R+D CSIC

Pollutants in the environment: 30-40 years from the ban to reach non-harmful levels

R+D CSIC 30 years

In the last three decades, scientists have make great progress in the detection of various pollutants in the environment and in living organisms. Pollutant accumulation in humans and animals (fish, dolphins, whales, birds, sea turtles, among others) has been demonstrated, as well as their distribution in the food chain, and scientists study their effects.

Among the different families of pollutant compounds present in the environment, the persistent organic pollutants (also known as POPs) are the most worrying because of their accumulation in living organisms. "Thirty years ago, this concern was focused on dioxins, carcinogenic and highly toxic compounds whose emissions into the atmosphere were then uncontrolled. However, measures were taken and now we can say that this problem is more under control," says Ethel Eljarrat, a researcher at Instituto de Diagnóstico Ambiental y Estudios del Agua del CSIC (IDAEA-CSIC). "It is not at zero level, but it is at non-risk levels. Ethel Eljarrat leads the Environmental and Water Chemistry for Human Health (ONHEALTH) research group at the IDAEA.

From 30 to 40 years to reach non-harmful levels

As with dioxins, other legislative measures in recent years have helped to reduce the presence of persistent organic pollutants in the environment. However, due to the high persistence of these compounds, it takes a long time: "it takes 30-40 years from the ban for POP levels to become non-harmful".

For example, PBDEs (polybrominated biphenyl ethers), which are used as flame retardants in a large number of products such as plastics and foams, were banned in 2004. However, in 2017 a new study revealed that samples taken from fish in European rivers still had levels of PBDEs. The study found levels thousands of times above the ones recommended by European regulation that had to be enforced by the end of 2021. More than 15 years after the ban, safe levels have not been reached.

"It takes 30-40 years after the ban for POP levels to become non-harmful"

It happens the same with PCBs (polychlorinated biphenyls), chlorinated compounds with various industrial uses (insulators, pesticides, paint additives, etc.). As they are toxic and carcinogenic, their use was banned in 1985. In subsequent years, they were still present in the environment.

In 2018, 33 years later, a study in Science found high concentrations of PCBs in tissues of killer whales. The work, led by Aarhus University (Denmark), warned that PCBs jeopardize the long-term viability of more than half worldwide killer whale population.

Widespread dispersion in environment and animals

In the recent decades, many studies have proved that different pollutants accumulate in living organisms and enter the food chain. Contaminants have been detected in terrestrial organisms, in birds and their eggs, as well as in aquatic organisms, from sea turtles and fish to marine mammals (dolphins and whales), among others.

In 2014, a CSIC study demonstrated the bioaccumulation of PBDEs in eggs of wild birds in the Doñana Natural Park. Years later, in 2017, another CSIC study revealed that pyrethroid insecticide pollutants are present in the eggs of wild birds in Doñana Natural Park. It has been documented that these pollutants can have neurological, carcinogenic and reproductive effects.

In the case of PBDEs, a family of more than 200 compounds with different degrees of bromination, it was assumed that PBDEs with smaller molecules (and therefore the least brominated) would accumulate more in organisms and be more toxic. The reason was that smaller molecules could penetrate cells better. In turn, it was thought that PBDEs with a higher degree of bromination, being larger molecules, could not pass through the cells of organisms and were therefore considered less toxic.

However, in 2006, the European Aquaterra project, where CSIC scientists participated, demonstrated the opposite: decabromodiphenylether, the PBDE compound whose molecule is the largest, can be ingested and can enter the food chain.
"As a result of this and similar studies, commercial PBDE mixtures based on decabromodiphenyl ether were also banned," explains Ethel Eljarrat.

In 2015, In 2015, an international research with dolphins showed that both banned and new-generation PBDEs cross the blood-brain barrier and accumulate in brain

Another relevant question is in which tissues and organs these toxic compounds accumulate, says Eljarrat. In the last years, several studies have studied this aspect. In 2015, an international research with dolphins showed that both banned and new-generation PBDEs cross the blood-brain barrier and accumulate in dolphins’ brains. The work raised many inquiries: do these pollutants have neurological effects? could the same be happening in humans?

Human studies

In humans, the presence of contaminants in placenta and breast milk has been studied, as well as their ability to be transferred from mother to foetus or infant.

In 2011, a study carried out jointly by the CSIC, the Marques Institute and the University of La Coruña, analysed the presence of endocrine disrupting pollutants in the breast milk of a selected group of 69 women from Catalonia and Galicia. Thirty-eight contaminants were analysed, including polychlorinated biphenyls (PCBs), organochlorine pesticides, polybrominated biphenyl ethers (PBDEs) and perfluorinated pesticides (PFCs). Only four of all samples were free of contaminants, and these four samples were from women in more rural settings.

In humans, Eljarrat points out, "we have these studies on the presence of contaminants in breast milk and some in placenta. But the big difficulty is to have access to other types of human tissue. For this reason, studies with other mammals is an option that allows us to discover the behaviour of contaminants, to see in which organs they accumulate most, and to extrapolate these results to humans.
In this case, scientists collaborate with biologists from different universities, as well as with environmental entities and organisations such as CIRCE (Conservation, Information and Study of Cetaceans), which works in the monitoring and protection of cetaceans. This alliance allows scientists to take samples of mammal bodies stranded on beaches. However, this type of sampling is biased and is not representative of the populations, as these are animals that have perished for some reason.

That’s why other ways of sampling live animals are required. Such as biopsies, which consist of obtaining a very small sample of tissue by means of a small puncture, which is harmless for the animal. This method of sampling is possible “because analytical chemistry techniques have improved so much that allow us to work with much lower levels of contamination than decades ago”.

Plastics and the circular economy

Currently, another major environmental problem is pollution from microplastics and the various chemical additives associated with plastic, such as plasticisers. "Plastic pollution is not new, but it became more evident a few years ago when the presence of plastics was detected dispersed throughout the world's oceans."

Compounds such as bisphenol A and phthalates, which are present in plastics, are of concern. The former was banned in 2018 in all food packaging for children aged 0-3 years. But it is still present in other products. These two toxic compounds are the most studied, but over the last few years it has been seen that other plasticisers can also cause environmental and health problems in living beings.

Plasticisers reach the environment and can be accumulated by organisms. A study by the IDAEA and the ICM-CSIC confirmed for the first time that dolphins accumulate organophosphate plasticisers. The results, published in 2019, showed that all the dolphins in the study accumulated these pollutants in all the tissues sampled (blubber, muscle, liver and brain). Levels of plasticisers were similar to those already seen with other legislated pollutants, such as PCBs (polychlorinated biphenyls) or PBDEs (polybrominated diphenyl ethers).

“Now that we are all considering recycling systems, we have to be careful with toxic additives, because the use of recycled material can reintroduce these compounds into the environment”

In other IDAEA-CSIC studies, these same plasticisers were detected in various marine organisms, in whales in the North Atlantic (in 2020), in sardines, anchovies and hake in the Mediterranean Sea (in 2021), and in loggerhead turtles off the Catalan and Balearic coasts (in 2021). What should be done in this situation? Would it be enough to ban these compounds?

This raises a new problem related to the circular economy, warns Ethel Eljarrat. When a toxic compound is banned, "it is no longer used in new products, but the compound is still present in all materials produced before and which have not yet reached the end of their useful life". Therefore, "now that we are all considering recycling systems, we have to be careful with toxic additives, because the use of recycled material can reintroduce these compounds into the environment".

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