Comparative Potency Method for Cancer Risk Assessment: Application to Diesel Particulate Emissions1

An estimation of the human lung cancer “unit risk” from diesel engine particulate emissions has been made using a comparative potency approach. This approach involves evaluating the tumorigenic and mutagenic potencies of the particulates from four diesel and one gasoline engine in relation to other combustion and pyrolysis products (coke oven, roofing tar, and cigarette smoke) that cause lung cancer in humans. The unit cancer risk is predicated on the linear nonthreshold extrapolation model and is the individual lifetime excess lung cancer risk from continuous exposure to 1 μg carcinogen per m³ inhaled air. The human lung cancer unit risks obtained from the epidemiologic data for coke oven workers, roofing tar applicators, and cigarette smokers were, respectively, 9.3 × 10^?4, 3.6 × 10^?4, and 2.2 × 10^?6 per μg particulate organics per m³ air. The comparative potencies of these three materials and the diesel and gasoline engine exhaust particulates (as organic extracts) were evaluated by in vivo tumorigenicity bioassays involving skin initiation and skin carcinogenicity in SENCAR mice and by the in vitro bioassays that proved suitable for this analysis: Ames Salmonella microsome bioassay, L5178Y mouse lymphoma cell mutagenesis bioassay, and sister chromatid exchange bioassay in Chinese hamster ovary cells. The relative potencies of the coke oven, roofing tar, and cigarette smoke emissions, as determined by the mouse skin initiation assay, were within a factor of 2 of those determined using the epidemiologic data. The relative potencies, from the in vitro bioassays as compared to the human data, were similar for coke oven and roofing tar, but for the cigarette smoke condensate the in vitro tests predicted a higher relative potency. The mouse skin initiation bioassay was used to determine the unit lung cancer risk for the most potent of the diesel emissions. Based on comparisons with coke oven, roofing tar, and cigarette smoke, the unit cancer risk averaged 4.4 × 10^?4. The unit lung cancer risks for the other, less potent motor-vehicle emissions were determined from their comparative potencies relative to the most potent diesel using three in vitro bioassays. There was a high correlation between the in vitro and in vivo bioassays in their responses to the engine exhaust particulate extracts. The unit lung cancer risk per μg particulates per m³ for the automotive diesel and gasoline exhaust particulates ranged from 0.20 × 10^?4 to 0.60 × 10^?4; that for the heavy-duty diesel engine was 0.02 × 10^?4. These unit risks provide the basis for a future assessment of human lung cancer risks when combined with human population exposure to automotive emissions.     

Positive youth development: thriving as the basis of personhood and civil society

Positive youth development is conceptualized within a developmental systems theoretical model. The role of thriving processes and civic engagement in positive youth development is discussed.     

Attitudinal acceptance of intimate partner violence among U.S. adults

Attitudinal acceptance of intimate partner violence (IPV) is an important correlate of violent behavior. This study examined acceptance of IPV using data collected from a nationally representative telephone survey of 5,238 adults. Multivariable logistic regression analyses were used to test for associations between sociodemographic characteristics, exposure to violence, question order, and acceptance of hitting a spouse or boyfriend/girlfriend under specific circumstances. Depending on the circumstance examined, acceptance of IPV was significantly higher among participants who were male and younger than 35; were non-White; were divorced, separated, or had never married; had not completed high school; had a low household income; or were victims of violence within the past 12 months. Participants were more accepting of women hitting men; they also were consistently more likely to report tolerance of IPV if they were asked first about women hitting men rather than men hitting women. Reports of IPV tolerance need to be interpreted within the context of the survey. Efforts to change IPV attitudes can be tailored to specific IPV circumstances and subgroups, and these efforts should emphasize that the use of physical violence is unacceptable to both genders.     

Internet use among college students: an exploratory study

The author and associates surveyed 1,300 college students in classrooms at eight academic institutions to identify how the students' use of the Internet has affected their social or academic lives. Although the typical Internet-using student uses the Internet for 100 minutes per day, a small group of students use the Internet to a degree that interferes with other aspects of their lives. Most of them are men and are found among the hard science academic majors. Some ideas for dealing with this problem are suggested.     

Family therapy trainees' evaluations of their best and worst supervision experiences

Supervisees in Commission on Accreditation for Marriage and Family Therapy Education-(COAMFTE) accredited and candidacy training programs were asked to describe their best and worst supervision experiences in terms of the context of training and supervision, the perceived personal attributes of the supervisor, and specific behaviors perceived to be enacted by the supervisor during supervision. Contextual factors such as supervision modality, frequency and duration of supervisory contacts, and sources of supervisory data appeared to distinguish between supervisees' perceptions of their best and worst experiences. These experiences were further distinguished by the supervisees' perceptions regarding the supervisor's level of interpersonal attractiveness, trustworthiness, and expertise. Key behaviors perceived to be enacted by supervisors during best and worst experiences clustered into several dimensions that included creating an open supervisory environment, communication and encouragement, attending to personal growth, and providing conceptual and technical guidance and direction.     

Continuous outcomes stochastically mismeasured as discrete random variables: a maximum likelihood approach

In an economic model of retirement behavior, a continuous dependent variable was required; the variable could only be estimated discretely with error, however. Parameter estimates using this dependent variable and ordinary least squares regression are inefficient. In th is paper, we develop a maximum likelihood procedure which adjusts for this heteroscedasticity.