美國聯邦疾病管制局(CDC)最近抽檢15種品牌嬰兒奶粉，結果全數含有過氯酸鹽(perchlorate)污染。過氯酸鹽是火箭燃料、照明彈、煙火和某些肥料中的有毒成份，目前已污染28個州的飲用水和土地，就連食品都含有低劑量成分。疾病管制局共檢測4種嬰兒奶粉，包括牛奶（含乳糖和不含乳糖）、豆奶粉和通常有合成胺基酸的元素配方。
在市面上販售的這四種嬰兒奶粉中，研究員都發現過氯酸鹽污染，其中又以含乳糖的牛奶粉所含比例最高。過氯酸鹽會減低甲狀腺素合成，並抑制人體吸收碘而影響甲狀腺的正常功能。甲狀腺是調節生長、代謝和發育的重要荷爾蒙，甲狀腺素不足，又稱甲狀腺機能不全症，會造成體重增加、心跳減緩、水腫、肌肉無力和疲倦。
美國國家科學院已發現，孕婦若患有甲狀腺功能不足或缺碘，他們的胎兒對過氯酸鹽污染也格外敏感。研究人員警告，倘若沖泡奶粉的飲用水也被過氯酸鹽污染，胎兒攝入的過氯酸鹽劑量便會超過美國環保署的建議安全量。
兩個受污染最嚴重的牛奶品牌在美國市佔率達87%(2000年)，但政府並未公佈廠牌名稱。這份研究甫發表在《環境流病期刊》（Journal of Exposure Science and Environmental Epidemiology），便引起各界對過氯酸鹽污染的重視。
領導研究團隊的施爾(Joshua Schier)博士與合作的疾管局環境危險因素和健康影響部門認為，受污染的奶粉使嬰兒每單位體重攝入過氯酸鹽劑量比成人為高。
疾管局研究員指出，食品藥物管制局(FDA)要求奶粉中必須添加碘，因碘可以減輕過氯酸鹽對甲狀腺的影響；目前奶粉中規定碘量範圍是每100大卡含5到75微克。
添加碘或許可以減輕過氯酸鹽的影響，但科學家仍警告，添加碘的奶粉不能保證避免「過氯酸鹽引起的甲狀腺功能不足」。
環保團體「環境工作小組」（Environmental Working Group）呼籲環保署長潔克森(Lisa Jackson)「揚棄布希政府對過氯酸鹽的政策──基本上就是包庇承包商和污染者迴避清除污染物的代價，目前應儘速立法規定飲用水安全過氯酸鹽含量標準，保護孕婦、嬰兒和其他可能因接觸這個化學物質而受害的人民。」
潔克森在參議院環境與公共事務委員會的委員會前，承諾加州議員、委員會主席鮑克瑟(Barbara Boxer)，她會「立即」減低飲用水中的過氯酸鹽污染；鮑克瑟先前曾多次呼籲立法管制過氯酸鹽安全量。目前，潔克森還未就過氯酸鹽污染採取全國性的防護措施。
All 15 brands of powdered infant formula tested by scientists with the federal government's Centers for Disease Control were found to be contaminated with perchlorate, a component of solid rocket fuel, flares, fireworks and some fertilizers. The chemical has been detected in drinking water in 28 states and territories and at low levels in food supplies.
The CDC researchers tested four different types of infant formulas - those made from cow's milk containing lactose, cow's milk-based but lactose-free, soy-based, and elemental formulas, typically consisting of synthetic amino acids.
Perchlorate was a contaminant of all commercially available powdered infant formula tested. Bovine milk-based powdered infant formula with lactose had a significantly higher perchlorate concentration perchlorate than soy, lactose-free, and elemental formulas.
Exposure to perchlorate has been shown to reduce thyroid hormone production and inhibit the uptake of iodide, which is required for healthy function of the thyroid gland. The thyroid controls human metabolism, growth and development - too little thyroid hormone, called hypothryroidism, leads to weight gain, low heart rate, water retention, poor muscle tone, and fatigue.
The National Academies of Science have identified the fetuses of pregnant women who have hypothyroidism or iodide deficiency as the subpopulation most sensitive to the effects of perchlorate exposure.
When powdered formula is reconstituted with water that is also contaminated with perchlorate, the infant may be ingesting more of the chemical than the so-called reference dose set by the U.S. Environmental Protection Agency, the researchers warned.
The two most contaminated brands, made from cow's milk, accounted for 87 percent of the U.S. powdered formula market in 2000, the scientists said, although they did not identify the formula brands tested.
The study, published in the current edition of the "Journal of Exposure Science and Environmental Epidemiology," raise fresh concerns about perchlorate contamination.
Led by Dr. Joshua Schier with the CDC's Division of Environmental Hazards and Health Effects, the researchers conclude that perchlorate exposure may be higher in infants on powdered forumla compared with older persons because infants consume more of the substance for their weight than older persons.
The CDC scientists pointed out that the Food and Drug Administration requires infant formula to be supplemented with iodine, a nutrient that can counter the adverse effects of perchlorate on the thyroid gland. The range of required iodine concentrations in formula is between five and 75 micrograms per 100kcal of energy.
Iodine supplements at higher levels may offer some protection from the effects of perchlorate, but the scientists warn that even adequate iodine intake among formula-fed infants is not guaranteed to prevent "perchlorate-induced thyroid dysfunction."
The Environmental Working Group is calling on U.S. EPA Administrator Lisa Jackson to "scrap Bush era perchlorate policies that shielded defense contractors and other big polluters from the costs of cleaning up perchlorate-contaminated water by setting a legally enforceable safe drinking water level that protects pregnant women, infants and others who are most vulnerable to the effects of this harmful chemical."
At her confirmation hearing before the Senate Environment and Public Works Committee, Jackson promised chair Senator Barbara Boxer of California that she would act "immediately" to reduce perchlorate contamination in drinking water. Boxer has repeatedly introduced legislation to protect the public from perchlorate exposure.
To date, Jackson has not announced any nationwide action to limit perchlorate exposure.
