Progeny Exposure Research Articles

Radon in Norwegian dwellings and the feasibility of epidemiological studies.

The results of a pilot study on radon in Norwegian dwellings are presented together with a discussion on the feasibility of an epidemiological study on the correlation between lung cancer and radon progeny exposure in dwellings. There are large variations in the mean radon concentration in Norwegian municipalities, and the population average indoor radon concentration is high (80-100 Bq m-3). The large variations and high absolute values, together with excellent lung cancer and smoking habit data, make it feasible to conduct epidemiological studies based on representative exposure data in the Norwegian population.

Estimates of lifetime lung cancer risks resulting from Rn progeny exposure.

Data on five mining populations exposed to Rn progeny have been used to estimate the lifetime risk of lung cancer resulting from occupational and environmental exposure under current standards. Slopes of dose-response relations for lung cancer show a tendency to decrease with increasing dose. Our best estimate of curvilinearity is given by raising dose to the power 0.92 +/- 0.07, but the improvement in fit beyond simple linearity is not significant. On the other hand, the addition of a cell-killing term significantly improves the fit of the linear model. In any event, linear extrapolation is unlikely to underestimate the excess risk at low doses by more than a factor of 1.5. However, these inferences about curvilinearity are highly subject to error from the choice of reference populations, dosimetry, and latency. Under the linear-cell-killing model, our best estimate of excess relative risk is 2.28 +/- 0.35 per 100 working level month (WLM) (a doubling dose of 44 WLM). Attributable risks in these five studies range from 3.4-17.8 per 10(6) person-yr WLM-1. Risks from Rn progeny appear to interact with age and smoking in a form intermediate between additive and multiplicative. The "relative risk" model is therefore preferable for projecting lifetime risks, but life-table projections are described for a wide variety of assumptions. Our best estimate of the effect of a 50-yr occupational exposure to 4 WLM yr-1 is 130 excess lung cancer deaths per 1000 persons (0.65 per 1000 person-WLM), with a range from 60-250 per 1000. Similar calculations for lifetime exposure to an additional 0.02 working level (WL) beyond normal background produces an estimate of 20 excess lung cancers per 1000 persons.

Indoor radon progeny exposure in the Florida phosphate mining region: a review.

This paper reviews the data generated in studies of land radioactivity and indoor airborne radon progeny associated with mined and reclaimed phosphate lands in Florida. Highest indoor radon progeny levels are associated with the slab-on-grade type of construction. Concentrations exceeding 0.03 WL are associated with overburden soils, deposits and fill, while concentrations up to about 0.03 WL are associated with tailings. The lower limit for distinguishing increases above non-enhanced natural concentrations is on the order of 0.01-0.02 WL. Results of this study show that about 25% of the land produced by present methods of mining and reclamation practices would require restrictions on the type of construction or would require special construction methods. It is projected that with modification of mining and tailings disposal practices, virtually all of the land produced by mining and reclamation would be satisfactory for unrestricted construction use.

Prediction of increased gamma fields after application of a radon barrier on concrete surfaces.

A sizable reduction of the indoor radon progeny exposure level is anticipated in structures from the application of a radon barrier to the indoor surfaces of concrete foundations, behind or in which uranium mill tailings exist. The predicted accumulation of radon and gamma emitting radon progeny behind the barrier was studied. Radon accumulations were modeled by application of linear diffusion theory to a multilayered system of porous media. A comparison of the gamma exposures associated with concentration profiles prior to and after application of a radon barrier resulted in the prediction of sufficiently low fractional increases to justify field testing of the barrier.

GENETICS OF RESISTANCE IN RUTABAGA TO TWO RACES OF PLASMODIOPHORA BRASSICAE

The York and Wilhelmsburger rutabaga cultivars, both resistant to races 2 and 3 of the clubroot pathogen, were crossed with the race 2- and 3-susceptible Laurentian cultivar. Race 2-resistant Ditmars S2 rutabaga selection was also crossed with susceptible Laurentian. Race exposure of F1 seedlings of resistant × susceptible crosses showed that resistance to races 2 and 3 was dominant. Susceptibility studies of F2 and backcross progenies showed that resistance to race 2 in York was controlled by a single major gene, whereas resistance to this race in Wilhemsburger was controlled by two major genes. Single major gene resistance to race 2 was indicated for the Ditmars S2 selection. This crucifer line is susceptible to race 3. F2 progeny exposures to race 3 showed that resistance was controlled by one major gene in both the York and Wilhelmsburger rutabaga cultivars.

Mutations in the sheep blowfly Lucilia cuprina (Wied.). I.—Studies on genes for white eye and dieldrin-resistance

The inheritance of white eye in Lucilia cuprina (Wied.) was investigated by means of a series of back-crosses repeated through ten generations. Since an approximate 1:1 ratio of white-eyed: red-eyed flies was observed throughout, it is concluded that white eye is due to a single recessive gene (w). Earlier work establishing that w is on an autosome is discussed.A test for the existence of a linkage group containing genes for white eye and dieldrin-susceptibility was then made. The exposure of back-cross progeny to discriminating levels of insecticide, and the pattern of mortality observed with scalar concentrations of dieldrin, indicated that genes for white eye (w) and dieldrin-susceptibility (rdi) are on different chromosomes.