SEAFOODNEWS.COM [Risk Policy Report] by Maria Hegstad September — 30, 2014 — EPA is facing calls from observers to consider pursuing a holistic risk-benefit calculus to project the estimated risks to the public from exposure to methylmercury (MeHg), in lieu of the agency's plan to update its 13-year old Integrated Risk Information System (IRIS) assessment of the substance that the public is exposed to by eating otherwise beneficial seafood.
During a recent EPA National Forum on Contaminants in Fish in Alexandria, VA, a National Oceanic and Atmospheric Administration (NOAA) official suggested that a broader "net effects" approach could be more useful to the agency than a traditional reference dose (RfD) — the maximum amount of a substance that EPA estimates can be ingested daily over a lifetime without associated adverse health effects occurring.
"If you use a net effects approach, do you even need" an RfD, asked Tony Lowery, the program coordinator for NOAA's National Seafood Inspection Laboratory, speaking at the EPA forum.
Ned Groth, a retired Consumer Reports toxicologist who consults for advocacy groups on mercury and seafood issues, asked, "Is it even practical to set a new RfD? Or [is it better to] take a second approach?"
In response to the suggestions, Vincent Cogliano — acting director of EPA's IRIS program — said the agency is pushing ahead with its planned update to the 2001 MeHg risk assessment in it pending five-year plan of environmental contaminants that will be re-assessed or added to the IRIS database. "We want to do assessments with the most important" chemicals and contaminants," Cogliano said of the five-year plan. "Either way, mercury and methylmercury are high on that list. These are assessments that we expect to take on in the future."
Cogliano indicated that IRIS assessors have been considering very preliminary questions for the anticipated MeHg study update. Staff is considering questions like "which agents should be evaluated," as well as "which exposure routes" and "most important, what key issues should be addressed," Cogliano said. He noted that staff is considering whether to assess MeHg alone, or to also include organic Hg, inorganic or total Hg in the assessment.
Cogliano spoke little about the upcoming assessment, and instead urged forum attendees to tell him which of the options would be most helpful to them in their risk assessment and risk management activities.
The comments at the Forum follow the recent release of EPA and the Food and Drug Administration's (FDA) updated joint draft advisory for pregnant women and children on how much fish to consume and what types of fish to consume. FDA performed a risk-benefit analysis to underpin that advisory, which provides a first-time floor or minimum amount of fish which should be eaten weekly as well as a maximum limit. Environmental groups have long expressed concerns about FDA's approach and have urged EPA to tighten its IRIS assessment as a counterbalance to FDA's emphasis on the benefits of eating fish.
"I'm a believer in integrated assessments. It's the only way to go," Groth said in public comments after Cogliano spoke. "But it's very hard to do. The IRIS program does risk assessments; I'm not sure who does benefits [assessments]. I think they are to be done separately and then put them together. I think the key question is net effects and for whom?"
Groth also suggested that instead of a traditional IRIS update that EPA consider performing an approach using the dose-response-based estimation of risk approach, an approach similar to that EPA uses when assessing the human health risks of carcinogens. Most recently, the National Academy of Sciences (NAS) encouraged EPA to use this approach in its long-running efforts to re-assess the human health risks of exposure to arsenic in the environment.
"We'll have to see," Cogliano replied to Groth's questions. "That [approach] is what we're trying to do with arsenic," he noted, but did not say whether the agency would pursue an alternative to the IRIS update.
Gary Ginsberg, a toxicologist with Connecticut's Department of Health, said the broader risk review suggested in place of the agency pursuing a traditional IRIS review is "very hard to do," like analyses of lead or other non-carcinogenic agents assessors would seek to review using a risk-specific dose approach.
An agency source explains that the risk-based approach is similar to how EPA assesses the human health risks of carcinogens. Rather than setting a distinct level below which no associated non-cancer health risks are anticipated over a lifetime of daily exposures, a risk-specific dose provides a slope. This means that a dose can be determined for a specific risk level, such as the 1 in 1 million or 1 in 10,000 excess cases of cancer used by agencies to set policies.
The idea would be to use human "epidemiology studies to estimate the dose-response relationship," the source says. "We have fish eating populations and levels, can we take those and create realistic dose-response — depending on how well the levels [of fish consumption] are characterized," the source adds.
This is the approach that NAS urged EPA to adopt when assessing the human health risks of exposure to low levels of arsenic, particularly in drinking water. The agency source indicates that this approach is likely easier to use in that case, compared to the ongoing MeHg assessment update. "With arsenic, it's perhaps a little easier, because [the studies are] done on reasonably stable populations with a single water source. It's uniform over time. The question is, is the mercury concentration [in American seafood] stable over time?"
One possible further complication for EPA's update to its MeHg assessment is the presence of the co-contaminant polychlorinated biphenyls (PCBs) in fish. PCBs are a ubiquitous environmental contaminant that EPA is also looking to re-assess in the IRIS program in the near future.
In a separate talk, Cogliano outlined some preliminary research he has done into the question of whether the toxicities of mercury and PCBs are additive — meaning they have combined effects on human health — and should be assessed together for the IRIS database.
Cogliano noted that NAS in its 2008 report "Phthalates and Cumulative Risk Assessment: The Task Ahead," urged EPA to simplify its policies for performing cumulative risk assessments, and look together at all contaminants that act upon the same target organ, regardless of their biological mode of action. The report specifically cited mercury and PCBs as an example of contaminants that should be assessed together, Cogliano noted.
Cogliano outlined some preliminary literature searches he has performed on the question, saying that he was "surprised by the results in the animal tox studies . .. they point to some kind of complex interaction."
His early conclusion is that "there is some evidence of additivity or more complex interactions," between mercury and PCBs in toxicity studies. "The effect modification [of the two contaminants together] is worth considering when we do our new dose-response [analysis] of mercury," Cogliano said.
Groth subsequently cautioned that it is "going to be very complicated to sort it all out. Since we get nearly all of our mercury [exposure] from fish, we also need to include the benefits of [eating] fish."
Cogliano replied, "That is one of the complications. . .. That's why it is important to have an assessment of toxicity so we can compare differing levels of Omega 3 [oils, in different types of fish. The oil is a nutritional benefit of consuming fish]. It's not what we in the IRIS program have done."
This story originally appeared on SeafoodNews.com, a subscription site. It has been reprinted with permission.