Poisons and Policy: Arsenic and Aflatoxins
In the past 24 hours, do you recall hearing anything about arsenic in rice? If you're in the United States, the answer is very likely, "yes!"
A great many pixels were spilled yesterday when Consumer Reports and the US Food and Drug Administration released -- almost simultaneously -- analytical data on inorganic arsenic concentrations in 200 samples of commercial rice products, particularly those grown in the southern US.
You can't do any better in understanding this story than reading, "Arsenic and Rice. Yes, again," on Deborah Blum's Elemental blog at Wired Science Blogs. Professor Blum has been discussing arsenic in the diet for a few years, an interest she developed while composing her superb book, The Poisoner's Handbook: Murder and the Birth of Forensic Science in Jazz Age New York.
Deborah's post puts in perspective the risks of inorganic (and organic) arsenic concentrations in food products such as rice relative to drinking water. Arsenic occurs in nature but exists in higher concentrations in water from areas where arsenical pesticides have been used in cotton farming or poultry deworming (the latter discussed in 2006 at NYTimes). While she closes in being critical of the FDA for lack of clear consumer guidance, let it suffice to say that no character in Blum's book was killed by poisoning with rice from Louisiana.
Pick your poison
What caught my attention yesterday was a completely different report from the US FDA -- actually a FDA ruling released by the Iowa Department of Agriculture and Land Stewardship. Corn containing one of the most potent natural toxins and carcinogens -- a class of compounds called aflatoxins -- can be legally blended with other corn for use in animal feed. A standing rule of the FDA, when invoked, allows farmers to blend corn containing up to 20 parts per billion of aflatoxins with corn containing lower concentrations (or none) of the toxin family. Here's where 20 parts per billion falls in the FDA's guidelines according to the Iowa Dept of Agriculture statement:
The other problem. Credit: Nakhonsawan Field Crop Research Center, Thailand.
The FDA has established guidelines for acceptable aflatoxin levels in corn based on its intended use. Corn containing aflatoxin in concentrations of greater than 20 ppb cannot be used for human consumption and cannot be used for feed for dairy animals or for immature livestock of others species. Corn containing aflatoxin at 100 ppb or less can be used in breeding cattle and swine and mature poultry. Corn with 200 ppb or less can be used with finishing swine greater than 100 lbs. in weight and corn with 300 ppb or less can be used in finishing beef cattle.
Where is this aflatoxin coming from anyway?
Aflatoxins are produced by a couple of species of Aspergillus fungus and concentrations of the toxins are sometimes elevated during drought seasons such as the current one affecting the US corn belt. (Yes, I normally equate fungal growth with damp conditions but drought stress has been long associated with increased crop susceptibility to insects and fungi such as Aspergillus.). Aflatoxins are dangerous to those who ingest them because our liver's attempt to metabolize them creates chemicals that attack our DNA and other cellular processes. In the short term, aflatoxin poisoning can cause liver damage and even death; chronic aflatoxin exposure can cause liver cirrhosis or cancer.
(Addendum: And the genus name Aspergillus? This open-access book chapter (PDF) by Dr. Joan W. Bennett cites the story of a Micheli, a Roman Catholic priest, who in 1729 studied the fungus microscopically and noted its resemblance to a holy water sprinkler, called the aspergillum or aspersorium. The Asperges is the rite in Roman Catholic Mass where it would be used.)
While allowing farmers to feed aflatoxin-containing feed to cattle, for example, presents low risk to human meat consumers, concern is reasonable for those who might consume milk from dairy cows given such feed. Hence, the FDA's Iowa ruling requires that aflatoxin levels be measured in milk. As indicated above, this feed is not to be used for daily animals but monitoring milk seems like a good preventive idea.
I was surprised to see this ruling getting little or no attention from the press yesterday. A Google search for "fda arsenic" netted 543 news articles while "fda aflatoxin" returned only 11 articles.
I'm not exactly sure why but my gut senses that public concern would have been greater for aflatoxin than arsenic. Then again, yesterday's news on arsenic was on products directly consumed by humans and was seeded by reports from both a major consumer magazine and the major governmental food regulatory agency. The aflatoxin ruling was for consumption of poisoned feed by livestock (that we then eat) and came from a state agricultural department rather than the FDA directly.
In my early toxicology training days, I worked with both arsenic salts (inorganic and organic) and aflatoxins (aflatoxin B1, to be exact). Seeing what 1 milligram per kilogram could do to a rat's liver scared the hell out of me (that's 1 part per million, or 1,000 parts per billion -- 50 times the upper limit of alfatoxins permitted in Iowa cattle feed). Arsenic, not so scary - at least at the doses I used. Heck, we even use inorganic arsenic as a drug to treat some leukemias (and organic arsenic compounds are in development for multiple myeloma).
Meh, or not?
But I recognize that my "educated" risk-analysis is just as flawed as anyone who is immediately alarmed by any amount of arsenic or aflatoxin allowed in our food. What exactly do these levels of contamination mean in real short- or long-term human health risk. As Blum pointed out, understanding risk is difficult if even our regulatory agencies are reticent to explicitly define what this all means.
Should I worry more about the auto and truck exhaust I breathe from the state road behind my house? The carpet shampoo I used last night or the solvent in the silicone spray I used on the motor? The black mold I found in my Water Pik? What about the risk of walking across the street after class tonight or driving home? I won't even get into how much I should worry about the PCBs in my adipose tissue from growing up near a Superfund site in northern New Jersey.
What should we be worrying about?
Press Release: FDA Approves Blending of Corn Containing Aflatoxin, Iowa Department of Agriculture and Land Stewardship, 18 September 2012. http://www.iowaagriculture.gov/press/2012press/press09182012.asp
Bennett JW (2010). "An Overview of the Genus Aspergillus," in Aspergillus: Molecular Biology and Genomics. Caister Academic Press. ISBN 978-1-904455-53-0
Aspergillus flavis. Credit: Mycology Online/University of Adelaide (click on photo for source)