Distribution of polychlorinated naphthalenes (PCNs) in the whole blood of typical meat animals

Scientometric trends and knowledge maps of global polychlorinated naphthalenes research over the past four decades

Polychlorinated naphthalenes (PCNs) were included in the banned list of the Stockholm Convention due to their potential to provoke a wide range of adverse effects on living organisms and the environment. Many reviews have been written to clarify the state of knowledge and identify the research needs of this pollutant class. However, studies have yet to analyse the scientometric complexities of PCN literature. In this study, we used bibliometric R and vosviewer programs as a scientometric tool to fill this gap by focusing on articles indexed on Web of Science and Scopus databases and those published between 1973 and 2022. A total of 707 articles were published within this period with a publication/author, author/publication, and co-authors/publication ratios of 0.45, 2.19, and 4.86, respectively. Developed countries dominated most scientometric indices (number of publications, citations, and collaboration networks) in the survey period. Lotka's inverse square rule of author productivity showed that Lotka's laws do not fit PCN literature. An annual percentage growth rate of 7.46% and a Kolmogorov-Smirnoff goodness-of-fit of 0.88 suggests that more output on PCNs is likely in years to come. More research is needed from scholars from developing countries to measure the supremacy of the developed nations and to effectively comply with the Stockholm Convention agreement.

Risks for animal and human health related to the presence of polychlorinated naphthalenes (PCNs) in feed and food

EFSA was asked for a scientific opinion on the risks for animal and human health related to the presence of polychlorinated naphthalenes (PCNs) in feed and food. The assessment focused on hexaCNs due to very limited data on other PCN congeners. For hexaCNs in feed, 217 analytical results were used to estimate dietary exposures for food-producing and non-food-producing animals; however, a risk characterisation could not be performed because none of the toxicological studies allowed identification of reference points. The oral repeated dose toxicity studies performed in rats with a hexaCN mixture containing all 10 hexaCNs indicated that the critical target was the haematological system. A BMDL20 of 0.05 mg/kg body weight (bw) per day was identified for a considerable decrease in the platelet count. For hexaCNs in food, 2317 analytical results were used to estimate dietary exposures across dietary surveys and age groups. The highest exposure ranged from 0.91 to 29.8 pg/kg bw per day in general population and from 220 to 559 pg/kg bw per day for breast-fed infants with the highest consumption of breast milk. Applying a margin of exposure (MOE) approach, the estimated MOEs for the high dietary exposures ranged from 1,700,000 to 55,000,000 for the general population and from 90,000 to 230,000 for breast-fed infants with the highest consumption of breast milk. These MOEs are far above the minimum MOE of 2000 that does not raise a health concern. Taking account of the uncertainties affecting the assessment, the Panel concluded with at least 99% certainty that dietary exposure to hexaCNs does not raise a health concern for any of the population groups considered. Due to major limitations in the available data, no assessment was possible for genotoxic effects or for health risks of PCNs other than hexaCNs.

The long-term spatial and temporal distributions of polychlorinated naphthalene air concentrations in Fildes Peninsula, West Antarctica

The knowledge of polychlorinated naphthalenes (PCNs) in the Antarctic atmosphere is quite limited compared to the Arctic. PCNs are a global concern because of their PBT characteristics (i.e., persistent, bioaccumulative, and toxic) and severe and often deadly biological effects on people and other animals. Therefore, the present study used a passive air sampling method to conduct long-term air monitoring of PCNs for almost a decade from 2013 to 2022, specifically on Fildes Peninsula, situated on King George Island, located in West Antarctica. The median sum of mono-CNs to octa-CN concentration (∑75PCNs) in the Antarctic atmosphere was 12.4 pg/m3. In terms of homologues, mono-CNs to tri-CNs predominated. Among these, the prevalent congeners observed were PCN-1 and PCN-2, originating from mono-CNs, followed by PCN-5/7 from di-CNs, and PCN-24/14 from tri-CNs, respectively. Between 2013 and 2022, the total levels of PCNs were found to have decreased approximately fourfold. Ratio analyses and principal component analysis (PCA) showed that the long-range atmospheric transport and combustion-related sources as the potential PCN sources in the study area. This paper provides the most up-to-date temporal trend analysis of PCNs in the Antarctic continent and is the first to document all 75 congeners (mono-CNs to octa-CN homologue groups).

Burden levels of polychlorinated dibenzo-p-dioxins, dibenzofurans, and polychlorinated biphenyls in typical edible meat animals

The concentrations and distributions of polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and polychlorinated biphenyls (PCBs) in the whole blood and meat of eight typical edible animals (chicken, donkey, horse, cattle, rabbit, sheep, duck, and pig) were illustrated. Total concentrations of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and PCBs (on a basis of liquid volume) in animal bloods were 142-484 pg/L and 46-62 ng/L, respectively. Total concentrations of PCDD/Fs and PCBs (on a basis of dry weight (dw) and lipid weight (lw)) in animal meat samples were 0.47-1090 pg/g dw (0.47-4513 pg/g lw) and 7.2-23 ng/g dw (10-776 ng/g lw), respectively. TEQs for both PCDD/Fs and PCBs in animal blood and meat samples were (67 ± 27) pg/L and (5.3 ± 14) pg/g dw (24 ± 56 pg/g lw), respectively. Besides, the dietary intakes of PCDD/Fs and PCBs were also estimated. Chicken and pig contributed more TEQs than other animals. Chicken contributed the most (95%) with high toxicity, followed by pig (3.4%) with high consumption. The dietary intake of chicken might pose risks to consumers who prefer to eat chicken products, who should comprehensively consider the essential nutrients and contaminants in food during dietary intake.

Concentration and risk assessment of PCNs in green tea in different locations in China

Polychlorinated naphthalenes (PCNs) were added to the Stockholm Convention list of persistent organic pollutants in 2015. PCNs are mainly unintentionally produced during industrial processes nowadays, and can be widely found in environmental media and foodstuffs. Dietary intake is the primary pathway for human exposure to PCNs. PCNs in different categories of foodstuffs have been reported. However, little information on PCN concentrations in green tea, a popular beverage worldwide is available. In this study, all 75 PCN congener concentrations and distributions in green tea samples (n = 102) from 11 regions in China were determined, and risk assessment of human exposure to PCNs through tea consumption was conducted. The PCN concentrations in all the green tea samples were 3.62-175 pg/g dry weight (mean 36.1 pg/g dry weight). Similar PCN homolog and congener profiles were found in green tea samples from different areas. The dominant PCN homologs in all of the green tea samples were di-CNs, tetra-CNs, and tri-CNs. No direct relationships were found between PCN emission sources and PCN concentrations in the green tea samples. The brewing technique could affect the PCN concentrations and homolog profiles in tea leaves. PCNs in green tea from China were found to pose little risk to humans.

The aryl hydrocarbon receptor: A predominant mediator for the toxicity of emerging dioxin-like compounds

The aryl hydrocarbon receptor (AHR) is a member of the basic helix-loop-helix/Per-ARNT-Sim (bHLH-PAS) family of transcription factors and has broad biological functions. Early after the identification of the AHR, most studies focused on its roles in regulating the expression of drug-metabolizing enzymes and mediating the toxicity of dioxins and dioxin-like compounds (DLCs). Currently, more diverse functions of AHR have been identified, indicating that AHR is not just a dioxin receptor. Dioxins and DLCs occur ubiquitously and have diverse health/ecological risks. Additional research is required to identify both shared and compound-specific mechanisms, especially for emerging DLCs such as polyhalogenated carbazoles (PHCZs), polychlorinated diphenyl sulfides (PCDPSs), and others, of which only a few investigations have been performed at present. Many of the toxic effects of emerging DLCs were observed to be predominantly mediated by the AHR because of their structural similarity as dioxins, and the in vitro TCDD-relative potencies of certain emerging DLC congeners are comparable to or even greater than the WHO-TEFs of OctaCDD, OctaCDF, and most coplanar PCBs. Due to the close relationship between AHR biology and environmental science, this review begins by providing novel insights into AHR signaling (canonical and non-canonical), AHR's biochemical properties (AHR structure, AHR-ligand interaction, AHR-DNA binding), and the variations during AHR transactivation. Then, AHR ligand classification and the corresponding mechanisms are discussed, especially the shared and compound-specific, AHR-mediated effects and mechanisms of emerging DLCs. Accordingly, a series of in vivo and in vitro toxicity evaluation methods based on the AHR signaling pathway are reviewed. In light of current advances, future research on traditional and emerging DLCs will enhance our understanding of their mechanisms, toxicity, potency, and ecological impacts.

An assessment of the estrogenic and androgenic properties of tetra- and hexachloronaphthalene by YES/YAS in vitro assays

Many persistent organic pollutants (POPs) exhibit endocrine disrupting activity but studies on some POPs, e.g., polychlorinated naphthalenes (PCNs), are very scarce. The present study investigates the (anti)estrogenic and (anti)androgenic activities of 1,2,3,5,6,7-hexachloronaphthalane (PCN67) and 1,3,5,8-tetrachloronaphthalene (PCN43) using the yeast estrogen and androgen reporter bioassays. Among the tested substances, antiestrogenic response was only shown by PCN67. The strongest inhibition of estrogenic activity (up to 17.4%) was observed in the low concentration ranges (5 pM - 0.5 nM) in the presence of 1.5 nM 17β-estradiol. Both tested compounds showed partial estrogenic activity with a hormetic-type response. However, both studied chemicals showed strong antiandrogenic effects: their potency in the presence of 100 nM 17β-testosterone for PCN43 (IC50 = 2.59 μM) and PCN67 (IC50 = 3.14 μM) was approximately twice that of the reference antiandrogen flutamide (IC50 = 6.14 μM). It cannot be excluded that exposure to PCNs, together with other endocrine disrupting chemicals (EDCs), may contribute to the deregulation of sex steroid hormone signaling.

Hexachloronaphthalene Induces Mitochondrial-Dependent Neurotoxicity via a Mechanism of Enhanced Production of Reactive Oxygen Species

Hexachloronaphthalene (PCN67) is one of the most toxic among polychlorinated naphthalenes. Despite the known high bioaccumulation and persistence of PCN67 in the environment, it is still unclear to what extent exposure to these substances may interfere with normal neuronal physiology and lead to neurotoxicity. Therefore, the primary goal of this study was to assess the effect of PCN67 in neuronal in vitro models. Neuronal death was assessed upon PCN67 treatment using differentiated PC12 cells and primary hippocampal neurons. At 72 h postexposure, cell viability assays showed an IC₅₀ value of 0.35 μg/ml and dose-dependent damage of neurites and concomitant downregulation of neurofilaments L and M. Moreover, we found that younger primary neurons (DIV4) were much more sensitive to PCN67 toxicity than mature cultures (DIV14). Our comprehensive analysis indicated that the application of PCN67 at the IC₅₀ concentration caused necrosis, which was reflected by an increase in LDH release, HMGB1 protein export to the cytosol, nuclear swelling, and loss of homeostatic control of energy balance. The blockage of mitochondrial calcium uniporter partially rescued the cell viability, loss of mitochondrial membrane potential (ΔΨ_m), and the overproduction of reactive oxygen species, suggesting that the underlying mechanism of neurotoxicity involved mitochondrial calcium accumulation. Increased lipid peroxidation as a consequence of oxidative stress was additionally seen for 0.1 μg/ml of PCN67, while this concentration did not affect ΔΨ_m and plasma membrane permeability. Our results show for the first time that neuronal mitochondria act as a target for PCN67 and indicate that exposure to this drug may result in neuron loss via mitochondrial-dependent mechanisms.

Temporal trends in polychlorinated naphthalene emissions from sintering plants in China between 2005 and 2015

The Chinese Government has established stringent policies since 2005 to control SO₂, particulate matter, and NO_x emissions from sintering plants with the aim of tackling severe air pollution in China. Notably, sintering is also important sources of polychlorinated naphthalenes (PCNs), but it is not clear whether the air pollution control policies have led to decreased PCN emissions. In this study, the PCN concentrations in 144 stack gas, 87 discarded fly ash, and 24 desulfurization by-product samples from 24 Chinese sintering plants were determined. This study revealed that desulfurization processes decreased PCN emissions by 47.2%-72.2%. However, these PCNs were not completely eliminated, and transformed to desulfurization by-product. PCN emission in such previously ignored solid residues, including of desulfurization by-product and fine particles, produced in the process of cutting down air pollutants emissions from Chinese sintering plants between 2005 and 2015 was found contained 324 kg, and these residues therefore need to be managed better than currently. Furthermore, PCN concentrations were higher from produced in old plants than produced in new plants, so it is necessary to increase the rate at which out-of-date sintering plants are eliminated. Phasing out old sintering processes decreased total PCN emissions in China by 1549 kg between 2005 and 2015.

Prenatal toxicity and maternal-fetal distribution of 1,3,5,8-tetrachloronaphthalene (1,3,5,8-TeCN) in Wistar rats

1,3,5,8-tetrachloronaphthalene (1,3,5,8-TeCN) is a Persistent Organic Pollutant (POP) that belongs to the group of polychlorinated naphthalenes (PCNs). The aim of the study was to investigate the maternal-fetal distribution and prenatal toxicity of 1,3,5,8-TeCN after its administration to pregnant Wistar rats during organogenesis. Radiolabeled 1,3,5,8-tetrachloronaphthalene-[ring-U-³H] was given by gavage at a dose of 0.3 mg per dam to evaluate its tissue distribution, and that of unlabeled 1,3,5,8-TeCN, at daily doses of 0.3, 1.0 or 3.0 mg kg b.w.^-1 to assess prenatal toxicity. After a single administration of 1,3,5,8-TeCN, the highest concentration was detected in maternal adipose tissue. The concentration in the brain, uterus, kidneys, adrenals, ovaries, lungs and liver established in dams were two to nine times higher than in the maternal blood. 1,3,5,8-TeCN penetrated the blood-brain-barrier and the placenta. The results obtained from developmental toxicity indicate that 1,3,5,8-TeCN did not cause maternal toxicity and was not embryotoxic or teratogenic. However, fetotoxic effects were observed after non-toxic doses for dams (1.0 and 3.0 mg∙b.w.^-1·day^-1). 1,3,5,8-TeCN did not induce congenital skeletal defects but increased the number of fetuses with sternum ossification delay. After a dose of 3.0 mg kg b.w.^-1·day^-1, significantly more fetuses were found with enlargement of the renal pelvis: unilateral in female offspring and bilateral in male offspring. At the doses used, 1,3,5,8-TeCN, unlike hexachloronaphthalene, was not a CYP1A1 inducer.

Polychlorinated naphthalene concentrations and distribution in feed raw materials

Concentrations and patterns of 75 PCN congeners in feed raw materials of animal and plant origin were investigated. Six types of feed raw materials of animal origin and three types of feed raw materials of plant origin from China were collected in 2016. The total concentrations of PCNs in the collected materials ranged from 147 to 1009 ng kg-1, with the highest occurring in fish meal. The mean PCNs concentration in feed raw materials of animal origin (551 ng kg-1) was higher than in those of plant origin (294 ng kg-1). Additionally, lower chlorinated PCNs were the main homologues in raw feed materials, while Di-CNs were the predominant homologues in all samples (mean: 53%), followed by tri-CNs (mean: 28%). The most abundant congeners were CN5/7 and 24/14. Additionally, the toxicity equivalencies (TEQs) of PCNs in the feed raw materials ranged from 0.010 to 0.046 ng TEQ kg-1, with the highest TEQ concentrations of PCNs detected in gluten meal. Together, CN5/7, 66/67, 65/70, and 73 contributed approximately 64% of the total PCN TEQs in raw feed materials. Concentrations of polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and polychlorinated biphenyls (PCBs) in the feed raw materials were detected to compare the TEQ distribution of those dioxin-like compounds. The mass concentrations of PCNs were 1-3 orders of magnitude higher than those of PCDD, PCDFs and PCBs, while the TEQ concentrations of PCNs contributed 2.0%-6.5% of the total TEQs of PCNs, PCDDs, PCDFs and PCBs in the feed raw materials.