Bad News in Baby Rice?
by Roberta Kwok on April 30, 2008 12:00 AM

Baby rice, the bland porridge sold in supermarkets for weaning infants, can contain potentially dangerous levels of arsenic, according to new research done in the United Kingdom. The discovery calls for more attention to food-production sources, the authors say, but experts are divided on the value of the study.

High doses of arsenic in drinking water can cause cancer when consumed over long periods of time. In the European Union and United States, there are stringent limits on arsenic levels in water but fewer restrictions for food. Rice has come under scientific scrutiny because it soaks up arsenic from the soil more readily than other grains do. In fact, studies have shown that some people in the United States are exposed to more arsenic by eating rice than any other food, although the health hazards associated with it are uncertain.

Andrew Meharg, an environmental chemist at the University of Aberdeen, U.K., decided to measure arsenic levels in baby rice, a precooked, dried, and milled rice product that is a staple for weaning infants. Meharg and colleagues analyzed 17 samples of baby rice from three manufacturers, all taken from supermarkets in Aberdeen. More than one-third of the samples contained levels of inorganic arsenic--the more toxic of the two arsenic forms normally found in rice--equal to or exceeding the legal limit of arsenic in food in China, which has stricter regulations than the European Union and the United States. A baby eating one serving per day would ingest more arsenic per kilogram of body weight than an adult drinking water with the maximum allowed E.U./U.S. dose, the team reports this month in Environmental Pollution.

The finding highlights the need for the European Union and the United States to restrict arsenic in food as well as water, says Meharg. "You can't say you have to highly regulate one source and totally ignore another source," he says, adding that babies deserve special precautions. Manufacturers could reduce their products' arsenic levels by buying rice from less polluted areas of the world such as California and some regions of India and Spain.

The study is "extremely important," says Ravi Naidu, a pollution scientist at the University of South Australia in Adelaide. "It shows that we need much tighter regulation on ... where food comes from."

Other experts are more cautious. The research raises some "potential concern," but scientists still need to establish whether arsenic-containing rice is actually harmful, says Michael Waalkes, a toxicologist at the National Cancer Institute who is based in Research Triangle Park, North Carolina. And Joyce Tsuji, a toxicologist at the science consulting company Exponent in Bellevue, Washington, warns that evaluating a baby's arsenic intake from rice against drinking water standards is an "apples to oranges" comparison because water standards are based on risks extrapolated from studies of lifelong, high-dose exposure, not short-term childhood exposure. "We should be careful before telling people to throw their rice out," she says.

砷和水稻：一个被忽视的癌症风险

稻谷是世界上30亿人口的主食，在亚洲尤为普及。但是支撑世界上一半人口的主食会存在增加患癌症风险的问题吗？这个问题起源于三大系列的发现，包括即将（以论文形式在学术期刊上）发表的数据，即水稻和水稻产品（如米糠和大米饼干）中砷含量提高在内的消息。

研究表明，大部分砷以无机形式即氧化物砷酸盐和亚砷酸盐存在，人们通过饮水的方式摄入而患病。这部分人患癌症的机率高于一般人。致力于研究作物中的污染物并且熟知这些新的研究结果的英国哈潘顿的洛桑研究所的生化学家史蒂夫.麦格拉思说:“这是一个严重的问题”。尽管稻米中积累的砷含量较低，但史蒂夫.麦格拉思认为“人们在日常膳食中如果摄入过多的稻米，会对身体产生危害。”

有专家提醒，没有任何数据表明吃稻米会引起癌症。德克萨斯州 A&M大学所在地的农作物科学家理查德 Loeppert说“水稻中的砷含量确实需要降低，但水稻中含砷的问题不会即时对人产生危害。”北京生态环境科学研究中心的首席研究员—环境生物学家朱永关表示：“我们对此仍没有xx的研究清楚，但砷仍然是砷。”

中国（政府）同意（对水稻含砷的问题不能掉以轻心）：（中国）是管制食物中砷的含量的少数国家之一。2005，政府把大米中砷的限量由700ug/kg降至150ug/kg.鱼类和其他海产品含有一种称之为arsenobetaine的有机化合物，若正常摄入海产品，这种化合物在很大程度上对人体是无害的。1993年，美国食品药品监督管理局在一个对贝类消费品的指导性的文件中提出，推荐人“每日可承受摄入”的无机砷的含量为130ug.但是，大多数国家，包括美国和欧盟在内，都没有法律限制食品中无机砷的含量。最近的研究结果将更快地推动监督调整进程。

朱永关和其他人没有等待，他们已经在寻找方法解决如何除去含有比小麦和其它谷物高10倍砷浓度的水稻的问题。可能采取的措施包括改变农场的做法，例如：在凸起的培育床上种植水稻以及采用遗传工程学的方法去除其中的砷等。这是一项紧迫的工作，有人说，由于全球的粮食危机，在矿场及冶炼厂附近种植的稻谷有所增加，而且在一些曾使用含有大量砷农药的棉花和其他作物种植地上种植的水稻也有所增加。与朱永关以及英国阿伯丁大学环境化学家的Andrew Meharg一起做研究的博士后研究员保罗.威廉说：“我们担心的是，越来越多被砷污染的贫瘠土地会被用于种植水稻。”

无机砷在单剂量100毫克可以通过减弱能量代谢的进程使人致死。低剂量长期潜伏对人体的影响更甚，这些影响最早是1980年代初期在印度和孟加拉国发现的。在一些地方，由于很多人饮用水依赖于被砷污染的水井而导致砷中毒，并因此爆发了以皮肤粗糙为前奏特点的，如皮肤癌以及膀胱癌等严重的疾病。被污染的水井每升水中通常含有数百微克砷，这远远高于世界卫生组织（WHO）所规定的每升水中砷低于10微克的水平，这一标准被大多数国家通过使用。一些砷自然含量高的地区一直在努力的开发替代供水（Science，2007年3月23日，1659页）。朱说：“数十亿美元用于减少水的砷含量，但即使我们解决水中砷含量高的问题，砷依然会进入大米中。”

麦格拉思和同事上个月在《环境科学与技术》的在线报道称，由于厌氧微生物分解得到砷元素，水稻很容易从湿泥土中吸收砷。（其他生长在有水环境作物，如莲藕，菱角，和水菠菜也往往含有高水平砷。）朱、威廉和麦格拉思注意到在本月《环境污染》的一篇文章中写到：世卫组织所限制的水中的砷含量相当于每天膳食中的10微克。在亚洲，若保守估计为平均每天消费大米200克，研究人员估计稻谷中砷的含量必需低至每千克50微克仍然低于世卫组织所规定水中砷的含量。然而，朱和他的同事报告，世界各地的调查发现，大米中无机砷的含量普遍超过50微克的阈值甚至可达到400微克每千克。

去年4月，麦格拉思的实验小组报告：在英国超级市场中出售的断奶婴儿所食用的米粥中砷的含量令人担忧，这一报告引起了轰动。根据他们在《环境污染》所得的调查结果，所抽取的婴儿大米食品中有35%砷含量超过我国允许值。