Lactation has long been considered the primary route of elimination and transfer of toxins such as heavy metals like mercury (Hg). However previous cetacean studies have revealed that the initial transfer and accumulation of heavy metals essential begins during pregnancy. In this case study this study we examined the mercury levels measured in blubber, kidney, liver and muscle tissue (µg/g wet weight) of Harbour porpoise (Phocoena phocoena) mother-fetus pair and calf from east coast of PEI National Park, Canada. 

The concentrations found were:

Hg was detected in all of the fetal tissues in ratios that reflect those of the mother and calf. While the greatest concentration was demonstrated in the liver, Hg levels in the fetal blubber should be noted as it was twice the amount of the mother and 10 times greater than the calf. Hg levels demonstrated by the calf were intermediate values between the mother and the fetus these differences could be accounted for by the maternal transfer of Hg through lactation and possibly post weaning food consumption.

The mobilization of Hg during pregnancy and its passage through the placental barrier into fetal tissue is an important factor that should be considered when estimating the effects of Hg and similar toxic compounds on populations the Harbour porpoise. Though in this study the concentrations of Hg are relatively low it remains unknown what impact Hg could have on a rapidly growing and developing fetus. These effects could be further exacerbated postnatally during the juvenile’s vital development and maturation when consuming contaminated maternal milk.