Monona,

Metaldehyde sublimes (at atmospheric pressure) around 234 F. Sublimation is simply a physical state change, from solid directly to a gas, not a chemical change. It has been noted that decomposition with partial regeneration of acetaldehyde occurs above 176 F.

Since the sublimed gas would immediately enter the relatively cool ambient temperature air, I would suspect very little decomposition of the metaldehyde to occur, but rather the gas would rapidly cool and solid metaldehyde recrystallize. This assumption appears consistent with the analytical work conducted.

I imagine metaldehyde can be procured as the plain vanilla chemical. Of course, the chemical manufacturer is required to provide an SDS and note the primary hazard on the chemical label, but I doubt a pesticide-use labeled product is utilized for this theater affect application. A pesticide label and EPA registration is required for material sold for one or more specific pesticide applications detailed on the pesticide label.

Dan

On Sep 11, 2018, at 12:35 PM, DCHAS Membership Chair <membership**At_Symbol_Here**DCHAS.ORG> wrote:

 

From: Monona Rossol <actsnyc**At_Symbol_Here**cs.com>
Re; new thread: pesticide question to boggle the mind

I need advice.  There is a product used on film and TV locations as artificial snow.  The SDS on the product says it is 98% metaldehyde.  And metaldehyde when exposed to high heat produces this snow-like stuff. This reaction has been known to magicians for years.  I looked it up a 1936 book of parlor tricks and there it was. The trick was done with pure metaldehyde in a dish with the "snow" reaction started by putting a hot soldering iron into the metaldehyde.

So this snow product is composed of
               1) 98% metaldehyde and
               2) about 2% of a chemical source of heat (probably a fuse-like cord).

Metaldehyde (CH3CHO4) is a polymerized acetaldehyde. More specifically, it is a cyclic tetramer of acetaldehyde and is used extensively around the world as a molluscicide in agriculture for the control of slugs to protect crops. Acetaldehyde is a gas. Polymerized acetaldehyde (metaldehyde), it is a white solid (usually in granules).

As for how metaldehyde makes snow, the theory that best fits these observations is that when heated, this white powder sublimes and re-solidifies in the form of the white fluffy flakes. The heat could convert it into some unregulated aldehyde-related chemical, but considering the white solid state, I'm guessing that the flakes probably are still metaldehyde.

The product was just used again on the film location and as usual, we had health complaints.  The producers hired a lab to "test the air" during the shoot. The lab chemists made an assumption that the metaldehyde converts to acetaldehyde when heated so they only tested the air for acetaldehyde and other aldehydes.  Their study found very low amounts, amounts so low that it is more likely that they came from the burning of the heat source chemicals.  Because IF the snow product, which is 98% metaldehyde DID all convert and become acetaldehyde gas, the amounts in the air would by vastly larger than the amounts found.  And IF the 98% of metaldehyde DID all convert to acetealdehyde gas, there would be NO SNOW.  It would just disappear into the air since it is a gas.

So the lab report supports the theory that the white stuff is, indeed, metaldehyde in a different form.   Until and unless the lab analyzes the white snow material and determines otherwise, I am assuming it is metaldehyde.

And metalaldehyde is toxic. For example, effective October 18, 2016, the EPA has set tolerances on various foods for methaldehyde to protect consumers from toxic effects (FR Doc. 2016-25166, amending ¤180.523 Metaldehyde; tolerances for residues).  The EPA re-registered metaldehyde as a Ôrestricted use pesticide' and required risk-reduction measures to be adopted due to the potential short-term and long-term effects on wildlife. The World Health Organization (WHO) classifies metaldehyde as a "moderately hazardous" pesticide (class II). The European Commission has adopted a directive that restricts pesticides levels to 0.1 ?g/L in drinking water ( the U.S. doesn't have an MCL for metaldehyde).

So it makes no sense to me that the product's metaldehyde is being thrown all over the whole location, in bits and pieces, some of it in particles small enough to inhale, get in the eyes, take home on your clothes, etc. The product is usually used outdoors, but there are times they are used indoors where exposure is even more concentrated.

MY QUESTIONS FOR YOU:

1.  Is the white stuff metaladehyde or an unregulated related chemical?
2.  Does anyone have an EPA contact that might actually want to look at this use of a pesticide?  We need to get this stuff out of our working lives.


Monona Rossol, M.S., M.F.A., Industrial Hygienist
President:  Arts, Crafts & Theater Safety, Inc.
Safety Officer: Local USA829, IATSE
Safety Consultant:  SAG-AFTRA
181 Thompson St., #23
New York, NY 10012     212-777-0062
actsnyc**At_Symbol_Here**cs.com   www.artscraftstheatersafety.org

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