PCB metabolism

Sipes, I.G. and R.G. Schnellmann. 1987. Biotransformation of PCBs metabolic pathways and mechanisms. Pages 97-110 in S. Safe (ed.). Polychlorinated Biphenyls (PCBs) Mammalian and Environmental Toxicology. Environ. Toxin Ser. 1. Springer-Verlag, New York. 

Metabolism. There is a paucity of information on PCB metabolism in fish. With the exception of one study of one study (25) metabolites of PCBs in fish have not been identified other than to say they were more polar than the parent compound (26,27,28,29). Also while effect of degree of chlorination on PCB metabolism in fish has been studied (26) effect of chlorine position has not. What is known is that fish in general metabolize PCBs at a slow rate in comparison to mammalian species (29,30,31) and that rate of metabolism appears to be inversely related to degree of chlorination (20,26). Table IV shows percentage of radioactivity... 

Effect of Degree of Chlorination on PCB Metabolism in Green Sunfish3... 

Along with degree of chlorination another determinant of PCB metabolism in fish is species. Green sunfish and goldfish rapidly metabolize 2,2, 5-trichlorobiphenyl whereas bullheads and rainbow trout metabolize it slowly (26,29). There is little evidence for PCB metabolism in brook trout fed 4-chloro-, 4,4 -dichloro-, 2,2, 5,5 -tetrachloro- or 2,2, 4,4, 5,5 -hexachloro-biphenyl (31) and this was confirmed in rainbow trout by less than 1% of 2,2, 5,5 -tetrachlorobiphenyl accumulated being recovered as polar metabolites (25). 

The main organ involved in PCB metabolism and excretion in fish is the liver. Metabolism of PCBs in fish liver homogenates has been demonstrated (29,30,32) and PCB metabolites are excreted into bile (25,28,34). What is not known is extent to which PCB metabolites excreted in bile are eliminated in feces. Also the role of kidneys, gills, intestine and skin in PCB elimination in fish has not been fully elucidated. The only study on urinary excretion of PCBs was in dogfish sharks and revealed that urine was not a major route of elimination (28). 

Bedard, D.L., Haberl, M. L., May, R.J. Brennan, M.J. (1987a). Evidence for novel mechanisms of PCB metabolism in Alcaligenes eutrophus H850. AppliedandEnvironmental Microbiology, 53, 1103-12. 

Within the group of PCB congeners, examples of both types of substrates can be found. The number and the position of the chlorines in the PCB molecule determine its three-dimensional structure and its reactivity. Four general rules for PCB metabolism have been suggested 66,20... 

In summary, the number and the positional substitution of chlorine atoms determines the pathway and the susceptibility to PCB metabolism. PCB congeners with 2,5-dichloro- or 2,3,6-trichloro-substituted phenyl rings form persistent MeS02-substituted metabolites, but also hydroxylated metabolites. These MeS02-PCBs are accumulated in adipose tissue and/or selectively retained in tissues. PCB congeners that are less susceptible to metabolism, possess five or more chlorine atoms and no adjacent, chlorine-unsubstituted meta-para-positions, can be metabolized to hydroxylated metabolites that may be retained in blood. 

OJ -< O o Wistar rats (male) PCB metabolism parent + metabolite levels in liver, blood, lung, [90,164]... 

Borlakoglu JT, Walker CH. 1989. Comparative aspects of congener specific PCB metabolism. Eur J Drug Metab Pharmcokinet 14 127-131. 

Brown JF. 1994. Determination of PCB metabolic, excretion, and accumulation rates for use as indicators of biological response and relative risk. Environ Sci Technol 28 2295-2305. 

Sipes G, Schnellmann RG. 1987. Biotransformation of PCBs Metabolic pathways and mechanisms. In Safe S, ed. Environmental toxic series, Vol. 1. Polychlorinated biphenyls (PCBs) Mammalian and environmental toxicology. Secaucus, NJ Springer-Verlag, Inc. 

First, Dr. Tryphonas discussed the Submitters assertion that rhesus monkeys are more sensitive to PCBs than humans. Noting that this comment on sensitivity is apparently based on information documented in an abstract ( Gillis and Price, 1996 ), and not in the peer-reviewed literature. Dr. Tryphonas questioned the validity of the assertion. On another note. Dr. Tryphonas did not agree that pathways for PCB metabolism differ qualitatively between rhesus monkeys and humans, as one Submitter suggests. In fact, according to research carried out in monkeys (Arnold et al. 

Discuss the toxicological parameters of PCBs in animal and human organisms and explain the differences in PCB metabolism in various living species. 

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