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Biomedical subjects

J C Barrett

Publications and source records attributed to J C Barrett.

404 records · Page 23Linked to original sources
PubMedDate not supplied

The carcinogenesis bioassay in perspective: application in identifying human cancer hazards.

The selection process for chemicals tested in the rodent carcinogenicity bioassay has been biased toward chemicals suspected of potential carcinogenicity. Results from carcinogenicity bioassays of 400 chemicals tested by the National Cancer Institute/National Toxicology Program (NCI/NTP) were analyzed to determine the dependence of positive results on chemical selection criteria: those suspected of being carcinogenic and those selected based on large volumes produced and widespread exposures. Of these chemicals, 210 (52%) induced carcinogenicity in at least one organ of one sex of one species of the four sex/species groups typically used by NCI/NTP. Only 92 of the 400 chemicals (23%) were positive in two species and thus by international criteria are considered likely to pose a carcinogenic hazard to humans. A total of 267 chemicals (67%) were selected as suspect carcinogens, and 187 (68%) of these were carcinogenic. Suspect chemicals account for 86% of chemicals with at least one positive result and account for 90% of chemicals considered positive in two species. The International Agency for Research on Cancer (IARC) lists only 5 of the 400 chemicals as carcinogenic to humans (group 1) and 10 as probably carcinogenic to humans (group 2A). The majority (80%) of the 133 chemicals selected only on production/exposure considerations were not carcinogenic in animals, even when tested at the maximum tolerated (or minimally toxic) dose. Only 9 (6.8%) were positive in two species, and none is listed in IARC groups 1 or 2A. Thus, on the basis of our analyses we predict that less than 5-10% of the 75,000 chemicals in commercial use might be reasonably anticipated to be carcinogenic to humans.

Animals↗
PubMedDate not supplied

The alignment and crystallization of family size preferences.

"A Monte Carlo simulation model of reproductive histories is used to derive inferences about preferred family sizes from those achieved at various durations of marriage. The method consists [of] inverting the relationships between these two distributions, which form respectively an input to and an output of the model. It emerges that in cohorts married in England and Wales at ages 20-24 in 1951, 1955 and 1961, there is an increasing preference for family sizes of two children." The results indicate that "estimated family size preferences appear to be remarkably stable within marriage cohorts, at least after 10 years duration of marriage. The methodological problems arising in the estimation of these preferences at short durations of marriage, with differential birth spacing, are discussed." (summary in FRE)

Birth Intervals↗