Study looks at mercury levels in newborns of Lake Superior basin
By By Sara Moses, GLIFWC Environmental Biologist
Odanah, Wis.—Catching and eating fish is not only nutritious, but for many it is also a valued tradition. As you sit down with your family or community to enjoy your catch, you should consider the fish consumption advisories issued by GLIFWC (www.glifwc.org/Mercury/mercury.html) and your state. The advisories are designed to help you limit your exposure to certain contaminants, while continuing to eat fish. Once familiar with the advisories for your area, you will be prepared to make wise decisions about the type and amount of fish you choose to eat.
One of the major contaminants found in fish that make consumption advisories necessary is mercury. Fish consumption is the main route of human exposure to mercury. You will notice that the mercury advisories generally provide two sets of advice: one for the general population and another, stricter guideline, for children and women of childbearing age. Why are two sets of advice needed? Mercury is a neurotoxin, meaning it can harm the brain and nervous system. This is especially true in the developing nervous system of fetuses, infants, and children. Therefore, it is recommended that children and women who are or may become pregnant, limit their mercury exposure to a greater degree than adult men or women beyond childbearing age.
Although mercury is especially dangerous to the developing nervous system, no studies directly measured mercury levels in newborns to determine if they are at risk. The Minnesota Department of Health (MDH) recently completed a study that looked at mercury levels in newborn babies in Minnesota, Wisconsin, and Michigan. Bloodspots, collected between 2008 and 2010 from a heel prick just after birth of 1,465 newborns were tested for mercury. Since mercury can cross the placenta from mother to fetus, the amount of mercury found in the newborn bloodspots reflects the mothers' mercury exposure during pregnancy. The infant's mercury levels were compared to the EPA's Reference Dose, the maximum level of mercury a person can be exposed to before there is considered to be a risk of negative health effects.
Most infants were found to have low or undetected total mercury levels. However, 8% of tested newborns had total mercury levels above the U.S. EPA's Reference Dose for methylmercury, the highly toxic form of mercury found in fish. Babies born during the summer months were more likely to have elevated mercury levels. This seasonal effect suggests that increased consumption of locally-caught fish during the warm months is an important source of pregnant women's mercury exposure in this region. No Michigan samples were above the U.S. EPA's Reference Dose, but 3% of the Wisconsin and 10% of the Minnesota infants were above this level. One possible explanation is that Minnesotans have reported eating more locally-caught fish than do people in Wisconsin or Michigan.
What can you do to protect yourself and your family? Consult the appropriate fish consumption advisory before consuming fish. Follow the advice provided for how often you can safely eat a given type of fish. In addition, consider catching and eating fish that tend to be lower in mercury, such as whitefish, herring, bluegill, sunfish, crappie or perch, rather than higher mercury species such as walleye, musky, northern pike and bass. Smaller fish also generally contain less mercury than larger fish of the same species. With this knowledge, you can confidently and safely eat fish.
More details about the mercury in newborns study are available on the MDH website: www.health.state.mn.us/divs/eh/hazardous/topics/studies/newbornhglsp.html