[USCC] Chicken Litter and Arsenic

[Maureen Reilly]

Vol 41 issue 3

ES&T News
Chicken litter and arsenic


The addition of roxarsone to chicken feed has stirred up debate ever since 
it was revealed that this organoarsenic compound can be transformed into 
more toxic inorganic arsenic (Environ. Sci. Technol. 2006, 40, 2864–2865). 
New research published in this issue of ES&T (pp 818–823) identifies the 
microorganisms that are responsible for the conversion and shows that 
carcinogenic arsenic is formed faster and more effectively than previously 
thought.


Stephen Ausmus, ARS/USDA
Researchers are concerned that arsenic in roxarsone, a chicken feed 
additive, readily contaminates groundwater and food crops. Roxarsone, or 
3-nitro-4-hydroxybenzene arsonic acid, is routinely used by most U.S. 
broiler-chicken farms as a feed additive to prevent disease and stimulate 
growth. Chickens primarily excrete roxarsone unchanged into their waste, 
which is typically applied as a fertilizer on the surrounding farmlands.

Previous research had shown that inorganic arsenic is slowly formed from 
roxarsone after litter composting or field application, but the responsible 
microorganisms or processes were not identified. John Stolz and his 
colleagues at Duquesne University now show that roxarsone is rapidly 
transformed to 3-amino-4-hydroxybenzene arsonic acid and inorganic As(V) in 
chicken-litter enrichments under anaerobic conditions.

The team found that bacteria of the Clostridium species are responsible for 
the transformation. “We see As(V) emerge in less than 10 days, which is much 
faster than previously observed,” says Stolz, who emphasizes that 
Clostridium species are indeed the dominant bacteria in chicken cecum and 
litter. In this way, inorganic arsenic could already be generated during 
manure storage, he says. The process is so efficient because the microbes 
gain energy from the roxarsone transformation and couple it to growth, 
presumably through an anaerobic respiration mechanism in which roxarsone 
serves as the terminal electron acceptor, Stolz explains.

“This is really elegant work that amplifies previous evidence on the 
environmental release of inorganic arsenic from roxarsone,” says Ellen 
Silbergeld of the School of Public Health at Johns Hopkins University. “I am 
concerned about the potential contamination of groundwater with inorganic 
arsenic in my local region [in Maryland], because we have a lot of poultry 
farms and most people here get their drinking water from groundwater,” she 
says.

On a broader scale, Silbergeld feels that the use of roxarsone is impeding 
the opportunities for alternative uses of poultry waste. “One of my students 
found inorganic arsenic in pelletized chicken waste that is sold as a garden 
fertilizer, and in this way people could get exposed to the arsenic through 
dust—[it’s] probably not such a good idea to use chicken waste in that way,” 
she adds. The coauthor of the new ES&T research, environmental chemist 
Partha Basu of Duquesne University, points out that a previous study found 
elevated arsenic levels in house dust near chicken farms (Environ. Forensics 
2005, 6, 83–89).

“In my view, the real threat of arsenic mineralization from roxarsone is the 
buildup of inorganic arsenic in agricultural soils onto which poultry litter 
is applied as manure,” says Andrew Meharg of the University of Aberdeen 
(U.K.), an expert in the biogeochemistry of arsenic. As(V) is relatively 
immobile in aerobic soils and, therefore, does not pose much of a risk there 
at slightly elevated soil concentrations, Meharg says. However, if arsenic 
levels build up, a possibility exists that it could transfer into food 
crops, he cautions. If the soils are used for anaerobic cultivation (e.g., 
rice), then the risk becomes larger because of transformation of As(V) into 
the more mobile As(III), he adds.

“This new research should stimulate the U.S. Food and Drug Administration to 
reconsider their approval of the use of roxarsone,” Silbergeld says, adding 
that roxarsone was approved before enough was known about its environmental 
impact. She mentions that the EU declared the use of roxarsone undesirable 
in 1999 and, consequently, has abandoned its use since then.

“The fact that roxarsone is still routinely used here [in the U.S.] and that 
they ignore that something toxic is getting into the environment is causing 
me a problem,” says Stolz. He points to a recent report by the Institute of 
Agriculture and Trade Policy, a nonprofit research and advocacy 
organization, which notes that the uptake of part of the roxarsone into the 
chicken body leads to elevated arsenic concentrations in the chicken meat 
sold in U.S. supermarkets. “The insidious thing about arsenic is the fact 
that it takes people decades to develop symptoms to chronic exposure,” Stolz 
says. “Some big U.S. companies raise chickens without using roxarsone and 
appear to manage,” he adds. —ANKE SCHAEFER