Focus on research: environmental chemist Pim de Voogt

‘Where does a substance end up if I throw it in the canal?' Pim de Voogt points at the window of his office on the Nieuwe Achtergracht. ‘How much of it will end up in the air, how much will end up in the fish? And just how toxic will it prove to be for those fish?' De Voogt is an environmental chemist at the IBED, where he has occupied the Special Chair in Chemistry of (Emerging) Water Contaminants since 2008. In this capacity, he has mainly focused on the study of water-soluble polar residues in the ecosystem.

Pim de Voogt

Photo: Bob Bronshoff

Polar and non-polar contaminants

The field of environmental chemistry has not been researching polar substances for all that long, De Voogt explains. Studies in the 1960s mainly focused on non-polar substances, such as insecticides (DDT) and waste materials (PCBs and dioxins). ‘Non-polar substances are characterised by the fact that they do not fully dissolve in water, and have an affinity with other non-polar substances such as fat.' Animals and humans store up any non-polar contaminants in their fat tissue, where the substances generally remain without causing too many problems. The animal will not suffer until the concentration becomes too high. If, for example, breeding birds start to use up their fat reserves, any DDT stored inside them will enter their bloodstream, with potentially life-threatening consequences.

The 1990s saw the field of environmental chemistry undergo a major transformation. A new technology helped shift the focus to polar organic substances, which had been almost impossible to examine at low levels until that point. ‘We owe a lot to the LC-MS: a machine that links liquid chromatography to mass spectrometry', De Voogt says ‘It allows us to detect much lower concentrations of polar substances, providing an enormous impetus to the study of these substances and their effects. Polar substances that end up in the environment take a very different course than their non-polar counterparts. For example, they generally dissolve in blood, which is similar to water. As a result, they are a lot more likely to reach critical receptors and may thus cause harmful effects.'

The introduction of new detection methods in the 1990s helped uncover a whole new range of polar substances in the environment. As De Voogt explains, however, this rise in contaminants is partially deceptive: ‘We can simply see more nowadays.' A case in point would be perfluorinated compounds, which are used to make textiles and other materials water and oil-resistant. These compounds are applied in pizza boxes, extinguisher foam, raincoats and textile fibres. ‘It wasn't until around 1996 that these substances were discovered in living polar bears, but they had already been in use since the fifties.' This apparent novelty of polar substances also explains the use of the word ‘emerging' in the title of his special chair, De Voogt explains.

Environmental effects and bio-tests

The detection of substances in nature is just one aspect of De Voogt's work. His research also focuses on the potential effects of polar substances. He finds it satisfying that the technique at the core of his 1990 doctoral thesis can now be applied to polar substances. Applying what are known as quantitative structure-activity relationships (QSARs), he uses the chemical structure of substances to predict their behaviour in the environment: water, humans or animals. ‘For example, we look at the number of polar groups within a molecule, or the relationship between the polar and non-polar elements. Does it matter which polar group is linked to the compound? How do substances react in different conditions; will they be absorbed when filtered through active carbon, or will they be destroyed by active ozonisation? In some cases, we create models to predict a substance's potential effects: how does the substance link to an enzyme, which part of the molecule will it link to, and how does it fit in in stereochemical terms?'

The new techniques used to detect polar substances also come with their own set of drawbacks. Water companies, for example, sampling the inflow of water to detect harmful substances, will find around 50 different substances per sample, De Voogt explains. And this merely represents a fraction of the thousands of substances potentially occurring in groundwater and surface waters. It would simply be impossible to detect and identify them all. This is why many researchers tend to use reverse testing nowadays. An assessment of the biological effects serves as the basis for a targeted search for harmful substances. This process applies bio-testing to - for example - expose fish embryos to potentially contaminated water. Embryos are highly sensitive to polluted water: developmental defects are a clear indicator of pollutants.

De Voogt: ‘This technique is known as effect-directed analysis. If I were to sample some water from the canal outside, I could then use bio-testing to measure whether it contained substances that could harm living organisms. If this turns out to be the case, I would then have to carry out further research to determine which substance is causing the measured effect.' This search for harmful substances is conducted by dividing the water sample into fractions and using various separation methods to divide the substances in the sample over the fractions. The bio-test is then repeated for each fraction; if the results are positive, the sample will be divided into smaller fractions. This process is repeated until, ideally, the fraction causing the problem consists of a single substance. ‘We will then have found the offending substance.'

Water quality in the Netherlands

Water purification companies apply this method to test drinking water sources. In addition to his tenure at the UvA, De Voogt is also a researcher at the KWR Watercycle Research Institute, the water research institute in which all drinking water companies in the Netherlands hold a stake. As a part of his duties at the Institute, De Voogt is responsible for the chemical fractioning of water samples. ‘We sort the molecules on the basis of their size, shape, polarity and acidity. I am interested in the sort of predictions you can make when a certain effect can be traced back to a specific fraction. As a result of the fractionation method employed, you are already familiar with some of the substance's properties.'

Working in collaboration with KWR, Researchers at VU University Amsterdam applied effect-directed analysis to detect three teratogenous substances (teratogenous = harmful during embryonic development) in soil sampled from below a waste disposal site in Brabant. These substances disrupt the development of the spine and air bladder in fish embryos. Serious effects, in De Voogt's opinion. ‘If leachate from the landfill were to seep into the system, it could have a harmful effect on the viability of fish populations.'

De Voogt aims to generate more general interest in his field. ‘The government regards knowledge as the Netherlands' prime export product for the future. This country has always had a wealth of knowledge when it comes to water-related issues. That means my discipline is essential to the Netherlands.' Environmental chemistry, he explains, is in need of more skilled scientists, which starts with a larger number of students. ‘One of the advantages of having two employers is being in a position to introduce students to the practical field during their studies. For example, I can show them how things work at water companies. The processes applied in fundamental research are often the exact same as those used by companies. We are already seeing a great deal of collaboration in this area, of which my tenures are a good example. It's this type of exchange that makes this such a fascinating field to work in.'

Professor Pim de Voogt will hold his inaugural lecture on Thursday 9 April.

Research programme: LOES

In 2002, researchers found that water in Dutch rivers such as the Dommel and Vecht was having endocrine disrupting effects on fish populations. Male fish were discovered with an excess of female gametes, while a shift could be seen in the ratio between male and female fish. Scientists from institutes including the Dutch National Institute for Public Health and the Environment, the Directorate General for Public Works and Water Management and various universities had conducted a study on this topic as a part of the LOES programme, the National Study of Estrogenic Substances. Pim de Voogt contributed to the study. ‘In some small rivers, up to 50% of the water is the effluent (outflow) of water purification plants', he explains. ‘If you consider that we can't remove a large number of polar substances from the water, it's hardly surprising that we found such effects.' The researchers found the river water to contain two polar substances with the potential to cause hormonal disruptions in fish, even in low concentrations: nonylphenol, a substance contained in cleaning agents and ethinyloestradiol, the active ingredient in the contraceptive pill.

So just how worried should we be, De Voogt asks, if river water is disrupting the fish population's hormonal regulation? To answer this question, he refers to a recent Canadian study. Researchers added ethinyloestradiol to an isolated lake with a healthy fish population and compared it to a lake containing no ethinyloestradiol. The concentrations added to the water were extremely low, comparable to those found in the Dutch rivers. The effects, however, proved significant. As was the case in the Dutch rivers, researchers found male fish with female gametes and a changed ratio between males and females. In three years time, the population of one species in the polluted lake had all but disappeared.

Published by  Faculty of Science

8 September 2012