Environmental Engineering Reference
In-Depth Information
concentration, and reducing overall risk by other means. Thus, the average U.S. outdoor concentra-
tion of 15 Bq m −3 (0.4 pCi L −1 ) would permit a water concentration of 150 Bq L −1 to be delivered if
alternative means of risk reduction are put in place. The risk reduction needed to reduce the total
risk could be, for example, home radon remediation that attained the same calculated risk reduction
in the population affected, similar to reducing the water to the 11 Bq L −1 value.
A policy perspective was prepared to investigate the various issues regarding remediation of
radon in drinking water (Hopke et al., 2000). The EPA and state agencies are responsible for water
quality under the 1996 amendment to the Safe Drinking Water Act, originally passed in 1974.
Radon is a known carcinogen and the maximum contaminant level was automatically set at zero.
The upper limit concentration of 11 Bq L −1 is considered because zero concentration could only be
measured with an uncertainty of 30%. These involve technical and social decisions concerning the
methods of risk reduction. There are varying opinions concerning the reduction in risk to a popula-
tion exposed versus risk reduction for a few individuals in the population. These and other issues
have yet to be resolved.
Some countries have strict 222 Rn in public water supply regulations. Beginning October 1, 1998,
the Swedish government required 222 Rn in public water supplies greater than 100 Bq L −1 be reduced,
and stated that water exceeding a concentration of 1000 Bq L −1 is unsafe and cannot be supplied.
Finland has set a recommended maximum limit of 300 Bq L −1 . The World Health Organization
(WHO) states that controls should be implemented if radon in public drinking water supplies exceeds
100 Bq L −1 . The USEPA is required to set a regulation for 222 Rn in drinking water in the United States.
The standard they have proposed is 11 Bq L −1 but to date (2003) no regulation has been set oficially.
21.8  OCCUPATIONAL RADON EXPOSURE IN UNDERGROUND MINES
The irst evaluation of lung cancer risk from radon decay products emerged from the high expo-
sures in underground uranium mines (UNSCEAR, 2006). Mine operators knew little of the haz-
ards involved with exposure to radioactive materials. In the United States, no Federal Government
agency had authority to regulate the health and safety of miners. Beginning in 1954, the Atomic
Energy Commission (AEC) had regulatory authority over the uranium industry after the mate-
rial was mined but had no authority to regulate the mining industry. The states where uranium
was mined had varied regulatory authority over the safety of miners but the agencies having such
responsibility had no experience with radiation problems. In 1949, the U.S. Public Health Service
(Holaday and Doyle, 1964) became concerned that the industry was exposing miners to a potential
health hazard based on the experience in the Czech mines. They made some measurements and
conirmed that airborne radioactivity concentrations were alarmingly high. The concentration in 24
Colorado mines ranged from 5 to 800 kBq m −3 (135-22,300 pCi L −1 ) (Lundin et al., 1971). There are
now 12 follow-up cohort studies for lung cancer risk in underground miners (UNSCEAR, 2006).
The data for nine studies are presented in the Section 21.12 on risk.
21.9  BRONCHIAL LUNG DOSE
Risk can be estimated from the bronchial dose delivered by the decay products and use of risk
factors based on the dose to A-bomb survivors (ICRP, 2007). The bronchial lung dose cannot be
measured in humans and must be calculated.
The relevant bronchial dose from radon is airway deposition of the solid aerosol particles of
short-lived alpha emitting decay products ( 218 Po, 214 Po). The short-lived decay products have an
effective half-life of 30 min for the chain. As the decay product atoms form in air from 222 Rn decay,
they rapidly attach to the ambient aerosol particles. Bronchial and pulmonary deposition is deter-
mined by the ambient particle size distribution. There are published short-term data on the size
distribution of radon decay products. The median diameter indoors is about 200-300 nm (Tu and
Knudson, 1988a,b; Reineking and Porstendorfer, 1986; Li and Hopke, 1993; NAS/NRC 1999a,b).
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