Strontium in milk

In the 1950s and 1960s, several nations conducted tests of nuclear warheads in the atmosphere. It was customary, following each test, to monitor the concentration of strontium-90 (a radioactive isotope of strontium) in milk. Why would strontium-90 tend to accumulate in milk ... 

The reported results for Cs in soil agreed well with the recommended values (see Table 9.15). On the other hand, results for strontium and plutonium in soil showed a tendency for overestimating (by as much as a factor of four). A similar tendency for overestimation was noted for strontium in milk (by as much as a factor of nine) and for caesium in milk (by as much as a factor of three). While results for strontium in... 

Garner (1971) and Ng (1982) have reviewed laboratory and field data on Fm. For strontium isotopes, it depends on the calcium content of the feed and the milk, and some time may elapse before an increased intake of Sr is fully reflected in milk. Sr, like Ca, is stored in the skeleton, and 50% or even more of Sr in milk may derive from bone, depending on the cow s calcium status (Comar et al., 1961). 

The analyte was concentrated (enrichment factor 200) but high levels of natural strontium in the separated fraction (of about 1 jxg mF ) meant higher detection limits (80 pg 1 ) due to peak tailing of Sr+ atm/z = 90 and the relatively low abundance sensitivity of ICP-SFMS at a medium mass resolution of 6 x 10 . This detection hmit in the separated fraction corresponded to a detection limit of O.TpgT in the original urine sample. The recovery of °Sr, determined by the described analytical method in spiked urine samples, was in the range 82-86 %. Decreasing the detection hmit for °Sr determination is recommended by the apphcation of a multiple ion collector ICP-MS due to improved abundance sensitivity. The analytical methods described can also be applied for the analysis of other body fluids, such as blood or human milk or for the determination of °Sr in bones. 

The isotope strontium-90 was introduced into the atmosphere by the atmospheric testing of nuclear weapons. Because of the chemical similarity of strontium to calcium, it now occurs with Ca in measurable quantities in milk, bones, and teeth as a result of its presence in food and water supplies. It is a radionuclide that undergoes beta emission with a half-life of 28 years. It may cause leukemia, bone cancer, and other related disorders. If we begin with a 16-/tg sample of fgSr, 8 /tg will remain after one half-life of 28 years. After 56 years, 4 /tg will remain after 84 years, 2 /ag and so on (Figure 26-6). 

Complexones such as EDTA (complexone III) [1-3] and DCTA (complexone IV) [4,5] are suitable eluents, but other complexing agents, such as citrate [3,6] and sulphate [7] are also applied. Barium has been separated from strontium and other metals by cation-exchange chromatography using mixed HCl-organic solvent eluents [8]. Strontium has been enriched and determined in sea water [5] and in milk [2]. 

As discussed in Section 3.4.2.2, absorbed strontium is eliminated in breast milk during lactation. The concentration of strontium in breast milk of 12 healthy women was estimated to be 74 pg/L (range, 39-93) and the Sr Ca concentration ratio was 0.24 pg strontium/mg Ca (Harrison et al. 1965). 

Radioactive strontium, like stable strontium, can be transferred to infants through breast milk of exposed mothers (Harrison et al. 1965). Ronnback (1981a) demonstrated that the numbers of oocytes (all stages) in the ovary was reduced in neonatal mice that were exposed to radioactive strontium in the milk of surrogate females that had been given high doses by injection. 

Hazzard DG. 1969. Percent cesium-134 and strontium-85 in milk, urine, and feces of goats on normal and verxite-containing diets. J Dairy Sci 52(7) 990-994. 

Platzner, I. T., Becker, J. S., and Dietze, H. J. 1999. Stability study of isotope ratio measurements for uranium and thorium by ICP-QMS. Atomic Spectroscopy 20(1), 6-12. Porter, C. R. and Kahn, B. 1964. Improved determination of strontium-90 in milk by an... 

One route, probably the most important, for ingestion of deposited activity is excluded from consideration in the previous paragraph. This is ingestion by humans of iodine-131 in the milk produced by cows grazing contaminated pastures. ERL of iodine-131, cesium-137, and strontium-89/90 in milk have been derived (42, 43) but only that of iodine-131 need concern us here (39). An estimate of the dose a young child would receive if milk were not banned is included in Table XI. 

Some investigators are finding activation analysis a useful method to determine trace elements, either in essential or nutrient forms or as contaminants, in various food products. Das et al. (217) have shown that many dairy products contain only nanogram amounts of Mn. Hingorani and Chandrasekaran (401), Moeller and Leddicotte (620) and Samuelsson (814) have determined the strontium content of activated milk by radiochemical separations. Molinski, el al. (623) used a rapid radiochemical separation method to determine nanogram concentrations of V in milk powder. Samuelsson (813) also determined submicrogram amoimts of copper in whole milk by activation analysis and Allaway and Cary (12) developed an activation analysis method to determine 0.1 ppm of Se in dried skim milk. 

Strontium radioisotopes in milk can be determined by making use of an ion exchange procedure. The milk sample is allowed to stand for 2 weeks to achieve a sufficient accumulation. Citrate and both yttrium and strontium carriers are added. The solution is applied onto a column of cation then anion exchangers. Strontium and yttrium are retained on the cation and anion exchangers, respectively. Yttrium is washed out from the anion exchanger with hydrochloric acid and precipitated as yttrium oxalate. After weighing the precipitate and determining the chemical yield the activity of the °Y is measured. In the presence of the yttrium oxalate is dissolved in concentrated nitric acid, and yttrium is extracted with tributyl phosphate. Lanthanum-140 remains in the aqueous phase. Yttrium is back-washed with nitric acid and precipitated as its oxalate. In an unfavorable case, i.e., when the amount of exceeds by several orders that of °Sr, the above separation procedure has to be repeated. 

The Soviet tests revived apprehension about the effects of fallout that had subsided after the summer of 1959. The immediate source of concern was iodine 131. Although scientists had recognized as early as 1954 that radioiodine from atomic fission presented potential hazards, they had given much greater attention to strontium 90. In 1957 the Public Health Service had established five monitoring stations that detected iodine 131 in milk samples. 

Ichikawa, R.A.Y.E. 1963 Strontium-calcium discrimination in rats feeding on rice, milk and commercial diets. Health Physics 9 717-720. 

Humans are exposed to radiation from the testing and explosion of nuclear weapons and the wastes of nuclear reactors and power plants. Strontium-90 is a fission product from nuclear reactors. It is of particular concern because it has a long half-life of 38 years and becomes concentrated in the food chain, particularly plants-to-milk. The ban on atmospheric testing of nuclear weapons has reduced this hazard. Strontium-90 does have some industrial uses. Most people in developed countries receive minor exposure to radiation through medical procedures such as X-ray and various treatments for some diseases. 

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