Total organic iodine

Effect of graded doses of iodide administered 30 min before killing on the thyroidal metabolism of iodine in rats. Values shown are mean SE (in brackets) of values obtained in 5 rats. For purposes of reference, the curve of total organic iodinations is shown as a dotted line in the lower 3 panels ( ). 

In all countries with developed medical care, X-ray contrast media can be expected to be present at appreciable quantities in sewage water. Clara et al [13] detected iopromide at a mean concentration of 3.84 pg in the influent of a WWTP receiving hospital wastewater, while in WWTPs without a hospital within their drainage area this contrast media was not present. lodinated X-ray contrast media are proved to contribute significantly to total absorbable organic iodine in clinical wastewaters up to 130 pg of iodine in the influent of municipal WWTP in Berlin and 10 mg in hospital sewage was detected [23]. 

In environmental waters, the most important oxidation states are iodide ( — 1) and iodate ( + 5). Most published methods for the analysis of radioiodine aim only to convert all species to one chemical form in order to determine a total concentration value for the particular nuclide of interest. However, some specialist methods designed for the analysis of the stable element such as that recently described by Woittiez et al. (1991) for the determination of iodide, iodate, total inorganic iodine and charcoal-absorbable (organic) iodine in seawater could presumably be adapted to provide information about the speciation of radioiodine as well. More difficult to adapt would be techniques such as polarography which have been useful in the measurement of the iodide/iodate system (e.g. Liss et al., 1973). 

It is not clear, however, in which chemical state the particulate iodine is present. Some studies reported it to be 103 but in others no 103 was found (see references and discussion in McFiggans et al. (2000)). Based on measurements of aerosol composition. Baker et al. (2000) state that iodine is present in aerosol in varying proportions as soluble inorganic iodine, soluble organic iodine and insoluble, or unextractable, iodine. Baker et al. (2001) measured the deposition of iodine in rainwater and in aerosol at Weyboume, North coast of Norfolk, UK. They found that iodide (I ) constituted 5-100% of total iodine deposition in both rain and aerosol. The rest was found to be iodate (10j") with a very small contribution from CH3I (<3% of the total iodine deposition). 

In pore waters the dissolved T concentrations, which are higher than the total iodine concentration in seawater, can be observed with decomposition of particulate organic matter (e.g., Figure IB). In Figure IB the T pore-water concentrations are in micromolar units, compared to the total iodine concentration in seawater of <0.5 (jlM. Thus, the pore waters contain several times the amount of iodine that is found in seawater. Increased T concentrations and significant amounts of organic iodine are found in anoxic basins such as the Black Sea (29, 39, 40). 

A method for the determination of iodide, iodate, organic iodine, and total iodine in seawater was developed by radiochemical NAA combined with ion-exchange preseparation (Hou et ai, 1999). The filtered seawater was passed through an anion-exchange column. The column was washed with deionized water, and the effiuent and washings were collected for the determination of the sum of iodate and organic iodine. The column was washed with... 

Figure 9.6 shows the vertical variation of dissolved (nonvolatile) organic iodine (DOI) at Sta. 17. DOI was obtained from the difference in T1 (total iodine = D + 107 + DOI) and from Huang ef a/., (2005). 

Organic iodine in seawater can be divided into (i) volatile compounds and (ii) nonvolatile compounds. Here, DOI will be used to refer to nonvolatile compounds. The presence of DOI in seawater was first described by Truesdale (1975). He observed an increase in the reactive iodine when seawater was irradiated with high-intensity UV light. In the 13 samples studied, its concentration ranged from <0.01 to 0.04pM. The ratio of DOI in total iodine was from <1% to 11%. 

The coexistence of various inorganic and organic iodine species, in different proportions, has been reported in various environments (Liss et al., 1973 Couture and Seitz, 1983 Yuita, 1992, 1994 Yamada et al., 1999 Muramatsu and Ohmono, 1988 Baker et al., 2001). Organically bound iodine can be a significant fraction of total iodine in aqueous systems and in the atmosphere. For example, methyl iodide is an important gaseous form of iodine in the marine atmosphere and in releases from nuclear fuel reprocessing facilities, while dissolved organo-I compounds comprise up to 50% of total iodine in aqueous samples from estuaries, rivers, and rain (Santschi and Schwehr, 2004). 

Various iodine species in different proportions exist in soil and sediments. Organically bound iodine, with fim-ited solubility and mobility, commonly comprises the major proportion of total iodine it is well-correlated with total organic matter, sesquioxides, and clay content. 

Although thyroid slices of hyperthyroid patients take up iodine more quickly than normal thyroid slices, the total iodine content of the thyroid gland (1.8 mg/g of dry weight in normal individuals) is consideraWy reduced in hyperthyroidism (0.26 mg/g of dry weight). The reduction affects both inorganic and organic iodine, but when all iodinated compounds in the thyroid are analyzed, thyroxine seems to be the compound most reduced in hyperthyroidism. 

Tests with an alkaline system (pH 8 to 9) yielded low overall volatility of iodine, giving partition coefficients in the range of 10 to 10 . Simultaneously, low levels of organic iodine species were formed (on the order of 0.1%), even when relatively large amounts of epoxy paint materials were present further, low iodine deposition onto the surfaces of the vessel took place. Under acidic conditions (pH 4 to 6), the total iodine partition coefficient was lower by a factor of about 100 and the organic iodide level was higher by about a factor of 10 (but still remained a small fraction of the total iodine) than under alkaline conditions. Moreover, wider acidic conditions an appreciable iodine buildup on vessel surfaces is to be expected which may constitute a significant delayed source of volatile iodine if the system equilibrium is disturbed (Ritzman et al., 1991). 

Addition of organic impurities such as methyl ethyl keton (MEK), a common paint solvent, to an aqueous I solution in the absence of radiation proved not to result in a measurable organoiodide formation. Under the influence of radiation, however, addition of MEK leads to an increase in the total airborne iodine concentration by more than an order of magnitude over a period of several hours, corresponding to a decrease of the steady-state iodine partition coefficient from 10 to 10 in the absence of MEK to about 10 after addition of this compound (Fluke et al., 1991). 

L. Gersh, T. Caspersson, Total protein and organic iodine in colloid and cells of single follicles of the thyroid gland. Anat. Rec. 78, 303-319 (1940)... 

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