Seeking PBT-free Silicone Sealants


Jim Vallette - February 1, 2013

Today, the Pharos Project released a new “common ingredients” record, this one for silicone adhesives and sealants. Silicones affix and seal many materials to buildings, from carpet backing to window framing. In the course of this research, we identified two ingredients of particular concern: cyclosiloxanes and organotin catalysts.

These chemicals are typically present in one-part RTV ("room temperature vulcanization") silicone adhesive systems. The silicones undergo a final reaction at the point of application in buildings.

Government agencies classify organotin catalysts, and the common cyclosiloxane known as D4, as persistent, bioaccumulative toxicants (PBTs). The Pharos Project screens materials against authoritative hazard listings to identify potential health hazards for those exposed to the material, including PBTs.  PBTs receive the highest priority for elimination followed by priority health effects: cancer, genetic mutation, reproductive or developmental harm and endocrine disruption.

Cyclosiloxanes are key building blocks for many silicone adhesives and sealants. One of the most common is octamethylcyclotetrasiloxane (D4).  Government agencies have linked this chemical to more ecological and human health impacts than other cyclosiloxanes.

The State of Oregon classifies D4 as a PBT, and the European Union has it on a list of potential vPvB (very persistent and very bioaccumulative) substances.

A State of California memo from 2008 notes, "Cyclosiloxanes appear to be persistent and to have long half-lives in people. The weak estrogenic activity of D4, in combination with its long half-life, poses potential concerns for exposed individuals."

The backgrounder, prepared for the California Environmental Contaminant Biomonitoring Program Scientific Guidance Panel, notes that  “Cyclosiloxanes are being touted as safer alternatives for a variety of uses.  It would be important to know if substitutes for existing chemicals are accumulating in the environment.  Biomonitoring cyclosiloxanes could detect rising levels in humans, which would be of concern because of the evidence of biological effects associated with these chemicals. These measurements would be an important tool for evaluating the public health efficacy of substituting cyclosiloxanes as less toxic alternatives for other chemicals.”

Organotin catalysts also are PBTs, according to the Oslo-Paris Commission, a consortium of 15 European countries a whose mission is to protect the marine environment of the North-East Atlantic.  These catalysts, particularly dibutyltin dilaureate (DBT), are common additives in one-component silicone mixtures.  In addition to this ecological hazard, organotin catalysts may be subject to conflict rules reporting by the Securities and Exchange Commission.

(Consumers beware: manufacturers generally do not list organotin catalysts in Material Safety Data Sheets, because they are present at less than 0.1% of the product by weight.)

Does your company manufacturer D4- and DBT-free silicone adhesives or sealants used in building construction? If so, we’d love to hear about your products, and have Pharos evaluate them.


Jim Vallette is the Research Director for the Healthy Building Network.