Sarah Habran, research fellow at the FRS-FNRS in the Oceanology Laboratory of ULg, and the international team of researchers who work with her visited the elephant seal colony at the Año Nuevo State Park, on the Californian pacific coast several times. With the help of park rangers, the scientists ‘’captured’’ some twenty mothers and their pup at regular intervals during lactation, as well as some twenty pups weaned (called weaners) during the post-weaning fast. Each individual was marked with the aid of hair dye, in order to better recognize the animals that were not among their samples. The concentrations of trace elements in the blood, blubber, hair and milk (during suckling) were analysed.

In addition to being interested in the levels of contamination by trace elements in the animals analysed, this study should provide an understanding of the mechanisms involved in the toxicokinetics of these substances. The scientists also wanted to know what happened to these “chemical products” after their absorption, how they passed from the mother to her pup, as well the “redistribution” of these elements in the tissues during the key periods involving a voluntary fast. 


And they succeeded! The research that was patiently carried out on the northern elephant seal showed the existence of transmammary transfer of mercury and selenium, two substances which transit from the mother to the pup through the milk. This study also suggests that the maternal transfer of selenium is high during suckling, while the transfer of mercury takes place mainly during the gestation period. Likewise, lactation and fasting affect the total levels of mercury and selenium in the blood and milk of the mother seals. The milk consumption and tissue deposition (that is to say growth and development) influence the dynamic (movements) of contaminating substances in the body of the pups. This underlines the importance of examining these processes carefully during the interpretation of the levels of trace elements in the context of biomonitoring. Furthermore, to the best of the knowledge of the researchers from ULg, the levels of concentration of mercury and selenium had not been previously determined in the northern elephant seals.


Additional toxicology studies will be necessary to understand the repercussions of these chemical transfers on the health of the elephant seals. But what is certain already is that the progress in the area of ecotoxicology is of paramount importance. This is particularly so because the levels of polluting substances present in the environment continue to grow in spite of measurements taken in matters of protection of ecosystems and the relative regulation of pollution over the last few decades.