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MOT(EHTG) is always manufactured as a mixture with DOT(EHTG). The MOT(EHTG):DOT(EHTG) mixture is added to polyvinyl chloride (PVC) and chlorinated polyvinyl chloride (CPVC) as a heat stabilizer intended to preserve the polymeric structure and properties of the resins during the final stages of fabrication into finished articles. After being blended into the PVC and CPVC resin, the stabilizers remain there throughout the subsequent processing steps. All systems are designed and maintained to ensure that moisture is kept away from the resin compound, since the presence of water creates significant problems during processing. Therefore, losses to water during blending and melt processing are very low, as these are designed to be “dry” processes. Furthermore, water is not used on a regular basis to clean equipment, wash out vessels, etc., and no wastewater is generated. Compounded PVC and CPVC material is solid and any spillage is cleaned up by vacuum or sweeping. Once the PVC or CPVC is melt processed into a final part, most of the mono-octyltin chemicals are strongly held within the resin and are highly resistant to leaching although some leaching of monooctyltin compounds may occur from some PVC products. During melt processing of PVC and CPVC, there is the possibility that mono-octyltins (and other ligands unspecified) can be released into the atmosphere. Measurements by Nowak (2003 cited in RPA 2002, updated 2003) of MOT released during a PVC calendering operation show the values to be 0.003% of the MOT processed being released (RPA 2002, updated 2003).

Mono-octyltin chemicals either leach out of PVC and CPVC articles, or are released into the atmosphere during the processing described above. As discussed by Muller (1989), there are a range of organotin chemicals that are in the PVC after processing which might leach out. However, all will be hydrolyzed to the constituent alkyltin (MOT) and the relevant anion (RPA 2002, updated 2003). These types of releases are discussed below, and the reader is also referred to the report by RPA (2002, updated 2003), where an in-depth discussion of these releases is provided.

Several studies have been done to examine environmental levels of mono-octyltins and their fate. Regarding environmental fate, most PVC and CPVC articles will either be recycled or landfilled at end of life.

Some research shows that approximately 80% of organotins detected in untreated wastewater are associated with suspended solids and are removed from wastewater primarily by sedimentation and adsorption into sewage sludge (Fent 1996).

Landfill leachate may directly enter the environment. Mersiowsky et al. (2001) and Mersiowsky and Ejlertsson (1999) found that the concentration of organotins in leachate samples from sanitary landfills were found to be in the low micrograms per liter range. In addition, it is expected that most leachate would be treated at on-site water treatment facilities or released into a municipal sewer. If landfill leachate should directly enter the environment, there would be dilution of the leachate resulting in lowered environmental concentrations than were measured in the leachate.

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