AMEM: A Tool to Estimate Human Exposure from Fire Retardants and Plasticizers in Plastics

A lot of plastics in our homes are not just made of polymer.  Many have monomeric additives within them and sometimes these additives represent a significant portion of the mass of the plastic.   For example, the plasticizer in flexible PVC  is typically greater than 10% and can be has high as 30-40%.  Phthalates are often used as the plasticizer to make PVC flexible.    All phthalates are monomers and all will diffuse out of the plasticized PVC matrix given enough time to do so.   The typical mechanism for plasticized items used indoors is for the plasticizer to diffuse out of the PVC and then partition into house dust.  Must of house dust is composed of our shredded skins cells and are therefore expected to be lipophilic.  The plasticizer would partition into the dust and the dust would be distributed within the residence.  Of course, some will be cleaned and removed but it is difficult to determine how much might be removed before human exposure may occur.  What we do know it that there is a significant amount of phthalates in the dust of some homes. The dominant source of exposure is anticipated to be hand to mouth ingestion of this dust with kids doing more than adults but adult doing at least some of this type of ingestion our entire lives.  

While researching this issue on the Internet I found the following data for a PVC “geomembrane” which is another way of saying a canal liner that was used to contain water.   They report that the PVC films was 30-35% plasticizer but I did not find out which plasticizer they used.   Their report shows the following loss of plasticizer to the water.

Service Years 2 4 5 9 14 19 Original Specification Value

Plasticizer Content Remaining 92.1% 67.7% 67.8% 65.6% 58.0% 54.3% None

Re: http://www.geocheminc.com/pvcfaqplasticizers1.htm

I am frankly not sure how this relates to plasticizer diffusing from a PVC product to its surface to be then transported within the indoor environment via dust; however, it is an interesting study.

It should be mentioned that plasticizers are the not only monomers to diffuse out of plastic.  Indeed, any monomer would be expected to do so including flame retardants.   Indeed, some flame retardants appear in the plastics of our electronic cases at concentrations around 10% and are thus prime candidate for the migration-to-dust-to-ingestion pathway.

It turns out there has been a tool around for some time that was developed in 1989 by Arthur D. Little, Inc for the  EPA Office of Pollution Prevention and Toxics, Economics, Exposure, and Technology Division, Exposure Assessment Branch (EAB).   It is an “oldie but goodie”.  Indeed, it is a DOS program that EPA claims can be run in the modern Windows (7 or 8? ) environment.    I keep an old PC around just to run this old stuff (it runs DOS 6.2, Windows 3.2 and Windows XP) so I am not sure if AMEM will run on Windows 7 or 8.  If anyone has any experience with this, please let me know.

You can download and learn about it at:  http://www.epa.gov/oppt/exposure/pubs/amem.htm   A cut and paste of some of the Q&A from this EPA site is presented below:

The model assumes:

·    The chemical is homogeneously distributed throughout the polymer and is not initially present in the phase external to the polymer,

·    Migration of the chemical is not affected by the migration of any other chemical or by the penetration into the polymer of any component of the external phase,

·    The migration is isothermal,

·    and Fick's law of diffusion and convective mass transfer theory applies.

How Does AMEM Work?

AMEM is a DOS-based software product developed in 1989 that uses a family of mathematical equations that address simple and complex scenarios for chemical migration through a specific polymer. The more complex equations require more input data. Using the model, you may:

·    Develop migration estimates,

·    Consider the effect of chemical partitioning between the polymer and the external phase,and

·    Consider the effect of mass transfer resistances in the external phase.

In all cases the model estimates the fraction migrated (i.e., the fraction of the chemical initially present in the polymer that migrates) after a specified duration. This model only provides one parameter needed to estimate exposure. The user must then use other equations and/or models to estimate exposure.

What Do I Need to Use AMEM?

Polymer category (i.e., Silicone Rubber, Natural Rubber, LDPE, HDPE, Polystyrene, or unplasiticized PVC) or diffusion coefficient of the polymer.  (MAJ Note: This is the first I have noticed the category of unplasticized PVC.  I think, however, the program and documentation might still present some insight for the estimation of phthalate out of PVC).

·    Molecular weight of additive.

·    Total polymer sheet thickness (cm) External phase (i.e., air, water, or solid)

·    One or two sided migration Time frame of interest

What Type of Computer System Do I Need?

·    Processor - IBM-compatible computer with a Pentium microprocessor (minimum speed: 33 MHZ)

·    Memory - 640K

·    Hard disk space - 2 MB

·    Operating System - AMEM is a DOS-based program, however, in can be run in a Windows environment by using key strokes not a mouse.

(Jayjock Note:  640k of memory and 2 MB of hard disk space really shows how far we have come since 1989).

 

If anyone knows of a better tool to answer these questions, please drop me a line and I may write about it here.