Comparison of Mineralization Dynamics of 2,4-Dichlorophenoxyacetic Acid (2,4-D) and 4-Chloro-2-Methylphenoxyacetic Acid (MCPA) in Soils of Different Textures

The degradation behaviour of 2,4-D and MCPA in four types of soil were determined from measurements of (CO2)-C-14 evolution over a period of 100 clays. The total C-14-organic volatile compounds evaporated from the soils during the experimental period and the residual C-14 in the soils at the end of the incubation period was also determined. The degree of mineralization was different for tested pesticides, and did not exceed 30% for 2,4-D or 46% for MCPA. The greatest mineralization of 2,4-D occurred in sandy soils containing the least amount of organic carbon, while in the case of MCPA, the highest level of mineralization was observed in loamy sand and silt loam soils. Volatilization was the most important mechanism of 2,4-D loss from soils and accounted for 46.6% of the total applied close for sandy loam soil. The emission of volatile organic substances from MCPA-treated soils was lower, with the maximum value of 10.5% being emitted from silt soil. A significant amount of the introduced radioactive material was recovered as residues. The level of C-14-extractable residues for pesticides was low and ranged from 0.9% to 4.9% of total radioactivity. However, the level of C-14-bound residues was significantly greater and ranged from 14.6% to 43.2% of total radioactivity.