Engineered nanoparticles in the aquatic environment

Published: 12 January 2017

'Release, transport and fate of engineered nanoparticles in the aquatic environment' is the title of Arjan Markus' thesis which he already successfully defended. Nanotechnology has brought us many benefits, think of smartphones for instance, but also miniature sensors, important in medical applications, “lab-on-a-chip” to name but a few. Less spectacular perhaps, but equally important and widespread is the use of nanoparticles in personal care products, paints and coatings and reinforced polymers.

Nanoparticles are, roughly speaking, particles smaller than 100 nm. Silver nanoparticles are used in medical textile, because they kill bacteria. Titanium dioxide and zinc oxide nanoparticles are used as UV filters in sunscreens, and in wastewater treatment to break down organic micropollutants. However, the properties that make them useful in personal care products and water treatment, may make them harmful for organisms in the aquatic environment. So it is important to know what happens to them once they enter the waste stream. One of the conclusions from the modeling study that was performed is that nanoparticles will mostly be attached to suspended matter, hence they are transported together

It is very difficult to distinguish them

As they are so small and are made from ordinary materials – zinc and titanium but also carbon, in the form of carbon nanotubes or spherical molecules – it is in general very difficult to distinguish them from natural soil or sediment particles. Often, electron microscopy in combination with other measurement techniques is used to identify these nanoparticles in water samples.Electron microscopic image of a cluster of nanoparticles, found in the sludge from a wastewater treatment plant.

nanoparticles found in the sludge

Electron microscopic image of a cluster of nanoparticles, found in the sludge from a wastewater treatment plant

Modeling the release and the subsequent transport and fate of nanoparticles can be used in two related ways:
• Complement monitoring programmes, as modeling gives insight in the spreading of contaminants and the concentrations in which they occur.
• Help understand the risks posed by the use of nanoparticles now and in the future.

Applied to the river Rhine

This was applied to the river Rhine. First, the release of nanoparticles from consumer products was estimated using literature data. Then a mathematical model for the fate of nanoparticles in the aquatic environment was set up, based on data and input parameters collected from published laboratory experiments. This knowledge together with information concerning the hydrology of the Rhine and the wastewater treatment plants in the Rhine basin was used to predict the nanoparticle concentrations under various release scenarios.

Comparison of the concentration of zinc nanoparticles Rhine

Comparison of the concentration of zinc nanoparticles to the total concentration of zinc, showing the relative contribution.

The model results suggest

The model results suggest that nanoparticles are mostly attached to suspended matter – so-called heteroaggregation (to clot together) being the most important process. Therefore they are transported along with suspended matter and will settle in the sediment if the circumstances allow. To examine the environmental risk of nanoparticles one needs to be able to estimate the release of nanoparticles but also to understand the behaviour of suspended matter.