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What to focus on for a clean environment?

The earth has more than 7 billion inhabitants, all of whom leave behind traces of pollution. However, not all forms of pollution have the same harmful effect. Leiden scientists help determine where we should put our priorities.

Insidious effect

Thirty years ago, the sewers of Amsterdam were simply emptied into the city’s canals, but today these same canals are so clean that every year several thousands of people swim in them for charity.  Overall, we are becoming more and more successful at protecting the environment from massive flows of waste.  The biggest challenge now is to address the more subtle effects of small doses of waste in the environment that can have an insidious impact on undermining the health of different species of animals.

Stress in the delta

Environmental toxicologist Thijs Bosker conducts research on the impact of foreign matter on ecosystems. His main interest is dynamic systems, such as deltas. In a delta, fresh water and salt water come together and the water conditions, such as oxygen levels and temperature, are subject to continuous change. The organisms that live in the delta are constantly having to adapt to new circumstances. ‘Places where a river flows into the sea are important both ecologically and economically,’ Bosker explains. ‘There is a wide variation of animals and plants, but river mouths are also where cities are often located. These cities cause pollution, which puts that already dynamic system under even more stress. We want to know how organisms cope with these issues. It’s a big challenge, because it’s difficult to model the dynamics of this type of ecosystem in the lab. These kinds of systems are something of a black box for science.’

The Rijn-Maas delta, here shown at the Maasvlakte near to Rotterdam, is a good example of an area where there is a high likelihood of a clash between economic and ecological activities.

Help from holidaymakers

Bosker researches new types of environmental pollution. He is mapping how many tiny particles of plastic enter the global environment. He is helped in his research by holidaymakers: they send samples of sand from all over the world to Leiden so that Bosker and his team can check how many ‘microplastics’ wash up in places as far apart as Iceland and Zanzibar.  The next step is to explore whether these plastic particles pose a risk for the flora and fauna. Bosker is also interested in the impact of pollution on the reproduction of different organisms. In the Gulf of Mexico, for example, he studied the impact the disaster with the Deep Water Horizon drilling platform had on the local fish population.  In Canada he works with paper manufacturers and local governments to study the effect of endocrine disrupters in their waste water on reproduction in fish.

Volunteers send in samples of sand from their holiday destinations.


‘If environmental pollution leads to dead fish floating in our rivers of streams,  that effect will be highly visible,’ Bosker says. ‘Fortunately, we are seeing this less and less. But what about if fish can no longer reproduce because their hormone system is disrupted, or if they can no longer escape animals that prey on them because their nervous system is impacted? These are the kinds of indirect environmental effects that are at the heart of our research. I believe it’s important to have a good understanding of all these risks, although it’s almost an impossible task to clean up all environmental waste; it would cost far too much. But if we understand the potential effects of all these substances in differing circumstances, then we are able to set priorities to limit environmental damage or even to prevent it. That way, we can better protect the environment, and that’s something I’m keen to contribute to.’

Global Microplastic Project

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