Thursday, May 17, 2018

Coffee, Acrylamide, and Proposition 65 - Part 3

California's Proposition 65 does two things:
  1. Proposition 65 requires businesses to notify Californians about significant amounts of chemicals in the products they purchase, in their homes or workplaces, or that are released into the environment. 
  2. By providing this information, Proposition 65 enables Californians to make informed decisions about protecting themselves from exposure to these chemicals. 
Therefore, I want to focus on two things as I move through this. First, is the acrylamide a "significant amount" and second, does knowing that there is acrylamide in a cup of coffee above the "safe harbor concentration of 0.2 micrograms per day" protect the individual?

Where to start on this...

Okay, so we need to get a bit sciencey here. Then we will bring in some math (or "maths" as the kids seem to call it these days).

Two questions:
  1. What is the risk of cancer if you drink Starbucks coffee?
  2. Should you be concerned?
I am going to say "trivial" to the first and "no" to the second. However, I need to show my work as to why.

Let's first define what a risk for cancer is. We need to understand the definition as that's the foundation on which the number is derived. It's that number that determines if Starbucks must place a Proposition 65 warning for those who enter their store to drink their coffee. 

Full disclosure here, I drink Starbucks and it is my favorite coffee. So there's my bias front and center...

Let's look at the definition we use in the biz of protecting public health because of chemical exposure have decided on for Cancer Risk:
The potential for exposure to a contaminant to cause cancer in an individual or population is evaluated by estimating the probability of an individual developing cancer over a lifetime as the result of the exposure. This approach is based on the assumption that there are no absolutely “safe” toxicity values for carcinogens.
Here is where it gets messy. We (them scientists looking at chemical exposure and cancer) decided that there is always a risk of cancer when you are exposed to a chemical where cancer is an outcome.

I think this model is incorrect, but it is what we decided on when determining a "safe" level for exposure of a chemical suspected of causing cancer.

For most chemicals that we classify as carcinogenic, we assume a "linear response," that is, at zero dose there will be zero risk:
What does “linear responses at low doses” mean? These chemicals are assumed to have no threshold for effects, and even one molecule of the substance is assumed to confer some increase in the risk of contracting a cancer. [Source]
 As I have pointed out in previous posts, when we talk about non-carcinogen chemicals, we assume a "non-linear" dose response curve.

Basically, what this curve shows is that there is a dose that a person (child, adult, elderly) could receive where we would see no observed adverse effects. We call that a NOAEL.
The highest exposure level at which there are no biologically significant increases in the frequency or severity of adverse effect between the exposed population and its appropriate control; some effects may be produced at this level, but they are not considered adverse or precursors of adverse effects.
When we graph this non-linear dose-response out, it looks like this:


You will notice that the graph starts at a dose of 7 mg before we start to see a response. Based on what we accept for non-carcinogens, in this graph, there is no difference between an exposure of a dose of zero mg up to 7 mg. This is know as the "threshold."
The threshold is the dose below which no effect is detected or above which an effect is first observed.
With carcinogens, there is assumed to be no threshold. Therefore, as stated previously, exposure to one molecule of the chemical produces a risk for cancer.

As this is the case, we assume that at zero exposure there will be zero risk. Since it is impossible to measure that, we take the data for cancer and dose that we see, and we force the non-linear dose-response curve into a straight line so that zero dose = zero cancer.


Pay attention to that last bit there in blue type. That's important as we look at Starbucks coffee, cancer risk, and California's Proposition 65.

Next Post: Coffee, Acrylamide, and Proposition 65 - Part 4


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