Long Exposure

November 12th, 2009

Views: 136

Posted by ChrisG at 10:32 am

Assessing chemical hazards is not easy; this interesting post from Richard Denison over at the EDF’s Chemicals and Nanomaterials blog points out some reasons why, mainly to do with a distinction (which, as I have noted before, is not unproblematic) between intrinsic hazard and the extrinsic, relational properties of chemicals which make a complex temporal procession of exposure scenarios possible.

The difficulties of measuring exposure are based on the complexity of the processes into which a chemical enters over time.

The highly variable nature of exposure poses a major challenge to exposure (and risk) assessment: It means that exposure assessment must be an ongoing activity, with the scope and frequency of its measurement sufficient to characterize the variation (spatial and temporal) in, as well as magnitude of, exposure. That’s but one reason why exposure assessment is often called the “weakest link” in risk assessment.

First, it’s difficult for public agencies to collect, collate and assess the kind of information necessary to establish whether humans or ecologies are undergoing exposure, given the distribution of exposure scenarios in time and space (production of chemicals, transportation, incorporation in products, use of products, disposal, degradation). Second, imagining exposure scenarios often relies on assumptions about the underlying processes which turn out to be wildly inappropriate:

Phthalates are very widely used in products ranging from plastics to cosmetics and other personal care products. They exhibit a range of toxicity, including to the liver, kidney, and male reproductive system. The first CDC National Report demonstrated surprisingly high levels of di-butyl phthalate (DBP) and di-ethyl phthalate (DEP) in U.S. residents in general, and for DBP, in women of child-bearing age in particular (see the first two letters here). Indeed, these data demonstrated high-end levels of DBP that were an order of magnitude higher than a prior estimate that had been developed based on industry-provided use data and expert judgment.

The political angle here is important: producing the required data, interpreting it and setting up appropriate monitoring programmes requires transparent, legally enforceable and long-term relationships between private and public bodies in order to monitor stuff, and thereby promote the common good. But there is a basic and familiar conflict of interest here:

It simply must be acknowledged that industry has a strong interest in maintaining that exposure to its chemicals is low, so the ability to independently measure and verify exposure data is critical. Yet physical access to many exposure “settings” (e.g., workplaces) is very limited and infrequent at best, even for government officials.

In other words, industry has an interest in being irresponsible, in limiting the scope of risk assessment to relatively simple, acute, and short-term scenarios. But such a focus elevates managing short-term uncertainty for competitive advantage by private interests over the need to manage longer-term uncertainty for the common good.

Not that such an approach is endemic to the economic system or anything.