Pesticides go off with a bang
Stockpiled nitro-containing pesticides can be disposed of safely by exploding them, a process that transforms toxic waste into a useful blasting agent in stone quarries.
4,6-Dinitro-o-cresol (DNOC) was banned as a pesticide in 1991 by the European Commission and the US Environmental Protection Agency due to its toxic effects on humans. But large stocks remain even now. In some European countries, including Poland, the main method of disposal was burial in sealed concrete containers that have since started to leak, so more effective measures are required.
In the first application of its kind, Jolanta Bieganska from the Silesian University of Technology in Gliwice, Poland, has used detonative combustion to destroy the pesticide completely. In its dry form DNOC is explosive, so it was mixed with ammonium nitrate fuel oil (ANFO), consisting of the fuel paraffin oil and porous ammonium nitrate as an oxidiser to excite the composition to detonation.
Although tests in an explosion chamber did not lead to complete decomposition of DNOC, outdoor tests in soil were more successful. Plastic containers containing the explosive mixture were placed 120cm deep in a borehole and ignited. Gas chromatographic analysis of the soil from the resulting crater revealed no detectable traces of DNOC. The absence of active components was confirmed when extracts of the soil had no effect on growing white mustard and oat seedlings.
In an unusual application, the mixture of DNOC with paraffin oil and ammonium nitrate proved to be equally effective as conventional ANFO as a blasting agent in a limestone quarry. The detonation rate measured for a 10m length in the borehole was 3600m/s and the explosion pressure and energy released were both more than 90 per cent of those achieved with ANFO.
'There are an estimated 60 000 tonnes of buried pesticides in Poland awaiting disposal,' said Bieganska. 'About 10 per cent of them are dinitrocresol and other nitro pesticides.' Now they can be destroyed efficiently while performing useful work in mining operations.
J Bieganska, Environ. Sci. Technol., 2005, 39, 1190