Polychlorinated naphthalenes (PCNs) are ubiquitous environmental pollutants that are structurally similar to other polychlorinated diaromatic hydrocarbons (PCDHs), such as polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), and biphenyls (PCBs). Despite being ubiquitous, much less is known about the fate, transport, and biological effects of individual PCN congeners than other PCDHs. The purpose of the current study was to utilize an in vitro assay (H4IIE-luc) to determine potencies relative to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) for 20 individual PCNs (from 75 possible congeners) and 6 Halowax mixtures. H4IIE rat hepatoma cells (H4IIE-Luc), which are stably transfected with an Ah receptor (AhR)-controlled luciferase reporter gene construct, respond specifically to AhR agonists and are thus a reasonable measure of AhR-mediated, or dioxin-like, activity. The most potent congeners were 1,2,3,4,6,7-hexa-CN (PCN 66), 1,2,3,5,6,7-hexa-CN (PCN 67), and 1,2,3,4,5,6,7-hepta-CN (PCN 73), with relative potencies as compared to TCDD of 0.004, 0.001, and 0.001, respectively. Significant structure−activity relationships were observed. For example, lateral substitution is an important determinant of AhR-mediated activity, but not sufficient, as illustrated by the inactivity of 2,3,6,7-tetra-CN to elicit AhR-mediated activity. Relative potencies of the Halowax mixtures with AhR-mediated activity were 0.0089, 0.000038, and 0.0000018 for 1051, 1014, and 1013, respectively. The relative potencies derived from this study were applied to literature-derived data on concentrations of PCN congeners in environmental mixtures to assess the potential contribution of PCNs to total TCDD equivalents (TEQs) in environmentally weathered complex mixtures.

Concentrations and composition of polychlorinated naphthalene (PCN) congeners were determined in soil, sediments, blue crab, striped mullet, and boat-tailed grackle collected near a chlor-alkali plant to determine their congener profile, bioaccumulation properties, and toxic potential. Concentrations of total PCNs as high as 23 µg/ g, dry wt, were found in sediments collected at the marsh contaminated by disposal of wastes from the chloralkali process. The spatial distribution of sediment-PCN concentrations was not related with those observed for polychlorinated biphenyls (PCBs). The PCN congener profile did not resemble those of any technical mixtures. Hepta-and octa-chloronaphthalenes were the most abundant congeners accounting for greater than 50% of the total PCN concentrations in soil and sediments. A characteristic profile of PCNs in samples collected at the chlor-alkali site suggests the formation of chloronaphthalene congeners during chlor-alkali process, as has been suggested for polychlorinated dibenzofurans (PCDFs). Concentrations of total PCNs in biota were 3-5 orders of magnitude less than in sediments. The profile of PCN congeners in biota was predominated by tetra-or penta-chloronaphthalenes, while hepta-and octa-chloronaphthalenes were not detected. Affinity of more chlorinated naphthalene congeners to sediment organic carbon and steric factors that affect membrane permeability have contributed to less bioavailability. The 2,3,7,8-TCDD equivalents (TEQs) estimated for PCNs in sediments and biota were greater than those reported for PCBs, PCDDs, or PCDFs. Our results suggest that the chloralkali process has been an important source of PCNs due to their formation in the process. The contribution of PCNs to dioxin-like toxicity in environmental media near the chlor-alkali process may overwhelm those due to PCBs, PCDDs, or PCDFs.

Polychlorinated naphthalene (PCN) and polychlorinated biphenyl (PCB) congeners were measured in whole body and fillet of fishes collected from Michigan waters, including the Great Lakes, during 1996−1997. PCNs were found in all the fishes analyzed including those from Siskiwit Lake, a remote lake located near the southern shoreline of Isle Royale National Park in Lake Superior. Concentrations of total PCNs in fishes ranged from 19 to 31 400 pg/g, wet wt, and varied depending on sampling location and species. Fishes from the Detroit River contained the greatest concentrations of both PCNs and PCBs. Concentrations of total PCNs in fishes from Michigan waters were significantly correlated with the concentrations of PCBs. As with total PCN concentrations, the profiles of PCN isomer/congener distribution in fishes varied among sampling locations and species. Fishes from the Detroit River contained PCN profile similar to that of Halowax 1014, whereas those from Siskiwit Lake and Lake Superior contained greater proportions of congeners which have great bioaccumulative potential. Estimated concentrations of 2,3,7,8-tetrachlorodibenzo-p-dioxin equivalents (TEQs) of PCNs ranged from 0.007 to 11 pg/g, wet wt. PCN congeners 66/67 and 69 accounted for greater than 80% of the TEQs contributed by PCNs. TEQs contributed by PCBs, estimated based on H4IIE bioassay-derived TEFs, were in the range of 0.06−11 pg/g, wet wt, which were similar to those contributed by PCNs. When international TEFs (I-TEFs) for coplanar PCBs were applied, estimated PCB-TEQs ranged from 0.46 to 79 pg/g, wet wt, which were 5−10 times greater than those that were estimated from H4IIE TEFs. PCB congener 126 contributed greater than 50% of the TEQs contributed by PCBs in all the fishes. Overall, when similarly derived TEFs were used, PCNs contributed 2−57% of the sum of TEQs of PCNs and PCBs.

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Concentrations of polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), naphthalenes (PCNs), biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), and nonylphenol (NP) were measured in a dated sediment core collected from Tokyo Bay, Japan, in order to study the history of contaminant inputs and fluxes. Concentrations of organochlorine compounds measured in this study increased gradually from the beginning of the early 1900s, reached a maximum in the early 1980s, and decreased steadily until the 1990s. The profile of isomer/ congener compositions of PCDDs/DFs and PCNs varied with depth, which suggested that the sources of input of these compounds varied at different periods. The possible changing sources of PCDDs/DFs and PCNs to the environment are discussed in the context of the concentration trends and congener-specific data. The composition of PCB congeners was uniform at the top 40 cm, which corresponded to the period of usage of technical PCB mixtures, suggesting that the major single source of PCBs in sediments was technical preparations. All of the above organochlorines were detected in sediment sections collected at 90 cm depth, which corresponded to the early 1900s, suggesting the occurrence of these compounds in pre-industrial sediments. The vertical profile of PAHs was similar to that found for organochlorines with the highest concentrations occurring in the early 1980s. The vertical profile of NP concentrations was different from those observed for restricted compounds such as PCBs and PAHs. NP concentrations were greater in surface sediments (0-12 cm) than those in subsurface sediments (12-30 cm). In general, the profile of residues of organic compounds reflected production and usage trends of the respective compounds, although there was a time lag of a few years between peak periods of usage and deposition in coastal sediments. Improvements in emission controls in the late 1980s and the early 1990s appear to have been effective in reducing the inputs of organic residues to the environment; however, the concentrations of several organochlorines in surface sediments are still greater than those found in sediments from the 1970s.

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Concentrations of polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), naphthalenes (PCNs), and biphenyls (PCBs) were measured in eggs of double-crested cormorants and herring gulls collected from Michigan waters of the Great Lakes. Concentrations of PCNs in eggs of double-crested cormorants and herring gulls were in the ranges of 380-2400 and 83-1300 pg/g, wet wt, respectively. Concentrations of 2,3,7,8-substituted PCDDs and PCDFs were 10-200 times less than those of PCNs in eggs whereas those of total PCBs (380-7900 ng/g, wet wt) were 3-4 orders of magnitude greater. While the profile of PCB isomers and congeners between double-crested cormorants and herring gulls was similar, the PCN isomer profile differed markedly between these two species. PCN congeners 66/67 (1,2,3,4,6,7/1,2,3,5,6,7) accounted for greater than 90% of the total PCN concentrations in herring gulls, whereas their contribution to total PCN concentrations in double-crested cormorants ranged from 18 to 40% (mean, 31%). The ratios of concentrations of PCDDs to PCDFs were greater in herring gulls than in double-crested cormorants collected from the same locations, suggesting the ability of the former to metabolize PCDF congeners relatively rapidly. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) equivalents (TEQs) contributed by PCNs in double-crested cormorant and herring gull eggs were 2-3% of the sum TEQs of PCBs, PCDDs, PCDFs, and PCNs. PCB congener 126 (3,3',4,4',5-PeCB) accounted for 57-72% of the total TEQs in double-crested cormorant and herring gull eggs.

Concentrations and profiles of tri- through octa-chloro-substituted polychlorinated naphthalene (PCN) congeners were determined in eighteen technical polychlorinated biphenyl (PCB) mixtures including Aroclors, Kanechlors, Clophens, Phenoclors, Sovol, and Chlorofen. PCNs were found in all the PCB mixtures at concentrations ranging from 5.2 to 730 μg/g. Concentrations of PCNs in Aroclor and Kanechlor mixtures were greater than those of polychlorinated dibenzofurans (PCDFs) present as impurities in these technical PCB preparations. Composition of PCN homologues varied among PCB mixtures. In general, highly chlorinated PCB mixtures contained greater percentages of more-chlorinated naphthalene congeners. Concentrations of PCNs varied by 3-fold among three different lots of Aroclor 1254. On the basis of measured concentrations of PCNs in PCB mixtures and global production estimates of PCBs, PCNs emitted from the use of PCBs was estimated to be 169 tons, which is less than 1% of the production of technical PCN mixtures such as Halowaxes. 2,3,7,8-Tetrachlorodibenzo-p-dioxin equivalents (TEQs) contributed by PCNs in technical PCB mixtures were less than those estimated for coplanar PCB congeners and PCDFs.