The Rainbow Trout
Radiation Protection Service
Ministry of LabourAEC Publication 97-03, June 1997
WHAT IS RADON?
Radon (222Rn) is a radioactive gas produced by the decay of
the naturally radioactive element uranium. Breathing air
containing radon gas can give a radiation dose to the lungs
which increases the risk of lung cancer. This is one of the
known causes of increased lung cancer rates in uranium
miners who can be exposed to especially high doses. The
cancer risk depends primarily on the radon concentration in
the air, the time spent breathing that air, and possibly,
other lifestyle or hereditary factors. Uranium is a very
common natural element, and is present in trace amounts in
virtually all soils. Radon is produced continually by this
uranium as it decays.
WHY IS RADON PRESENT AT SOME FISH
FARMS?
Groundwater from a pumped well, spring or artesian supply
has passed through a soil or rock substrate and dissolved
the radon released by the uranium present there. If the
water is agitated, or if air or other gases are bubbled
through it, then dissolved gases such as radon are released
from the water into the air. Fish farms often use large
amounts of groundwater which is agitated, aerated, or
degassed deliberately as it flows throughout the facility.
Depending on the concentration of radon in the water, large
amounts of this hazardous gas can be released into the
atmosphere, and high radon concentrations are possible if
the tanks or water treatment systems are inside a building
where the gas can accumulate. This is especially true in
poorly ventilated buildings.On the other hand, fish farms without indoor facilities will have low radon concentrations in the air and present little or no risk to the farmer.
There is no evidence that water-borne radon has any impact on the fish itself, or to consumers who eat these fish. Neither is there any hazard associated with people who handle the fish or the water that contains the radon. Therefore, the risk factor is associated primarily with inhalation with subsequent lung pathology occurring because of radiation damage to the pulmonary cells.
The potential for high radon exposure in a fish farm will depend on many factors, and there is no general rule of thumb to asses the risk at any particular site. Thus, each farm site should be assessed on a case-by-case basis and further investigated if necessary.
RADIATION GUIDELINES
Radiation doses received by nuclear energy workers (NE) from
artificially produced radionuclides or naturally radioactive
materials used in the nuclear fuel industry, are regulated
by the Atomic Energy Control Board (AECB). Radiation doses
to other types of workers (eg. fish farmers) from
'naturally' occurring radioactive materials (NORM) are not
similarly regulated. A Federal/Provincial Working Group on
NORM has recommended specific guidelines so that workers
exposed to NO RM have the same standards for safety as do
nuclear energy workers. The table below compares AECB
Regulations with the NORM Working Group Guidelines.|
Annual Worker
Dose (millisieverts/annum) |
AECB Regulation
|
NORM Working Group
Guideline |
|
Less than 1
|
Review workplace
|
Review workplace
|
|
Between 1 to 5
|
Identify as NE worker; inform,
train, and review workplace for dose reduction
|
Identify as NORM worker; inform,
and review workplace for dose reduction
|
|
Between 5 to 20
|
Personal dose monitoring
radiation protection program
|
Personal dose monitoring, NORM
management program
|
|
20
|
Upper limit for exposure
|
Upper limit for exposure
|
The Working Group recommends an investigation of the workplace to estimate individual exposure doses to the workers when NORM is known to be present. Practices causing individual worker doses greater than 1 mSv/a should be identified, the workers informed, and dose control measures instituted. In accordance with standard radiation protection principles, information and dose control measures are encouraged even when doses are less than 1 mSv/a.
FISH FARM MEASUREMENTS
During 1995-1996, the Ontario Ministry of Labour-Radiation
Protection Service, carried out a detailed radon study in
four provincial fish culture stations and found that the
radiation doses to the workers were less than 1 mSv/a at
three stations, but were 2-5 mSv/a at one station. Dose
control measures are now in place at that station. However,
this is not the worst case, since doses over 20 mSv/a have
been found at fish farming operations in the United States.
Thus, the problem is known to exist at operating fish farms
and is not simply a hypothetical situation.
ACTION PLAN
In light of the above information, fish farming operations
are obvious environments where workers risk receiving doses
over 1 mSv/a. The Aquaculture Extension Centre, University
of Guelph, in cooperation with the Ministry of
Labour-Radiation Protection Service, wishes to carry out a
Province-wide study to determine whether radon presents a
significant risk to the Ontario aquaculture community.
Participation in this study is strictly voluntary. The dose
limits and actions recommended in the NORM Guidelines are
not regulations per se, but are the basis for
industry-specific Codes of Good Practice based on worker
safety.Each participating farm will be visited by pre-arrangement to collect information such as water flow, building volume and lay-out etc., as well as to sample the water to measure the dissolved radon concentration, and to place radon detectors in building work areas to measure airborne levels. Three more sets of detectors will be installed at 3 month intervals. Measurements will be made by the Radiation Protection Service at no charge to the farmer. At the end of the 12 month period, the average annual dose to a worker will be estimated, and reported in strict confidence, only to the farm owner. Only summary information not related to any identifiable location will be released. The Radiation Protection Service will assist the farmer in interpreting results, and will communicate radiation protection standards to owners and workers. Working in concert with the Aquaculture Centre, the Radiation Protection Service will help the farmer examine various options to eliminate the problem if one exists. In many cases, simple and inexpensive upgrades to building ventilation may be all that is necessary to correct the problem.
For further information related to radon and aquaculture, feel free to contact the Aquaculture Centre, University of Guelph at 519-824-4120 ext. 56216, or the nearest office of the Ministry of Labour.
REFERENCES