Submitted to: Journal of Agriculture and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/18/2006
Publication Date: 12/1/2006
Citation: Smith, D.J., Hakk, H., Larsen, G.L. 2006. Tissue distribution, elimination, and metabolism of sodium [36cl]perchlorate in lactating goats. Journal of Agriculture and Food Chemistry 54:8829-8835.
Interpretive Summary: Perchlorate is a strong oxidizing agent that occurs naturally at very low concentrations in ground waters. Several locations within the United States are contaminated with perchlorate from industrial sources, however. Because perchlorate at high doses can inhibit processes within the human thyroid gland, some in the scientific community have expressed concern that developing infants and children may be more sensitive to the effects of perchlorate than adults. This concern was accentuated with the discovery of perchlorate in commercial milk samples and in health supplements used by pregnant or nursing women. Therefore, a study was conducted to determine how much of a perchlorate dose is excreted in milk of dairy goats. Goats were used instead of cows because of the expense associated with the use of the radiolabeled perchlorate. We showed that although most of the perchlorate dosed to goats was converted to chloride (a component of table salt) prior to excretion, a significant proportion of the perchlorate was excreted intact into milk. The perchlorate was completely excreted in milk and urine within 72 hours of dosing, indicating that perchlorate does not tend to accumulate in lactating ruminants.
Technical Abstract: Perchlorate has contaminated water sources throughout the US, but particularly in the arid Southwest, an area containing large numbers of people and few water sources. Recent studies have demonstrated that perchlorate is present in alfalfa and that perchlorate is secreted into the milk of cows. Studies in lactating cows have indicated that only a small portion of a perchlorate dose could be accounted for by elimination in milk, feces, or urine. It was hypothesized that the reminder of the perchlorate dose was excreted as chloride ion. The purpose of this study was to determine the fate and disposition of 36Cl-perchlorate in lactating dairy goats. Two goats (60 kg) were each orally administered 3.5 mg (16.5 microcuries) of 36Cl-perchlorate. Blood, milk, urine, and feces were collected incrementally until slaughter at 72 hours. Total radioactive residue (TRR) and perchlorate concentrations were measured using radiochemical techniques and liquid chromatography mass-spectrometry (LC-MS-MS). Peak blood levels of TRR occurred at 12 h (~195 ppb) post dose; peak levels of parent perchlorate, however, occurred after only 2 h suggesting that perchlorate metabolism occurred rapidly in the rumen. The serum half-life of perchlorate was estimated to be 2.3 h. By 24 h perchlorate was not detectable in blood serum, but TRR remained elevated (160 ppb) through 72 h. Milk perchlorate levels peaked at 12 h (155 ppb) and were no longer detectable by 36 h, even though TRR were readily detected through 72 h. Perchlorate was not detectable in skeletal muscle or liver at slaughter (72 h). Chlorite and chlorate were not detected in any matrix. The only radioactive residues observed were perchlorate and chloride ion. Bioavailability of perchlorate was poor in lactating goats, but the perchlorate that was absorbed intact was rapidly eliminated in milk and urine.