Saturday, July 28, 2007

The trouble with regulations…

…is that they rely on assumptions, so regulations can only be as effective as their assumptions are accurate.

Regulations are also mired in verbosity and jargon, and steeped in complexity, making them nearly unapproachable by the average person. And yet, regulations are all that stand between us and the harm that comes from poisoning our air, food, and water. We have little choice but to rely on the expertise of others, who must write effective regulations and see that they’re enforced: a costly, but essential, function of government.

The foundation of all regulations are the assumptions upon which they’re built, so it’s obvious that if the assumptions are flawed, the regulations will likewise be flawed. Environmental chemists in Canada* have been examining the assumptions that underlie regulations addressing a major class of chemical pollutants—“persistent organic pollutants” (POPs)—that are persistent because they are resistant to breakdown, typically tending to accumulate in the food chain, especially in fatty tissue; organic because they are carbon compounds that are the subject of organic chemistry (very different from the “organic” of organic food); and pollutants because they are toxic to living organisms. Some better known POPs are pesticides, solvents, PCBs, and dioxins.

When regulatory agencies began addressing pollutants, it was understood that pollutants that bioaccumulate (by magnifying in concentration as one organism eats another, and is then eaten by another, etc., in increasing trophic levels right on up the food chain) are the most treacherous, because higher level predators (like us) can end up consuming very high amounts of a pollutant that was originally present in the environment at a relatively low level. Thus, the primary regulatory focus has wisely been on such bioaccumulating toxics known as POPs.

The trouble is that in defining POPs, regulators chose to measure their bioaccumulating potential in fish, for reasons that remain unclear to me. After all, we are not fish, and there are many non-fish terrestrial organisms, and we all have very different life circumstances, beginning with the fact that we are air-breathers. Indeed, this turns out to be a very flawed assumption in the regulatory model.

POPs have traditionally been evaluated using a measure called KOW, an indicator of a substance’s solubility in water, roughly:

High KOW** substances are highly hydrophobic and poorly metabolized and poorly excreted in aquatic organisms, and tend to accumulate in fat, and this is a reliable predictor of which compounds will bioacumulate in fish.

High KOA*** substances are only moderately hydrophobic, are poorly metabolized, and are poorly excreted, and thus will bioaccumulate, in air-breathing organisms.

Regulations currently address compounds that have a high KOW but not those that have a high KOA and therein lies the problem.

The graph below illustrates what happens in real food webs that are contaminated by a low KOW but high KOA compound, i.e, one that would not be considered bioaccumulative by current regulations:

Kelly, et al., 2007
Note the dotted blue line, that of the piscivorous (water-breather) food web. This data shows a lack of bioaccumulation (with the concentration of the ß-HCH remaining constant all the way up the food chain), and this data would be what current regulation is based upon.

In contrast, note the solid green line, that of the terrestrial (air-breather) food web. This data shows a strong bioaccumulation that occurs in just three trophic levels. Note also that the concentrations measured are on a logarithmic scale, so the concentration in the caribou is about 10 times that found in the lichens it grazes on, while the concentration in the wolf is another 100 times more concentrated than that of the caribou, or a 1000 times higher concentration than that of the organism at the base of the food chain.

Unsurprisingly, the solid blue line, indicating the marine mammal food web which includes both air- and water-breathers, has a slope that is intermediate to that of the other two food webs. However, the resultant concentrations in the top predators of this food web exceed those found in the terrestrial web, simply because there are more intermediate trophic levels. [Humans are included in the “marine mammal” food web because they are consuming both air- and water-breathing marine organisms.]

The key point here is that while the regulators assume that given its low KOW, ß-hexachlorohexane is non-bioaccumulative, and thus regulate it as such, it is actually highly bioaccumulative in the real-world environment that includes terrestrial organisms and marine mammals. The authors of this study estimate that about one-third of organic chemicals currently in commerce fall into this low-KOW / high KOA class of compounds, that may currently be regulated as toxic, but are not regulated as the more hazardous bioaccumulating class of toxic compounds that many of them are.

This is a very big deal, but unfortunately, the topic is sufficiently complex that news coverage is very scant. One hopes the regulators are paying attention in our stead.

*2007. Kelly, B., Ikonomou, M., Blair, J. Morin, A., Gobas, F. “Food Web-Specific Biomagnification of Persistent Organic Pollutants.” Science, 317:236-239.

**High KOW compounds are more precisely defined as those substances having a high octanol-water partition coefficient, but a complete understanding of this is not needed for a general understanding of the issue.

***High KOA have a high octanol-air partition coefficient.


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