I was surprised (not much really shocks me) to learn that arsenic (it's a metalloid, close enough) is an additive in various commercial brands of chicken feed. (HT Jill R) By some estimates over 70% of US broilers are fed arsenic laced feed as an anti-parasitic and growth promoter. How did "the king of poisons" and a known carcinogen become an additive in food animal feed?
Volumes have been written arsenic use and pollution (coal combustion, metallurgy, electronics), I hope only to illuminate one way we've helped arsenic spread from natural occurring deposits to a worldwide toxin.
Arsenic in the field
Arsenic was first used as an insecticide during the 1st century ce by farmers in China. In the West, there isn't much mention of arsenic in agriculture, except as a rodentcide, until the late 1800's when its use exploded. From the 1870s through the 1950s, hundreds of millions of pounds of arsenical compounds were sprayed on apple orchards, vineyards, cotton, tobacco and vegetable farms in the United States and Europe.
Spraying lead arsenate in apple orchards
So effective was this miracle substance at controlling specific pests, entomologist E.G. Packard was moved to wax poetic early in the new century:
Spray, farmers, spray with care,
Spray the apple, peach and pear;
Spray for scab and spray for blight,
Spray, O spray and do it right...
Spray your grapes, spray them well,
Make first class what you’ve to sell,
The very best is none too good,
You can have it, if you would....
-Packard, Fruitman Gazette 1906
As arsenic use increased, poisonings became relatively frequent occurrences. From poisoned apples exported to Britain in 1925 to poisoned French wine sickening sailors in 1932, arsenic made its way into food and drink, animals, people, soil and water. When DDT was introduced in the late 40's, it took over a decade to reduce arsenic's continued dominance as the "go to" pesticide. (After the clear and immediate danger of arsenic, DDT was seen as a much safer product, imagine that.)
A secondary source of arsenic in agriculture is fertilizer. Mineral fertilizers contaminated with arsenic (and cadmium and lead) are still routinely used. Ironite, a popular lawn fertilizer, has about 4000ppm of arsenic in it, enough to classify it as a toxic waste. (Some soils naturally contain higher amounts, but that is a poor reason to spread more around. The manufacturer claims it is not in a bioavailable form, therefore harmless.) And of course, there is arsenic in animal feed.
Arsenic moves around, stays put
Arsenic has a very complex chemistry in the environment depending on soil ph, available minerals and metals. In inorganic (non-carbon containing) compounds, it is far more toxic and carcinogenic. When the manufacturer of Ironite claim their arsenic is harmless, they are referring to an organic arsenic compound. Unfortunately, biological processes by living organisms in soil and water stand by to convert it into hazardous compounds. The millions of tons sprayed still resides primarily in the soil where it was applied, in cases remaining in the first few inches of topsoil, sometimes moving deeper in the subsoil or into wells and aquifers. Luckily, there is no evidence of uptake by tree fruit, though old orchards and farms converted to other uses may have to undergo some form of toxic remediation. (There were reported poisonings of mushroom hunters eating morels from abandoned orchards in the NYS Catskills.) In the southeast where rice is planted on former cotton acreage, arsenic readily converts to its toxic form in flooded paddies. (Rice from areas in Louisiana have shown very high levels of inorganic arsenic.)
Arsenic as a Feed Additive:
Arsenic was once a widely prescribed medicinal and anti-parasitical. At certain doses, it can mimic health and vigor. (The racehorse Phar Lap was poisoned in an attempt to get faster times out of him.) Farmers noticed that chickens and pigs consuming low doses gained weight faster, their flesh rosy in color at slaughter. The amount of arsenic needed to get the desired result is a few mg per kg of feed. Although the arsenic in animal feed is in an organic form, when digested a portion is converted to an inorganic, toxic compounds. Both types remain, in part, in the animal for your consumption. The FDA has set a limit of 500ppb for chicken meat, 2400ppb for chicken livers. (Test samples by consumer groups of chicken in supermarkets and fast food joints range from 10 to 50 ppb. Some organic birds have shown low levels of arsenic, pointing to other environmental sources.)
Much of the arsenic fed to chickens is excreted, making their waste, a source of fertilizer, a potential hazardous substance. Multiplying the amount in feed by the tons used it's estimated we continue to produce 1.7 to 2.25 millions of pounds of arsenic annually from this source. Much of this waste is composted and used as fertilizer, spread on farmland in many states where it can be taken up by crops. It can also migrate to bodies of water where under anaerobic conditions converts to inorganic compounds.
Who gets fed this mix? It’s not just chickens. It’s in turkey and pig feed as well and it may not just be large producers that use it. (Tyson Food and Perdue supposedly do not use arsenic supplemented feed any longer.) If it’s in commercial feed, it is available to small flock holders as well as corporate concerns. As Jill noted, the EU banned its use in the 1990’s. It is the only governmental body to do so. Representative Steve Israel (D-NY) bill has introduced (H.R. 3624) known as the "Poison-Free Poultry Act of 2009", to end arsenic use in feed. Currently there are no cosponsors to this bill.
Arsenic in You
We all have some arsenic in us. (Update: Arsenic is seen by some scientists an essential element, though its specific use in the body is not known). The adverse effects of arsenic on human beings is arguably the most carefully studied in history. Aside from its immediate toxic effects, neurological and circulatory damage, we've learned of arsenic's ability to cause cancer, change metabolic functions (diabetes) and has recently be shown to be a potent hormone disruptor. Arsenic causes oxidative stress and chromosomal damage linked to skin, lung, bladder, stomach, liver and colon cancer. It is oddly a carcinogen that inhibits cancer in lab animals. Arsenic is also used in some cancer treatments, adding to the complexity of the element's effect in the human organism. Limited human test trials show our ability to excrete arsenic varies greatly by individual, some of tolerate arsenic much better than others. Most at risk are children, infants and fetuses. The FDA's maximum "recommended" daily exposure/ingestion for inorganic arsenic is about 130 micrograms. (A grain of sand is about 25 micrograms.) Depending on where you live, your daily dose of arsenic comes primarily from water, possibly air pollution and your diet. Shellfish, sea vegetables (kelp), and fish can be very high in arsenic, followed by chicken, and rice. Vegetables also take up arsenic, leafy greens have a great affinity for it.
Cleaning Up the Mess
Since arsenic is a naturally occurring part of the earth's crust, our goal is to prevent anthropogenic arsenic pollution where possible, and clean up what we've already put out there. The use of composted biosolids shows ability to bind arsenic in the soil, but much depends on underlying soil chemistry. A more effective way to remove arsenic may be to use plants and fungus that have an affinity for arsenic, sequestering the biomass after uptake. Removing it from farming is a no-brainer.
For more info on arsenic and poultry, I refer you to an excellent study:Playing Chicken: Avoiding Arsenic in your Meat by the Institute for Agriculture and Trade Policy.