The EOH students’ projects investigated the byproducts of disinfecting drinking water, how mercury may impact men’s sperm, and the impacts of infants’ exposure to manganese from mining waste
EOH MPH Culminating Experience Presentations on Disinfection Byproducts, Mercury, and Manganese
Three EOH MPH students presented their culminating experiences (CEs) in June. Reshma Arrington’s topic was "The Occurrence of Trihalomethanes and Haloacetic Acids in Chlorine Treated Water: a Regional Analysis of the State of Maryland." Emily Ryan presented "Exposures to Mercury and Sex Chromosome Disomy in Faroese Men." The subject of Sarah Scheinfeld’s CE was "Multi-media Exposure Assessment of Manganese in Infants Living Near a Mining-related Superfund Site." All of the presentations were very well-attended.
Arrington educated her audience--including her infant son, Aatish, who was impressively attentive--about the public health risks posed by exposure to compounds that can be generated as a byproduct of using chlorine to disinfect drinking water. She focused on two groups of compounds that include probable carcinogens which are routinely monitored by drinking water providers, trihalomethanes and haloacetic acids. Arrington’s literature search showed that there is some evidence of a synergistic relationship resulting from simultaneous exposure to both groups of compounds. With the aid of her advisor, Associate Professor Peter LaPuma, she decided to investigate if there was any evidence that compounds from either group influenced concentrations of the other group at any given time of the year.
In the course of her investigation, Arrington collected many hundreds of data points from counties and municipalities throughout Maryland and entered them by hand. She said that she did not find any evidence of a strong linear seasonal relationship between any single component of the trihalomethanes or haloacetic acids with the total concentration of the other group. She found a higher rate of both groups of compounds exceeding the maximum contaminant levels (MCLs) set by the U.S. Environmental Protection Agency during colder months, but the water was also sampled less frequently at that time. She also found that trihalomethane levels tended to increase in warmer months and haloacetic acid levels varied throughout the year.
Arrington’s data also brought to light an as-yet-unexplained mystery. For some reason, the levels of the both trihalomethanes and haloacetic acids spiked by 10 to 20 times in Baltimore City last year, rising far above the MCLs for the compounds, a trend not seen elsewhere in the state. Arrington wasn’t able to determine why this occurred, but she said it certainly raises questions about what happened in Baltimore City last year.
Mercury and sperm
Ryan’s presentation described her efforts to investigate whether exposure to mercury may have an impact on the health of sperm. The condition of having an incorrect number of chromosomes is known as aneuploidy, and the most frequent form of it is sex chromosome disomy. Disomy results when chromosome pairs fail to separate during cell division, Ryan explained to her audience. About 5% of all human conceptions are estimated to involve aneuploidy; this normally results in pregnancy loss, but it can also produce children with severe physical and mental disabilities.
Some recent studies have linked exposure to environmental contaminants with disomy. After consulting with her advisor, Professor Melissa Perry, Ryan set out to investigate whether human exposure to mercury was linked to disomy by focusing on a group of men from the Faroe Islands who can be exposed to high levels of the metal through their diets. People from these islands, a self-governing country within the kingdom of Denmark, are widely known to be exposed to higher than average levels of mercury because a high proportion of their diet comes from seafood. Their diets can include consumption of pilot whales, which can contain high mercury levels.
Since 1986, five prospective cohort studies have been following Faroese children to evaluate whether the population’s diet is associated with any health outcomes. Ryan’s investigation involved men from the 1986 cohort as well as men recruited to participate in a semen quality study. The Perry Lab used fluorescence in situ hybridization (FISH) to evaluate the men’s semen for disomy.
As Ryan anticipated, the men they studied had high levels of mercury in their blood, much higher than the levels in U.S. men. They were also much more likely to be current or former smokers, a confounding factor for disomy. Ryan used a variety of statistical analyses and models to analyze the data.
What Ryan found was that for many of the men, higher levels of mercury in their blood were associated with a decreased risk of sperm disomy. This may be due to the men’s high seafood diets, she hypothesized. Previous studies have linked healthy diets to improved semen parameters, she explained. However, she stressed that more research is needed to further define this relationship.
Manganese from chat
Scheinfeld began her CE project while she was interning with the U.S. Environmental Protection Agency’s Office of Children’s Health Protection. She worked with her advisor, Assistant Professor Ami Zota, to combine her interests in nutrition, environmental exposures, and children’s health. Her work focused on infants’ exposures to manganese, which is an essential nutrient at certain levels but can be toxic at both lower and higher levels, near the Tar Creek Superfund site in Oklahoma, one of the largest Superfund sites in the U.S.
The huge piles of mining waste, known as “chat,” at the Tar Creek site tower above homes built in the community. Manganese is one of the many contaminants that residents in the local communities can be exposed to via air, water, and soil.
Scheinfeld’s focus on infants’ exposures to environmental manganese was inspired by the association of early life exposures to manganese with adverse neurodevelopmental outcomes. The concentrations of the element in women’s blood increases during pregnancy and it is actively transported across the placenta. “A potential danger for those with increased environmental exposure is the presence of manganese in infant formula and breast milk,” Scheinfeld said. Because formula can be fortified with manganese, the levels in formula tend to be many times higher than breast milk, she explained.
Infants’ activity patterns and behaviors, such as playing on or near the ground and placing their hands and other objects in their mouths, can place them at higher risk of environmental manganese exposure, Scheinfeld explained. They also eat, drink, and breathe more per kilogram of body weight and go through critical windows of development where organs, metabolic pathways and hormonal systems are still maturing. “Interference during these times by environmental hazards can have irreversible effects,” she said.
The effects of infants’ exposure to environmental manganese during their first year of life have not been the subject of much research. To study this, Scheinfeld capitalized on a subset of a prospective birth cohort study conducted at the Tar Creek site by the Harvard School of Public Health’s Center for Children’s Environmental Health and Disease Prevention Research. The study included both biological and environmental sample collections from 53 mothers during pregnancy, when their infants were born and at 6 months and one year of age, as well as questionnaires collecting information about how infants were fed.
After evaluating the results statistically and adjusting for potential confounders, Scheinfeld found manganese concentrations in dust to be a potential significant predictor of the infants’ body burden, as measured in blood and hair. None of the infants in the study had manganese levels below the minimum 3 micrograms/day or above the maximum of 2000 micrograms/day. However, Scheinfeld stressed that this maximum was actually established for children between the ages of 1 and 3, noting that no standards exist for infants due to uncertainty over negative health effects and the inability to handle excess manganese during the first year of life.
While dust was an important source of exposure to manganese, particularly to breast-fed infants, the study showed that diet was the main source of exposure for both breast- and formula-fed infants. The work also suggested that the intake of manganese via dust may be more important for determining the maternal body burden of dust than an infant’s body burden, she said. The contribution from diet was over two-fold higher in formula-fed infants than in breast-fed babies.