Blood chloroform levels in late pregnancy tied to higher risk of SGA newborns


By Marilynn Larkin

NEW YORK (Reuters Health) - Chloroform (trichloromethane; TCM) exposure in late pregnancy from drinking water and other disinfection byproducts (DBPs) was associated with a higher risk of small-for-gestational-age (SGA) newborns in an observational study.

"The process of disinfecting waste water has caused widespread human exposure to DBPs, including among pregnant women," Dr. Carmen Messerlian of the Harvard T. H. Chan School of Public Health in Boston told Reuters Health by email. "DBPs are reproductive and developmental toxicants in laboratory animals, but studies of exposure during specific periods of pregnancy on adverse birth outcomes in humans have lacked clarity."

"We measured two groups of DBPs in this study, and their routes of exposure are different," she explained. "The volatile trihalomethanes (THMs) are measured in blood and exposure mainly occurs through inhalation and absorption during daily water-use activities. In contrast, ingestion of water is thought to be the main route of exposure to nonvolatile haloacetic acids (HAAs), measured in urine."

"During the pandemic, individuals are disinfecting surfaces more than usual," she noted. "However, (DBP exposure) depends on the type of cleaning methods and products used to disinfect the environment. Use of ethyl alcohol, for example, does not lead to DBP exposure. Oxidizing disinfectants - e.g., chlorine or ozone - can be used to clean surfaces, which will inevitably result in DBP contamination and possible human exposure."

As reported in Environmental Health Perspectives, Dr. Messerlian and colleagues studied 4,086 blood and 3,951 urine samples collected across pregnancy trimesters among 1,660 mothers in China.

Blood samples were quantified for biomarkers of THMs: TCM, bromodichloromethane, dibromochloromethane, and bromoform. Urine samples were quantified for biomarkers of HAAs: dichloroacetic acid and trichloroacetic acid. Birth outcomes were collected from medical records

Blood TCM concentrations in the second trimester were associated with an elevated risk of SGA when comparing exposure groups - i.e., middle versus lowest (RR, 2.34) and highest versus lowest (RR, 2.47).

Third-trimester blood TCM concentrations were also associated with an increased risk of SGA when comparing the second tertile with the first (RR, 2.61).

Maternal blood TCM concentrations were significantly higher from 23 to 34 weeks gestation for SGA versus non-SGA births. No correlations were seen with other blood and urinary DBP biomarkers for SGA, low-birth weight, or preterm birth.

Dr. Messerlian said, "Our key message is that exposure to DBPs found in municipally treated water, particularly in mid-to-late pregnancy, might be associated with an increased risk of small-for-gestational age. Our findings should be considered by clinicians in routine care of pregnant women, given the potential impact of DBPs on fetal growth."

"Our recommendation for clinicians is to suggest that pregnant patients, or women trying to conceive, use a water filter at home, shorten the frequency and duration of bathing or showering, reduce swimming pool activities, and minimize their use of chlorine-based cleaning products to reduce DBP exposures," she concluded.

Dr. Jamie Alan, Associate Professor in the Department of Pharmacology and Toxicology at Michigan State University in East Lansing, commented in an email to Reuters Health, "It is notable to say that this is a correlative study, not a causative study. There are several limitations, including the fact that the study included many women from a lower socioeconomic status, and genetic factors that influence metabolism of these compounds were not assessed. Therefore, these results may or may not be applicable to a larger population."

Nonetheless, she said, "Drinking water sources in general are a good thing to bring up to pregnant women and women who have recently had babies. There are many potential concerns with water sources, including nitrates, lead, etc."

There is "a possibility that bleach-containing products could contribute to low birth weight," she noted. However, she added, clinicians "also have to take into account the risk versus benefit of disinfecting compared to contracting COVID or influenza when pregnant. In short, it's complicated."

"To be safe, drinking bottled or filtered water is a good option," she advised. "Also, using disinfectants in a well-ventilated area is always a good suggestion. If someone else in the household can disinfect further, even better."

SOURCE: Environmental Health Perspectives, online October 7, 2020.

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