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PCE contamination


Polyacrylamide is added to soil and pesticides,
it may be a major problem?

Prof. Joe Cummins / Department of Biology / University of Western Ontario 8aug02

e-mail: jcummins@uwo.ca

Acrylamide is a building block for the polymer, polyacrylamide, a material used in genetics in molecular biology laboratories as a matrix for separating nucleic acid components during DNA sequence analysis and during protein identification. In the world at large polyacrylamide is used in water purification to flocculate suspended organic matter, in irrigation water to improve soil texture and in pesticide formulations to limit spray drift. Recently the world health organization (WHO) had a closed meeting to reveal the finding that cooked vegetables had significant levels of acrylamide (1). The finding received worldwide notice because acrylamide is a potent nerve toxin in humans and effects male reproduction, causes birth defects, and cancer in animals. The WHO releases implied that the acrylamide finding was a surprise and that the pollutant probably arose from cooking the vegetables (1).

The WHO report failed to mention the extensive global use of polyacrylamide in pesticide formulations and in soil treatment and the predictable residues of the polymer in vegetables such as potato or in grain. The addition of polyacrylamide to pesticide formulations is considered a trade secret and rarely reported while the soil treatment in irrigation water covers a million or more acres in the United States (US) and very large farmland areas worldwide. Even though the coverage of food crops with polyacrylamide formulations is staggering there seem to no available reports on polyacrylamide levels in food crops. The United States Department of Agriculture (USDA) serves a s both promoter and regulator of the use of polyacrylamide (PAM) in agriculture and that agency does not appear to have required thorough testing of the human and environmental consequences of polyacrylamide use..

Polyacrylamide is designated a non-toxic additive and that may explain why there has been little concern over its accumulation in food crops. Of course polyacrylamide may be contaminated with its toxic building block, acrylamide, and for that reason a limit of 500ppm acrylamide in polyacrylamide preparations has been arbitrarily determined to be acceptable for use in agriculture or water treatment. Furthermore, the polyacrylamide preparations (PAM) used in irrigation is most frequently a copolymer associated with acrylic (3) or other polymer plastic to provide stability, the polyacrylamide used in water treatment is often the co-polymer while the product used in pesticide formulations is protected as a trade secret but is likely to be a co-polymer.

It has been reported that PAM hydrogels degrade to release acrylamide and acrylate (4)[acrylate is a known teratogen] and corporate Material Data Safety Sheets sometimes indicate that acrylamide is a foreseeable degradation product of PAM and that acrylonitirile (a mutagen and carcinogen) and cyanide are thermal decomposition products of polyacrylamide super absorbent (5). There are studies showing that acrylamide is released from polyacrylamide after exposure to light and elevated temperature (6,7) while other studies concluded that acrylamide is not released from polyacrylamide during degradation (8,9). Glutarimide (a component of the drug thalidomide) a pharmacologically active compound was identified as a significant breakdown product of heated polyacrylamide and the authors of that study stressed the need for fuller study of the breakdown products of polyacrylamide (9). There seems to be a clear-cut difference of opinion over the breakdown products of polyacrylamide. The authorities who maintain that acrylamide is not a breakdown product of polyacrylamide stress that those who identify acrylamide as a breakdown product do not find the chemical as a large proportion of the breakdown products of polyacrylamide. That seems to be a specious argument, as if the thermal degradation products dioxin or polyaromatic hydrocarbons are inconsequential because they are produced in relatively small amounts when they are among the most dangerous pollutants known. Moreover, the studies claiming to find little or no acrylamide in the breakdown products of polyacrylamide seem to have ignored the fact that the materials used commercially are most frequently co-polymers of acrylic acid or other polymers and the actual breakdowns usually take place on the surface of plant roots, leaves or stems or in the soil matrix.

Certainly, polyacrylamide residue levels in food crops should have been studied as soon as polyacrylamide began to be used in pesticide formulations and irrigation water and such residues should be studied in the future. Regulatory agencies, such as, USDA and the Food and Agricultural Organization of the United Nations seems to be negligent in approving widespread employment of polyacrylamide hydrogels and pesticide additives without having undertaken realistic analysis of the breakdown products and potential pollutants consumed by humans or released to the environment. It is rather discomforting to learn that foods we eat may be saturated with plastic polymer and their unspecified breakdown products and soon we may be saturated as well.

References

1.Weiss G. “Acrylamide in food: Uncharted territory.” Science 2002, 297,27.

2. PAM Research Project USDA http://www.ars.usda.gov/is/AR/archive/jul02/form0702.htm

3.Hadar,H. and Keren,K. “Anionic polyacrylamide polymers effect on rheological behavior of sodium-montmorillonite suspensions” 2002 Soil Sci Soc Am J 66,19-25

4.Calker-Scott,L. “The myth of polyacrylamide hydrogels” http://www.cfr.washington.edu/research.mulch/myths/hydrogels.pdf

5.Castlre International Resources “Material safety Data Sheet; Crosslinked polyacrylamide, superabsorbent polyacrylamide and super absorbent polymer” 1999 by Dale Greenwood - Castle International Resources Company. http://www.hydrosource.com/web_clp/990310/Msds0399.htm

6. Smith E, Prues S and Ochme F. Environmental degradation of polyacrylamides: Effect of artificial environmental conditions. Ecotoxicology and Environmental Safety 1996, 35,121-35.

7.Smith E, Prues S and Ochme F. Environmental degradation of polyacrylamides: II Effects of outdoor exposure. Ecotoxicology and Environmental Safety 1997, 37,76-91.

8.Leonard M. Ver Vers. Determination of acrylamide monomer in polyacrylamide degradation studies by high performance liquid chromatography. Journal of Chromatographic Science 1999, 37,486-94

9,Caufield,M,Qiao,G. and Solomon,D. “Some aspects of the properties and degradation of polyacrylamides” 2002 Chemical Reviews DOI: 10.1021/cr010439p

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