Hazardous Sites & Substances

Mercury in Newborns in the Lake Superior Basin

Introduction

The “Mercury in Newborns in the Lake Superior Basin” study was conducted by the MDH Environmental Health Division from 2007 to 2011, in collaboration with state newborn screening programs in Minnesota, Wisconsin, and Michigan. It was primarily funded by the U.S. Environmental Protection Agency (EPA), with additional funding provided by the MDH Division of Environmental Health and the MDH Environmental Health Tracking and Biomonitoring Program.

What was the purpose of the study?

The main goal of this study was to see how much mercury newborn babies have in their blood. Fetuses, infants, and young children are most at risk from mercury exposure because small amounts of mercury can harm the developing brain and nervous system. The mercury measured in newborns represents exposure to the fetus that occurred near the time of birth. Most mercury exposure to unborn babies occurs when the mother eats fish or shellfish contaminated with a form of mercury called methylmercury.

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How was the study conducted?

While a newborn is still in the hospital, a few drops of blood are routinely collected from the baby’s heel to send to a state’s newborn screening program. Newborn screening programs test for a number of heritable or congenital conditions. The Mercury in Newborns in the Lake Superior Basin study tested total mercury in blood left over from newborn screening. In Minnesota, informed consent was obtained from a parent before a baby’s blood was tested for mercury. To be eligible, the mother had to reside in Minnesota, Wisconsin, and Michigan; near Lake Superior. From 2008 to 2010, a total of 1,465 babies were tested.

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What were the results?

Most infants were found to have low or undetected total mercury levels. However, 8% of tested newborns had mercury levels above the safe dose limit for methylmercury (the form of mercury found in fish) set by U.S. EPA. This means that some pregnant women in the Lake Superior region have mercury exposures that need to be reduced.

The blood samples were anonymized; meaning, there was no personally identifying information attached to the blood sample. However, information was retained on the baby’s sex, month and year of birth, state of residence, and whether the mother lived in an urban or non-urban area (Minnesota only).

No relationships were seen between the level of mercury and the baby’s sex or urban/non-urban residence.
However, babies born during the summer months were more likely to have an elevated mercury level. 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 dose limit, 3% of the Wisconsin samples were above, but 10% of the Minnesota samples had elevated levels of mercury. One possible explanation for this higher level is that Minnesotans have reported eating more locally-caught fish than do people in Wisconsin or Michigan.

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What are the strengths and limitations of this study?

This is the first study to directly measure and report mercury levels in newborns, a group vulnerable to the neurotoxic effects of mercury.
Making use of pre-collected newborn screening blood spots made it possible to measure mercury in a large sample of newborns without the need for invasive and medically-unnecessary procedures.
Because this is the only study to report mercury levels in newborns, it is unknown whether these levels are also representative of other newborns and how these results compare to maternal and fetal mercury levels reported in other studies.
Although the seasonal effect suggests the source of mercury was methylmercury from eating fish, only total mercury was measured in this study. While several studies have shown that eating fish is the way most people are exposed to mercury, other sources are possible, including dental fillings, broken thermometers, or cosmetic uses of mercury such as skin lightening creams or folk uses. Follow-up studies are needed to further investigate the sources of mercury exposure in this population.

How will the study results be used to improve public health?

MDH has been sharing specialized fish consumption information with women and their health care providers. Even so, the study results show that pregnant women and those planning pregnancy need more information on how to select fish low in mercury. As a result of the study, MDH is strengthening outreach and communication efforts to health care providers and others, to ensure that the public has information that promotes eating fish low in mercury.

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