Arsenic in Rice: Part 16 - Rice Eaters and Bladder Cancer

Consumer Reports tells their readers:

Our resulting analysis of 3,633 study participants found that on average, people who reported eating one rice food item had total urinary arsenic levels 44 percent greater than those who had not, and people who reported consuming two or more rice products had levels 70 percent higher than those who had no rice.

This leads them to view the arsenic they detected in food products as such:

“Despite our taking into account other common sources of arsenic, and no matter which way we sliced the data, we see a very strong association between rice consumption and arsenic exposure,” says Stahlhut, who along with Navas-Acien led a similar analysis of NHANES data for our January 2012 article on arsenic in juice. That analysis found that study participants who reported drinking apple or grape juice had total urinary arsenic levels that were on average nearly 20 percent higher than those who didn't.

 Which leads them to this conclusion:

Consumers Union, the advocacy arm of Consumer Reports, urged the FDA to set a 3 ppb limit for total arsenic in apple and grape juice.

I am going to come back to that...but right now we still need to look at what we know so far.

• Urinary arsenic concentrations give a good biomarker of the absorbed dose of arsenic, since about 70% is excreted in the urine. (AJE)
• Rice eaters had arsenic levels that were 44 percent greater than those that do not consume rice. (CR)
• The average amount of rice consumed is one cup. (EHP)
• Consumer reports measured the amount of inorganic arsenic in one serving of rice and found the highest level to be 9.6 μg per 1/4 cup. (CR)

In my last post I attempted to show what is in play:

• ...if a 1/4 cup serving size that exceeds the New Jersey drinking water standard of 5 ppb is considered by Consumer Reports to be "troubling," "worrisome," "cause for concern," or "potentially harmful." 
• ....consuming one full cup of this rice must therefore result in four times more "troubling," "worrisome," "cause for concern," or "potentially harmful."

In all my previous posts I have tried to show that "troubling," "worrisome," "cause for concern," or "potentially harmful," that results from consuming 1/4 cup of rice that exceeds the New Jersey drinking water standard of 5 ppb for arsenic must be because of some risk of harm.

Because Consumer Reports sees harm if a serving is above 5 ppb, that harm must therefore be based on bladder cancer since that is what the NRC based the slope factor on used to support New Jersey's 5 ppb drinking water standard.

And because bladder cancer is also what IRIS is using for the Cancer Slope Factor - potency - they propose for arsenic, exceeding any number above "0" for arsenic increase the risk of bladder cancer.  New Jersey accepts a one in one million risk as acceptable which means 0.003 μg/L would be considered "safe."  Understanding reality, NJ set on a limit of 5 μg/L as acceptable based on the ability to treat the water as well as accurately test for an amount that low.  Therefore 0.003 μg/L "safe" became "safe" at 5 μg/L.

I then looked at urinary total arsenic that was reported by the CDC.  This led me to write in my last post:

So...if Mexican Americans and Asians consume more rice than Whites...and rice eaters have more urinary total arsenic than non-rice eaters...and the Cancer Slope Factor assume a potency whereby consuming more increase the risk harm...and that potency was used to that justify the New Jersey drinking water level of 5 ppb...and that Cancer Slope Factor, now proposed by the IRIS, is based on bladder cancer in woman...

Which I concluded with this:

...we would, therefore, expect to see more bladder cancer in Mexican Americans and Asians, especially in women...shouldn't we?

I want to stress here that all of my sources are the same sources as used by Consumer Reports and their experts.  They are all from reputable sources.  I am looking at the same data, facts, and figures that they look at and I don not see "troubling," "worrisome," "cause for concern," or "potentially harmful," for any of the rice they tested.

We are missing a lot, and I do mean a lot, of data to conclude "troubling," "worrisome," "cause for concern," or "potentially harmful," when exceeding 5 ppb per serving up to a maximum of 10 ppb.

If rice eaters have more urinary total arsenic then non-rice eaters, should we see more bladder cancer in those groups that consume rice on a daily basis?  So back to this question I posed:

...we would, therefore, expect to see more bladder cancer in Mexican Americans and Asians, especially in women...shouldn't we?

I went to the National Cancer Institute and looked up the data on bladder cancer from the Surveillance and Epidemiology and End Result (SEER) database.  Here is what they say:

Source

Now, with those estimate numbers in mind, let's look at what the EPA's IRIS is basing the proposed arsenic Cancer Slope Factor on:

2010 Draft IRIS Page 150-151

The EPA is proposing a Cancer Slope Factor on women's risk for bladder cancer.  This means that women appear to be more susceptible to the harm of bladder cancer from exposure to arsenic.  The "potency" of arsenic as a bladder cancer carcinogen is based on women and bladder cancer.  All things considered, when consuming a cup of rice, women and men receive the same dose of arsenic.  Same with drinking water.  There is a slight difference in urinary total arsenic between men and women.

CDC

If women are more susceptible to bladder cancer - the life-time risk - then wouldn't we see a higher incidence in women since consumption of arsenic seems to be the same?  That Cancer Slope Factor is derived from a line drawn through data points that looked at arsenic dose and incidence of cancer.  It assumes that there is a linear relationship between what was seen at high doses (the Morales data) and what should - theoretically - be seen at low doses.  It assumes a line going all the way to zero.  Zero dose, Zero risk of bladder cancer.

Let's look at those numbers in terms of an incidence rate for bladder cancer:

Source

EPA's proposed IRIS Cancer Slope Factor assumes a "safe" concentration of arsenic for a risk of one in 10,000 to be 0.14 μg/L (which is based on a consumption of 2 liters of drinking water per day).

Let's look at the incidence of bladder cancer in rice eaters.  Notice how Asians and Hispanics, two groups we know consume rice, have lower bladder cancer incidence than whites for both men and women.

I don't know...the numbers just don't support the theoretical potency for arsenic and bladder cancer the EPA is proposing.  Dr. Honneycutt with the TCEQ elaborates the same observation:

For bladder cancer alone, the incidence risk calculated by USEPA based on final draft values for males/females is 3.1E-04 per μg/L. Therefore, based on 2 μg/L as an average drinking water concentration, the estimated bladder cancer risk for the US population would be 6.2 per 10,000 or 62 per 100,000. However, the actual occurrence of bladder cancer in the US is about 23 cases per 100,000 (males/females combined). It would take 3 times the actual bladder cancer incidence for US males/females combined to even make possible the 62 cases per 100,000 estimated due to arsenic exposure from drinking water alone. Thus, the incidence risk calculated by USEPA final draft values for bladder cancer appears to be inaccurate and overly conservative. (emphasis mine)

Which brings us to this point.

If the theoretical Cancer Slope Factor is based on bladder cancer, and the incidence of bladder cancer does not match the theoretical risk being calculated, should we accept the theoretical risk as the basis for determining a "safe" threshold or for "establishing health criteria?"

If that Cancer Slope Factor proposed by EPA does not estimate the bladder cancer risk correctly, exceeding the New Jersey 5 ppb threshold for a 1/4 serving of rice will not be "troubling," "worrisome," "cause for concern," or "potentially harmful."

And if that's true, advocating for a "3 ppb limit for total arsenic in apple and grape juice" - which would be carried over for rice - is not warranted.

That's an important point to acknowledge.  It is the whole reason I spend time writing these posts.  If we are going to draw a line in the sand and claim "safe" on one side, then we will need to address what will it mean for the products that have concentrations above that threshold and fall on the other side of the line?



Not only does the science behind toxicology demand that we get this right, there are ethical considerations that need to be made as well.


Next Post: Arsenic in Rice: Part 17 - The Ethical Considerations of a Threshold


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