UDC 614.73:616-057:622.34

A. D. Alterman, A. V. Bykhovsky, A. Kh. Khodzhimatov

Effectiveness of Measures to Reduce Airborne Radon Daughter-Product Concentrations and Morbidity among Workers at a Polymetallic Mine

Tajik Republican Sanitary and Epidemiological Station, Dushanbe; All-Union Central Institute of Occupational Safety, Moscow; Adrasman Medical and Sanitary Unit, Adrasman, Tajik SSR

Elevated concentrations of radon and its daughter products in the air of underground workings, caves, and basements, compared with atmospheric air, were discovered as early as the beginning of the twentieth century (in Germany by Elster and Geitel in 1901, and in the Turkestan region by L. S. Kolovrat-Chervinsky in 1914). Many investigators subsequently established (for a literature review, see A. V. Bykhovsky, 1963, 1969) that the highest radon concentrations occurred in uranium mines before anti-radon measures were implemented (the mean concentration of radon daughter products was approximately \(10^6\) MeV/L, and the maximum approximately \(10^7\) MeV/L); in non-uranium mines under the same conditions, the corresponding values were \((1–3)\cdot10^4\) and \(1.6\cdot10^7\) MeV/L (Wagoner et al., 1963; A. D. Alterman et al.). Modern technical measures have made it possible to reduce the mean concentration of radon daughter products in uranium mine air to \((1–4)\cdot10^5\) MeV/L (in the United States, according to J. C. A. E. data for 1967) and even to \((1–3)\cdot10^4\) MeV/L (in the USSR; A. V. Bykhovsky et al., 1969).

The public health significance of radon contamination of mine air is now quite evident from the work of Wagoner et al. (1964, 1965), Lundin et al., de Villers, and Windish, who demonstrated an association between increased mortality from respiratory cancer among workers in uranium and certain non-uranium mines and high concentrations of radon daughter products in the air (mean values exceeding 10 times the mean permissible concentration established by NRB-69, namely \(0.4\cdot10^5\) MeV/L). The question of the effects of concentrations close to permissible levels remains unresolved.

In this connection, we believe that data characterizing general morbidity in non-uranium mines with elevated concentrations of radon daughter products in the air may be of interest. According to I. G. Fridlyand, a noticeable worsening of the course of so-called general (nonoccupational) diseases under certain industrial conditions may in fact be the only manifestation of the adverse effects of mildly expressed harmful factors in the working environment.

We analyzed morbidity among workers employed in the underground workings of the Karamazar mine in 1962–1968 in relation to changes in the composition of mine air and certain other working conditions following the implementation of radiation safety measures in 1965. The first observation period extended from 1962 through the first half of 1965; the second extended from the second half of 1965 through 1968. During the first period, the mean (median) concentration of radon daughter products, based on the Tajik Republican Sanitary and Epidemiological Station’s analysis of 199 air samples, was \(0.7\cdot10^5\) MeV/L in all active workings and \(1\cdot10^5\) MeV/L at working faces (\(0.7\) at stoping faces and \(1.8\cdot10^5\) MeV/L at development faces). In the second period, according to the mine’s dosimetry laboratory, which analyzed 3,089 samples, the median concentration fell to \(0.072\cdot10^5\) MeV/L in all active workings, including \(0.076\cdot10^5\) MeV/L at working faces: \(0.074\cdot10^5\) MeV/L at stoping faces and \(0.078\cdot10^5\) MeV/L at development faces. Airborne dust levels also fell over the same period. According to the arithmetic mean, \(M\pm m\), calculated from measurements by the dust and gas laboratory of the Karamazar paramilitary mine rescue squad, they declined from \(3\pm0.5\) to \(1.3\pm0.1\) mg/m³ in all active workings and from \(3.9\pm0.3\) to \(1.5\pm0.5\) mg/m³

Table 1

Levels of lung irradiation by radon progeny among workers in the underground workings of the Karamazar mine from 1962 through 1965 (first half of the year)

at the faces (at production faces, from $3.5\pm0.3$ to $1.4\pm0.06$ mg/m³; at development faces, from $4.3\pm0.8$ to $1.5\pm0.08$ mg/m³).

At the request of sanitary personnel, welfare facilities for workers were improved during this period to reduce radioactive contamination of protective clothing and skin: uninterrupted operation of showers, drying, and regular laundering of protective clothing were established. At the same time, intensified ventilation and the extensive use of water for dust control increased air humidity and the degree of wetting of protective clothing, while air velocity more than doubled (to over 0.3 m/s in development workings and over 0.5 m/s at production faces).

To assess the effects of radon progeny, it is important to know the dose of radiation they deliver to the respiratory organs. Table 1 presents the calculated levels of lung irradiation among mine workers during the first period.

For the calculation, we used data on the concentration of radon progeny in air and values of lung filtering capacity (LFC), obtained by A. D. Alterman and co-authors from measurements made among underground workers at mining enterprises in the Tajik SSR in 1968–1969. The mean values were determined from measurements of shift-average LFC over 394 person-shifts, including 219 person-shifts among face workers. The quantity $\mathrm{LFC}=V_tK$, which characterizes the lungs’ removal of aerosols from the air passing through them per unit time, relates the concentration of aerosols in inhaled air to their intake into the lungs by the simple equation:

\[ \bar q\cdot\mathrm{LFC}\cdot\Theta=Q, \]

where $\bar q$ is the mean aerosol concentration in inhaled air, and $Q$ is the intake of aerosols into the lungs during the inhalation period $\Theta$. When $\bar q$ for radon progeny is expressed in units of “latent energy,” $Q$ directly represents their energy released in the lungs during inhalation.

For the calculation, we also used doses to basal cells of the pulmonary epithelium under standard breathing conditions (pulmonary ven-

…ventilation \(V_f=20\) L/min, retention coefficient \(K=0.25\), whence ФСЛ \(=5\) L/min), according to studies by Altshuler et al. (from the work of A. V. Bykhovsky et al., 1969).

As can be seen from Table 1, the estimated radiation doses to the basal cells of the pulmonary epithelium could have amounted to 15–59 rad/year in the first period.

Since НРБ-69 does not establish maximum permissible doses for irradiation of the respiratory organs by radon progeny, and only their content in air is regulated, the last two columns of Table 1 present calculated annual average concentrations that result in the release of radiation energy from radon progeny in the lungs (calculated from measurements of \(\bar q\) and ФСЛ) under standard breathing conditions. These concentrations amounted to 2–8 СДК. In the second period, exposure levels decreased 10- to 23-fold: the maximum calculated annual average concentration of radon progeny did not exceed 0.3 СДК.

Throughout the observation period (1962–1968), lead-zinc, bismuth, and fluorite ores were mined at the mine. The ore extraction technology, mining systems employed, and mining and geological conditions underwent no substantial changes. The average annual number of people employed in underground workings was 189 in the first period and 343 in the second.

Workers received medical care from a medical unit that had 50 beds until 1967 and 75–100 beds from 1967 onward. During the observation period (1962–1968), the following occupational diseases were identified: grade I silicosis, 1 case; suspected silicosis, 1 case; vibration disease, 9 cases (2 in the first period and 7 in the second observation period); pulmonary tuberculosis, 1 case; and lip cancer, 1 case. No illnesses suspected to be radiation-related were noted. No cases of respiratory cancer were recorded.

Morbidity was analyzed using the following method. An individual record with a detailed occupational history was compiled for each person employed in underground workings for at least 6 months between 1962 and 1968. Morbidity data from outpatient records and medical histories were entered into the record. The duration of illnesses was determined from entries in the medical documentation concerning certificates of exemption from work and sick-leave certificates issued. Each physician visit that did not result in the issue of a document exempting the worker from work was conventionally counted as 0.5 day of illness. Injuries, infectious diseases (except influenza), tumors, and occupational diseases were excluded from the analysis. The person-day of work was taken as the unit of observation. Person-days of work and days of illness were calculated as calendar days.

The indicators (numbers of days of illness and numbers of cases relative to the number of person-days of work) were calculated with an error determined by the formula:

\[ m=\sqrt{\frac{Pq}{n}}, \tag{1} \]

since they characterize binary variation. As is well known, the indicators commonly used to characterize morbidity involving temporary loss of work capacity (numbers of cases and days relative to the average annual number of workers) are not binary, which precludes the use of formula (1) to calculate their errors (V. A. Mozglyakova; L. E. Darsky; M. S. Katsnelbaum). The error of the mean duration of a case was determined by the formula:

\[ m=\frac{\sigma}{\sqrt{n-1}}. \tag{2} \]

The age distribution of workers, based on the number of person-days worked by individuals divided into four age groups (20–29 years, 30–39 years, 40–49 years, and 50 years and older), underwent no substantial…

Table 2

Incidence of respiratory diseases among Karamazar mine workers engaged in underground mining (number of cases per \(10^4\) person-days worked, \(P \pm m\), in the numerator; mean duration of one case, \(M \pm m\), in the denominator)

…changes. Age standardization of the respiratory disease rates yielded very small differences (2–6%) between the standardized and crude rates, allowing only crude rates to be used thereafter. To identify possible changes in the severity of respiratory diseases, additional measures were calculated: the number of days spent in hospital relative to the number of person-days worked, and their percentage of all days of illness.

As is well known, the rules governing sick-leave payments changed during the second observation period: from 1967, workers with 5 to 8 years of service received 80% of their earnings, and those with more than 8 years received 100%, instead of 70% and 80–90%, respectively, before 1967. This, together with increased access to inpatient treatment, may have increased the corresponding morbidity measures.

The results of the morbidity analysis are presented in Table 2.

Among all workers, respiratory disease morbidity measured in days of illness fell by 23% in the second period (\(P<0.01\)), primarily owing to a reduction in the mean duration of one case (by 28%, \(P<0.01\)). The number of days spent in hospital also fell (by 44%, \(P<0.01\)), and their share of all days of illness declined from 29% to 21% (\(P<0.01\)). It should be noted that, in the second period, morbidity among persons who had worked underground during the first period did not differ substantially from that among those who began work in the second period, with the exception of pneumonia. Although the rate of days of illness from pneumonia among the former fell by 29% compared with the first period (\(P<0.05\)), it was 10 times higher than among the latter (\(P<0.01\)). In the first period, morbidity measured in days of illness was higher among face workers than among other workers (by 44%, \(P<0.01\)); in the second period, it fell and did not differ significantly from that among the other workers, whose morbidity remained virtually unchanged.

Similar changes were observed in the groups of eye diseases and diseases of the teeth and oral cavity: a significant reduction in morbidity in the second…

…during the period occurred only among face workers (a twofold and 1.7-fold change, respectively, in days of illness, \(P<0.01\)).

In the second period, the incidence of pustular skin diseases decreased among both face workers and other workers, possibly as a result of improved sanitary and welfare services.

The incidence of influenza increased among face workers (the frequency increased while the duration of each case decreased somewhat). However, a substantial decrease among the other workers resulted in an overall reduction in the number of days of illness. These changes were apparently due to the epidemiological characteristics of the spread of infection.

The incidence of “other” diseases, comprising seven groups of diseases analyzed separately, increased mainly because of an increase in diseases of the gastrointestinal tract and cardiovascular system. In both periods, the incidence of “other” diseases was higher among face workers than among the other workers.

Conclusions

1. Implementation of a comprehensive program of radiation safety and industrial hygiene measures at a polymetallic mine reduced the mean concentration of radon daughter products in underground mine air from 4.5 MAAC (at development faces) to 0.3 MAAC. This reduced the radiation dose to the workers’ respiratory organs (the basal cells of the pulmonary epithelium) from 15–59 rad/year in 1962–1965 to 1.5–2.6 rad/year in 1965–1968.

2. Concurrently with the reduction in radiation exposure of the respiratory organs, the mean airborne dust concentration fell from 4.3 to \(1.4\ \mathrm{mg/m^3}\), and sanitary and welfare services for the workers improved (provision was made for drying, laundering, and repairing work clothes, uninterrupted operation of showers, etc.).

3. Comparison of morbidity indicators before and after implementation of the measures shows a statistically significant reduction in the severity of diseases of the respiratory organs and the mucous membranes of the eyes and oral cavity among face workers in 1965–1968, while the corresponding indicators for the same diseases among the other workers remained virtually unchanged.

A statistically significant reduction in the incidence of pustular skin diseases was observed among all persons employed underground.

References

Alterman A. D., Ruzer L. S., Urusov S. A. Health Care of Tajikistan, 1971, no. 1, p. 36. — Bykhovsky A. V. Hygienic Issues in Underground Uranium Ore Mining. Moscow, 1963. — Bykhovsky A. V., Chesnokov N. I., et al. Experience in Combating Radon in Mining Operations. Moscow, 1969. — Darsky L. E. Health Care of the Russian Federation, 1967, no. 2, p. 23. — Katsnelbaum M. S. Ibid., p. 25. — Mozglyakova V. A. Ibid., 1965, no. 11, p. 23. — Fridlyand I. G. The Role of Adverse Occupational Factors in the Onset and Course of Certain Diseases. Leningrad, 1966. — Altshuler et al. Health Phys., 1964, vol. 10, p. 1137. — Elster J., Geitel H. Physiolkal Z., 1901, Bd. 2, S. 590. — Lundin F. E. et al. Hlth. Phys., 1969, vol. 16, p. 571. — De Villiers A. J., Windisch J. P. Brit. J. industr. Med., 1964, vol. 21, p. 94. — Wagoner J. K. et al. New Engl. J. Med., 1963, vol. 269, p. 284. — Wagoner J. K. et al. J. A. E. A., Vienna, 1964, vol. 1, p. 37. — Wagoner J. K. et al. New Engl. J. Med., 1965, vol. 273, p. 181.

Received February 18, 1972.

Efficiency of Measures of Decreasing the Concentration of Radon Daughter Products in the Air and Morbidity Rate of Workers at a Polymetal Mine

A. D. Alterman, A. V. Bykhovsky, A. Kh. Khodzhimatov

Introduction of a complex of sanitation measures at a polymetal mine diminished the content of radon daughter products in the mine air from 4.5 to 0.3 of mean annual concentration, decreased the mean content of dust from 4.3 to \(1.4\ \mathrm{mg/m^3}\), improved the sanitary service of workers

and brought about a 2-fold and more increase of the air current rate in the mines. A significant alleviation of the gravity of diseases of respiratory organs, of ocular and oral mucosa was noted among the coal hewers and no practical changes in the signs of similar diseases could be traced among the rest of the workers. This fact evidences favorable effect produced by the decrease of the content in the air of both radioactive and nonradioactive aerosols on the morbidity rate, than the negative effect of the increase of the air current rate in the mines on the health of workers.