For now, the results show that the contamination profile of these mammals does not depend exclusively on their place in the food chain. The gender and age of the animals must also be applied to this data. While analyses show that it is mainly males that are the victims of persistent organic pollutants, the study also reveals that younger whales suffer the most, sometimes with tragic results. “The problem with the young population is that there is a significant transfer of these molecules (Editor’s note: PCB, DDT, and others) to offspring, both by means of the placenta during the 12 or thirteen months of pregnancy, and during lactation”, explains Krishna Das. “The transfer is even more efficient by means of lactation because the whales produce milk which is very rich in fat and is very dense which facilitates transfer. In some species of dolphins, some authors have put forward the theory that the rate of transfer from mother to first-born is high enough to cause the death of the fœtus. It is to the first-born that the mother transfers a maximum of pollutants which can be as high as 80% of the overall level. The transfer of pollutants decreases in offspring after the first-born”. The possible short-term consequences of the persistent nature of organic pollutants are serious and numerous: an increase in the mortality rate, miscarriages, disease, stillborn calves, malformations and deformities of offspring, weakening of the immune system and increased risk of disease. In the long-term, it is probable that this could lead to reproduction impairment. Moreover, as Krishna Das reminds us “Populations have already diminished since the stock ratio recorded in the 18th century. It must be said that whales have had a troubled history! First they were captured in great numbers by the whaling industry which had a huge impact on many species. Sperm whales were regularly hunted and their populations were already greatly reduced in relation to their numbers of 200-300 years ago. This was compounded by many other factors of which chemical pollution was one, but also many others (noise pollution, getting caught in fishing nets and interference with the animals due to navigation instruments). All of these are stress factors that can threaten the well-being or even the survival of a species in the long-term”. Apart from their effect on marine mammals, these lipophilic pollutants constitute a real danger for mankind also because they can act as endocrine disrupters, which like whales we also have in our body tissues. “They can affect puberty in adolescents. These pollutants are considered to be obesogenic”. (Read : Precocious puberty and DDT)

What solutions?

Given these observations, it is vitally important that counter measures be put in place. Progressive banning of PCBs and DDTs globally, the two dominant lipophilic pollutants in terms of their presence in the marine environment, has contributed to significantly improving the situation. “With regard to the species, it is difficult to compare the levels of pollution from one era to another because the analytical techniques have greatly evolved. The levels are lower. In some species that are being used as sentinels, a reduction in PCB levels has been detected since these chemicals were banned forty years ago” but the problem is that “we have reached a plateau and we must redouble our efforts to get beyond this plateau”. Better controls and checks are required with regard to sources of pollutants. Even if the legislation exists, there is little hope of moving things forward down the line if no control mechanism has been implemented. “PCBs are still present in the environment; they are not authorised but they are present in old equipment that is still used in the developing world. In Brazil. Stocks of old PCBs are stolen in factories. This proves that there is a demand for them on the black market”. This illegal underground market must be prevented at all costs.

PCBs and DDTs are not the only pollutants that require urgent attention. A lot of waste is released into the atmosphere and the sea. Compounds similar to dioxins, dioxin and furan, for example, have also been singled out. The levels of these are somewhat weak but are linked to any kind of combustion activity. “When we burn waste in our garden, dioxins and furans are released and forest fires are natural sources of these”. However, other sources of these are not natural at all and serve as a reminder that, if we want to have effective legislation, we will need to be proactive rather than reactive which means that it will be necessary to anticipate the appearance of new pollutants on the market that are intended to replace those that have been banned. To this extent, the study carried out by Marianna Pinzone and her colleagues was the most exhaustive possible as it involved research into pollutants that are not banned and are still in use. “PCBs have been banned, but new molecules have been created which are curiously similar to those that have been banned and that therefore have similar effects. Flame retardants like (PBDE or polybrominated diphenyl ethers) have been analysed. Many of these are spread in family homes (furniture, materials etc.).” That said, the main group of pollutants in terms of concentrations remains the PCBs followed by DDTs. But all the others are detectable and have been detected. “We are currently facing a cocktail of pollutants and it is the possible combined effect of these pollutants that is relatively unknown”.

The study and preservation of marine mammals represents a major challenge for the future. These species are emblematic and remind us that the health of mankind is intimately linked to its environment.