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Biomedical subjects

K S Crump

Publications and source records attributed to K S Crump.

12 recordsLinked to original sources
PubMed1992

Exposure to airborne asbestos in buildings.

The concentration of airborne asbestos in buildings and its implication for the health of building occupants is a major public health issue. A total of 2892 air samples from 315 public, commercial, residential, school, and university buildings has been analyzed by transmission electron microscopy. The buildings that were surveyed were the subject of litigation related to suits alleging the general building occupants were exposed to a potential health hazard as a result of exposure to the presence of asbestos containing materials (ACM). The average concentration of all asbestos structures was 0.02 structures/ml (s/ml) and the average concentration of asbestos greater than or equal to 5 microns long was 0.00013 fibers/ml (f/ml). The concentration of asbestos was higher in schools than in other buildings. In 48% of indoor samples and 75% of outdoor samples, no asbestos fibers were detected. The observed airborne concentration in 74% of the indoor samples and 96% of the outdoor samples is below the Asbestos Hazard Emergency Response Act clearance level of 0.01 s/ml. Finally, using those fibers which could be seen optically, all indoor samples and all outdoor samples are below the Occupational Safety and Health Administration permissible exposure level of 0.1 f/ml for fibers greater than or equal to 5 microns in length. These results provide substantive verification of the findings of the U.S. Environmental Protection Agency public building study which found very low ambient concentrations of asbestos fibers in buildings with ACM, irrespective of the condition of the material in the buildings.

Air Pollutants↗
PubMed1989

Statistical analysis of data on airborne asbestos levels collected in an EPA survey of public buildings.

Data from a recent EPA study of airborne asbestos levels in 49 buildings occupied by the General Services Administration (GSA) are statistically analyzed. The study focuses on differences between indoor and outdoor levels, and on differences among buildings with no asbestos-containing material (ACM) (6 buildings), buildings with ACM generally in good condition (6 buildings), and buildings containing damaged ACM (37 buildings). Seven indoor samples and a single outdoor sample were collected from most buildings and analyzed by TEM (transmission electron microscopy) using a direct preparation method. No statistically significant differences were detected in asbestos levels between indoors and outdoors or among the three categories of buildings. The average indoor concentration of asbestos was 0.00073 fibers/cc (f/cc) for all fibers and 0.00007 f/cc for fibers 5 microns or longer. The current OSHA occupational standard is 0.2 f/cc for fibers 5 microns or longer as measured by phase-contrast microscopy.

Air Pollutants, Occupational↗
PubMed1979

Dose response problems in carcinogenesis.

The estimation of risks from exposure to carcinogens is an important problem from the viewpoint of protection of human health. It also poses some very difficult dose-response problems. Two dose-response models may fit experimental data about equally well and yet predict responses that differ by many orders of magnitude at low doses. Mechanisms of carcinogenesis are not sufficiently understood so that the shape of the dose-response curve at low doses can be satisfactorily predicted. Mathematical theories of carcinogenesis and statistical procedures can be of use with dose-reponse problems such as this and, in addition, can lead to a better understanding of the mechanisms of carcinogenesis. In this paper, mathematical dose-response models of carcinogenesis are considered as well as various proposed dose-response procedures for estimating carcinogenic risks at low doses. Areas are suggested in which further work may be useful. These areas include experimental design problems, statistical procedures for use with time-to-occurrence data, and mathematical models that incorporate such biological features as pharmacokinetics of carcinogens, synergistic effects, DNA repair, susceptible subpopulations, and immune reactions.

Animals↗
PubMed1977

Confidence intervals and test of hypotheses concerning dose response relations inferred from animal carcinogenicity data.

Confidence intervals and hypothesis tests are developed for dose-response relations based on dichotomous data from animal carcinogenicity experiments. The functional form of the dose-response curve comes from the Armitage-Doll multistage carcinogenesis model and involves a polynomial in the dose-rate, with non-negative coefficients. Asymptotic distributions of the maximum likelihood estimators of these coefficients are used to construct confidence bounds on risk at a given dose and on the dose corresponding to a given risk. Likelihood ratio tests are developed for the presence of a positive dose-related effect and for the existence of a positive slope to the dose-response curve at zero dose. The latter test is of practical importance since a positive slope of the dose-response curve at zero dose rules out any "threshold-like" behavior and would often mean that any concentration low enough to insure a negligibly low cancer risk (e.g., 10(-6)) would be too low to be economically useful for applications such as food additives. Simulation experiments are performed to provide guidelines for applying the theory.

Animals↗
PubMed1976

Fundamental carcinogenic processes and their implications for low dose risk assessment.

Various possible models of carcinogenesis are analyzed with respect to low dose kinetics. The importance of background carcinogenesis upon the shape of the dose-response curve at low dose is emphasized. It is shown that, if carcinogenesis by an external agent acts additively with any already ongoing process, then under almost any model the response will be linear at low dose. Measures of the degree of linearity are obtained for multistage models of carcinogenesis, where it is shown that throughout the dose range where the extra risk is less than the spontaneous risk linear extrapolation must be quite accurate.

Carcinogens, Environmental↗
PubMedDate not supplied

Airborne asbestos levels in buildings: maintenance worker and occupant exposures.

A substantial number of air samples have been collected during the past few years to measure airborne asbestos levels in buildings with asbestos-containing materials (ACM). These samples fall into two categories: (i) samples collected to measure the exposure of workers while they were engaged in routine maintenance and repair activities; and (ii) samples collected during normal building activity to measure prevalent levels in buildings. The measurements derived from these samples have been compiled and summarized to provide estimates of the airborne asbestos exposure of workers engaged in routine maintenance and repair work and by other building occupants. These data indicate that maintenance and repair workers in buildings with ACM, after accounting for the frequency and duration of these types of activities, have annual exposure levels ranging from a median value of 0.002 fibers per cubic centimeter (f/cc) per year to 0.02 f/cc per year at the 90th percentile. Building occupants not involved in maintenance and repair work experience average exposure levels ranging from 0.00003 f/cc to 0.0005 f/cc.

Air Pollutants, Occupational↗