Diaper crystals in food-growing soil?
Short version: those diaper crystals
may be safe to mix into soil you are growing food in, but doing so is probably not saving money long-term and there may be other drawbacks. I would suggest using crushed charcoal from local wood instead of diaper crystals if you want/need an economical and more securely safe method to increase the moisture content of food-growing soil.
Long version, with all the details and evidence:
Regarding the safe use for growing food of those super water-absorbent crystals commonly found in diapers (and available in bulk via chemistry and garden supply houses) when they are mixed in potting and bedding soil, I scanned around a bit to see what I could find.
I have used polysodium acrylate (PSA) crystals --the most common form of this type of hygroscopic material-- many times in the laboratory but not in soil mixes for growing food which people would later eat. Some materials which are rated safe and nonhazardous for nonfood uses can become problematic when ingested, and the break-down products of those compounds even more so.
Here are the MSDS for PSA in a couple of different formats:
http://www.unitednuclear.com/msdssodiumpoly.htm
and
http://209.85.173.132/search?q=cache:iIbcUV0T0MkJ:www.stevespanglerscience.com/uploads/file/MSDS/MSDS%2520for%2520Water%2520Gel.pdf+MSDS+polysodium+acrylate&hl=en&ct=clnk&cd=2&gl=us&client=firefox-a
The MSDS statements indicate that PSA is safe unless inhaled or eaten in large quantity (whereupon it would be a problem due to swelling, not toxicity).
According to Zohuriaan-Mehr & Kabiri (2008) in "Superabsorbant Polymer Materials - A Review" (
http://209.85.173.132/search?q=cache:Amj9SQ6g6sAJ:sid.ir/en/VEWSSID/J_pdf/81320080606.pdf+MSDS+polysodium+acrylate+hygroscopic+crystals&hl=en&ct=clnk&cd=2&gl=us&client=firefox-a) these "materials cannot return to their starting monomers, i.e., they are scientifically irreversible to toxic initiating materials. Here, like so many polymers, the starting toxic monomers are converted chemically to totally non-toxic product via polymerization reaction [2-6]. SAPs are organic materials with well-known general structure. For instance, the agricultural SAP with the name of “cross-linked acrylamide/potassium acrylate copolymer” has been recorded in the most valid data centre of chemicals, i.e. the Chemical Abstracts, with CAS No. 31212-13-2. In the material safety data sheet (MSDS) of the superabsorbent manufacturers, they are called as “Safe and Non-toxic Material” [146-149]. The conventional SAP materials are neutral and inert. They are moderately bio-degraded in the soil by
the ionic and microbial media to convert finally to water, carbon dioxide and organic matter [146-151] Therefore, SAPs do not contaminate the soil and environment. They do not exhibit systemic toxicity (oral LD50 for rate 5000 mg/kg). In addition, their safety in the soil has been approved by the Agriculture Ministry of France (APV No 8410030) [146]. Research has shown little or no consistent adverse effect on soil microbial populations [152]. The environmental fate of SAPs and their microbial degradation was investigated by many researchers [152-157]. The researchers at the University of California, Los Angles (UCLA) found that no toxic species were remained in soil after several-year SAP consuming [158]." (Page 19).
A careful reading of the whole article, however, indicates the PSA can uptake, hold, and concentrate pesticides or other toxins.
In Iwahashi (2003) "Mechanism for Degradation of Poly (Sodium Acrylate) by Bacterial Consortium No. L7-98" (
http://www.jstage.jst.go.jp/article/jbb/...e/-char/en) a number of specifics are indicated regarding PSA breakdown products. Some of the chemical groups found in PSA's decomposition are fairly active, which is neither good nor bad, it just means they are available to react with whatever else may be present.
As I read the data it seems as if using these hygroscopic crystals in your soil mix to grow vegetables to be eaten raw or cooked will probably not cause anyone to become ill. Probably, but there may be some as-yet unknown aspects to all this. Personally, I think I would rather use activated charcoal mixed into the gardening soil before I would add polysodium acrylate crystals into my food-growing soil. (Using PSA in potting soil for ornamental plants may be cost-effective, but eventually that soil may end up in a compost heap and mixed back together with food-growing soil, so even there I think I would hesitate to use the polysodium acrylate crystals).
Charcoal is way less expensive, especially if you make it yourself from guava wood; please see JWFITZ's well-informed comments in the Punaweb thread "Words of the Lagoon ...on sustainability and culture" at
http://www.punaweb.org/Forum/topic.asp?TOPIC_ID=6319&whichpage=2 for more detail on that process. Charcoal is also infinitely longer-lasting than PSA and I suspect charcoal not only retains water in a porous lattice structure but also ongoingly facilitates the development of that ultimate magic ingredient in soil, humus, via facilitating bacterial and fungal action on the vast surface areas and interstices of the charcoal particles.
[Cross-posted to Words of the Lagoon ...on sustainability and culture]
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"Facts are stubborn things; and whatever may be our wishes, our inclinations, or the dictates of our passion, they cannot alter the state of facts and evidence."
Pres. John Adams, Scholar and Statesman
"There's a scientific reason to be concerned and there's a scientific reason to push for action. But there's no scientific reason to despair."
NASA climate analyst Gavin Schmidt
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