The power and limitations of science in the selection of building materials
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The U. S. Green Building Council’s PVC report tells us there is no scientific justification for singling out PVC and awarding a point for avoiding it through the LEED rating system. In some application areas, the life-cycle impacts of competing materials are worse. This is the case with cast iron, used for drainage piping in buildings. The coking ovens used in its manufacture produce emissions that are worse than those of PVC manufacture, use, and disposal.
The PVC report emphasizes life-cycle assessment (LCA), which examines the environmental and health effects of a product (or service) over its entire life cycle, from raw material extraction through manufacture, transportation, use, and disposal. To conduct an LCA, researchers first tabulate the flows from each step in the product’s life cycle: raw materials and energy in; products, waste, and emissions out.
Once they have this inventory, they estimate the impact of each of those flows, generating scores in a series of impact categories such as climate change, habitat alteration, water pollution, and human health. In the effort to create more environmentally responsible buildings, LCA is a critically important tool. But at the same time, we can’t rely exclusively on the results provided by LCA, which presents a conundrum.
One of the fundamental challenges with LCA—and comparing the LCA of one product to that of another—is that we are typically examining different types of impacts yet wanting to come up with an overall ranking in terms of greenness. In comparing products, not only are we trying to compare apples to oranges, but we’re often comparing the color of apples to the taste of oranges. LCA helps us quantify the life-cycle environmental burdens of products (environmental damage during harvesting or mining, pollution from manufacturing, embodied energy, toxins released during disposal, etc.), but one still has to establish a weighting for these different burdens.
LCAs allow us to either aggregate these environmental and health burdens or examine certain impact areas separately. While PVC may not be worse than certain other materials when environmental and health impacts are aggregated, according to the USGBC report, PVC is almost always worse than these competing materials when examined relative to cancer risk.
We know a lot about the risks of air pollution, and we know a fair amount about the toxicity of substances to various ecosystems, such as aquatic environments. However, we know very little about causal relationships between environmental exposures to particular substances and maladies that may take decades or even generations to appear, as can be the case with cancers.
As a result, the impact assessment formulas used in LCA are not very comprehensive, but they do assign significant cancer risks to certain compounds, such as dioxins, that have been studied extensively. Dioxins can occur when highly reactive elements such as chlorine are mixed with hydrogen and carbon (which describes exactly the construction of PVC) and the chlorinated material is burned under uncontrolled conditions. PVC came out looking worse in the final report from USGBC than it did in an earlier draft report, partly because the later document included estimates of dioxin emissions from PVC in landfill fires.
As if it were not difficult enough to account for the effect of carcinogens in the life-cycle assessment of PVC, even less is understood about certain additives. A growing body of scientific literature focuses on the phthalate plasticizers in PVC as being potentially harmful endocrine disrupters, and such findings may force us to revise LCA analyses.
Research that has appeared in various peer-reviewed journals, including the U.S. National Institute of Health Sciences’ Environmental Health Perspectives, and the American Chemical Society’s Environmental Science & Technology, indicates that certain substances—including phthalate plasticizers used in PVC products such as flooring and wall coverings, bisphenol-A used to produce polycarbonates and epoxies, and certain bromenated flame retardants used in foam cushioning and expanded polystyrene insulation—can disrupt the endocrine systems of fish and humans. Scientists are only beginning to understand how these substances effect the production of hormones that control growth and development.
In addition to LCA, as a tool for informing product selections, there is also the Precautionary Principle, adopted by the U.S. Green Building Council last year as one of its six guiding principles. The argument is: When we don’t understand the effect of chemicals on our health, we should be cautious in our use of products containing those chemicals. In other words, the Precautionary Principle suggests it may make sense to take action to avoid harm from something in advance of incontrovertible scientific proof about the risks or if there are indications that delay on taking action will cause further harm. The risk with the Precautionary Principle is that it could cause us to avoid one material, such as PVC, even though the alternatives to that material could be worse; the need to understand these relative risks is why LCA is so important.So what does all this mean relative to green building and PVC? The USGBC PVC report showed us that PVC is bad enough that we should continue to look for alternatives. But, we also need to use life-cycle assessment to ensure that the substitutes we find for PVC aren’t, in fact, worse from an environmental and health perspective.
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