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Trace Elements in Abiotic and Biotic Environments
Radon as a noble gas should not be bioaccumulated. However, the accumulation
has been reported for Rn progeny, such as 210 Pb in cephalopods and 210 Po in marine
birds, mushrooms, cephalopods, and coastal sand dune wild legumes (ATSDR
2012c).
Radon concentrations in groundwaters vary from 1 to 50 Bq/L for rock aquifers
in sedimentary rocks, from 10 to 300 Bq/L for wells dug in soil, and from 100 to
50,000 Bq/L in crystalline rocks.
Surveys in the EU countries have shown that Rn concentrations in surface waters
are very low, usually well below 1 Bq/L. The highest contents are usually associated
with high U concentrations in the bedrock. A characteristic of Rn concentrations
in rock aquifers is their variability; within a region with fairly uniform rock types,
some wells exhibit concentrations far above the average (EC 2001). Significant seasonal variations in concentrations have also been observed (EC 2001).
36.3 HUMANS
Raised lung cancer rates have been reported from a number of cohort and case–
control studies of underground miners exposed to Rn and its decay products. These
include particularly U miners, but also groups of Fe ore and other metal miners, and
one group of fluorspar miners. Several small case–control studies of lung cancer
have suggested a higher risk among individuals living in houses known or presumed
to have higher levels of Rn and its decay products than among individuals with lower
presumed exposure in houses (IARC 1988).
222 Radon and its decay products are carcinogenic to humans (Group 1) (IARC
1988, 2013). When Rn gas is inhaled, densely ionizing α particles emitted by deposited short-lived decay products of Rn ( 218 Po and 214 Po) can interact with biological
tissue in the lungs, leading to DNA damage. Because even a single α particle can
cause major genetic damage to a cell, it is possible that Rn-related DNA damage
can occur at any level of exposure. Therefore, it is unlikely that there is a threshold
concentration, below which Rn does not have the potential to cause lung cancer
(ATSDR 2012c).
The primary pathway for human exposure to Rn is inhalation, both indoors and
outdoors. Ambient outdoor levels are the result of Rn emanating from soil or released
from coal, oil, and gas power plants. Outdoor Rn levels are typically much lower
than indoor Rn levels. Soil gas intrusion into buildings accounts for the majority of
indoor Rn levels. However, indoor Rn levels can also originate from water used for
domestic purposes, outdoor air, and building materials.
Exposure to high concentrations can occur in any location, with geologic Rn sources.
Relatively high-level occupational exposure can occur among workers in underground
mines (U, P, Sn, Ag, Au, V, hard rock) and sites contaminated with Rn precursors
(Ra, U, or Th), as well as in any underground places. Also air of hospitals that used Ra
needles for therapy may contain elevated Rn amounts.
Lung cancer risk in cigarette smokers and recent ex-smokers is associated with
Rn, as demonstrated by increased lung cancer risk, with increasing cumulative exposure. The risk to nonsmokers is 25-fold lower (ATSDR 2012c).