Efficiency of a bagasse substrate in a biological bed system for the degradation of glyphosate, malathion and lambda-cyhalothrin under tropical climate conditions

BACKGROUND: After the rinsing of spray equipment, the rinsing water contains polluting products. One way to avoid pollution is to bring the rinsing water over a purification system, a biological bed. The system consists of an impermeable tub filled with a biomix substrate that facilitates biodegradation of pesticides. Usually, straw is one component of the biomix. The objective of this study was to assess the efficiency of an unusual substrate, bagasse, a residue of sugar cane, for the degradation of three pesticides, glyphosate, malathion and lambda-cyhalothrin. RESULTS: Results showed that more than 99% of malathion and glyphosate were degraded in 6months. In the biological bed, the DT50 value for malathion was 17days, for glyphosate 33days and for lambda-cyhalothrin 43days. The degradation rate of aminomethylphosphonic acid (AMPA) residues from the degradation of glyphosate was slower than that of the other pesticides (DT50 69days). Finally, the innocuousness of the biomix after 6months of degradation was confirmed by biological tests. CONCLUSIONS: Although the degradation rates of the three pesticides in the present bagasse-based system were similar to those under temperate conditions, the degradation conditions were improved by comparison with those in soil under the given tropical conditions. Further benefits of this system are pesticide confinement, to avoid their dispersion in the environment by liquids or solids, and a lower overall cost. Finally, possibilities for optimising the bagasse-based system (e.g. management of the water content and nature of the biomix) are discussed.  2008 Society of Chemical Industry