Coffee, Acrylamide, and Proposition 65 - Part 4

My last post ended with this graph:

Source

Let's focus on that last statement in blue type.

Because we (us public health people who look at chemical exposure) have decided that any exposure to a chemical known, or suspected, to cause cancer presents a risk, once we force the data of the doses we use and the cancers we see to form a straight line from zero through our splatter of data points, we now get the ability to assign risk.

Yay for us!

Only problem is, this forced line from zero dose = zero risk, tells us that at some dose above zero we will have some particular risk.

Remember that this is based on the assumption that all exposure to a carcinogen presents a risk.

Some of us say horse feathers! Lest you think I am the only one, let's look at what this guy from the Department of Pharmacology and Toxicology, School of Medicine, University of Louisville, writes:

The linear plot for dose is very deceptive and compresses low doses so that evaluation in that range is impossible; however, this has not heretofore been clearly recognized. This paper is an attempt to demonstrate that deception and the difficulty in evaluating effects at low doses. 

Deception...

Interesting word choice, but that's what guys like me think about using a linear plot where zero exposure = zero risk and anything above that - even one molecule - presents a risk.

If that line we produce is deceptive, then the statement in blue presents a situation whereby the "Safe Harbor" dose may be deceptive. From that paper:

The thresholds that are demonstrated from the animal experiments can be used to calculate safety factors for human exposure. In some instances human exposures are at or very near the thresholds in animal experiments. This indicates that humans are more resistant to the carcinogenic effect of at least some chemicals.

What he is arguing is that we can look at carcinogens in a similar manner (non-linear) as we do non-carcinogens.

This means that the safe harbor Proposition 65 has come up for acrylamide - 0.2 micrograms per day - is only applicable if that straight line starting at zero is correct.

That concentration of 0.2 is derived using the slop of the line that they plot starting at zero does/zero response.

That concentration of 0.2 is considered Safe Harbor because it is the highest concentration per day where the cancer risk is less than one in 100,000.

Any situation whereby a person could consume more than 0.2 micrograms of acrylamide in a single dose (one cup of coffee) would therefore trigger the Proposition 65 warning notice:

Unless Starbucks et. al. could make an argument that a concentration above 0.2 micrograms per day is okay as an Alternative Significant Risk Level (ASRL) because the benefits of drinking coffee exceed the increase risk of cancer above one in 100,000.

Hopefully you can start to see the absurdity in this, although to be fair, we have not yet determined how much acrylamide could be consumed in that one cup of coffee and what the increase in cancer risk would be.

More math...yay!



Next Post: Coffee, Acrylamide, and Proposition 65 - Part 5