Monday, March 24, 2008

Making Lists: Dr. Cal's thoughts on priortizing chemicals

Guest blogger, Dr. Cal Baier-Anderson, a toxicologist at the University of Maryland, Baltimore; and Environmental Defense, adds her own thoughts about prioritizing chemicals (also check out the list created by J. Lowe from Impact Analysis in the comments section of Fav Five.)

A few years ago at a professional meeting I participated in a panel on the chemical perchlorate, which was receiving a lot of attention as an emerging drinking water contaminant. Perchlorate, an oxidizing agent that is used in rocket fuel, can block the uptake of iodide in the thyroid. One member of the audience suggested that focusing attention on perchlorate was a waste of time and money, that there are other chemicals that are more important. Make a list, I challenged the group; professional organizations and industry should step up to the plate and identify the top 10 chemicals of concern, from an industry perspective. It is certainly not an easy task, as Emily pointed out, many different lists can be made, depending on what features are most important.

With tens of thousands of chemicals in commerce, chemical prioritization is a hot topic. The traditional risk assessment process focusing on one chemical at a time requires a lot of data collection: the identification of the most important hazard endpoints (a prioritization process in and of itself); determination of dose-response for the priority endpoint, the characterization of exposure; and the assessment of risks. Chemical prioritization can be based on hazard, it can be based on likelihood of exposure, or it could be based on risk, incorporating both hazard and exposure. Many environmental groups argue that there is so much uncertainty in the risk assessment process that it is better to focus on hazard, emphasizing carcinogens, mutagens, reproductive toxicants, and endocrine disruptors. This has lead to the creation of lists, such as California’s Proposition 65 list of carcinogens, mutagens and reproductive toxicants (CMR), which requires that products containing a chemical on this label their products with a special notice.

Chemicals that can be classified as persistent, bioaccumulative and toxic (PBT) are also considered to be high priority chemicals. EPA initially devised a list of PBT chemicals, but then developed a computer program that evaluates individual chemicals to score them as to PBT properties. Persistence and bioaccumulation are determined by basic chemical properties, whereas toxicity is based on aquatic toxicity data.

With public attention focused on chemicals in consumer products, many companies are critically evaluating their products’ ingredients to determine if they are made with chemicals of concern. But how can we define chemicals of concern? Based on hazard, or based on risk? Some companies have developed their own restricted substances list that contains chemicals that the companies believe to pose some unacceptable risk to their workers and/or consumers. REI has a list, but a simple Google search of “restricted substance list” will uncover many more.

At the recent SOT meeting in Seattle, there was a session on hazard vs. risk-based approaches. Many state governments and large companies are defaulting to hazard-based approaches as a simpler approach to removing chemicals of concern from consumer products. Several prominent toxicologists opined that focusing on hazard without considering exposure will result in time and money wasted on chemicals posing very little risk. But as my colleague noted during the discussion, there are many folks in the environmental community that are wary of our capacity to predict exposure, citing numerous examples where it was initially predicted that there would be no exposure, and the experts were wrong: PCBs, Bisphenol A, phthalates, PFOA, PBDEs…If we can’t correctly predict exposure, then confidence in the risk assessment plummets, shifting focus to hazard.

A new approach is being promoted by some very smart people: alternatives assessment. Rather than making simple restricted substances lists, focus on what are the alternatives and compare using a suite of criteria. These assessments can be used to drive continual improvement in materials safety – protecting workers, the environment and consumers. Makes sense to me!

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