Environmental mercury exposure during pregnancy and lactation: practical advice to minimize risks.
Environmental exposure to mercury during pregnancy may present a health hazard to both the mother and the unborn child. In utero, or via early life breast feeding, exposure to methylmercury has been linked to both physical and mental defects, including brain, vision, and hearing damage (March of Dimes Foundation, 2012; Komyo, Masumi, & Motohiro, 2010; Oken et al., 2013; Sakamoto, Chan, Domingo, Kubota, & Katsuyuki, 2012). During a 1955-1959 epidemic of babies born with severe cerebral palsy-like syndromes in Minamata, Japan, methylmercury (MeHg) was identified in a landmark study as a causative risk (Takeuchi, Morikawa, Matsumoto, & Shiraishi, 1962). Historically, this epidemic, known as Minamata disease, brought worldwide attention to the risk of mercury, and MeHg. Subsequent studies of MeHg, a form of mercury often found in water supplies and fish, have indicated that the developing brain in its prenatal and infant stages, is vulnerable to MeHg exposure (Cace et al., 2011; Choi, 1989; Clarkson, 2002; Clarkson, Laszlo, & Myers, 2003; National Research Council [NRC], 2000; Oken et al., 2013; World Health Organization [WHO], 2013). Additional studies support that the mercury element does transfer from mother to fetus through the placenta (Boucher et al., 2012; Butler et al., 2006; Sakamoto, Chan, Domingo, Kawakami, & Murata, 2012; and Sakamoto, Murata, Kubota, Nakai, & Satoh, 2010). In addition, research has been conducted on transfer through breast milk during the first three months of life (Sakamoto et al., 2012).
Exposure to mercury surprisingly difficult to avoid
In addition to documented scientific research on the potential detrimental effects of mercury on humans, vast amounts of emotionally heated lay literature claims that there is no level of mercury that is safe. In response, numerous articles claim that the danger is over-inflated and limited to high-level exposure. To compound the issue, there is on-going debate regarding what is safe mercury consumption in some healthy food sources, predominately certain fish. For many expectant parents, this array of conflicting information causes unnecessary confusion and worry.
However, recognizing the potential dangers of mercury is not enough because it is a substance surprisingly difficult to avoid. Elemental mercury is a naturally occurring element found in air, water, or the ground and is unique in the fact that in its purest state, it is a silvery liquid. As a gas, it is colorless and odorless. Common items that may contain mercury include: light bulbs, deodorants, fish, and some preservatives. Even a common glass thermometer, if broken, contains elemental mercury. In addition, a small quantity of elemental mercury is found in some dental fillings. As a naturally occurring element, mercury may be found in water supplies in the form of methylmercury. Natural or man-made sources of mercury contamination of water may occur from volcanoes or burning coal or other pollution. This in turn affects certain large fish that when consumed by a pregnant woman may be a risk to the fetus.
With a focus on prevention, this article examines existing scientific research discussing the potential short and long-term effects of prenatal exposure to mercury. A review of current literature is offered as a guide to healthcare educators and providers to address potential hazards of mercury exposure. In addition, practical advice on ways to avoid accidental exposure to the heavy metal is offered. In short, the purpose of this writing is to provide concise information to healthcare educators and providers on the risks of mercury consumption or exposure and to relate practical information that should be useful when counseling expectant parents.
Review of Literature
Environmental toxins, including mercury, may enter the body through several potential avenues or entry points. These may include breathing gas vapors containing mercury, handling the liquid form of mercury or dirt contaminated by the element, or in a food source, particularly some types of fish, predominately predatory fish. Although the amount of mercury in these fish is not generally considered harmful to adults, it may accumulate over time and be a concern during pregnancy or lactation. According to research at the David Geffen School of Medicine at the University of California, Los Angeles, mercury is now found in the blood of one in three women (Laks, 2009).
Levels of mercury in fish may not be considered harmful to adults, but may accumulate over time and be a concern during pregnancy or lactation.
Perhaps one of the more controversial topics discussed in the medical literature regarding mercury concerns the preservative thimerosal. Marques, Dorea, and Bernardi (2010) conducted research on the effect of thimerosal, a preservative in tetanus-diphtheria vaccines, on women and their unborn child during development and after birth through breastfeeding. Thimerosal contains a small amount of methylmercury, a neurotoxicant that may cause developmental delays. However, when used, thimerosal conserves the tetanus-diphtheria which helps protect the unborn child and mother from bacterial diseases.
Marques et al., (2010) began collecting data in 2000 on pregnant women aged 15-45 years of age at the Pre-natal Clinics of Rondonia. Nineteen of the mothers did not have any exposure to the thimerosal while 63 were given vaccine-containing thimerosal. At birth, Apgar scores and hair samples were obtained from the mothers and their babies. Following birth, the 82 participants breastfed their babies during the initial six month postnatal period, then a trained professional tested the Gesell Developmental Schedules (GDS) on each child. GDS tests neurodevelopment reflexes, voluntary reactions, motor development, visual and auditory communication. A development quotient from the GDS of 68 or less points out a significant delay in more than one area, whereas a 69-85 score indicates some sort of organic impairment.
Researchers found that there were no significant differences between the mothers who received the thimerosal in the tetanus-diphtheria vaccine while pregnant versus the mothers who did not receive the thimerosal at all while pregnant. However, the infants' hair mercury at birth did correlate to the mothers' hair mercury. Since thimerosal contains a small amount of methylmercury, but did not cause a significant difference at the six month GDS test, no significance was attributed to the vaccination containing thimerosal. Implications from the study did support that methylmercury does cross the placenta; however it is still unknown at what level methylmercury would correlate to detrimental fetal effects.
In addition to transfer during pregnancy, some literature has alluded to potential detrimental effects of neonatal and early childhood vaccinations that contain thimerosal. In a study conducted by Mrozek-Budzyn, Majewska, Kieltyka, & Augustyniak (2012) the relationship between neonatal exposure to thimerosal and child development showed a potential adverse association. The study sample consisted of i96 infants born between January 2001 and March 2003 to mothers who attended ambulatory prenatal clinics in Krakow. Vaccination history (date and the type of the vaccine) was extracted from physicians' records. Child development was assessed using the Bayley Scales of Infant Development (BSID-II) measured in one-year intervals over 3 years and statistical measures adjusted for potential confounders. An adverse effect of neonatal thimerosal containing vaccine (TCV) exposure was observed for the psychomotor development index (PDI) in the 12th and 24th months of life ([beta] = -6.44, p < 0.001 and [beta] = -5.89, p < 0.001). No significant effect of neonatal TCV exposure was found in the 36th month. The overall deficit in the PDI attributable to neonatal TCV exposure measured over the course of the three-year follow-up (GEE) was significantly higher in TCV group ([beta] = -4.42, p = 0.001). MDI scores did not show the adverse association with neonatal TCV exposure (Mrozek-Budzyn et al., 2012).
Hypotheses that exposure to thimerosal may be associated with increased risk of autism spectrum disorder (ASD) led to research by Price et al. (2010). The study examined relationships between prenatal and infant methylmercury exposure from thimerosal containing vaccines and an association with autistic spectrum disorder. A case-control study was conducted with a sample of 256 children with ASD and 752 controls matched by birth year and gender. Logistic regression was used to assess associations between ASD exposure to thimerosal during prenatal, birth-to-1 month, birth to-7-month, and birth-to-20-month periods. There were no findings of increased risk for any of the ASD outcomes (Price et al., 2010).
It has also been hypothesized that early exposure to thimerosal, a mercury-containing preservative used in vaccines and immune globulin preparations, is associated with other neuropsychological deficits in children. Research was conducted with 1047 children between the ages of seven and ten years who had documented exposure to thimerosal as a preservative in a vaccine. The association between current neuropsychological performance and exposure to mercury during the prenatal period, the neonatal period (birth to 28 days), and the first 7 months of life was assessed using standardized tests for 42 neuropsychological outcomes. The researchers concluded that the study does not support a causal association between early exposure to mercury from thimerosal-containing vaccines and immunoglobulins and deficits in neuropsychological functioning at the age of seven to ten years (Thompson et al., 2007).
While the threat of thimerosal continues to be researched, the Centers for Disease Control and Prevention report that there is no convincing evidence of harm caused by the low doses of thimerosal in vaccines. However, in July 1999, the Public Health Service agencies, the American Academy of Pediatrics, and vaccine manufacturers agreed that thimerosal should be reduced or eliminated in vaccines as a precautionary measure (Centers for Disease Control and Prevention [CDC], 2012. Since 2001, with the exception of some influenza (flu) vaccines, thimerosal is not used as a preservative in routinely recommended childhood vaccines (CDC, 2012).
Vapors and Direct contact
Another potential source of mercury contaminate is through vapor or direct contact. Pollutants in the air, from coal-fired power plants, cement kilns, refineries and smelters may contain mercury and be inhaled or settle onto the ground and reside in dirt. Recently there has been an upsurge in concern regarding Compact Fluorescent Lights (CFL). The average CFL contains about four milligrams of mercury and is considered a very small amount. Other common household objects, such as watch batteries have five times the mercury, and older thermometers have 500 milligrams. Proponents for the use of CFLs argue that efficiency, when compared to the use of electricity required to power an incandescent bulb, outweighs any concerns by decreasing the energy required from coal-fired power plants that release mercury into the air. While this argument may be true, the reality is that CFLs do present a hazard to anyone, but particularly vulnerable are pregnant women and young children.
Information that may be useful to share with pregnant women is provided in a factsheet by the Connecticut Department of Public Health [CDPH] (Connecticut Department of Public Health [CDPH], 2013). Should a CFL be broken, the pregnant mother, any small children should exit the room immediately. Pets may track any mercury throughout the home and should be removed from the area as soon as possible also. Any form of forced air, such as a central heat or air condition should be turned off to prevent immediate spread of mercury laden vapor; opening a window for at least 15 minutes to air out the room is recommended. A pregnant woman should not clean up the broken bulb but should ask someone else to do so. Protective gloves and mask are recommended while cleaning up the area; using a sticky tape, such as duct tape to pick up small slivers of glass or mercury is recommended rather than using a vacuum cleaner. If a vacuum cleaner is used, the bag should be changed and disposed of properly as it may transmit mercury vapors when later used. All debris, tape, or vacuum bags should be bagged in plastic and taken to an outside trashcan immediately (CDPH, 2013).
Good Fish: Bad Fish?
Nutritionists often suggest that pregnant women include fish in their diet as a good source of protein, iron, B vitamins, and zinc. In addition, the omega-3 fatty acids and docosahexaenoic acid (DHA) can promote fetal neurological growth. Women who typically follow a vegetarian diet may be advised to add an additional protein source and fish may be more acceptable to them than other forms of animal protein. The benefits of fish are certainly supported, however many claims may be somewhat biased or unsupported.
One benefit to pregnant women who eat fish during their pregnancy may be that they tend to have better moods, particularly less anxiety. In a research study that examined whether dietary patterns and the inclusion of seafood are associated with high levels of anxiety during pregnancy, Vaz, Kac, Emmett, Davis, & Golding (2013) concluded that a relationship between dietary patterns, particularly from seafood intake, reduce high anxiety symptoms during pregnancy. Yet in another study by Makrides et al. (2010) the consumption of fish oil during pregnancy did not show evidence of a benefit to mother's mood or the babies' cognitive development. In an experimental two-group study of pregnant women, the effect of 800 mg of a DHA-rich fish oil supplement was compared to that of a vegetable oil (rapeseed, sunflower, and palm) supplement and showed no benefits for depression and no cognitive difference in their babies (Makrides et al., 2010).
This conflicting information is often confusing to expectant parents and of interest to researchers. Sagiv, Thurston, Bellinger, Amarasiriwardena, & Korrick (2012) conducted a perspective birth cohort study that determined the association of prenatal mercury exposure and fish intake's beneficial health to mothers' and unborn children versus the dangers mercury can cause on neurodevelopment, and specifically with attention-deficit/hyperactivity disorder (ADHD). One might think that if eating seafood improves protein intake and provides essential nutrients to the fetus and the mother, what is the negative potential? However, there are worries that too much intake of fish will lead to high levels of methylmercury, which, as previously mentioned, is a developmental neurotoxin (Oken et al., 2013). Nearly all methylmercury exposures in the U.S. occur through eating fish and shellfish (Environmental Protection Agency [EPA], 2013). One neurologic syndrome that potentially may be linked to mercury is Attention Deficit Hyperactivity Disorder (ADHD). Boucher et al. (2012) conducted the study on Inuit children in Arctic Quebec and linked these school-age children to multiple types of ADHD.
The study population consisted of 788 infants recruited at birth between the year 1993 and 1998 at St. Luke's Hospital located in New Bedford, Massachusetts. Eligibility requirements were that mothers be 18 years and older and reside in New Bedford, Acushnet, Fairhaven, or Dartmouth for the duration of their pregnancy, and for infants to undergo vaginal birth and neonatal examination. At 8 years of age, a neuropsychological assessment was given to 607 children. Of these, 421 children (n=421) had maternal hair mercury concentrations, and 515 (n=515) obtained fish consumption data. During the exposure assessment, the researchers collected and archived maternal hair 10 days postpartum and analyzed maternal hair for mercury concentrations. The researchers collected prenatal fish consumption data using a frequency questionnaire shortly after birth of the infant. During the outcome assessment they assessed inattentive and impulsive behaviors using the Conners Rating Scale-Teachers (CRS-T), Neurobehavioral Evaluation System 2 Continuous Performance Test (CPT), and the Wechsler Intelligence Scale for Children-Third Edition (WISC-III). Statistical analyses were conducted using a multivariable regression (Sagiv et al., 2012).
Sagiv et al. (2012) concluded that higher mercury levels were found in mothers who were older, married, had a higher income, did not smoke or use illicit drugs 1 year prior to infants birth, were Caucasian, consumed more fish during pregnancy, and gave birth to boys. In this study, increased hair mercury levels were associated with ADHD behaviors. Increased maternal fish intake can produce protective mechanisms that alleviate ADHD behaviors. Like most other issues when involving fish consumption while pregnant or breastfeeding, more research is needed to prove benefit vs. detriment of fish consumption during pregnancy (Sagiv et al., 2012).
In a similar study, Boucher et al. (2012) conducted a prospective, longitudinal study of the children in the Canadian Arctic. The objective of this study was to determine the relationship between developmental exposures to environmental toxins, including methylmercury, to behavioral issues in Inuit school age children. The study participants were examined from birth to school age, with a total of 279 (n=279) participants. Measurement tools used were Teacher Report Forms (TRF) and Disruptive Behavior Disorders Rating Scale (DBD). The TRF was restricted to analyze internalizing, externalizing, and attention problems. Parents and teachers completed the DBD. The DBD tested for four major disorders: two types of ADHD, ODD, and CD. Umbilical cord blood samples were taken from study participants (n=208) in the Cord Blood Monitoring Program, study participants (n=57) in the Environmental Contaminants and Child Development Study, and an additional i4 participants (n=14) that participated in both studies. Blood samples (20 mL) were analyzed for levels of mercury and binary logistic regression analyses were used for statistical analyses. The study concluded there was a strong correlation between Hg levels in children and attention problems on the TRF score chart. The conclusion suggested interventions need to be conducted to reduce prenatal exposure to MeHg.
Not only do pregnant women have to worry about the much talked about healthy nutrients fish can provide while pregnant versus the dangers too much of the wrong fish can cause on the neurodevelopment but also where the fish themselves reside. For example, Eto, Marumoto, and Takeya (2010) conducted a research study of the pathological changes in adult, infantile, and fetal forms of Minamata disease (MD). MD is typically classified as a food-borne methylmercury (Me-Hg) intoxication caused by fish and shellfish consumption during 1953 in Minamata and Kumamoto Prefecture, Japan. Eto et al. (2010) described that the cause of the MeHg in the fish pollution developed from chemical wastes that were dumped into the Minamata Bay by Chisso Co. acetaldehyde plant in 1951. This process continued for 17 years, thus causing fish and shellfish to become contaminated with environmental pollutants and became toxic for human consumption. Only later was it discovered that when consumed MeHg can have devastating affects on neurological functions (Eto et al., 2010).
Eto et al. (2010) conducted an extensive clinical history of a 29 year-old female diagnosed with MD that resided in Minamata. Her parents were also diagnosed with MD. In 1959, her mother's hair contained 101 parts per-million (ppm) total mercury. As an infant, she was primarily fed breast milk mixed with formula. Clinical manifestations of MD as an infant included retarded development, poor suckling, and her neck was not fixed at six months of age. At age three, she developed convulsive seizures. At age eight, she demonstrated retarded somatic and mental developments which included copious salivation, being nonverbal, and bedridden. A neurological examination concluded the presence of spastic quadriparesis, primitive and pathological reflexes, increased deep-tendon reflexes, and ankle clonus. External strabismus and abnormal dentition were also noted. She died at the age of 29 from bronchopneumonia. At two years of age her total hair mercury was 61.9 ppm and 5.4 ppm when she was 17. Autopsy pathology concluded the brain exhibited diffuse atrophy of the cerebral cortex and white matter, corpus callosum thinning and status marmoratus of the thalamus. Histochemical analysis revealed mercury deposits located in the kidney, liver and brain tissues (Eto et al., 2010).
Mahaffey et al. (2011) conducted an in depth review of the literature to uncover the latest knowledge on the risks and benefits of eating seafood during pregnancy and the potential affects to the fetus. The detailed introduction described the healthy benefits of consuming fish due to the n-3 polyunsaturated fatty acids, and then concluded that most human exposure to methylmercury is through eating fish (Mahaffey et al. 2011). The literature review first describes evidence that the greatest levels of n-3 polyunsaturated fatty acids are found in certain types of fish: sockeye salmon, farmed trout, farmed salmon, Copper River salmon, Coho salmon, brozini, fresh bluefin tuna, albacore tuna canned in water, and tootfish. The article then explains that because older, larger, and higher trophic level fish species tend to have more methylmercury, pregnant women should lower or eliminate them all together. Examples of fish that pregnant women should avoid, or limit, are shark, tilefish, swordfish, and large bluefin tuna. Fish that may present with a low-moderate methylmercury level do not require a complete avoidance as many, such as mackerel, salmon, and sardines have some of the greatest n-3 polyunsaturated concentrations. The nutritional benefits outweigh the risks to the mother and fetus. However, quantity of these fish should be limited. Recommendations based on a review of the literature recommend two servings of fish per week.
Pregnant women may feel that there are conflicting rules and advice from family, friends, or healthcare providers. Many mothers find themselves confusing what is on the "good to do while pregnant" list with the "avoid while pregnant" list; this includes the decision for eating the right fish, in the right amount, during pregnancy (Bloomingdale et al., 2010). Research by Lando, Fein, & Choiniere (2012) was conducted via a questionnaire and discovered that postpartum (n=522) and pregnant (n=1286) women were more likely to be conscious of mercury as a problem in food. The study also identified that pregnant women tended to consume a smaller amount of fish per week, based on these concerns, and therefore may not ingest the optimal health benefits from fish (Lando et al., 2012). This report correlates with Bloomingdale's et al. (2010) findings that discovered many pregnant women could not recall all of the facts about mercury advice; specifically which fish were the best to eat or which fish were the most dangerous to eat. As a result of their uncertainty, they decided to avoid fish consumption entirely. Identification of this prevalent mindset leads to concern that those pregnant women and their unborn children may miss an important source of healthy nutrients found in fish (Bloomingdale et al. 2010).
It is important for health care educators and providers to be aware of the controversies and latest evidence-based information to provide reassuring and accurate information to their clients. Educators and health care providers should also seek to understand the best educational strategies to support pregnant women maintaining a nutritional diet, including consuming safe fish, in the acceptable quantity. Oken et al. (2013) conducted a randomized controlled educational pilot intervention in the Boston, MA area aimed to encourage fish consumption throughout pregnancy. This trial took place from April 2010 to October 2010, and involved pregnant women from 12-22 weeks that were 18 years old and older. Of the two independent groups, the first consisted of an advice group (n=20), which contained an 8-page booklet that gave the health effects of Docosahexaenoic acid (DHA) an omega-3 fatty acid. This information supported fish intake and a list of 29 encouraged high DHA, low mercury fish to consume were provided. In addition, the fish that should be avoided was included. The booklet included a shopping list notepad and a wallet sized card summarizing all the information in the brochure. The other independent group (n=20) consisted of the same advice, plus a $40 Whole Foods gift card at the baseline visit, and they also received additional gift card mailed to them for a total of $120($10/week). The dependent group (n=21) was provided a 7-page "Pregnancy Food Guide" and a one-page list of "Food Don'ts." Both of these are commonly handed out at prenatal care visits. The results were similar in all three groups; however, the most statistical significance was seen in the advice and gift card group (n=20). Overall, the randomized trial concluded an increased intake of high DHA fish with low levels of mercury in all the groups, which implies that information presented by health care providers is effective for influencing dietary patterns during pregnancy (Oken et al., 2013).
The consumption of fish has long been a debate for pregnant women. The nutrient rich benefits of docosahexaenoic acid (DHA) weigh against the potential negative effects for both physical and mental disabilities in children attributed to methylmercury. The challenge is finding a way to balance the two. The research reviewed reveals that there are ways to keep both levels in check by eating only certain fish while avoiding other types. Fish such as sockeye salmon, farmed trout, and farmed salmon all contain rich levels of DHA, and are considered safe for pregnant women. The long-lived fish that may have accumulated methylmercury and should be avoided during pregnancy include shark, mackerel, and swordfish. Quantity is also a concern and some fish included on the safe list should be eaten in limited quantities. The benefits and alternatives of fish oils and algae should be suggested for women, who are vegetarian, or allergic, or simply do not care to eat fish (Mahaffey et al. 2011).
Health care professionals, particularly those providing childbirth education need to be aware that many women are confused regarding this subject and therefore are at risk. Education is important for these women, as Bloomingdale et al. (2010) revealed when he discovered that most of the women in the study avoided fish because they were not positive about all the information revolving around mercury and fish. A practical tip for childbirth educators is that providing a wallet size card that defines guidelines for safe fish consumption during pregnancy is effective (Figure 1). There are many apps for smart phones or tablets that guide all aspects of pregnancy and provide easy access; an example is one from the Mayo Clinic (2013) that provides a section on essential nutrients. Just as important as providing written and or electronic sources of information, educators should discuss the issues with their clients and answer their questions so that they are informed and confident in their dietary choices.
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Kelley Peters is a Baccalaureate student nurse at Middle Tennessee State University. Her research interests include neonatal intensive care and women's health.
Stephanie Rhoades is a Baccalaureate student nurse at Middle Tennessee State University. Her research interests include neuroscience and women's health.
David Andrew Ezzell is a Baccalaureate student nurse at Middle Tennessee State University. His research interests include cardiology and nephrology.
Jonathan Holland is a Baccalaureate student nurse at Middle Tennessee State University.
Deborah Weatherspoon, PhD, RN, CRNA, COI is an Assistant Professor in the School of Nursing at Middle TN State University. She teaches a variety of nursing subjects both on-ground and online. Her research interest include maternal and child health and educational technology.
Figure 1. General Recommendations for Fish consumption during Pregnancy and Lactation (American Pregnancy Association, 2013; Mayo clinic, 2013) Fish Recommendations Sockeye salmon Good 8-12 ounces/week Farmed trout Good 8-12 ounces/week Shark Bad Avoid altogether Farmed salmon Good 8-12 ounces/week Tilefish Bad Avoid altogether Copper River salmon Good 8-12 ounces/week Coho salmon Good 8-12 ounces/week Swordfish Bad Avoid altogether Large Bluefin tuna Bad < 2 ounces/week Brozini Good 6 ounces/week Fresh, small Bluefin tuna Good 6-8 ounces/week Albacore tuna canned in water Good < 6 ounces/week Tootfish Good 6 ounces/week
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|Author:||Peters, Kelley; Rhoades, Stephanie; Ezzell, David Andrew; Holland, Jonathan; Weatherspoon, Deborah|
|Publication:||International Journal of Childbirth Education|
|Date:||Oct 1, 2013|
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