I appreciate your effort to abide by the facts, but I would advise not to put too much trust in process inventory data for definitive determinations on toxic chemical releases from polymer life cycles. Industry-generated polymer life cycle data sets have a history of conveniently simply ignoring chemical flows such as dioxin that have significant uncertainties or political ramifications or both.

See my paper entitled "Toxic Data Bias and the Challenges of Using LCA in the Design Community" (http://www.healthybuilding.net/pvc/Toxic_Data_Bias_2003.html) for a discussion of this and other related phenomenon that can overwhelm LCA tools and lead them to results that have an appearance of precision but are completely misleading.

It is also instructive on this point to follow the history of the USGBC Technical Science Advisory Committee assessment of PVC which initially concluded based on standard LCA modelling and process inventories that PVC was not substantially different from a set of other materials assessed. But in the second round of assessment using a wider range of analytic tools and incorporating additional data that LCA misses or does not handle well, the conclusions changed substantively. Specifically they found that with the inclusion of end of life impacts not accounted for by LCA (accidental landfill fires and backyard burning), "the additional risk of dioxin emissions put PVC consistently among the worst materials for human health impacts."

While LCA tools and inventories can be highly useful for assessing energy and material flow related impacts, we have a long way to go before process inventories can provide reliable information for assessing the health impact of material life cycles.

The single aspect of the dialogue around "worst-in-class materials" that disturbs me most is the complete lack of discussion of Precautionary Principle.

We can talk about life cycle, science and measurable impacts, but we too often lose site of the ultimate goal, which is a world in which NO materials are toxic or create negative impacts of any kind. That goal can seem untenable, but the only way we can back out of the disasters we have created is to take practical steps and design our way out. Shooting too low won't get us there.