74. Prenatal exposure to legacy contaminants and visual acuity in Canadian infants: a maternal-infant research on environmental chemicals study (MIREC-ID) (lay summary)

Polevoy C, Arbuckle TE, Oulhote Y, Lanphear BP, Cockell K, Muckle G, Saint-Amour D. Environmental Health 2020 Feb 7;19(1):14. doi: 10.1186/s12940-020-0567-2

Prenatal exposure to high levels of some environmental chemicals can have harmful effects on infant and child development. A number of research studies have examined associations between early life exposure to chemicals and effects on child behavior and learning.  However, limited research has been done on potential effects of various chemicals on infant vision.  Visual acuity (seeing small letters or numbers on an eye chart) is difficult to assess in children.  In infants, the Teller Acuity Card (TAC) test is typically used.  In this test, a series of rectangular cards showing different sizes of black and white stripes are presented to the infant.  The test records the infant’s eye preference or reaction to the cards (if the infants turn their eyes toward the card when they see black and white stripes).  Another tool is the Visual Evoked Potentials (VEP) where the infant’s brain activity is recorded while black and white stripes of different sizes are presented on a computer screen.

The aim of this study was to measure associations between prenatal exposure to legacy persistent organic pollutants or metals and visual acuity in infants from the MIREC-ID Study.

Levels of the persistent pollutants PCBs (polychlorinated biphenyls) and PBDEs (polybrominated diphenyl ethers), along with the metals lead and mercury were measured in maternal blood during pregnancy, as well as in umbilical cord blood.  The researchers assessed the infant’s visual acuity around 6 months of age using the Teller Acuity Card (429 infants) and Visual Evoked Potentials (63 infants).

The researchers observed no association between exposure to any of the chemicals studied and results using the Teller Acuity Card.  There was some data to suggest an association between higher levels of mercury in cord blood and lower visual acuity using the VEP.

In conclusion, these results suggest that subtle, but detectable changes in infant visual acuity can be identified in a population prenatally exposed to higher mercury concentrations.   Mercury occurs naturally in the environment at low levels; everyone is exposed to some level of mercury in air, water and food.  The major sources of exposure to mercury are through consumption of certain types of large fish (see:  https://www.canada.ca/en/health-canada/services/food-nutrition/food-safety/chemical-contaminants/environmental-contaminants/mercury/mercury-fish.html), as well as use of mercury in various cultural practices and hobbies, including some types of jewellery, such as glass pendant necklaces and some artist’s paints.