Environmental Tritium in Trees at AECL, Chalk River, Ontario.(1)

 

The paper on Environmental Tritium in Trees, by R.M. Brown, AECL Chalk River, (circa 1978, ed. CCRC) looked at techniques for providing a convenient means of monitoring dispersal of Tritium from nuclear facilities. Our intent in discussing it here is to provide a comparison of known results of tritium sampling from beside a contaminated lake and beside reactor stacks, NRU Chalk River and Ontario Hydro's NPD, Rolphton with results from tritium sampling in Pembroke, where a tritium light factory is operated by SRB Technologies. (see sampling results)
 
Abstract: "The distribution of environmental tritium in the free water and organically bound hydrogen of trees growing in the Chalk River Nuclear Laboratories (CRNL) has been studied. The regional dispersal of HTO (tritiated water) in the atmosphere has been observed by surveying the tritium content of leaf moisture. Measurement of the organically bound tritium in the wood of tree ring sequences has given information on past concentrations of HTO taken up by trees growing in the CRNL Liquid Waste Disposal Area (see LDA 24k .gif). For samples at background environmental levels, cellulose separation and analysis was done. The pattern of bomb tritium in precipitation of 1955 - 68 was observed to be preserved in the organically bound tritium of a tree ring sequence. Reactor tritium was discernible in a tree growing at a distance of 10 km from CRNL. These techniques provide convenient means of monitoring dispersal of HTO from nuclear facilities."
 
The paper analyzed tritium content in maple trees in the Perch Lake Basin, Chalk River Nuclear Laboratories (CRNL). Current levels were reflected in the moisture of leaves and historic levels in tree ring growth. The Liquid Waste Disposal Area provided an area of tritium dispersal in the natural environment as the surface and ground waters there, have an elevated level of reactor-produced tritium. While it is claimed in the paper that these concentrations are not high enough to constitute a health hazard (!? ed. CCRC), they do provide spikes which could be measured more easily than tritium in the general environment.
 
Tree 1: Located on the east shore of Perch Lake where the atmospheric HTO level is raised by influx of reactor HTO evaporated from the lake (where tritium is concentrated at 4,800 Bq/L. pg. 409), but the soil and ground waters are relatively low in tritium.
 
Tree 2: Located in a drainage path from the Liquid Waste Disposal Pit where the concentration of atmospheric HTO is low compared to the concentrations of soil and ground water HTO (84,000 Bq/L. in 1978. Fig.3).

Table 1 ( in Bq/L water)

free water from

Tree 1

Tree 2

Atmosphere

~600

 .
Leaves

444 - 516

1104

Leaf stalks

168 - 180

 .
Twig wood

141 - 162

 .
Trunk wood

141

 .
Trunk bark

141

 .
Root wood

168

 .
Soil

92.4

9,024

Ground water

90

 .

The study found that the concentration of tritium in leaves was closer to atmospheric levels than to that in the soil and ground waters which contribute the transpirational stream of the tree. "Evidently, the leaf moisture equilibrates with the surrounding atmospheric moisture. HTO diffuses back into the tree and the water of the woody parts of the tree appears surprisingly well-mixed at a concentration intermediate between those of the soil and atmospheric conditions."

In tree 2, the leaves had a much lower level of HTO than the soil and ground waters and is related to the atmospheric level. This suggests the use of leaves as a means of monitoring the atmospheric HTO in the general environment and in the conclusion remarks at paper's end, a means of observing regional atmospheric dispersal of HTO from an industrial source. "Concentrations established in such vegetation by a given release are particularly relevant to population exposure considerations since they combine contributions from atmospheric moisture, precipitation and soil water averaged over a few weeks time."
 
In a discussion after the paper proper, W. Roether (unknown scientist, ed. CCRC) stated, "that we made a study of tritium concentrations in wine and we looked into the relationship in tritium concentration between air humidity and water in, e.g. the leaves. I think it is obvious that there has to be a dependence on humidity. In a case where the air humidity is 100%, no water will be sucked up the stem, but the stomata of the leaves will be open and the water in the leaves will approach the tritium concentration of the air moisture, whereas at 0% humidity the leaves will only contain water drawn up from the soil. Therefore, the higher the humidity, the more will the tritium concentration in the leaves represent that of the atmospheric moisture."
 
In our test sample of poplar leaves from behind the mini-mall where the SRB tritium light factory is situated, it is shown that the level of tritium is 1890 Bq/L. Compare this to the table above where a tree growing beside a contaminated lake shows less tritium at1104 Bq./L. In another chart presented in the above paper, 'HTO in free water of poplar leaves in the vicinity of CNRL and Ontario Hydro NPD power station, July 1978 ', the levels of tritium beside the stacks at each reactor are 1040 Bq/L. at CNRL and 1728 Bq/L. at the NPD station, Rolphton. This clearly shows that the levels of Tritium around the SRB plant in Pembroke are needlessly high at best and dangerous at worst.
 
(1 ) Brown, R.M. 'Environmental Tritium in Trees.' in IAEA-SM-232/44, (circa 1979): 405-417

see discussion of health effects of Tritium in the environment

Darlington Tritium data / Bruce Tritium data / Pickering Tritium data / tritium in vegetation trends: 1982 to 1998/ Pembroke, ON tritium test results

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