Improvements in glass capillary gas chromatographic polychlorobiphenyl analysis

Aroclor misidentification in environmental samples: how do we communicate more effectively between the laboratory and the data user?

Disposal of carbonless copy paper (CCP) paper sludge during the 1960s contaminated a site in the USA with PCBs. Despite historic records of CCP sludge disposal and absence of evidence of any other disposal, a dispute arose among the parties over the source of the PCBs. Aroclor 1242 is well documented as the PCB mixture used in CCP, yet Aroclors 1242, 1248, 1254, and 1260 were reported by the analytical laboratory. How could the PCBs at a single, small site be reported as four different Aroclors? Some claimed that there had to be at least four Aroclors source inputs to the site. Disposal of four different Aroclors at this site would simply defy logic and the historic record. Weathering of the mixtures is part of the story. A larger issue is the conflict between the intent of the USEPA 8082 method to determine the total PCB content in environmental samples to facilitate environmental cleanup and disposal decisions within a regulatory context versus the data users' intent to identify the PCB sources. This inappropriate extension of the data leads to erroneous conclusions. To mitigate problems like this, laboratory analysis requests need to be matched to the intended data usage; conversely, the data must not be over-interpreted beyond the limits of the method. The PCB analysis community needs to develop a better articulation of the limits of Aroclor identification for the broader community that may naïvely assume that if the laboratory reports "Aroclor 1248," then someone must have placed Aroclor 1248 at the site. After all, when a laboratory reports "lead" or "chloroform," those identifications are never in question.

Carcinogenicity of "non-dioxinlike" polychlorinated biphenyls

Complex technical mixtures of polychlorinated biphenyls (PCBs) cause liver and thyroid neoplasms in rodents, whereas very few data are available on the carcinogenic potency of single non-dioxinlike (NDL) PCB congeners. In most genotoxicity assays technical PCB mixtures and individual congeners were inactive, suggesting that PCBs act as indirect, nongenotoxic carcinogens. Various mechanisms, including suppression of apoptosis in preneoplastic cells or inhibition of intercellular communication, have been suggested to be active in liver tumor promotion by PCBs. A decrease in thyroid hormone levels after PCB treatment has been suggested to play a role in the development of thyroid neoplasms in rats; however, other mechanisms may also be involved. Results from a chronic carcinogenicity study in rats indicate that not the dose of total PCBs but the total TCDD or toxic equivalents (TEQs) associated with "dioxinlike" (DL) constituents within a technical mixture are mainly if not exclusively responsible for the development of liver neoplasms in female rats. Quantitative comparison reveals almost identical dose-response curves for the total TEQs in various technical PCB mixtures and for TCDD as inducers of hepatic neoplasms in female rats. Tumor promotion experiments have shown, however, that, after initiation with a genotoxic carcinogen, technical PCB mixtures and individual DL-and NDL-PCBs act as liver tumor promoters in rodents. Based on these data, a weak carcinogenic potency of individual NDL-PCB congeners cannot be excluded. In epidemiological studies, increased mortality from cancers of the liver, gallbladder, biliary tract, gastrointestinal tract, and from brain cancer and malignant melanoma were observed in workers exposed to a series of technical PCB mixtures. A significant association between PCB concentrations in adipose tissue and non-Hodgkins lymphoma was found in another study. While in all human studies mixed exposure to DL-and NDL-PCBs occurred, no comprehensive data are available on the relative contribution of NDL-PCBs to the overall external and/or internal PCB exposure in those cohorts.

Polychlorinated biphenyls in nonaccumulating, century-old sediments: sources, signatures, and mechanism of introduction

This study documents the occurrence of highly chlorinated PCB congeners in stream sediment deposited over 100 years ago. Penta- to heptachlorinated congeners (> 80%) have been found at concentrations up to 78.8 ng/g (dw) in core samples of a small, rural tributary of Lake Ontario. Lower chlorinated congeners and other organochlorine compounds occur sporadically; 210Pb and 137Cs are lacking. The most plausible mechanism is accumulation of dissolved-phase PCBs in permeable sediments adjacent to the creek channel. The similarity between core and air samples collected in the drainage basin suggests derivation from a residual fraction of atmospherically derived PCB congeners.

Congener-specific distribution of polychlorinated biphenyls in brain regions, blood, liver, and fat of adult rats following repeated exposure to Aroclor 1254

Our previous in vitro studies with both isolated organelles and primary neuronal cell cultures found that intracellular signal transduction can be perturbed by some noncoplanar PCBs at exposure levels of </=10 microM. However, it is not clear whether such concentrations are achievable in brain in vivo. Also, the pattern of congener disposition and quantities of the PCB accumulation in tissues of animals exposed to commercial PCB mixtures is not well studied. In the present study, we have conducted PCB congener-specific analysis in different brain regions, liver, blood, and fat of adult male Long-Evans rats dosed orally with Aroclor 1254 (0 or 30 mg/kg/day; once per day, 5 days/week for 4 weeks) in corn oil. Twenty-four hours after the last dose, rats were euthanized, and the brains were removed and dissected to obtain cerebellum, frontal cortex, and striatum. Liver, blood, and fat samples were also collected at the same time. Congener-specific analysis of PCBs was performed by high-resolution gas chromatography with electron capture detection. While PCB concentrations in control rat brain regions were less than 0.02 ppm, total PCB congeners in treated animals accumulated to much higher levels. Total levels in the frontal cortex, cerebellum, and striatum were 15.1 +/- 0.3, 13.1 +/- 1.7, and 8.2 +/- 2.6 ppm, respectively. The levels of PCBs in the fat, liver, and blood were 0.041, 0.002, and 0.001 ppm in control rats and 552, 38.3, and 1.6 ppm in treated rats, respectively. In addition to the differential total uptake between tissues, there was differential accumulation of PCBs with respect to the number of chlorines. In all the tissues, the more lightly chlorinated (tetra- and penta-) congeners accumulated less than their respective proportions in the parent Aroclor 1254 mixture. On the other hand, heavily chlorinated (hexa- to nona-) congeners accumulated more than the proportion of these congeners found in Aroclor 1254 mixture. This shift toward accumulation of heavily chlorinated congeners seems to be more pronounced in the brain than liver and fat. Predominant congeners (5-32% of total PCBs) detected in different brain regions, blood, liver, and fat are: 2,3,3',4',5,6- (no. 163) + 2,2',3,4,4',5- (no. 138) (coeluted); 2,2',4,4',5,5'- (no. 153) + 2, 2',3,3',4,6'- (no. 132) (coeluted); 2,3,3',4,4',5- (no. 156) + 2,2', 3,3',4,4',6- (no. 171) (coeluted); 2,3',4,4',5- (no. 118); 2,2',4,4', 5-(no. 99); and 2,3,3',4,4'- (no. 105). These congeners together accounted for about two thirds of the total PCB load in brain. All these predominant congeners are ortho-substituted and therefore are noncoplanar in nature. The total PCB concentrations accumulated in brain were as high as 50 microM (based on average molecular weight of 326.4 for Aroclor 1254) and, at these concentrations, intracellular second messengers were significantly affected in neuronal cultures and brain homogenate preparations in vitro. These results indicate that concentrations that altered Ca2+ disposition and second messenger systems in vitro are achievable in brain in vivo following repeated exposure.

Decreases in dopamine concentrations in adult, non-human primate brain persist following removal from polychlorinated biphenyls

Adult male non-human primates, Macaca nemestrina, were orally exposed for 20 weeks to 3.2 mg/kg per day of either Aroclor 1016 or Aroclor 1260 made up in corn oil. Following cessation of exposure, the animals were observed for either an additional 24 or 44 weeks. After killing, regional brain concentrations of biogenic amines and polychlorinated biphenyls were determined by high-performance liquid chromatography (HPLC) and gas chromatography (GC), respectively. Brain dopamine (DA) concentrations were significantly decreased, compared to controls, in all polychlorinated biphenyl-exposed animals. Most importantly, in spite of significant decreases in brain polychlorinated biphenyl concentrations observed following removal from exposure (an average decline of 60%), there was no statistically discernible relationship of the changes in brain DA concentrations to either time following removal from polychlorinated biphenyls or brain polychlorinated biphenyl concentrations. These findings demonstrate that sub-chronic exposure of the adult non-human primate to polychlorinated biphenyls results in long-lasting changes in brain DA concentrations.

Neurotoxicity of polychlorinated biphenyls: structure-activity relationship of individual congeners

Neurotoxicity of Polychlorinated Biphenyls: Structure-Activity Relationship of Individual Congeners, Shain, W., Bush, B., Seegal, R. (1991). Toxicol. Appl. Pharmacol. 111, 33-42. Experimental and epidemiological data indicate that polychlorinated biphenyls (PCBs) may function as neurotoxicants. The mechanism(s) of action of PCBs in the brain is not well understood. One reason for our lack of understanding of PCB action in the central nervous system is that, in general, commercial mixtures of PCBs have been used for these experiments. We used a homogeneous cell line, PC12 cells, to investigate the relative potency of 43 individual PCB congeners. The neurotoxicant action of PCB congeners was measured as a decrease in cell dopamine content. We first described the potency of individual congeners; 2,2'-dichlorobiphenyl was the most potent congener (EC50 = 65 microM). The structure-activity relationships described in these experiments indicated that (i) congeners with ortho- or ortho-, para-chlorine substitutions were most potent; (ii) chlorination in a meta position decreased cell dopamine content in ortho-substituted congeners, but had little effect in ortho-, para-substituted congeners; and (iii) increasing congener chlorination did not correlate with a decrease in potency, though total chlorination of a ring appeared to reduce potency. Second, we determined that potency did not correlate with either cellular PCB content or gas chromatographic retention time. Finally, experiments with 2,2'-dichlorobiphenyl indicated that PCBs and not their metabolites were the toxicants. Thus, PCB congeners decrease cell dopamine content by interaction at specific sites that have preference for ortho- or ortho-, para-substituted congeners. The neurotoxic action of PCBs may occur by a different mechanism than PCB hepato- and immunotoxicity since these effects are most sensitive to non-ortho-substituted, dioxin-like, congeners.

Comparison of effects of Aroclors 1016 and 1260 on non-human primate catecholamine function

Adult male non-human primates, Macaca nemestrina, were orally-exposed to corn oil or corn oil containing either Aroclor 1016 or 1260 at doses of 0.8, 1.6 or 3.2 mg/(kg.day) for 20 weeks. Brain concentrations of biogenic amines and individual PCB congeners were determined following exposure. Aroclor 1016 significantly decreased concentrations of dopamine and its metabolites in the caudate, putamen, substantia nigra and hypothalamus but did not alter neurotransmitter or metabolite concentrations in the globus pallidus and hippocampus. Total PCB concentrations ranged from 1 to 5 ppm with only three congeners detected (2,4,4'; 2,4,2',4' and 2,5,2',5') making up, on average, 72%, 18% and 7% respectively of the total residue in brain. There were no discernible differences in the congener make-up between brain regions. Aroclor 1260 reduced dopamine concentrations in the caudate, putamen and hypothalamus but produced no effects in the substantia nigra, globus pallidus or hippocampus. Aroclor 1260 concentrations ranged from 18 to 28 ppm with the highest levels found in the hippocampus. Of the congeners that made up more than 5% of the total residue in brain, all were hexa- and heptachlorinated di-ortho-substituted congeners. There were no discernible differences in congener make-up between brain regions. We conclude that: (1) ortho-substituted non-planar congeners are responsible for the observed changes in neurochemical function; (2) both Aroclor 1016 and Aroclor 1260 decrease dopamine concentrations by similar mechanisms; and (3) based on differences in brain concentrations of Aroclor 1260 congeners compared to Aroclor 1016 congeners, lightly-chlorinated congeners are more effective in reducing central dopamine concentrations than are the more highly chlorinated congeners.

Accumulation of polychlorobiphenyl congeners and p,p'-DDE at environmental concentrations by corn and beans

The uptake of polychlorinated biphenyl (PCB) congeners present at low concentrations in the environment was investigated in leaf composites of four crop species and final fruits at two sites. All four species preferentially accumulated the same eight congeners, although not in the same degree or rank. No bean species demonstrated a significant increase in accumulation over time, and corn significantly reduced its PCB load over time. Mechanisms are suggested for such behavior. Fruits were 100 times less contaminated than plant leaves.

Variations in polychlorinated biphenyl congener composition in eggs of Mediterranean water birds in relation to their position in the food chain

The concentrations of the principal PCB congeners and the SigmaPCB were determined in eggs of eight species of water birds collected in two areas of the Mediterranean region. The results for SigmaPCB levels indicate statistically significant differences between the species; in the Po delta the higher values are for those species which feed mainly on fish. Differences exist between the congeners and their percentages when compared with the total residue. Tetrachlorobiphenyls constitute a larger proportion of the SigmaPCB in Avocet and Black-winged Stilt, two species whose diet consists mainly of invertebrates. The main component in all the species is 22'44'55' and its presence varies between 11.4% in Avocet and 21.2% in Audouin's Gull. It is suggested that there is a link between the uptake of PCBs and the position of the species in the food chain.