The hair, blood and milk samples taken from both the mother and the new-born makes it possible to quantify the transfer of pollutants associated with lipids and therefore very present in the milk. But even before suckling for the first time, the calf has already been exposed to pollutants for a long time. “While taking blood samples from young newly-born animals, we also noticed that they were already strongly contaminated by certain pollutants, notably from mercury.  This signifies that there is an efficient transfer of certain trace elements from the placenta. On also study samples of lanugo a soft layer of downy hairs that the calves synthesize in the uterus and which they lose very quickly. This lanugo contains significant concentrations of toxic elements”. 

The effect of mercury on the white blood cells  

In order to better understand the immunotoxic effect of methylmercury, different in vivo, approaches were attempted in collaboration with scientists in Germany (prof. Ursula Siebert) and Professor Marie-Claire Gillet (Mammalian Cell Culture Laboratory, ULg). The white blood cells, mainly T lymphocytes from harbour seals were isolated and placed in culture in order conduct an in vitro study of their immune response to exposure to toxins. In culture, these cells do not generally survive longer than 72 hours, which is very short, but they are the workers of the immune system. “During a doctoral project”, explains Krishna Das, “We focused more specifically on the effects of methylmercury. Present in fish, this methylmercury causes strong levels of contamination in seals. The objective was not to determine the acute toxicity of methylmercury which has been known for a long time: the molecule seriously affects the nervous system and embryo development. We were interested in exposing the lymphocytes to concentrations that reflected those in the animals of the North Sea in order to observe the severity of adverse effects related to this level of poisoning”. 

Observations by electron microscope confirmed the suspicions of the two researchers. The pollutant greatly affected the mitochondria of the common seals, a highly toxic contact which caused apoptosis or cellular death of the lymphocytes. “At the same time, we had to remain prudent in our conclusions. An in vitro study does not reflect what is happening in the entire seal. Once it enters the blood, methylmercury follows a complex path and ends up in the liver where, astonishingly, it is no longer in methylated form. This observation, which was made as far back as the 1980s, tends to show that the seal is capable of partly neutralizing the toxicity of mercury thanks to selenium”. 

The search for biomarkers

Biomarkers are the responses of an organism to stress. In science, the objective is to identify them and determine their causal link to a disease. The interest here is twofold. Not only is this kind of approach less invasive (a blood sample is sufficient to make a diagnosis), but these responses often appear very early, sometimes well before a disease is identified. “This type of approach was developed in hospitals”, explains the researcher. “A sizeable part of the fight against cancer, in particular, has contributed to the identification of predictive biomarkers in blood samples. This is the case with certain proteins whose deficiency or increased presence in terms of concentration increases the possibility of contracting certain types of cancers”. The method was developed in clinics in order to complete the arsenal of weapons used in other disciplines such as ecotoxicology. “With regard to the question of poisoning in seal populations, this research component remains at the preliminary stage but is showing promise. German colleagues (including K. Lehnert as first author) have, for example, established a relationship between certain trace elements with a variation in the secretion of interleukin 10, an anti-inflammatory cytokine, a process which disrupts the immune response. We still need to further develop the identification of these biomarkers and an understanding of the mechanisms involved”.