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Trapping pollutants

Once a new pollutant is identified until tools and regulations are developed for its control, what exactly do scientists in their research? The case of organic pollutants in water is a paradigmatic example of a long and complicated research. Includes since finding how pollutants spread in the environment and their toxicity, until the establishment of regulations and the development of analytical methods.

One of the places where scientists measured the PBDE levels, in the Llobregat river.A study developed by scientists Ethel Eljarrat and Damià Barceló, CSIC scientists at the Instituto de Diagnostico Ambiental y Estudios del Agua (IDAEA), discovered that fishes in European rivers accumulate high levels of  PBDEs, flame retardants which were forbidden in Europe more than 10 years ago.

The levels are so high, said the scientists, that surpass thousands of times the maximum allowable quantities by the European Water Directive (2013/39 / UE), which will be mandatory threshold levels at the end of 2021. Hence, the scientists say, it is going to be virtually impossible to accomplish the regulation.

The case of the PBDEs

PBDEs are brominated compounds (they have bromine atoms) and belong to the group of the so called persistent organic pollutants. They have been used for years to avoid or delay the spread of fire in many commercial products, such as clothing, electronics, furniture…

PBDEs have been found in rivers in Europe, America, Asia and, although in lower concentrations, in Africa and Antartida. As they are lipophylic, they accumulate in the fat of organisms. In the rivers, many fishes have been found to have flame retardants, like carps, trouts, eels or catfishes.  About their toxicity, PBDEs have been linked to disruptions in the endocrine, thyroid and reproductive systems.

European rivers accumulate high levels of  PBDE, flame retardants which were forbidden in Europe more than 10 years ago

If detected levels are so high, what should be done? The study brought the attention on the need to revise and change the threshold levels of PBDEs. “Some experts think that PBDE threshold levels included in the Directive are not appropriate. This Directive establishes Environmental Quality Standards (EQS) to preserve aquatic ecosystems, but the threshold levels have been chosen taking as a reference studies of one of the most toxic PBDE and their effects on rodents”, says Ethel Eljarrat.

Eljarrat speaks about the BDE-99, one of the most harmful PBDE, which was included by European experts in a review of priority substances to be included in the European Directive.

Following recommendations of that review, the maximum value allowed in water was established in 0,0085 nanograms of PBDE per gram. But other experts point out that such a level is based on toxicity found in animals and, contrarily, ecosystems could tolerate higher levels with no risk: they propose up to 44 nanograms.  Nevertheless, Ethel Eljarrat says, even changing the threshold level, “concentrations we have found on fishes would still be too high”.

“Changing legal threshold level is complicated”, says Damià Barceló, a CSIC’s research professor and a renowned expert in the area. “The proposal has to go through groups of experts or European agencies, like the food safety agency (EFSA) or the chemical products agency (ECHA), which make a report based generally on toxicological and ecotoxicological studies”.  Once the report is finished, the proposal is brought to the European General Directorate for Environment, which can take a decision if there are enough evidences or can, in its turn, propose the change to the European Parliament to be approved. All the process takes long time”.

Establishing the threshold...

To establish a threshold level, the legal framework includes two types of toxicity studies: environmental and human. Several tests are required to consistently demonstrate that substances are toxic. As Benjamí Piña, a CSIC scientist explains, in the case of environmental toxicity, regulations require to demonstrate toxicity with  aquatic organisms: a vertebrate (usually a fish), a crustacean and a plant or algae. This is the case for water pollutants, remarks Piña, because in the case of atmospheric pollution the requirements are totally different.

Once the results are obtained, the smallest amount of pollutant that produces harm is taken as a reference and it is reduced by a factor -normally 10 but it could be another- to propose a legal threshold. For example, if a compound is toxic at a minimum of 0,5 grams per liter, it will be reduced by 10 and a threshold of 0,005 per liter will be proposed. 

To establish a threshold level, the legal framework includes two types of toxicity studies: environmental and human.

On the other hand, to have evidence that a compound is toxic for humans, essays on two species (rats and mice, usually) are required. Again, the lowest concentration of pollutant that produces harmful effects is taken and reduced by a factor of 1000, to obtain a more restrictive threshold level. So, if the essays show evidence of toxicity at levels of 0,5 grams per liter, experts will propose a threshold of 0,0005 grams per liter (0,5 milligrams). Nevertheless, sometimes a clear safety threshold cannot be established, therefore experts propose an acceptable amount.

Ethics and essays

Research is also focused on improving, reducing and avoiding tests with animals, as well as minimizing potential pain. This is the so called RRR guide (refining, reducing and replace). The idea is to refine essays to make them more effective, therefore reducing the number of them (avoiding unnecessary replications), and replacing the tests with animals for other options with non-conscious organisms or tissues.

Among the options for avoiding animal testing, there are cells, invertebrates like Daphnia magna (pictured), also popularly known as water fleas, or zebra fish embryos.

Among these other options, there are cells, invertebrates like Daphnia magna, also popularly known as water fleas, or zebra fish embryos, living beings that, according to the current knowledge, are non-sentient. Their use as model organisms is still being investigated.

The Toxicology group of the IDAEA-CSIC is  researching the use of  zebra fish embryos (a team led by Demetrio Raldua) and the water flea Daphnia magna (a team led by Carlos Barata) for analyzing the effects of dioxins, estrogens, neuroactive and  obesogenic compounds (like tributyl tin or TBT).

…And the detection methods

Parallel with toxicity studies, another essential part of the research is developing detection methods, which have to be sensitive and accurate enough to detect the levels established in regulations.

The issue is to develop methods to detect, isolate and measure the pollutant in very different substances and mixtures

In the IDAEA-CSIC laboratories, scientists work in the detection of organic pollutants in aquatic and terrestrial environments, in samples from nature and food. The issue is to develop methods to detect, isolate and measure the pollutant in very different substances and mixtures: earth, water, sediments, mud, muscle or fat from an animal, among others.

Like in many other regions and countries, Catalonian and Spanish administrations have their plans and programs for monitoring and controlling water quality in rivers and lakes. Several places are chosen as control spots, where samples are collected. Antoni Munné, from the Catalan Water Agency (ACA), explains that many compounds are difficult to be detected and besides the regulations establish very low threshold levels (nanograms per litre), what implies the need to take the samples to very specialized laboratories.

In these situations, portable tools are a good alternative, like kits, to analyze the sample immediately in the same place where it has been collected. These kit devices are based on antibodies, bacteria or other molecules which specifically recognize some pollutants: they interact or bind to the pollutant, and a reaction is triggered which will reveal the presence of the pollutant.

These tools are useful for environmental surveillance by Administrations but also for monitoring the discharge of industrial wastewaters or the water quality in fish farms.

In this field, projects are numerous. For instance, the Barcelona Material Science Institute (ICMAB), developed an accurate sensor to detect mercury, actually a non-organic pollutant. The device, developed in collaboration of the universities of Murcia (Spain)  and Regensburg (Germany), was thought to be implemented in portable devices.Biosensor based on the use of bacteria similar to human biota.

Another example are the European projects ‘Sea on a chip’ and ‘Bravo’, aimed at developing small floating platforms for continuously monitoring sea pollution, especially dioxins, pathogens and drugs in fish-farms. The platforms would work as small laboratories, with several biosensors and the electronic devices to send wíreles the results of the test.

These projects count on the contribution of several European research centers,  universities and companies. Among them, there are the Institut de Quimica Avançada de Catalunya (IQAC), the Barcelona Science Materials Institute ((ICMAB), the IDAEA-CSIC, and the Nanoscience and Nanotechnology Centre (CIN2).

Sometimes, it is not so important to detect a specific pollutant but to find out whether  water is drinkable or is toxic because the interaction of pollutants in it, whatever they are. How to do it with a single device? An innovative strategy has been proposed by a team at the Barcelona Microelectronics Institute (IMB-CSIC). It is a sensor based on bacteria similar to the human biota: if the water sample is toxic for the bacteria in the sensor, it will be also for humans and animals.

Where do pollutants go?

How do scientist know about pollutants dispersion? Ethel Eljarrat and Silvia Diaz-Cruz, CSIC scientists, explains the case of pyrethroid insecticides and solar filters, quite new compounds. Scientists assert these pollutants have spread to the environment, but they hardly know their environmental behavior. Two recent studies have shown first time that bird eggs of different species in the Spanish natural park of Doñana contain pyrethroid insecticides and solar filters, which demonstrates that exists a pre-birth transmission of these compounds.

wo recent studies have shown first time that bird eggs of different species in the Spanish natural park of Doñana contain pyrethroid insecticides and solar filters. Picture: EBD/CSIC.

The mother-offspring transmission of pyrethroid insecticides and solar filters has been demonstrated also in mammals (dolphins). Similarly, another study demonstrated that pregnant women had these pollutants in the placenta.

Another study in dolphins showed that some pollutants can pass through the protective barrier of the brain, alerting that possibly this could also happen in other mammals, including humans.

The way how pollutants move through nature is also relevant, as they can travel long distances. There, a research work demonstrated that male fishes are mutating into females in isolated and remote lakes in the Pyrenees and Tatras mountains, as a consequence of the endocrine disruptors pollutants. These pollutants are dispersed by air and can reach very remote sites, as the scientists Joan Grimalt and Benjamí Piña, co-authors of the study explained.

Environmental field studies are essential to prepare environmental surveillance strategies

These studies are essential to understand  how pollutants spread and possible effects on organisms and ecosystems, and to plan environmental surveillance strategies. In other words, to know what pollutants have to be controlled and where.

To solve problems with organic pollutants several approaches are required, says Damià Barceló. It is necessary to improve the methods for cleaning waters, with advanced treatment techniques, which sometimes are expensive and difficult to implement. But also it is necessary to work on prevention.

All of us have to collaborate. Administrations have to improve the water treatment and citizens have to be aware of the problem.  “We must use less chemical products in our daily life, less quantity of personal care products –like toothpaste, which contains triclosan, an omnipresent pollutant-, less drugs – it is not necessary 600 mg of ibuprofen, for instance, it is enough with 200 mg…”, says Barceló.

The bad news, as Sílvia Diaz-Cruz and Ethel Eljarrat say, is that “we are often late”. All this research requires decades and the attention dedicated to developing less toxic compounds is insufficient. In the meanwhile, we keep using and spreading polluting compounds into the environment… ‘everything is too slow’, they say.


Mercè Fernández
Unidad de Comunicación / CSIC Cataluña


General Directorate of Environment European Comission

UE Water Directive

Instituto de Diagnóstico Ambiental y Estudios del Agua (IDAEA)

Instituto de Microelectrónica de Barcelona (IMB-CNM)

Instituto de Ciencias del Mar  (ICM)

Instituto de Ciencia de Materiales de Barcelona (ICMAB)

Agencia Catalana del Agua (ACA)

Water management, Spanish Ministry of Environment (Ministerio Agricultura, Pesca, Alimentación y Medio Ambiente)