Effects of PBBs on cattle. IV. Distribution and clearance of components of firemaster BP-6.

Abstract

Sixty dairy animals were utilized in seven experiments to determine aspects of the distribution and clearance of FireMaster BP-6. Experimental protocols of various studies provided daily exposures from 0.25 to 25,000 mg, exposures for I to 202 days, and total study periods from 10 to 1100 days. Necropsy of 28 animals provided information on residue concentrations in 35 tissues, and the excretion in milk was determined in 15 animals. These studies showed that the major brominated biphenyls of this commercial mixture were absorbed from the gastrointestinal tract and appeared in the blood plasma within 4 hr. With continued exposure to the residue plasma concentrations reached a steady state by 15 days. Free PBB was not detectable in urine. During PBB feeding feces was the major route of excretion, representing approximately 50%o of the amount fed to animals not displaying signs of toxicosis. Following withdrawal of PBB, fecal concentrations declined to 1 to 2% of concentrations during dosing, yet, feces remained the major excretory route in nonlactating animals. In contrast, in post-exposure lactating animals milk fat became an important excretory route removing three-times the quantity of residue cleared in feces. Following parturition, concentrations of PBB in milk fat declined approximately twofold in 6 days. Thereafter, the residue concentration in milk fat was approximately 0.4 that in depot fats. PBB had a predilection for lipid tissues with similar concentrations in various depot fats. Concentrations of the residue were notably low in tissues of the nervous system despite the high content of lipid material. Liver contained residue concentrations that were disproportionately high when compared to the lipid content of the organ. Calves born to PBB-exposed cows had similar distribution of residues in body tissues although concentrations were less than those of the dam.

Toxicity of polybrominated biphenyls (PBBs) in Domestic and laboratory animals.

“…As a result of this differential rate of elimination, those components that are more slowly removed seem to become more concentrated relative to the other PBBs (28). The rates of metabolism appear to be determined primarily by the location of the bromine in the biphenyl molecule and secondarily by the bromine content or the availability of two adjacent unsubstituted sites in the biphenyl molecule (26)(27)(28)(29). Similar relationships have been reported for the PCBs (48,49).…”

“…These studies indicate that PBBs are rapidly and almost completely absorbed (absorption apparently decreases with increasing bromine con-177 tent) from the gastrointestinal tract and are initially distributed widely throughout the body tissues with major concentrations in liver and fat (1,5,(29)(30)(31)(32)(33)(34)(35)(36)(37)(38)(39)(40)(41)(42)(43)(44). Based on the available data, the PBBs in Firemaster BP-6 are apparently metabolized to give hydroxylated degradation products by metabolic routes that are similar to those for the structurally related polychlorinated biphenyls (14,(45)(46)(47)(48).…”

“…Absorption, Distribution, Biotransformation and Elimination of PBBs An understanding of the true biological behavior of PBBs in the form of Firemaster BP-6 is complicated by the nature of the commercial product which is a mixture of compounds whose biological activity differs according to the position of bromine in the molecule and to a lesser degree by the number of bromines in the molecule (26)(27)(28)(29).…”

“…Pharmacokinetic studies in rats have revealed that the individual PBBs in Firemaster BP-6 are eliminated from the body at different rates (26)(27)(28)(29). As a result of this differential rate of elimination, those components that are more slowly removed seem to become more concentrated relative to the other PBBs (28).…”

Effects of PBBs on Cattle. I. Clinical Evaluations and Clinical Chemistry

“…Instead, PBB appeared to be a threshold toxin since toxicity was not evident during exposure and in the two years following exposure in our experimental animals given 250 mg/day or less. Although placental transport of PBB has been demonstrated in these animals (22) teratogenic effects have not been observed.…”