Differential Effects of Two Lots of Aroclor 1254: Congener-Specific Analysis and Neurochemical End Points

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Environmental Health Perspectives Volume 109, Number 11, November 2001

Differential Effects of Two Lots of Aroclor 1254: Congener-Specific Analysis and Neurochemical End Points

Prasada Rao S. Kodavanti,¹ Narayanan Kannan,² Nobuyoshi Yamashita,³ Ethel C. Derr-Yellin,¹ Thomas R. Ward,¹ Deborah E. Burgin,^4,5 Hugh A. Tilson,¹ and Linda S. Birnbaum⁴

¹Neurotoxicology Division, National Health and Environmental Effects Research Laboratory, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina, USA; ²Department of Marine Chemistry, University of Kiel, D24105, Kiel, Germany; ³National Institute for Resources and Environment, Hydrospheric Environmental Protection Department, Tsukuba, Japan; ⁴Experimental Toxicology Division, National Health and Environmental Effects Research Laboratory, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina, USA; ⁵Curriculum in Toxicology, University of North Carolina, Chapel Hill, North Carolina, USA

Abstract

Aroclor 1254 is a widely studied commercial polychlorinated biphenyl (PCB) mixture which, by definition, contains 54% chlorine by weight. Recent reports indicate substantial differences in the congener composition among Aroclor lots and hence their biologic effects. We designed the current study to compare the effects of two lots of Aroclor 1254 (lots 6024 and 124-191) . We analyzed these two lots for PCB congeners, polychlorinated dibenzofurans (PCDFs) , polychlorinated naphthalenes (PCNs) , and polychlorinated dibenzodioxins (PCDDs) . We used previously established techniques for analyzing intracellular Ca²⁺ buffering and protein kinase C (PKC) translocation to test their biologic activity in neuronal preparations. PCB congener-specific analysis indicated that ortho and non-ortho congeners in these two lots varied in their percent contribution. Among all congeners, the percentages of non-ortho congeners (PCBs 77, 81, 126, and 169) were higher in lot 6024 (2.9% of total) than in lot 124-191 (0.02% of total) . We detected no dioxins in these two lots (< 2 ppb) . Although there are some differences in the congener composition, total PCNs were similar in both lots: 171 ppm in lot 6024 and 155 ppm in lot 124-191. However, total PCDFs were higher in lot 6024 (38.7 ppm) than in lot 124-191 (11.3 ppm) . When we tested these two Aroclors on Ca²⁺ buffering and PKC translocation in brain preparations, the effects were significantly different. Although lot 124-191 was more potent on PKC translocation than lot 6024, lot 6024 was slightly more active on Ca²⁺ buffering than lot 124-191. These effects could not be attributed to the differences in the percentage of non-ortho congeners or PCDFs because they were inactive on these two parameters. The effects could not be attributed to PCNs because the levels were almost similar. The effects seen with two lots of Aroclor 1254 in neuronal cells were also not predicted based on the TCDD toxic equivalents (TEQs) , although TEQs predicted the effects on ethoxyresorufin-O-deethylase (EROD) or methoxyresorufin-O-deethylase (MROD) activities. It is possible that the differential effects seen in neuronal cells could be caused by differences in the composition of ortho-congeners in these two mixtures, because PCBs with ortho-lateral substitutions can exhibit different activities on the selected neurochemical end points. Because of these differential effects with different lot numbers, the composition of Aroclor mixtures used in investigations should be disclosed. Key words: Aroclor 1254, dioxins, polychlorinated biphenyls, protein kinase C, toxic equivalents. Environ Health Perspect 109:1153-1161 (2001) . [Online 5 November 2001]

http://ehpnet1.niehs.nih.gov/docs/2001/109p1153-1161kodavanti/ abstract.html

Address correspondence to P.R.S. Kodavanti, Neurotoxicology Division, MD 74B, National Health and Environmental Effects Research Laboratory, U.S. Environmental Protection Agency, Research Triangle Park, NC 27711, USA. Telephone: (919) 541-7584. Fax: (919) 541-4849. E-mail: kodavanti.prasada@epa.gov
We thank J. Cogliano of NCEA and N. Walker of NIEHS for their comments on the earlier version of this manuscript.
D.E.B. was supported in part by the National Institute of Environmental Health Sciences under T32-ES07126 and by the U.S. EPA under cooperative agreement CT902908. Preliminary findings presented in this article were presented at the 38th Annual Meeting of the Society of Toxicology, New Orleans, Louisiana, 14-18 March 1999.
The research described in this article has been reviewed by the National Health and Environmental Effects Research Laboratory, U.S. EPA, and approved for publication. Approval does not signify that the contents necessarily reflect the views and policies of the agency nor does mention of tradenames or commercial products constitute endorsement or recommendation for use.
Received 18 December 2000 ; accepted 2 May 2001.

Introduction

Polychlorinated biphenyls (PCBs) belong to a large group of halogenated aromatic hydrocarbons and consist of 209 theoretically possible congeners with different numbers and positions of chlorines (1,2). These compounds were commercially produced as Aroclor mixtures in the United States by the chlorination of biphenyl, which produces technical mixtures containing a given chlorine content depending on the duration of the chlorination process. Although all 209 congeners can be synthesized, the reaction conditions in the commercial processes favor certain substitution reactions leading to particular composition of the technical mixtures, which are identified by the weight percentage of chlorine content. For example, Aroclor 1254 contains 54% chlorine by weight, as indicated by the last two digits in the numeric designation (1-5).

These compounds were used widely in industry as heat transfer fluids, hydraulic lubricants, dielectric fluids for transformers and capacitors, flame retardants, plasticizers, and sealants and in carbonless copy paper because of their chemical and thermal stability, dielectric properties, and miscibility with organic compounds. These same properties have now contributed to their ability to cause environmental and human health problems (6-9). PCBs are distributed throughout the entire ecosystem including soil, air, and water (10). They are also highly likely to bioaccumulate in the food chain because of their lipophilicity, and they therefore belong to a class of environmental chemicals called persistent bioaccumulative toxicants (PBTs) (11).

PCBs have a wide range of effects in humans, including chloracne, diverse hepatic effects, decreased birth weight in the offspring of occupationally exposed mothers, decreased pulmonary function, eye irritation, subtle endocrine disturbances, cancer, and learning and memory deficits (10-13). Several of these effects have also been demonstrated in animals during adult and developmental exposure to commercial PCB mixtures such as Aroclor 1254 (6,7,9,11,14,15). In animal models, some individual PCB congeners and commercial PCB mixtures have shown tumor-promoting activity (16). The information from these animal studies with commercial PCB mixtures has been used in the risk/exposure assessment of PCBs and related environmental chemicals (2,15). However, recent reports using high-resolution gas chromatography (HRGC) indicate substantial differences in the congener composition among Aroclor lots (17,18); hence their biologic effects could be different. Toxicity studies with Aroclor 1254 have produced varied results (19,20), but these differences were attributed to the animal species or dosing paradigm rather than to the composition of Aroclor 1254. We designed the current study to study the effects of two lots of Aroclor 1254 (lots 6024 and 124-191) obtained from AccuStandard (New Haven, CT, USA) on the neurochemical end points that were previously reported to be sensitive to PCBs in neuronal preparations (21-23) and to compare the effects with the PCB congener composition and other contaminants in these two lots of Aroclor 1254. These two lots of Aroclor 1254 have been used widely by investigators for the last several years.

Materials and Methods

Chemicals. Aroclor 1254 (> 99% purity) with lot numbers 6024 and 124-191 were purchased from AccuStandard. For neurochemical experiments, we prepared stock solutions of two Aroclor 1254 lots by dissolving them in dimethyl sulfoxide (DMSO). A 2-µL aliquot of stock solution (different concentrations) was added to the buffer to yield the desired final concentrations. DMSO (2 µL/mL) had no significant effect either on ⁴⁵Ca²⁺ uptake or ³H-phorbol ester binding.

Animals. Timed pregnant female (13 days of gestation) and adult male (90-120 days) Long-Evans rats were obtained from Charles River Laboratory. Pregnant dams were housed individually and adult rats were housed two per cage in

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Last Updated: November 5, 2001

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