Study on Biodegradation and Dissipation of 14C-Carbofuran in Clay Soil from Loukkos Perimeter, Northwestern Morocco

Mineralization and dissipation of 14C-ring labeled carbofuran (2,3-dihydro-2,2-dimethylbenzofuran-7-yl-methylcarbamate), one of the highly toxic N-methyl carbamate pesticides, in an untreated Vertisol Moroccan soil used for sugar beet cultivation was studied under laboratory conditions over a period of 63 days. The experiment was conducted in flooded and non-flooded conditions. Carbofuran mineralization was determined by monitoring the 14CO2 production from soil amended with U-ring14C-carbofuran. Under both conditions, higher mineralization rates of 14C-carbofuran were observed. The extent of mineralization being more in moist (19.2%) than in flooded conditions (12.4%). In both conditions, the soil extractable pesticide residues decreased with time, while the bound residues gradually increased. The extractable 14C-activity disappearance rate was much higher in flooded than in non-flooded conditions. At the end of the experiment, 15.8% and 31% of applied dose were recovered as extractable residues under flooded and moist conditions respectively. Soil bound residues were formed to the extent of 33.3% of the applied dose in flooded soil, while 29.1% was formed in non-flooded soil. The amount of the organic volatiles was much higher in flooded condition (18.2%), as compared to 5.6% in non-flooded soil. The main degradation product formed was carbofuran phenol. The results confirm that carbofuran is more rapidly mineralized in soil under moist than flooded conditions; likewise it is important to note the large difference in degradation rate of the substance in moist and flooded soils.