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Soil-additive hydrogels (water gels, water crystals) contain AND break down into toxic gick

 
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Y'all know I am a scrounger.  I don't buy fancy soil amendments, so those expensive bags of polymer water-retaining crystals they sell at the garden centers never appealed to me.  Doesn't matter if they work or what they are made out of -- too expensive.  

But the other day, a "free" box at a garage sale turned up half a dozen dollar store jars of already-hydrated water beads, the kind they sell for flower arranging.  I figured I might stir them into my potting soil mix.  From what I have read, they can last for years in the soil, and hold onto lots of water, keep your pots from drying out so fast.  But I'm not mixing mystery-polymers into the soil I grow food with without doing some research first!

It was surprisingly difficult.  The Wikipedia entry for Water Crystal Gel does, however, mention that they are made from polyacrylamides.  That was ... concerning.  Poly means "many" and I already knew that acrylamide is a poison.  But, you know, some molecules are so stable they just don't break down, I'm no chemist, maybe I was worrying needlessly.  I kept poking at Google.  

Endless pages of marketing for this stuff.  All kinds of uses.  Some of the water gels are made from food starches -- but they are more expensive, and much more fragile, and near as I can tell, none of the ones sold for agricultural use are the food-starch kind.  The ag ones are all polyacrylamides.  And nobody wants to talk about what happens to them in the soil when they "stop working", which everybody agrees they eventually do.

Finally, I found somebody with an opinion that Permies will want to be hearing.  Meet Linda Chalker-Scott, Ph.D., Extension Horticulturist and Associate Professor, at the Puyallup Research and Extension Center, Washington State University.  She writes in The Myth of Polyacrylamide Hydrogels:

Hydrogels are increasingly popular with homeowners who add them to vegetable gardens, container plants, annual beds, lawns, and perennial landscapes. The most commonly available are polymers of acrylamide and potassium acrylate.

...

Hydrogels are routinely touted as pH-neutral, non-toxic, environmentally friendly compounds, which they are in their polymerized form. The fact remains that after five years virtually all hydrogel will be depolymerized through natural decomposition processes. The rate of degradation is increased especially in the presence of fertilizer salts (and no, it doesn’t make any difference if these are synthetic or organic fertilizers).

...

Hydrogels are constructed of acrylamide units. When hydrogels break down, they release potassium acrylate and acrylamide. Acrylamide is a lethal neurotoxin and has been found to cause cancer in laboratory animals. It readily passes through the skin and can be inhaled as dust. Unfortunately, the chemical data sheets on hydrogels do not mention the fact that within a few years they will be composed entirely of these acrylamide units. Since polyacrylamide is defined as “not readily biodegradable” (less than 10% is degraded after 28 days), some sellers of hydrogels actually promote their products as “nonbiodegradable!”

Who is at risk to acrylamide exposure? Workers in the nursery and landscape industry who routinely use hydrogels may become exposed to them as they degrade and become toxic. Homeowners who add hydrogel-containing potting mix to their landscapes or compost piles are exposed. Dogs, cats, and wildlife that come in contact with these substances are at risk. On a larger scale, entire ecosystems are at risk as acrylamide is water-soluble and can easily enter watersheds.

One of the greatest pleasures of gardening is getting your hands into good, rich soil and breathing in its aroma. I believe that the increased, and indiscriminate, use of polyacrylamide hydrogels is an extremely serious hazard to human health and to the environment.



More information comes from Jeff Schalau, Associate Agent, Agriculture & Natural Resources, at the University of Arizona Cooperative Extension, Yavapai County.  In Hydrogels: Are They Safe? he writes:

Gardeners are concerned with the safety of PAM hydrogels. As the name suggests, polyacrylamides consist of many linked acrylamide subunits. Acrylamide is a known neurotoxin in humans and is suspected to be carcinogenic as well. During the manufacture of PAM gels, residual acrylamide is present as a contaminant and strictly regulated in the United States to levels no more than 0.05% or 500 ppm for agricultural use. However, an international study recommended that polyacrylamide gels used in cosmetics contain a residual monomer level of only 0.1 to 0.5 ppm. Therefore, the PAM hydrogels manufactured for agricultural and garden use can contain much greater concentrations of (1,000 to 5,000 times) toxic acrylamide than that found in personal products causing concern among some users.

Additional health issues can be presented by exposure to the more or less intact polyacrylamide gel where toxic effects have documented. Health risks associated with the breakdown products of PAM hydrogels are entirely unknown, but exposure risk could be great to gardeners and green industry workers that are exposed over time.

Given the findings presented above, I cannot recommend the use PAM hydrogels for use in home gardens.



(I added the italics/emphasis to the second-from-last paragraph above.)

That's good enough for me.  I won't be mixing these molecules into my garden soil.  
 
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Neck Coolers

So I wonder if these things are toxic too?

I started using these years ago as a way to stay cool and now I have skin cancers and vertigo . I noticed that after many uses, wetting them , then drying out, then rewetting, over and over again, they would get slimy, like the beads were breaking down and slime was coming out on to my skin.  Just wondering if I have poisoned myself?

I stopped using them and went to more of a cloth/chamois type cooling wrap.
 
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And what about these things? Anybody know if these would be toxic. These are actually put into water like sand bags so wouldn't they leach into the waterways that are flooding? Anybody know if there have been any studies on these?

Flood barriers
 
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Miles Flansburg wrote:Neck Coolers

So I wonder if these things are toxic too?

I started using these years ago as a way to stay cool and now I have skin cancers and vertigo . I noticed that after many uses, wetting them , then drying out, then rewetting, over and over again, they would get slimy, like the beads were breaking down and slime was coming out on to my skin.  Just wondering if I have poisoned myself?

I stopped using them and went to more of a cloth/chamois type cooling wrap.



Ugh!  Those are almost certainly manufactured using the same polyacrylamides.  I have used those neck coolers myself -- I bought one once for a cross-country road trip in July in a classic car with no air conditioning.  I rehydrated it in my food cooler full of ice and meltwater, too. And those sources I linked do seem to suggest that when the long-chain polymers break down, the slime left over is not good stuff.
 
Dan Boone
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Miles Flansburg wrote:And what about these things? Anybody know if these would be toxic. These are actually put into water like sand bags so wouldn't they leach into the waterways that are flooding? Anybody know if there have been any studies on these?

Flood barriers



The one saving grace in all of this is that -- from what little I can tell -- acrylamides are themselves mostly water-soluble.  Which means, that in soil in your garden or wherever else these products are used, when they break down into toxic acrylamides, the toxins will be flushed "away" over time.  But of course there is no "away" -- it just becomes someone else's problem lower in the watershed.  And of course it's hard to say how long the flushing "away" process requires, or how far they are transported (all the way to the ocean?) during a large flood event.

One of my links suggested that these products are usually listed as "non-biodegradable" because less than a certain percentage degrades within thirty days.  As short-sighted as that is, my guess would be, that means nobody has bothered to study the transport or ultimate fate of the breakdown components in the flood-control application.  
 
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