Isnin, 26 November 2012

Pencemaran Arsenik

Pencemaran Arsenik

Kajian terkini di USA menunjukkan bahawa terdapat paras arsenik yang tinggi dalam beras dan jus epal serta jus anggur. Bagaimana dengan keadaan di Malaysia? adakah makanan yang kita makan selamat daripada keracunan arsenik? Arsenik adalah bahan semulajadi dalam tanah yang pernah disembur dengan racun makhluk perosak dan ditabur baja kimia untuk mendapatkan hasil yang lumayan. Arsenik ini akan tersimpan lama dan kekal dalam tanah, seperti juga merkuri dan logam berat yang lain. Disebabkan arsenik ini mudah larut air, maka ia mudah meresap dari tanah ke dalam tumbuhan yang kita makan. Jadi sisa-sisa arsenik ini terdapat pada semua bahagian tumbuhan, terutamanya di daun. Apabila tumbuhan ini dimakan, maka arsenik ini akan masuk ke dalam tubuh manusia.

Disebabkan padi ditanam di kawasan berair, ia lebih mudah menyerap arsenik berbanding dengan tumbuhan daratan. Kajian juga menunjukkan arsenik dalam padi lebih banyak terkumpul di bahagian kulit padi/sekam yang dibuang apabila padi diproses untuk mendapatkan beras putih. Ini menunjukkan beras perang lebih banyak mengandungi arsenik berbanding beras putih. Selain tumbuhan, makanan laut juga banyak mengandugi arsenik yang berbahaya. Awas dengan suplemen kalsium, diperbuat daripada makanan laut, yang mengandungi paras arsenik yang tinggi. Terdedah kepada paras arsenik yang tinggi dalam badan boleh menyebabkan kematian. Terdedah kepada paras arsenik yang sederhana menyebabkan penyakit kardiovaskular, kesan kepada paru-paru dan masalah pernafasan yang lain, masalah dalam perkembangan otak kanak-kanak, keguguran pada ibu hamil, dan berat kelahiran bayi yang kurang berbanding normal.

Terdedah kepada paras arsenik yang rendah dalam tempoh masa yang lama pula menyebabkan pening kepala dan muntah-muntah, mengurangkan jumlah sel darah merah dan putih, menyebabkan denyutan jantung tidak normal, merosakkan salur darah, menyebabkan semut-semut atau kebas di tangan dan kaki. Arsenik yang tinggi juga dikaitkan dengan kenaikan kadar kanser kulit, kanser paru-paru, dan lain-lain. Di antara tanda-tanda seseorang itu terdedah kepada arsenik dalam tempoh yang lama ialah mendapat kanser kulit, tompok-tompok hitam atau tahi lalat kecil-kecil di tangan, kaki dan badan. Cara yang disarankan bagi mengelakkan pengambilan arsenik daripada paip air ialah dengan menggunakan penapis air. Walaupun kandungan arsenik yang berlebihan ini tidak dikesan di Malaysia, kita harus berhati-hati dan mengambil langkah berjaga-jaga….Artikel berkaitan dipanjangkan di bawah ini…

How arsenic gets into foods, and what it means for you.
By Brenda Goodman, MA
Reviewed by Louise Chang, MD

Recent investigations have found the toxin arsenic in rice and apple juice. Consumer Reports published results of their tests of 88 samples of apple and grape juices. Nine samples had more arsenic than the federal government allows in drinking water. In a separate analysis of government nutrition data, researchers commissioned by Consumer Reports also found that Americans who reported drinking apple or grape juice had arsenic levels in their urine that were 20% higher than people who didn’t drink those juices. Similarly, researchers at Dartmouth Medical School found that pregnant women who reported eating rice had higher levels of arsenic in their urine than women who didn’t eat rice. Eating just half a cup of rice a day, the researchers reported, could expose someone to just as much arsenic as if they had been drinking water at the government’s maximum allowable limit. Should you be worried about being exposed to arsenic in food? The author consulted experts who study arsenic to answer your questions.

What is arsenic and how does it get into foods?
Arsenic is a naturally occurring element that’s found in soil and water. It has also been used by farmers as a pesticide and a fertilizer. It is also used to preserve pressure-treated wood. Like lead, mercury, and other heavy metals, arsenic can persist in soil for years after it is applied to crops. Much of the rice grown in the Southern U.S., for example, grows in paddies that were once cotton fields. Cotton farmers are known to have used arsenic-based pesticides to control bugs called boll weevils. Other studies have shown that arsenic content in soil is higher around rivers and may be related to soil texture. Clay soils have more naturally occurring arsenic. Because of its chemical structure, plants mistake arsenic for necessary nutrients and readily absorb it from the soil.

Are there particular foods that it’s in?
“All plants pick up arsenic,” John M. Duxbury, PhD, a professor of soil science and international agriculture at Cornell University in Ithaca, N.Y., says in an email. “Concentrations in leaves of plants are much higher than in grains of plants. Thus, leafy vegetables can contain higher levels of arsenic than rice, especially when they are grown on arsenic-contaminated soils.” But because we eat a much lower volume of leafy greens compared to other kinds of foods,

“arsenic intake from this source is also low,” Duxbury says. Rice appears to be particularly vulnerable to arsenic contamination because it grows in water. Arsenic dissolves easily in water. So drinking water has long been monitored as a source of exposure to arsenic. Because rice is grown in paddies, which are flooded with water, it can be exposed to higher amounts of arsenic than plants grown in drier soils, Duxbury says. Tracy Punshon, PhD, a research assistant professor at Dartmouth College in Hanover, N.H., has X-rayed rice grains to see where they store arsenic. She found that arsenic concentrates in the part of the grain called the germ, which is removed to make white rice. That means brown rice has higher concentrations of arsenic that white rice. Studies by Scottish researchers have found higher levels of arsenic in rice grown in the U.S. than in basmati or jasmine rice from Thailand or India. The highest levels of arsenic in U.S.-grown rice came from Southern states. The lowest levels were detected in rice grown in California. Seafood also has high levels of arsenic, though most experts believe the form of arsenic in seafood to be nontoxic. Calcium supplements made from seafood may also contain high amounts of arsenic.

What are the potential health consequences?
At very high levels, arsenic can be fatal. At lower levels, arsenic can cause nausea and vomiting and decrease the amount of red and white blood cells produced by the body. It also causes abnormal heart rhythms, may damage blood vessels, and causes a pins and needles sensation in the hands and feet. However, far less is understood about what happens to people when they are exposed to low levels of arsenic over a long period of time. “This is a relatively new area of research,” says arsenic expert Ana Navas-Acien, MD, PhD. It’s clear that arsenic is associated with higher rates of skin, bladder, and lung cancers, says Navas-Acien, an assistant professor of environmental health sciences and epidemiology at Johns Hopkins Bloomberg School of Public Health in Baltimore. “When a substance is a carcinogen, it’s generally a carcinogen through the whole range of exposure levels,” she says. At lower levels, it probably causes fewer cases of cancer, though the risk is still there. Beyond cancer, she says, more evidence suggests that low to moderate levels of exposure — just about the U.S. standard for drinking water of 10 parts per billion — may cause cardiovascular disease. Chronic arsenic exposure may also affect the lungs, leading to breathing problems. In children, Navas-Acien says emerging evidence suggests that arsenic may cause problems with brain development. Arsenic may also contribute to problems with pregnancy like miscarriages and low birth weight.

Should I stop drinking juice, or should my kids?
People shouldn’t shun the juice aisle, says Richard W. Stahlhut, MD, MPH, a toxicologist at the University of Rochester in New York. But it’s probably not a bad idea to cut back if you or your kids drink a lot of juice, Stahlhut says, or to be careful about the kinds of juice that you drink. “Anytime you can easily avoid something, avoid it,” he says, but don’t drive yourself crazy. “You can’t be perfect. If the goal is perfection, you’re doomed,” Stahlhut says. “The rest of us are getting exposed.”

Is organic juice/rice/other foods any better, in terms of arsenic risk?
Since arsenic persists in the soil for years, organically grown produce isn’t any safer than conventionally grown food, Duxbury says.

Is arsenic tested for in foods?
The FDA tests for arsenic in some foods through a program that looks for harmful substances in food. There is no standard for arsenic in foods, and the FDA says that when it finds inorganic arsenic — the toxic kind — it considers those findings on a case-by-case basis and takes regulatory action where necessary. In September, the FDA said it was considering setting a standard for fruit juice.

What are the signs that someone may have gotten too much arsenic from their diet?
Chronic exposure to arsenic has very few symptoms, especially at the low levels seen in Western countries. Long-term exposure to arsenic from water is known to cause skin discoloration that looks like freckles or small moles on the hands, feet, or trunk.

What should you do if you experience those symptoms?
If you’re concerned you may have been exposed to arsenic in food or water, a doctor can test for arsenic in your blood, urine, hair, or fingernails. If you’re concerned you may be getting arsenic from well water, you can test the well and use water filters to remove the arsenic from your drinking water.

What is the difference between organic and inorganic arsenic?
In the environment, arsenic combines with oxygen, chlorine, and sulfur to form inorganic arsenic compounds. In plants and animals, arsenic combines with hydrogen and oxygen to form organic arsenic compounds. Inorganic kinds of arsenic are thought to be the most dangerous for human health, but very little is known about organic arsenic. “This is a controversial topic with an ongoing debate amongst toxicologists,” Duxbury says.

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