presence of 0.3-1.0 μM Phe, Ret, Flu, and Pyr for 4 days suppressed SERCA expression in a concentration-dependent manner, with maximal inhibition of 49 %, 65 %, 39 % (P < 0.05), and 18 % (P > 0.05), respectively at 1 μM. Current findings indicate divergent effects of submicromolar PAH concentrations on SERCA: stimulation of SERCA activity in acute exposure and inhibition of SERCA expression in chronic exposure. The depressed expression of SERCA is likely to contribute to the embryo- and cardiotoxicity of PAHs by depressing muscle function and altering gene expression.

The seasonal change of PAHs in Svalbard surface snow

The Arctic region is threatened by contamination deriving from both long-range pollution and local human activities. Polycyclic Aromatic Hydrocarbons (PAHs) are environmental tracers of emission, transport and deposition processes. A first campaign has been conducted at Ny-Ålesund, Svalbard, from October 2018 to May 2019, monitoring weekly concentrations of PAHs in Arctic surface snow. The trend of the 16 high priority PAH compounds showed that long-range inputs occurred mainly in the winter, with concentrations ranging from 0.8 ng L-1 to 37 ng L-1. In contrast to this, the most abundant analyte retene, showed an opposite seasonal trend with highest values in autumn and late spring (up to 97 ng L-1), while in winter this compound remained below 3 ng L-1. This is most likely due to local contributions from outcropping coal deposits and stockpiles. Our results show a general agreement with the atmospheric signal, although significant skews can be attributed to post-depositional processes, wind erosion, melting episodes and redistribution.

Exposure to retene, fluoranthene, and their binary mixture causes distinct transcriptomic and apical outcomes in rainbow trout (Oncorhynchus mykiss) yolk sac alevins

Polycyclic aromatic hydrocarbons (PAHs) are widely spread environmental contaminants which affect developing organisms. It is known that improper activation of the aryl hydrocarbon receptor (AhR) by some PAHs contributes to toxicity, while other PAHs can disrupt cellular membrane function. The exact downstream mechanisms of AhR activation remain unresolved, especially with regard to cardiotoxicity. By exposing newly hatched rainbow trout alevins (Oncorhynchus mykiss) semi-statically to retene (32 µg l^-1; AhR agonist), fluoranthene (50 µg l^-1; weak AhR agonist and CYP1a inhibitor) and their binary mixture for 1, 3, 7 and 14 days, we aimed to uncover novel mechanisms of cardiotoxicity using a targeted microarray approach. At the end of the exposure, standard length, yolk area, blue sac disease (BSD) index and PAH body burden were measured, while the hearts were prepared for microarray analysis. Each exposure produced a unique toxicity profile. We observed that retene and the mixture, but not fluoranthene, significantly reduced growth by Day 14 compared to the control, while exposure to the mixture increased the BSD-index significantly from Day 3 onward. Body burden profiles were PAH-specific and correlated well with the exposure-specific upregulations of genes encoding for phase I and II enzymes. Exposure to the mixture over-represented pathways related to growth, amino acid and xenobiotic metabolism and oxidative stress responses. Alevins exposed to the individual PAHs displayed over-represented pathways involved in receptor signaling: retene downregulated genes with a role in G-protein signaling, while fluoranthene upregulated those involved in GABA signaling. Furthermore, exposure to retene and fluoranthene altered the expression of genes encoding for proteins involved in calcium- and potassium ion channels, which suggests affected heart structure and function. This study provides deeper understanding of the complexity of PAH toxicity and the necessity of investigating PAHs as mixtures and not as individual components.

Salmo trutta is more sensitive than Oncorhynchus mykiss to early-life stage exposure to retene

Salmonids are known to be among the most sensitive fish to dioxin-like compounds (DLCs), but very little is known about the sensitivity of the brown trout (Salmo trutta), which has declined and is endangered in several countries of Europe and Western Asia. We investigated the sensitivity of brown trout larvae to a widespread dioxin-like PAH, retene (3.2 to 320 μg.L^-1), compared to the larvae of a salmonid commonly used in toxicology studies, the rainbow trout (Oncorhynchus mykiss). Mortality, growth, cyp1a induction and the occurrence of deformities were measured after 15 days of exposure. Brown trout larvae showed a significantly higher mortality at 320 μg.L^-1 compared to rainbow trout larvae. While the occurrence of deformities was only significantly increased at 320 μg.L^-1 for the rainbow trout, brown trout larvae displayed pericardial edemas and hemorrhages already at 10 or 100 μg.L^-1. cyp1a induction was increased significantly already at ≥3.2 μg.L^-1 for the brown trout, versus ≥32 μg.L^-1 for the rainbow trout. Least square regression analysis of the concentration-response relationships suggested that S. trutta larvae were at least 2 times more sensitive than O. mykiss larvae for cyp1a induction. The present study suggests that S. trutta larvae are more sensitive than O. mykiss larvae to a potent DLC, retene. As it is possible that S. trutta populations have declined partly because of pollution by DLCs, we recommend generating more data regarding the sensitivity of threatened fish populations, in order to ensure better risk assessment.

Temperature determines the rate at which retene affects trout embryos, not the concentration that is toxic

The toxicity of waterborne retene (7-isopropyl-1-methyl phenanthrene) to post-hatch embryos of rainbow trout (Oncorhynchus mykiss) was assessed at 5 and 11 °C. Survival times of retene-exposed embryos were 70 % longer at 5 °C than at 11 °C, but survival times and LC50 s did not vary when time was expressed as degree-days (thermal units), i.e., at a common stage of development. The size of survivors decreased with increasing retene concentrations, but not with temperature. Retene did not bioconcentrate to any extent (bioconcentration factors < 2) at either temperature, indicating effective biotransformation by embryos. However, concentrations of retene metabolites were slightly higher at 5 °C, suggesting slower excretion rates than at 11 °C. The relative expression of cytochrome P450 proteins (CYP1A) did not vary with temperature but increased with retene concentration, as indicated by cyp1a mRNA concentrations. The induction of CYP1A protein by retene exposure was evident in the vasculature of eye, brain, heart, kidney, liver, gill, mouth, intestine, muscle, and yolk-sac. However, immunohistochemical staining was greater at 5 than at 11 °C for all tissues except liver and muscle. Overall, temperature effects on retene toxicity disappeared when the duration of embryo development and retene exposure were expressed as thermal units (degree-days). Temperature controlled the rate of embryo development and the rate of toxicity (time to a toxic endpoint), but not the concentrations that were toxic.

Oxidative stress, mutagenic effects, and cell death induced by retene

Retene (RET) is the most abundant polycyclic aromatic hydrocarbon (PAH) released upon burning of cellulose, although it is not considered as one of the priority PAHs and is not included for risk assessments by the US Environmental Protection Agency (US-EPA). There are only a few studies concerning the toxic effects of RET. To the best of our knowledge, this study is the first one to examine whether RET, in an environmental concentration, plays a crucial role in the induction of oxidative stress in A549 lung cell line, and its consequence as such as mutagenicity and cell death. Our results revealed that RET was able to significantly decrease cell viability only at 72 h of exposure, increase oxidative stress, mitochondrial membrane potential and mitochondrial contents, leading an increased reactive oxygen species (ROS) production. Mutagenic activity was not detected in Salmonella strains, suggesting that RET does not induce base-pair substitution (TA100), frameshift (TA98 and TA97a) and transition/transversion (TA102) mutations. However, exposure to RET led to a significant increase in micronuclei (MN), nucleoplasmic bridges (NPBs), and nuclear buds (NBUDs) frequency, as well as cell death, mainly due to necrosis. Taken together, the results of our study provide new evidence suggesting that RET promotes oxidative stress, contributes to the processes of genomic instability, and favors necrosis. Thus, we highlight the importance of including RET in routine environmental analyses in the future as a potential risk factor involved in complex diseases and carcinogenesis.

Biomass burning source identification through molecular markers in cryoconites over the Tibetan Plateau

Cryoconite is a dark, dusty aggregate of mineral particles, organic matter, and microorganisms transported by wind and deposited on glacier surfaces. It can accelerate glacier melting and alter glacier mass balances by reducing the surface albedo of glaciers. Biomass burning in the Tibetan Plateau, especially in the glacier cryoconites, is poorly understood. Retene, levoglucosan, mannosan and galactosan can be generated by the local fires or transported from the biomass burning regions over long distances. In the present study, we analyzed these four molecular markers in cryoconites of seven glaciers from the northern to southern Tibetan Plateau. The highest levels of levoglucosan and retene were found in cryoconites of the Yulong Snow Mountain and Tienshan glaciers with 171.4 ± 159.4 ng g^-1 and 47.0 ± 10.5 ng g^-1 dry weight (d.w.), respectively. The Muztag glacier in the central Tibetan Plateau contained the lowest levels of levoglucosan and retene with mean values of 59.8 ng g^-1 and 0.4 ± 0.1 ng g^-1 d.w., respectively. In addition, the vegetation changes and the ratios of levoglucosan to mannosan and retene indicate that combustion of conifers significantly contributes to biomass burning of the cryoconites in the Yulong Snow Mountain and Tienshan glacier. Conversely, biomass burning tracers in cryoconites of Dongkemadi, Yuzhufeng, Muztag, Qiyi and Laohugou glaciers are derived from the combustion of different types of biomass including softwood, hardwood and grass.

Profile of particulate-bound organic compounds in ambient environment of Srinagar: a high-altitude urban location in the North-Western Himalayas

Twenty-four hourly samples of total suspended particulate matter (TSPM) were collected once a week over 17 months in the ambient environment of Srinagar (altitude 1524 m), an urban montane location in the North-Western Himalayas. The samples were analyzed to identify and quantify the presence of diverse organic compounds (OCs) using thermal desorption gas chromatography mass spectroscopy (TD-GCMS). Non-polar organic compounds-n-alkanes, polycyclic aromatic hydrocarbons (PAHs), and molecular tracers (retene and nicotine), were detected in the TSPM samples. Molecular diagnostic ratios, derived from the quantified n-alkanes and PAHs in TSPM, assisted in characterization of the contributing sources. Significant variation in the planetary boundary layer height (meters) with change in season (summer to winter) in this region, also, affected the observed variation in the temporal profile of TSPM-bound OCs. TSPM-bound OCs were predominantly contributed from petroleum and biomass combustion; to a lesser extent from biogenic sources. High concentrations of retene and nicotine, known molecular tracers for coniferous wood combustion and tobacco smoke, respectively, were detected in the winter samples. Seasonal variation in TSPM-bound retene corresponded with the periodicity of biomass burning activity in the region. The benzo(a)pyrene equivalent (BAPE) concentrations, a measure for the carcinogenicity of TSPM-bound PAHs was calculated and the value exceeded the prescribed international standards in winter. This finding poses a major health concern for the inhabitants of this region. High BAPE concentration of PAHs during winter was linked to fossil fuel and biomass combustion, where the prevalent meteorology and topography played a synergistic role.

Vertical distribution of AhR-activating compounds in sediments contaminated by modernized pulp and paper industry

Increased ethoxyresorufin-O-deethylase (EROD) activity is a sensitive biomarker of exposure to the chemicals which activate the aryl hydrocarbon receptor (AhR) and induce the cytochrome P450 system, such as many polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and polychlorinated biphenyls (PCBs). Pulp bleaching was one of the main sources of PCDDs and PCDFs until elemental chlorine free (ECF) and total chlorine free bleaching processes since 1990s have remarkably decreased but not completely eliminate discharges of these chemicals. In addition, historically contaminated sediments may act as a source of these persistent contaminants. In this study, the contamination history and recovery of a watercourse heavily loaded by the chemical wood industry were studied by analyzing PCDDs, PCDFs and PCBs from vertical sediment samples and by measuring hepatic EROD activity from rainbow trout intraperitoneally dosed with the sediment extracts. No PCDDs or PCDFs were found above the chromatographic limit of detection from the study area and only small amounts of PCB congeners 101, 138, 153, and 180 were present. No increased EROD activity was observed in fish indicating the absence of any AhR-activating compounds in the surface sediment, to about 15 cm depth, representing about the last 20 years when kraft pulping and ECF bleaching with activated wastewater treatment have been used. It can be concluded that nowadays organochlorines and other AhR-ligands do not harm the previously heavily polluted watercourse.

Kinetics of mixed function oxygenase induction and retene excretion in retene-exposed rainbow trout (Oncorhynchus mykiss)

The polycyclic aromatic hydrocarbon 7-isopropyl-1-methylphenanthrene (retene) induces mixed function oxygenase (MFO) activity of fish. Bile levels of retene and its metabolite(s) were measured in relation to exposure time, exposure concentration, and induction of MFO activity. Synchronous fluorescence spectrometry provided a rapid means of measuring the amount of retene present in the bile of exposed fish, whereas conventional fluorescence spectrometry was used to quantify the amount of retene metabolites. Based on bile analysis, increased retene exposure resulted in an increased uptake of retene and a curvilinear increase in hepatic MFO activity. Retene was present in the bile within 6 h of initial exposure. However, retene metabolite(s) only appeared in the bile after MFO induction had occurred, 12 h after exposure had commenced, suggesting that MFO activity is required for metabolism. Transfer of fish to clean water after 48 h of exposure resulted in a rapid decrease in the presence of retene and its metabolite(s) in the bile, with a calculated half-life of about 14 h. In vitro additions of retene directly to the ethoxyresorufin O-deethylase assay demonstrated that retene is capable of acting as a competitive inhibitor. Thus, retene contamination of postmitochondrial supernatant (S9 fraction) could result in false-negative results in the MFO assay. The MFO activity in extrahepatic tissues (gills, heart, and kidney) was not significantly induced with retene exposure. Thus, the major site of retene metabolism seems to be in the liver. These results confirm that retene is rapidly taken up, metabolized, and excreted by rainbow trout, and that retene metabolism and excretion are linked to hepatic MFO induction.