The accumulation of toxicological clues

“At the beginning of the 2000s, we observed an increase in the beaching of porpoises and seals on Belgian coasts”, recalls Krishna Das. “The scientists sought to understand the causes of death. I had the benefit of access to samples taken by Thierry Jauniaux, from the Faculty of Veterinary Medicine who had been studying the causes of death in these marine mammals and I began to observe the concentrations of trace elements. I wanted to understand what led an animal to be contaminated or not. The age of the animal, for example, its diet, its state of health or even whether it was possible to establish a link between the diseases observed and the levels of concentration of the pollutants. This epidemiological-type approach, where we establish statistical correlations between toxic elements and diseases was the subject of my doctoral thesis”. It was an interesting first research component. The beaching of these mammals provided access to an enormous quantity of tissues without the need to capture large mammals in their natural environment. But this approach soon showed its limitations. “By only studying the beached porpoises and whales, we had no measurements from a control population. We could only study sick individuals. And these statistical correlations did not necessarily signify a connection between cause and effect. Other proofs were necessary and therefore other methods to complete this research”.  There was yet another major difficulty. The traditional toxicological approach requires a control group and a test group in the laboratory to whom pollutants would be administered. The development of diseases would be in line with a directly observable causality report. But what works for rats in a laboratory does not work for large wild animals that evolve in a fully natural environment and showing significant inter-individual differences. Such an approach would encounter many obstacles and raise important ethical questions. Therefore another type of approach needed to be developed. Each approach had its weaknesses and its limits but it also led to new research possibilities and revealed new clues all of which provided proof. 

From beaching to capture campaigns 

A complementary approach studying beached individuals therefore results in the capture of animals in their natural environment which is only possible by developing an international network. In the case of harbour seals, the species endured several epizootic diseases. This phenomenon encouraged German researchers (Professor Ursula Siebert, Institute for Terrestrial and Aquatic Wildlife Research (ITAW)at the University of Veterinary Medicine Hannover) to focus their interest on these animals in their environment. “Twice a year, the German team organizes capture campaigns in the North Sea. The infrastructure and logistical means deployed are colossal. The seals captured are then weighted and measured, and blood, hair and saliva samples are taken from them. This is a somewhat holistic approach whose main challenge is to understand the state of the population. The blood samples enable cell culture and a relatively in-depth analysis of the pollutants in direct relation to the life of the animal. Studying the hair enables observation of the evolution of health over a much longer time-scale which is important because trace elements are integrated during the entire growth of the hairs which sometimes represents a period of several months”. On the other hand, harbour seals are particularly fearful animals. All the precautions taken to limit the invasive character of the operation were taken and the captures took place in May and September and avoided calving periods. When panicked, the mother could abandon the calf and flee.

In contrast, the capture of grey seals, organized in Scotland with the University of Saint Andrews (Dr. Paddy Pomeroy, Sea Mammal Research Unit, Scottish Oceans Institute, University of St Andrews), concerned only females at the moment when they return to land to suckle their young. “They are slightly less fearful than harbour seals. As for the males, they are large and quite aggressive so we avoid approaching them! But from a scientific point of view, these studies are complementary to the capture of harbour seals and are particularly interesting from the point of view of understanding the transfer of energy between the mother and her calf. When suckling, the mothers fast for three weeks and produce milk which is almost 50% fat. Many pollutants are then passed to the new-born. In addition, among many species of marine mammals, we can observe a decrease in the concentrations of the pollutants in females (in accordance with the number of pregnancies and lactation events) so these levels do not stop increasing in males. This transfer from mother to young is at a maximum in the case of the first-born”.