131I In Milk Research Articles

Metabolism of I131 by Dairy Cows During Long Term Daily Administration of the Radioisotope

The results of fifteen trials on nine cows given I131 twice daily for about 14 days are presented in this paper. The cows showed a thyroid I131 level equivalent to 79 per cent of a daily dose, put about 1 per cent of the daily dose of I131 into each 1 of milk and showed a milk/plasma I131 ratio of 2:3. Approximately 5 per cent of the I131 of the milk was found to be bound to protein at the end of 2 weeks of receiving I131. The total I131 found in milk, thyroid and whole body was followed in two cows from the start of I131 dosing. When the decay of I131 was accounted for, the per cent of milk I131 was found to plateau at about 8 days while that of the body and thyroid did not plateau during the experiment. The amount of I131 in milk was maximum at about 3 days and reached a peak in the thyroid and body at about 10–8 days, respectively. Data are presented to show that the level of stable iodine in the diet of the cow may affect the movement of I131 into milk.

I-131 IN MILK AND THYROID OF DAIRY CATTLE FOLLOWING A SINGLE CONTAMINATION EVENT AND PROLONGED DAILY ADMINISTRATION.

A sing1e I/sup 132/ contamination event of forage was simulated by administering I/sup 131/--labeled feed to dairy cattle twice daily for 31 days, all feed samples being spiked on day one with 5 mu C I/sup 131/ per sample. Peak milk concentration in the dairy cattle occurred on the fourth day with about 0.4% of the first day's dose of 10 mu C observed per 1 of milk. The peak thyroid concentration in the cattle occurred after 1 week and was about 70% of the first day' s dose of I/sup 131/. In a second study, 5 mu C of I/sup 132/ were fed daily to three cows starting before parturition and continuing for a period of 6 months of lactation. Apparent equilibrium of I/sup 131/ in the thyroid was reached after 2 weeks and approached twice the daily feeding level. A suggestion of increased thyroid uptake occurred following parturition. The I/ sup 131/ concentration in the colostrum was 2-3 times that in the milk on the seventh day of lactation, after which time a gradual increase was observed. The per cent of the daily dose of I/sup 131/ appearing in the milk varied from 0.4 to 1.0% over amore » 6month period. Following an increase in the daily stable iodine content of the cow's diet from 5 mg to 2 g per day, milk concentration of I/sup 131/ decreased 50% and thyroid concentrations decreased more than 90%. (auth)« less

DIFFERENTIAL ACCUMULATION OF I-131 FROM LOCAL FALLOUT IN PEOPLE AND MILK.

Abstract Marked differences in accumulation of I131 in milk and people were recorded during July and August, 1962, along fallout trajectories with origins at the Nevada Test Site. Iodine131 was measured in milk from thirty-nine dairy farms situated in geographically and ecologically different areas of Utah, and in twenty-four persons residing on these farms. Total I131 intake during this incident, assuming consumption of one l. milk/day, ranged from 0 to 800,000 pc. Total body and thyroid burdens of people from farms paralled levels in milk produced on their farms. Accumulation in milk was correlated with feeding practices; highest accumulation was found in milk and people from farms where cattle were fed freshly-cut green alfalfa or were grazing on wet meadows. Little I131 appeared in the milk of cattle fed uncontaminated feed which had been stored prior to the arrival of fallout. Highest I131 levels occurred on farms at high altitudes.

I-131 DOSE TO HUMAN THYROIDS IN NEW YORK CITY FROM NUCLEAR TESTS IN 1962.

Abstract—During the U.S. and U.S.S.R. nuclear weapons tests in 1962, the I131 content was measured in 456 human thyroids dissected at autopsies of New York residents with no known history of thyroid disease. Measurements were also made of thirty-one fetal thyroids, including five cases in which the maternal thyroids were also available for post-mortem study. In addition, in vivo measurements were made of the uptake of I131 in eleven normal adults who consumed known amounts of fresh milk contaminated with I131 from the weapons tests. Daily measurements of the milk distributed in New York City revealed that the average concentration of I131 was 38 pc/l. during the period from May 19, when this nuclide was first detected in the city, until January 5, 1963, when the study was discontinued. The maximum concentration was 370 pc/l. late in September. The most heavily exposed members of the population of New York City, based on measurements of dissected thyroids, received a thyroid dose of 40 mrad as a result of the 1962 nuclear tests. During a comparable period of time, in vivo measurements of adults who were consuming an average of 0.82 1. fresh milk/day disclosed the mean thyroid burden in the group to be 300 ± 130 pc compared to a mean of 88 ± 74 pc for the dissected thyroids during the same period. Although the latter thyroids were shown to contain less I131, on the average, than the in vivo cases selected from relatively heavy milk drinkers, the Medical Examiner's cases gave higher I131 values than hospital cases that came to autopsy. Using the measured values of I131 in milk as a basis of calculation, it is estimated that a child whose thyroid weighs 2 g and who consumes 1 l. milk/day received a dose of 140 mrad during the period covered by this study. The highest concentration of I131 in the thyroids of this series was 630 pc/g in a 20-mg thyroid from a 3-month fetus.

131I concentrations in blood, milk, urine and faeces of dairy cows following a single dose of radio-iodine

1. The concentrations of 131I in milk, urine, and faeces were compared to the total and non-proteinbound radio-iodine of blood after a single dose of radio-iodine to cows that were being maintained on diets providing about 3·5 or 12-16 mg. of stable iodine per day.2. In general, the 131I concentrations in milk and urine tended to parallel the non-protein-bound 131I of blood. Faecal 131I levels of the low-iodine cows tended to parallel that of the whole blood, whereas it followed the non-bound radio-iodine of blood for cows on the higher stable iodine diet.3. Compartmental analysis of the concentration curves showed a component with a T½ of from 10 to 22 hr. being common to both groups of cows. The second component of the curves constructed for the cows on the higher iodine intake had a T½ of from 41 to 58 hr. The second component for the low-iodine cows had a T½ that ranged from 83 to 169 hr. for the urine, faeces and non-bound radio-iodine of blood and 1200 and 1580 hr., respectively, for the faecal and whole-blood curves.4. A greater proportion of bound radio-iodine was observed in the milk and blood of cows on the low-iodine diet than for the cows on the higher iodine intake. The proportion of bound 131I in blood increased with time, but the bound 131I of milk was relatively constant.

Effect of Feeding Thyroxine on Secretion of I131 in Milk

Summary The metabolism of single doses of NaI 131 was studied in eight comparisons with lactating cows fed 80mg l-thyroxine daily, paired either with their identical twins or with their own performance in adjacent periods when no thyroxine was fed. Two additional cows fed thyroxine and their identical twin controls each received 1 mc I 131 -labelled l-thyroxine. Thyroxine feeding, which began 2 wk before dosing and continued through seven-day collection periods, increased milk production and excretion of I 131 from both the iodide and thyroxine doses in milk, urine, and feces. Orally administered thyroxine increased rate of deiodination and plasma clearance of the thyroxine dose. Although more I 131 from the iodide dose was secreted in milk of thyroxine-fed cows, the concentration of activity per milliliter of milk did not differ significantly from that of controls. Thus, most of the greater excretion of I 131 via the milk when thyroxine was fed was related to higher milk yield.

I-131 accumulation by the lactating rat mammary gland.

The mammary glands of lactating rats fed a low-iodine diet accumulated 50% of an injected I131 dose or five times as much as the thyroid gland and twice as much as excreted by the kidneys in 17–24 hr. Rats which accumulated greater amounts of I131 in their mammary glands had significantly lesser thyroidal I131 uptakes. KClO4 and methimazole significantly reduced accumulation of I131 in milk, KClO4 being the more potent. Methimazole acted primarily in reducing the binding of I131 to milk protein. The concentration of I131 in milk, trichloroacetic acid-precipitable I131 in milk and in plasma, and ratio of milk I131 to plasma I131 were significantly reduced by the addition of iodide to the diet. The amount of I131 in the milk was not correlated with the amount of milk secreted. Exogenous thyroxin inhibited thyroidal I131 uptake but did not influence accumulation of I131 by the mammary gland. Injection of thyrotrophin restored thyroidal uptake of I131 but did not affect accumulation of I131 by the mammary gland.

Effect of Mild Hyperthyroidism upon Secretion of I131 in Milk of Dairy Cattle

Summary Six lactating dairy cows were administered 100 µd. I 131 intrajugularly. Samples of milk were analyzed daily for five days for the content of I 131 present. During the first 24 hr. from 4.9 to 7.2% of the injected dose of I 131 appeared in the milk, with a mean of 5.8%. During the five-day period, the total mean percentage of the injected dose increased to 8.2, with a range of 6.9 to 9.2%. The experiment was repeated with the same cows during a period when each cow was receiving exogenous thyroxine equal to 50% above its individual winter thyroxine secretion rate. In spite of the fact that daily milk secretion increased an average of 22%, the mean percentage of the injected dose of I 131 appearing in the milk during the first 24 hr. was reduced to 2.9, with a range of 1.9 to 3.9%. The mean total percentage of I 131 appearing in the milk during five days was 4.8, with a range of 3.4 to 6.0%. The per cent decline in I 131 in the milk followed an exponential course in both experiments. Mild hyperthyroidism thus reduced the I 131 secretion in milk 50% the first 24 hr., and 41% during the five-day period. It was pointed out that dairy cattle transfer relatively low amounts of I 131 to their milk and that this amount is further reduced by mild hyperthyroidism.

Fission products and the dairy cow III. Transfer of 131iodine to milk following single and daily dosing

1. The transfer of 131I to milk has been studied in dairy cows following oral administration of carrierfree material in single doses as sodium iodide or as elementary iodine and in daily doses as sodium iodide.2. The total recovery from milk during the 6 days following administration of a single dose in twentyeight experiments on fifteen animals ranged from 1·3 to 19·4% of the dose with a mean value of 5·5%. The variations in recovery can be attributed largely to differences in the milk yield.3. There was no significant difference in the biological availability of 131I administered as iodide or iodine.4. The change in concentration of 131I in milk with time following daily dosing did not follow the predicted course, a peak value being observed in most animals after 1–3 days, followed by a fall and a subsequent rise to a steady value lower than was expected.5. The presence of a concentrating mechanism in the udder has been demonstrated by administration of sodium thiocyanate. Comparison of the milk total 131I: plasma dialysable 131I ratio at different times of the year indicates that the concentrating ability may be lower in the summer than in the autumn-spring months.