Two recent studies have revealed previously unreported trace levels of mercury in high fructose corn syrup. Both studies cited older mercury cell manufacturing practices as the source of the contamination. The Corn Refiners association challenged the claims, stating that at least one study "appears to be based on outdated information with dubious significance," and citing the U.S. Food and Drug Administration's listing of HFCS as safe for use in food.
In processing corn to make HFCS, caustic soda is used to separate the starch from the corn kernel and to balance out pH. Two primary types of caustic soda, mercury cell and membrane cell are used for this process. It is suspected that in facilities that use mercury cell caustic soda, some mercury leaches out into the end product.
"The mercury can volatize, turn into gas and distribute throughout the machinery and the environment of the manufacturing plant, and we think that's how the mercury winds up in products such as high fructose corn syrup," said study co-author Dr. David Wallinga of the Institute for Agriculture & Trade Policy. "It's clear that this happens because when these plants are decommissioned they are mercury-polluted and require cleanup."
While not all HFCS manufacturing plants use mercury cell technology, currently, food manufacturers are not require to list their source of HFCS.
Samples were taken from HFCS from both manufacturers and consumer products. In one study, nine out of 20 HFCS samples had some level of mercury. In the second study, one-third of products, including snack bars, barbeque sauce, yogurt and chocolate syrup, contained traces of mercury.
According to the studies, a worse-case scenario that involved consuming 50 grams of the most contaminated HFCS daily would result in an intake of .28 micrograms of mercury daily from HFCS.
"I used the same numbers [as the study] and did a more sophisticated analysis including the variability of HFCS consumption and sources and came up with a measurement of .1 micrograms per day," said Carl Winter, director of FoodSafe Program and food toxicologist at the Department of Food Science Technology, UC-Davis. "The important thing is to know how much we are exposed to. Most toxicology is reported for methyl mercury, which is the most toxic because it is absorbed directly into the blood stream, whereas elemental mercury is absorbed 10,000 times slower."
The study calculations do not define what type of mercury is found in HFCS, and currently, the Environmental Protection Agency has only defined human toxicity levels for methyl mercury at .1 micrograms per day, usually acquired from eating fish or getting amalgam fillings.
However, both studies expressed concern about exposure to any mercury in a common food ingredient. According to the Environmental Health study, "…it is imperative that public health officials evaluate this potential source of mercury exposure, as HFCS is presently ubiquitous in processed foods and therefore significantly consumed by people all over the world. Mercury in any form — either as water-soluble inorganic salt, a lipid-soluble organic mercury compound, or as metallic mercury — is an extremely potent neurological toxin."
"The best amount of mercury exposure would be none at all," said Wallinga. "We only have a formal level from EPA for methyl mercury, and we don't know what we are dealing with in the HFCS, so we go to the common sense approach. We have a way to make caustic soda without employing mercury so then why, from a policy standpoint, wouldn't it be better to make these ingredients without using mercury? According to some, the other technologies are more efficient, and most plants have converted, so why not convert the rest?"
"Clearly it's great to know as much as you can about all of these issues," said Winter. "I think it might have been a surprise to some to see findings of mercury in HFCS, but these are very preliminary reports. They do not differentiate the types of mercury that may be found and the findings are based on multiple samples that might not accurately reflect manufacturing. I would say it is premature to make any conclusions that changes are necessary in the HFCS manufacturing practices but I would say that this will probably stimulate greater monitoring of mercury levels."
"For consumers, the simplest solution for now may be to avoid foods containing HFCS, particularly when it's high on the label," the study from IATP said. "Even if U.S. chlor-alkali plants discontinue using the mercury-based process, there are other plants worldwide that still do, and they export to the United States. American consumers are still likely to eat food products containing HFCS that may be contaminated with mercury from these plants. Beyond this fact, HFCS content, particularly high on the label, is a signal for a highly processed food high in added sweeteners (and therefore calories), and often high in added fats as well."