Arsenic in Rice: Part 15 - Urine From Rice Eaters

Continuing on...

Here is what we have been told 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)

For those of you who are interested in how consumer Reports came up with that value of 9.6 μg per 1/4 cup, I am going to assume it was based on this methodology.  Consumer Reports "PDF with complete details of our test results" lists the concentration of inorganic arsenic as a part per billion (ppb).

PDF with complete details of our test results

214 ppb is most likely from a weight to weight analysis.  So in this case there were found to be 214 μg of inorganic arsenic per kilogram (kg) of rice.  Consumer Reports calculates a 1/4 cup serving size to contain 45 grams of rice:

Using some algebra...if one kg of rice contains 214 μg of inorganic arsenic, 45 grams of rice will contain 9.63 μg, and that concurs with what Consumer Reports shows in their report:

So the next question will be, what amount of inorganic arsenic do folks actually consume?  This is where it gets a bit tricky.  It seems that the results on urinary arsenic is for total arsenic.  We want to look at inorganic arsenic, the form of arsenic that may contribute to bladder cancer.

With that in mind, let's assume that the total urinary arsenic is inorganic arsenic.  Here is what we find, according to the Centers for Disease Control (CDC)

CDC

Consumer Reports tells us that "people who ate rice had arsenic levels that were 44 percent greater than those who had not," and "certain ethnic groups were more highly affected, including Mexicans, other Hispanics, and a broad category that includes Asians."

You can see that Mexican Americans have a higher mean urinary total arsenic than non-Hispanic whites, but non-Hispanic blacks are even higher.  What we don't have is data on Asians.  Now, based on all of this, rice eaters consume more arsenic than non-rice eaters.  This is confirmed by the Dartmouth study on children:

Results: The median total urinary arsenic concentration among children who reported consuming rice was 8.9 μg/L  compared with 5.5 μg/L among those who did not consume rice. 

That median is based on 1/4 cup of rice.  The Dartmouth researches also report:

After adjusting for potentially confounding factors, and restricting the study to participants who did not consume seafood in the preceding 24 hr, total urinary arsenic concentration increased 14.2% with each 0.25 cup increase in cooked rice consumption.

What we know now is that rice consumption is a potential source of arsenic exposure.

Assuming that the impact for rice and water on the total urinary arsenic is similar for an adult as it is for a child...and considering that the mean reported by the CDC is for both rice eaters and non-rice eaters, we can assume that a Mexican American eating one cup of rice would have approximately 15.8 μg/L urinary total arsenic. (9.29 x 1.142 = 10.6 X 1.142 = 12.1 x 1.142 = 13.8 x 1.142 = 15.8)

Dr. Smith tells us - based on the Mormon cohort research he cited:

Urinary arsenic concentrations give a good biomarker of the absorbed dose of arsenic, since about 70% is excreted in the urine.  Excretion of arsenic in urine as a function of exposure to arsenic in drinking water. (AJE) 

If the average amount of urine produced is 2 liters per day, a Mexican American consuming on average one cup of rice would therefore be consuming an absorbed dose of about 45 μg of total arsenic to produce 15.8 μg/L of total urinary arsenic.  ([45 * 0.70] / 2) = 15.8 μg/L

I assume my math and logic are both correct on this.

Point here is this.  If the total arsenic Consumer Reports found in the Martin Long Grain Brown Rice was 398 μg/Kg, consuming one cup of this rice would produce a total dose of  72 μg total arsenic.  If 70% of that is excreted in the urine as total arsenic, we would see 50.4 μg in the total urine produced in a day.  If the average amount of urine is 2 liters, this would equate to a urinary total arsenic concentration of about 25 μg/L.

What does all this math mean?  Look at it this way.  If Mexican Americans consume more rice than whites, and the average urinary total arsenic in a Mexican American is 9.29 μg/L, if Dr. Smith is correct and Urinary arsenic concentrations give a good biomarker of the absorbed dose of arsenic, since about 70% is excreted in the urine.  The exposure dose is about 28 μg for a person producing 2 liters of urine.  That's 28 μg from all sources.

Now that 70% excretion was calculate from drinking water.  It is possible that the majority of arsenic in the rice is excreted through the feces.  If that's the case, we can assume that this arsenic was not made available for harm (bladder cancer), which seems to be supported by the CDC data on rice eaters.

Since we do have evidence that rice eaters have more urinary total arsenic than non-rice eaters, we can ask the question, do those groups who are considered to consume more rice show a higher incidence of bladder cancer compared to those who do not.

Here is where that CDC report comes in handy.  It appears that Whites have lower urinary total arsenic than Mexican Americans and Blacks.  If , according to Dr. Smith's contention that "urinary arsenic concentrations give a good biomarker of the absorbed dose of arsenic, since about 70% is excreted in the urine," those with higher mean concentrations of urinary total arsenic must be consuming more food products with higher concentrations of arsenic.

Not sure about Blacks, but Mexican Americans were singled out by Consumer Reports as being rice eaters:

And certain ethnic groups were more highly affected, including Mexicans, other Hispanics, and a broad category that includes Asians.

We can assume that their higher urinary total arsenic must come from the consumption of rice.  And, if one cup is the average amount of rice consumed, that's a lot of arsenic consumed with the rice.  Remember that Consumer Reports looked at a rice serving size of 1/4 cup.

Which brings us back to "troubling," "worrisome," "cause for concern," or "potentially harmful."

You see - well at least as I see it - 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 result in four times more "troubling," "worrisome," "cause for concern," or "potentially harmful."

As Consumer Reports sees it there will be 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.  Bladder cancer is also what IRIS is using for the Cancer Slope Factor - potency - they propose for arsenic.

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...

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

If those who consume rice have higher concentrations of urinary total arsenic, and there is a linear dose-response as the EPA's ATSDR contends, those who consume rice should show a higher bladder cancer incidence.

Drum roll please.....

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


.