Sunday, November 13, 2005

PBB Ground Still Worth Zero

A blast from the past resurfaced in the Detroit News. PBB in Michigan. This goes to some musings about persistent organic pollutants. POP's, and the regulations controlling them, are front in the war over environmental protection.

POP's include PBB [mentioned here] but more broadly PCB's, dioxin, organochlorine pesticides. Risk assessment debates center on whether there are directly observable health effects in people, arising from exposures and body burdens which exist, or whether public health measures must be taken based on extrapolation from laboratory data in animals.

The history is from the Dodger's age addled memory. In 1973, polybrominated biphenyl (PBB) was added to cattle feed sold in Michigan, and apparently only in Michigan. Cows got sick, some died. Some of the dead cows were made into cattle feed and fed to other cows. Herds were culled, dead cows buried in land fills and through 1975 Michigan super markets would advertise "No Michigan Meat Sold Here."

PBB extrapolations include some directly observable health effects from animals, in this case, cows.

Laboratory studies established high dose toxicity; lab studies generally only can measure toxicity in the high dose range, because of small experimental group sizes, and also because rates of the health effect in control groups establish a floor below which health effects can't be seen. For PBB, carcinogenicity and liver toxicity presented from dietary exposures in the 3-30 parts per million range [ppm].

The Dodger got tired before finding a correlation of dietary levels to body burdens as measured by serum PBB concentrations. Serum PBB's in these studied women were in the range of 1-5 pbb [parts per billion.]

These studies individual fall in the realm of providing "some" evidence for health effects of PBB among exposured Michigan women. The menstrual study might be called "equivocal."


Toxic town
Danger still stalks the families of tiny Michigan community
By Brad Heath / The Detroit News

It's site of PBB accident

The Velsicol Chemical plant closed in 1978.

But the real turning point came five years earlier, when workers there mistook bags of the flame-retardant PBB for animal nutrients. The chemical, believed to cause cancer, was mixed into livestock feed and distributed to farms around the state. Thousands of cows and more than a million chickens had to be slaughtered.

Velsicol never recovered. When the plant shut down, the company dug a hole in the ground and unceremoniously bulldozed the remains of their operation into it. Four years later, the company signed an agreement with the federal government requiring it to cover the dump with a layer of clay and surround it with an underground wall to keep the chemicals there from leaking out. In return, the government promised Velsicol Chemical, which took over the plant in the 1960s, it wouldn't have to pay for future cleanups.

The wall didn't work.

Environ Health. 2005 Aug 9;4:15.

Menstrual function among women exposed to polybrominated biphenyls: a follow-up prevalence study.

Davis SI, Blanck HM, Hertzberg VS, Tolbert PE, Rubin C, Cameron LL, Henderson AK, Marcus M.

Department of Epidemiology, Rollins School of Public Health, Emory University, 1518 Clifton Road, Alanta, GA 30322, USA.

BACKGROUND: Alteration in menstrual cycle function is suggested among rhesus monkeys and humans exposed to polybrominated biphenyls (PBBs) and structurally similar polychlorinated biphenyls (PCBs). The feedback system for menstrual cycle function potentially allows multiple pathways for disruption directly through the hypothalamic-pituitary-ovarian axis and indirectly through alternative neuroendocrine axes. METHODS: The Michigan Female Health Study was conducted during 1997-1998 among women in a cohort exposed to PBBs in 1973. This study included 337 women with self-reported menstrual cycles of 20-35 days (age range: 24-56 years). Current PBB levels were estimated by exponential decay modeling of serum PBB levels collected from 1976-1987 during enrollment in the Michigan PBB cohort. Linear regression models for menstrual cycle length and the logarithm of bleed length used estimated current PBB exposure or enrollment PBB exposure categorized in tertiles, and for the upper decile. All models were adjusted for serum PCB levels, age, body mass index, history of at least 10% weight loss in the past year, physical activity, smoking, education, and household income. RESULTS: Higher levels of physical activity were associated with shorter bleed length, and increasing age was associated with shorter cycle length. Although no overall association was found between PBB exposure and menstrual cycle characteristics, a significant interaction between PBB exposures with past year weight loss was found. Longer bleed length and shorter cycle length were associated with higher PBB exposure among women with past year weight loss. CONCLUSION: This study suggests that PBB exposure may impact ovarian function as indicated by menstrual cycle length and bleed length. However, these associations were found among the small number of women with recent weight loss suggesting either a chance finding or that mobilization of PBBs from lipid stores may be important. These results should be replicated with larger numbers of women exposed to similar lipophilic compounds.

Epidemiology. 2002 Mar;13(2):205-10.

Growth in girls exposed in utero and postnatally to polybrominated biphenyls and polychlorinated biphenyls.

Blanck HM, Marcus M, Rubin C, Tolbert PE, Hertzberg VS, Henderson AK, Zhang RH.

Biological and Biomedical Sciences Division, Rollins School of Public Health, Emory University, Atlanta GA 30322, USA.BACKGROUND: Accidental contamination with polybrominated biphenyls (PBBs) of the Michigan food supply in 1973 led to the exposure of more than 4000 individuals and to formation of the PBB cohort registry (1976-1979). At enrollment, measurements were taken of serum PBB and polychlorinated biphenyl (PCB), possible endocrine disrupting chemicals. METHODS: We examined the association of estimated PBB and PCB exposure during pregnancy with current height and weight in 308 daughters, 5-24 years of age (mean age 15.2 years), born to women in the cohort. We estimated prenatal PBB exposure using maternal enrollment serum PBB and a model of PBB elimination. Prenatal PCB exposure was estimated using maternal enrollment serum PCB because background-level exposure through diet was ongoing. Self-reported height and weight were obtained from a 1997-1998 health survey. RESULTS: We found no association between prenatal PBB exposure and either daughter's current height or daughter's weight adjusted for height; however, prenatal PCB exposure above 5 parts per billion was associated with reduced weight adjusted for height. Exposure through breastfeeding did not modify the association. CONCLUSIONS: Mothers with PCB levels above the median had daughters whose current weights were 11 pounds lower than that of the daughters whose mothers had levels below the median. This study provides evidence that prenatal exposure to PCBs may affect growth.

Fundam Appl Toxicol. 1993 Nov;21(4):451-60.

Comparative carcinogenicity of polybrominated biphenyls with or without perinatal exposure in rats and mice.

Chhabra RS, Bucher JR, Haseman JK, Elwell MR, Kurtz PJ, Carlton BD.

National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709.

Chronic toxicity and carcinogenicity studies of a polybrominated biphenyl mixture (PBB) were conducted in F344/N rats and B6C3F1 mice of each sex. ...

During the perinatal period, rats were exposed to PBB at dose levels ranging from 1 to 10 ppm and adult exposure concentrations ranged from 3 to 30 ppm in the diet. In the mice, the dose levels ranged from 3 to 30 ppm in both perinatal and adult exposure portions of the chronic studies.

... Perinatal exposure alone (through dietary administration of 10 ppm PBB to the dams) had no effect on the incidences of neoplasms in female F344/N rats, but in male rats, perinatal exposure was associated with a marginally increased incidence of hepatocellular adenomas that may have been related to chemical administration. In male and female B6C3F1 mice, perinatal exposure to 30 ppm PBB resulted in significantly increased incidences of hepatocellular neoplasms. In adult-only dietary exposure studies, PBB was carcinogenic in male and female F344/N rats and male and female B6C3F1 mice based on increased incidences of hepatocellular neoplasms. ...
perinatal exposure enhanced the susceptibility of female rats receiving adult exposure of 10 or 30 ppm to the induction of liver neoplasms. For male and female rats, a combined analysis of the incidences of leukemia in the adult-only, perinatal-only, and combined perinatal and adult exposure groups revealed an apparent association between increasing incidences of mononuclear cell leukemia and exposure to PBB

BrooklynDodger warns the reader that mononuclear cell leukemia in the rat is best observed in bioassays using mortality adjusted statistics. Few, maybe no industry sponsored bioassays use mortality adjusted statistics. Additionally, some public health opponents advocated ignoring all liver tumors in rodents, others emphasize ignoring mouse liver tumors.]

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