Despite being taken out of use in the United States and other countries, chloridazon is still common in Europe 60 years after being introduced by BASF. In America and other places, it is no longer used because it can be toxic to humans, does not break down in nature and will eventually seep into the groundwater.
Water purification plants can break down chloridazon, using UV light, but unfortunately the breakdown products of chloridazon are also toxic.
A new method using clay can solve the problem, a study finds. By creating neatly spaced slits in a clay mineral, researchers were able to filter the water of the herbicide, and then reuse the clay after removing the pollutant by heating the material.
"Clay is a layered mineral," explains University of Groningen Professor of Experimental Solid State Physics Petra Rudolf. "The layers have a negative charge and are separated by positive ions. We can replace those with molecular pillars of our own design." The natural clays are first washed and then treated with sodium salts. The sodium replaces the natural positive ions between the layers. "These sodium ions are surrounded by a water mantle, which pushes the layers slightly further apart. By simply adding the pillar molecules to the water, they will replace the sodium."
These pillars are usually made of silicon oxide, with an added chemical group that defines the affinity of the cavities. The added was copper ions to attract the chloridazon and its breakdown products. The functionalized clay absorbed the herbicide in significant amounts: nearly 900 milligrams per kilogram of clay.
The first results were obtained using 10 times the highest concentration of chloridazon measured in the environment. Furthermore, the experiments were performed in clean water. The next step will be to to repeat this in real groundwater, to see if other compounds affect the absorption. If all these tests yield positive results, the next question is how to make this clay into a product that can be used in water treatment. By altering the width of the slits and changing the affinity of the pillars, different chemical compounds could also be caught by the functionalized clay. A similar system could be created using other layered materials, such as graphene oxide.
Until then, all those sugar beets in Holland are coming with an extra chemical additive.