A solid matrix could be used for controlled release of herbicides, say a team of workers from the UK.

Dermot O'Hare of the University of Oxford explained how layered double hydroxides (LDH) have been used to absorb chlorophenoxyacetic acids, a family of herbicides. These agents can be stored in the LDH matrix and released on demand, explained O'Hare.

The herbicide complexes are stored, or intercalated, in the LDH by an ion exchange mechanism. Layered double hydroxides are made up of positively charged layers with anions between the layers to balance the charge. The anions are replaced in the matrix in the ion exchange process.

Some of these complexes are more easily absorbed than others, said O'Hare. This means the technique could be used for selectively absorbing or purifying the complexes. The team note that one particular chlorophenoxyacetic acid herbicide has been partially banned from use as it contains tiny quantities of the highly toxic compound dioxin.

Venkat Reddy from Iowa State University, Ames, US, agreed that the compounds developed by O'Hare and his team could be useful for storage and release of acid-based agrochemicals. 'They have developed a potential method for the purification of acid-based herbicides containing toxic organic impurities in minute levels,' he said.

O'Hare said the team would like to develop their work into a commercial application and are currently looking for an industrial partner. In the future, he explained, they would like to have more selectivity and more control of the release characteristics in their system.

Katherine Davies