Iodine Status of Mother-Infant Dyads from Montréal, Canada: Secondary Analyses of a Vitamin D Supplementation Trial in Breastfed Infants.

BACKGROUND: Most pregnant or lactating women in Canada will not meet iodine requirements without iodine supplementation. OBJECTIVES: To assess the iodine status of 132 mother-infant pairs based on secondary analyses of a vitamin D supplementation trial in breastfed infants from Montréal, Canada. METHODS: Maternal iodine status was assessed using the breastmilk iodine concentration (BMIC). Singleton, term-born infants were studied from 1-36 months of age. Usual (adjusted for within-person variation) iodine intakes were estimated from urinary iodine and creatinine concentrations. Iodine status was assessed using median urinary iodine concentrations (UICs) and by estimating inadequate intakes by the cut-point method using a proposed Estimated Average Requirement for infants 0-6 months of age (72 µg/d). RESULTS: At 1, 3, and 6 months of age, 70%, 63%, and 3% of infants, respectively, were exclusively breastfed. From 1-36 months of age (n = 82-129), the median UICs were ≥100 µg/L (range, 246-403 µg/L), which is the cutoff for adequate intakes set by the WHO for children <2 years. Almost all (98%-99%) infants at 1 and 2 months, 2 and 3 months, and 3 and 6 months of age had usual creatinine-adjusted iodine intakes ≥ 72 µg/d. The median BMIC was higher (P < 0.001) at 1 month compared to 6 months of lactation [1 month, 198 µg/kg (IQR, 124-274; n = 105) and 6 months, 109 µg/kg (IQR, 67-168; n = 78)]. At 1 and 6 months, 96% and 79% of mothers, respectively, had a BMIC ≥ 60 µg/kg, the lower limit of a normal reference range. The percentages of mothers that used a multivitamin-mineral (MVM) supplement containing iodine were 90% in pregnancy and 79% and 59% at 1 and 6 months of lactation, respectively. CONCLUSIONS: The iodine status of infants was adequate throughout infancy. These results support a recommendation that all women who could become pregnant, who are pregnant, or who are breastfeeding take a daily MVM supplement containing iodine.

Rapid and efficient autoclave digestion for the extraction of iodine-129 from urine samples.

A new method was developed to extract 129I from urine samples and measure it using accelerator mass spectrometry (AMS). The samples were pre-treated in an autoclave with hydrogen peroxide and were then acidified with nitric acid, followed by the precipitation of iodine as silver iodide (AgI) for measurement by AMS. This new procedure is substantially faster than previous methods for the extraction of iodine from urine and results in less chemical waste. The efficiency and reproducibility of this method were evaluated by using 125I as a yield tracer, eventually giving a recovery above 99%. To achieve this, several iterations of the method were required. The method was then successfully applied to measure 129I/127I isotopic ratios and 129I concentrations in 25 human urine samples. The AMS results for 129I in urine ranged 3.3 × 106 atoms/L to 884 × 106 atoms/L and the isotope ratio (129I/127I) in human urine ranged from 7.38 × 10-12 to 3.97 × 10-10 with a median of 1.29 × 10-10. This new method will be useful for investigations into the sources of iodine in the human diet and their relative importance for iodine sufficiency.

The seasonal fluctuations and accumulation of iodine-129 in relation to the hydrogeochemistry of the Wolf Creek Research Basin, a discontinuous permafrost watershed.

The long lived radioisotope (129)I is a uranium fission product, and an environmental contaminant of the nuclear age. Consequently, it can trace anthropogenic releases of (129)I in watersheds, and has been identified as a potential means to distinguish water sources in discharge (Nimz, 1998). The purpose of this work was to identify the sources and mass input of (129)I and trace the transport, partitioning and mass balance of (129)I over time in a remote watershed. We monitored (129)I and other geochemical and isotope tracers (e.g. δ(14)CDIC, δ(13)CDIC, δ(2)H, δ(18)O, etc.) in precipitation and discharge from the Wolf Creek Research Basin (WCRB), a discontinuous permafrost watershed in the Yukon Territory, Canada, and evaluated the use of (129)I as a water end-member tracer. Radiocarbon and geochemical tracers of weathering show that discharge is comprised of (i) groundwater baseflow that has recharged under open system conditions, (ii) spring freshet meltwater that has derived solutes through closed-system interaction with saturated soils, and (iii) active layer drainage. The abundance of (129)I and the (129)I/(127)I ratio correlated with geochemical tracers suggests varying contributions of these three water end-members to discharge. The (129)I concentration was highest at the onset of freshet, reaching 17.4×10(6) atoms/L, and likely reflects the lack of interaction between meltwater and organic matter at that time. This peak in (129)I was followed by a decline over the summer to its lowest value. Mass balance calculations of the (129)I budget show that the input to the watershed via precipitation is nearly one order of magnitude higher than the output suggesting that such arctic watersheds accumulate nearly 90% of the annual input, primarily in soil organic matter. Temporal variations in discharge (129)I concentrations correlated with changes in discharge water sources suggesting that (129)I is a promising hydrologic tracer, particularly when used in concert with other stable and radioisotopes.

Extraction of (129)I and (127)I via combustion from organic rich samples using (125)I as a quantitative tracer.

Iodine-129 ((129)I) is a biophilic, naturally occurring radioisotope (half-life: 1.57 × 10(7) years) that has been released in large quantities by nuclear fuel reprocessing. This iodine has cycled throughout the globe and chiefly the northern hemisphere and can be found in a wide variety of environmental materials, particularly organic rich soil and organic matter. Extracting iodine reliably from solid samples has been done by a variety of methods, however, pyrohydrolysis has been the most widely used. There is a wide variation between existing pyrohydrolysis techniques and this raises questions about the quantitative recovery of iodine from method to method. In order to quantify iodine recovery from pyrohydrolysis we have spiked samples with an iodine-125 radiotracer prior to combustion and trapping in an alkaline solution. Inorganic (125)I tracer was used as well as humic acid labeled with (125)I to simulate the behavior of (129)I and (127)I in complex organic substances and extract iodine regardless of how it is partitioned. Using these tracers we explored the effect on recovery of (125)I under a variety of combustion parameters. These include carrier gas flow rate and iodine volatilization temperature. We observed that the best recoveries of (125)I were at flow rates between 400 and 800 mL/min and most (125)I recoveries were above 85%. The experiment to determine the temperature at which iodine volatilizes from the sample showed two distinct trends for the release of iodine. One trend showed that most iodine is released at approximately 525 °C, while the other trend showed that the samples needed to reach 800 °C and remain there for at least an hour. These findings illustrate the usefulness and importance of using a quantitative recovery tracer for every iodine extraction. We then combusted and precipitated several Atlantic Ocean seaweed and standard reference materials for AMS analysis as AgI. The (129)I concentration of the seaweed ranged between 4.4-5.5 × 10(9) atoms/g and the (129)I/(127)I ratio was 2.3-2.9 × 10(-9), both of which compare well to published values for Atlantic seaweed. The results for the standard reference materials also agree with specified values indicating that this technique is reliable. By optimizing pyrohydrolysis conditions and testing the recovery of iodine with a (125)I tracer it is possible to quantify and maximize recovery from organic samples. This will allow for the investigation of variations in the (129)I concentration and (129)I/(127)I ratio with a high degree of precision in complex, organic rich samples.