The effect of exposure route on the distribution and excretion of hexachloronaphthalene in rats

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.

Comprehensive Evaluation of Dietary Exposure and Health Risk of Polychlorinated Naphthalenes

Intake from food is considered an important route of human exposure to polychlorinated naphthalenes. To our knowledge, several studies have quantified dietary exposure but only in European countries and measuring only a few of the 75 congeners. In addition, the influence of source diversity on human exposure has seldom been assessed. We analyzed 192 composite food samples composed of 17,280 subsamples from 24 provinces in China to measure the concentrations of polychlorinated naphthalenes and estimate their daily intake and potential health risks on a national scale. The estimated cancer risk was in the range of 6.8 × 10^-8 to 4.6 × 10^-7. We compared our findings for 75 congeners with reports in the literature that quantified only 12 congeners. We estimate that these 12 congeners contribute only approximately 4% to the total mass daily intake of polychlorinated naphthalenes and 70% to the total toxic equivalent quantity, indicating underestimation of dietary exposure. The contributions of combustion-associated congeners to the total concentrations of polychlorinated naphthalenes were in the range of 31-52%, suggesting that the ongoing unintentional release of these compounds from industrial thermal processes is an important factor in polychlorinated naphthalene contamination and human exposure in China.

Burden and Risk of Polychlorinated Naphthalenes in Chinese Human Milk and a Global Comparison of Human Exposure

Polychlorinated naphthalenes (PCNs) are carcinogenic contaminants. Residues from historical production and ongoing unintentional releases from industrial thermal sources have led to the ubiquitous presence of PCNs in the environment. Our previous study has revealed that unintentional releases may be the main sources of PCNs in human milk from China. However, an assessment of PCN burden in human milk and exposure differences between historical residues and unintentional release exposure has not been conducted. In this study, we performed the first comparison of human exposure to PCNs and evaluated the differences between the estimated health risks from historical residues and unintentional releases. Three characteristic PCN congener patterns found in Chinese human milk specimens collected from 100 cities/counties can be considered characteristic of PCN exposures in regions with unintentional industrial releases as the main PCN sources. The health risk assessment suggested potential noncarcinogenic health effects in infants aged 0-6 months. The hazard index calculated for infants in Sweden indicates a strong impact of historical residues that nonetheless decreases over time, and a comparison of the hazard indices calculated for China and Ireland suggests that ongoing unintentional formation and release of PCNs from industrial processes should be a matter of public health concern.

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.

Developmental toxicity of hexachloronaphthalene in Wistar rats. A role of CYP1A1 expression

Hexachloronaphthalene (HxCN) is one of the most toxic congeners of polychlorinated naphthalenes (PCNs). This study assesses the prenatal toxicity of HxCN after daily administration at doses of 0.1-1.0mg/kg b.w. to pregnant Wistar rats during organogenesis. We evaluated also the expression of CYP1A1 mRNA and protein in the livers of dams and fetuses, as well as the placenta. The results indicate that 0.3mg/kg b.w. was the lowest HxCN toxic dose for dams (LOAEL) while a dose of 0.1mg/kg b.w. was sufficient to impair the intrauterine development of embryos/fetuses without maternal toxicity. Regardless of the applied dose, HxCN generated embryotoxic effects. Dose-dependent fetotoxic effects were associated with HxCN exposure. HxCN was found to be a strong inducer of maternal and fetal CYP1A1. Expression of CYP1A1 mRNA in the placenta appears to be the most sensitive marker of HxCN exposure.

The toxicological effects of halogenated naphthalenes: a review of aryl hydrocarbon receptor-mediated (dioxin-like) relative potency factors

There is no doubt that chloronaphthalenes (PCNs) and their brominated counterparts (PBNs) are dioxin-like compounds, but there is less evidence for mixed bromo/chloronaphthalenes (PXNs). In this article we review information relating to the dioxin-like potency of PCNs and PBNs obtained in vivo, in vitro, and in silico. The aim was to help and improve the quality of data when assessing the contribution of these compounds in the risk analysis of dioxin-like contaminants in foods and other sample types. In vivo and in vitro studies have demonstrated that PCN/PBN congeners are inducers of aryl hydrocarbon hydroxylase, ethoxyresorufin O-deethylase, and luciferase enzymes that are features specifically indicative of planar diaromatic halogenated hydrocarbons such as dioxin and dioxin-like compounds. PCNs in the environment are of multisource origin. The limited data on PBNs in the environment suggest that these also appear to originate from different sources. The toxicological data on these compounds is even scarcer, most of it directed toward explaining the exposure risk from accidental contamination of feed with the commercial PBN containing product, Firemaster BP-6. The occurrence of PBNs and PXNs is possible as ultra-trace environmental and food-chain contaminants produced at least from combustion processes at unknown concentrations. Available toxicological and environmental data enable a focus on PCNs as dioxin analogues to an extent that specific local or regional environmental influences could result in a risk to human health. There is the possibility that they may act synergistically with the better-known classic dioxin and other dioxin-like compounds. PBNs and PXNs are much less studied than the dioxins, but are known to be products of anthropogenic processes that contaminate the environment. A continuously increasing use of bromine for manufacture of brominated flame retardants over the past three decades is anticipated as a stream of "brominated" wastes, that when degraded (combusted), will release PBNs and PXNs. This calls for advanced analytical methods and greater interest toxicologically to understand and control pollution and exposure by PBNs and PXNs. Particular congeners of bromonaphthalene in single studies were found to be much more toxic than their chlorinated counterparts. In addition, brominated/chlorinated naphthalenes also seem to be more potent toxicants than PCNs. About 20% of PCN congeners exhibit a dioxin-like toxicity with relative potencies varying between around 0.003 and 0.000001, but additional and more rigorous data are needed to confirm these figures. Recent food surveys have estimated a small but relevant human exposure to these compounds in foods, giving an additional source of dioxin-like toxicity to those compounds already covered by the World Health Organization-Toxic Equivalency Factors (TEFs) scheme. Given the additivity of response postulated for other dioxin-like compounds, it would seem unwise to ignore this additional contribution. Few data available showed that PBN congeners also exhibit a dioxin-like toxicity and are even more potent than PCN congeners, but the relative potency values were not derived for them until now. There are no toxicological data available for PXNs.