Stable iodine

Metabolically, radionuclides are handled in the same way as stable elements of the same atomic numher. Thus radioactive iodine simulates stable iodine, being concentrated in the thyroid gland so predictably that its rate of uptake provides an accurate measure of thyroid function. The metabolism of other radionuclides also is sufficiently characteristic so that their patterns of uptake, distribution, translocation, and excretion are similarly predictable. 

According to C. F. Barwald and A. Monheim (1835), the decomposition is accelerated by the presence of organic substances. J. Milbauer tried the effect of thirty-two metal chlorides of sodium tungstate and molybdate of uranyl sulphate and of sulphuric, selenic, arsenic, and boric acids on the photo-decomposition of chlorine water, and found. that none accelerated but that most retarded the action. Chlorine catalyzes the decomposition of bromine water and bromine, chlorine water while iodine does not accelerate, but rather retards the reaction, probably by forming relatively stable iodine compounds. A. Bcnrath and H. Tuchel found the temp, coeff. of the velocity of the reaction with chlorine water between 5° and 30° increases in the ratio 1 1 395 per 10°. 

Accidents with nuclear reactors or nuclear bombs can expose large numbers of people to several decay products of uranium, and iodine isotopes are among the most abundant compounds released in such reactions. It is therefore logical to use salts of stable isotopes of iodine to prevent the accumulation of radioiodine in a person or population at risk of such exposure. The accidents in Windscale (UK), Three Mile Island (USA), and particularly Chernobyl (Ukraine) drew attention to such problems. The major question is therefore whether the potential adverse effects of stable iodine when given indiscriminately to large... 

The main adverse effects of stable iodine are shown in Table 1. 

Iodine should be given to the general population if the risk of radioiodine exposure is sufficient (over 15-100 rem), but people with increased susceptibility to the adverse effects of iodine (previous thyroid disease or known serious allergies) should be excluded (11-16). In elderly people the benefit of stable iodine probably does not outweigh its potential adverse effects, while in pregnant women and infants the benefit to harm balance is not established rapid evacuation of such people from fallout zones should be given the highest priority (SEDA-11, 358). 

Helsing E, Dukes MNG. The Safety of Stable Iodine When Used to Provide Protection against Nuclear Fallout. Internal Advisory ReportCopenhagen WHO Regional Office for Europe . 1986. 

Radioactive isotopes of iodine are handled by the thyroid in the same way as stable iodine and are therefore actively concentrated, incorporated into thyroglobulin, stored, metabolized, and secreted as thyroid hormones. Small amounts of radioactive iodine are therefore ideal probes to analyse the uptake of iodine, the distribution of iodine in the gland, and possibly even its turnover and incorporation into thyroid hormones. Larger amounts of radioactive iodine selectively radiate the thyroid gland and therefore selectively impair the function of the follicular thyroid cells and eventually destroy them. 

Ocean disposal requires that the 1Z9I release rate (by leaching) must be less than the mixing rate of the ocean to insure adequate mixing of the 1Z9I with stable iodine. No thermal stability requirements are seen for this dispersion strategy. 

The particulate activity trapped on the membrane filters in the sampling packs increased during the first hour (Fig. 3.2). The concentration of condensation nuclei in air in the reactor shell was 1.2 x 1010 m-3. Megaw May showed that an accommodation coefficient of 5 x 10-3 (compare Section 1.12) would explain the observed rate of increase in particulate iodine due to adsorption on the nuclei. The subsequent decline in particulate activity was due to deposition of nuclei on surfaces. Surprisingly, in this and other experiments, release of stable iodine vapour into the containment shell 4 h after the start of the experiment made little difference to the concentration of particulate 132I. Subsequently, Clough et al. (1965) showed that the amount of... 

Elsewhere, two-component samplers were operated to separate the particulate and gaseous (Ig) fractions of iodine from Chernobyl, without attempting to distinguish inorganic and organic gaseous forms. The lpHg ratio was about 0.25 in Scandinavia (Devell etal., 1986), 0.2 at Harwell (Cambray et al., 1987), 0.5 in Japan (Aoyama et al., 1986) and 0.5 in New York (Leifer et al., 1986). The particulate fraction may have been derived partly from discrete particles of fuel disseminated in the accident, but it is noteworthy that the distribution between lp, I, and l0 observed at Munich is not dissimilar to the distribution of stable iodine as reviewed in the next section. 

Table 3.2 shows measurements of particulate and gaseous stable iodine in the atmosphere. Moyers et al. (1971) used membrane filters and activated charcoal to collect the particulate and gaseous fractions in air at Boston, and found the ratio Ip/Ig to be correlated with the concentration of particulate lead in the air. It was not inferred that Ip was combined with particles of lead, but rather that the concentrations of lead served as an index of the total airborne particulate. Moyers et al. expressed their results as... 

It is believed that CH3I is produced by marine algae and released from seawater, and that this constitutes the main source of stable iodine in the atmosphere (Lovelock et al., 1973). Elemental iodine may be liberated from the sea surface by ultraviolet light (Miyake Tsunogai, 1963), or by the action of ozone (Garland Curtis, 1981), but I2 is dissociated very rapidly by photochemical action, and its mean residence time in daylight air is less than a minute. 

In the Idaho experiments, 5 mg of stable iodine carrier were added to the 1311 in the preparation of the source. There were no significant differences in vD with source/sample distances up to 300 m. In the Jiilich experiments, sources of 25 g I2 were released, and the deposition was assessed from the increase in stable iodine on the herbage, at ranges of about 20 m, giving values of vD not very different from those obtained in Idaho. This suggests that the predicted rapid photolysis of I2 vapour does not affect its deposition greatly at source/sample distances of a few hundred metres. 

Only limited information is available on the washout of radioiodine vapour by rain. Measurements of stable iodine in rain, compared with iodine vapour in air (Whitehead, 1984), give a value about 30 for the washout ratio W, defined as the ratio (I per kg rain)/(I per kg air). For a moderately heavy rainfall of 1 mm h-1, this would imply a velocity of deposition in rain of 7 mm s-1, which is the same order of magnitude as the velocity of dry deposition. The washout ratio of particulate fission products is typically about 500 (Table 2.12), so radioiodine deposited in... 

Volatilisation may be more significant when appreciable quantities of stable iodine carrier are present. Heinemann Vogt (1980) measured... 

The transfer factor Fm from feed to milk is defined in equation (2.11) as the activity per litre expressed as a fraction of the activity ingested daily by the cow. Numerous measurements of Fm have been made by dosing cows with iodine isotopes or by comparing radioactive or stable iodine in milk and in the herbage eaten by the cows. Table 3.6 shows a selection of the results. Fm depends on the yield of milk and on seasonal factors (Gamer, 1971), but it does not appear to depend on the chemical form of the iodine (Bretthauer et al., 1972). Gamer (1971) recommended Fm = 5 x 10 3 d l-1 for UK conditions, but noted that US results tended towards a higher value. 

P Puumalainen, P Sikanen and H Olkkonen (1979) Measurement of stable iodine content of tissue by coherently and Compton scattered photons. Nucl. Instrum. Methods 163, 261-263. 

The first evidence for the existence of a stable iodine cation was obtained by Masson (2) in 1938. He postulated the presence of Ig" and Ig in solutions of iodine and iodic acid in sulfuric acid in order to explain the stoichiometry of the reaction of such solutions with chlorobenzene to form both iodo and iodoso derivatives. Later, Symons and co-workers (6) gave conductometric evidence for I3 formed from iodic acid and iodine in 100% sulfuric acid and suggested that Ig" " may be formed on the basis of changes in the UV and visible spectra when iodine is added to la solutions. Gillespie and co-workers (7) on the basis of detailed conductometric and cryoscopic measurements confirmed that Ig is formed from HlOg and Ig in 100% sulfuric acid according to Eq. (1). The Ig cation may also be prepared in fluoro-... 

Naumann et aO have prepared pure CF3IO by the action of O3 on CF3I the same product could also be produced by the reaction of CF3IF2 and Si02 in MeCN between —40 and 0°C. These workers also isolated the more stable iodine(v) derivative from the reaction (19) the oxide difluoride CF3IOF2 was shown to be an intermediate in this reaction. 

XRF is not a new method since the first measurements of stable iodine in the thyroid by Hoffer et al. (1968), the use of XRF has spread to include several other elements in medical apphcations, as well as applications in occupational and environmental surveillance. Today, XRF is primarily used as a nondestructive method for investigation of metals, minerals, environmental samples, food constituents, and body fluids. Examples of in vivo XRF elemental analysis are measurements of lead in bone (Ahlgren and Mattsson, 1979 Somervaille et al., 1985 Todd and Chettle, 1994) and studies on cadmium, mercury, gold, and platinum (Ahlgren and Mattsson, 1981 Borjesson et al, 1993, 1995), but the method is not, to our knowledge, used clinically as a tool in the routine assessment of thyroid function. Some in vivo applications of the method are listed in Table 3.1. 

Jockheer, M.H. (1983). Stable iodine and thyroid function, in (eds M. Jonckheer and F. Deconinck), X-ray Fluorescent Scanning of the Thyroid. Martinus NijhofF Publishers, Boston, MA, pp. 100-116. 

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