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The Effect of High 2,4-D Concentrations on Degradation and Carbon Dioxide Evolution in Soils¹

ABSTRACT

A laboratory experiment was conducted to determine the degradation of high concentrations of 2,4-D (2,4-dichlorophenoxyacetic acid) and CO₂ evolution in three soils. Two forms of 2,4-D, technical grade and formulated, were added to each soil at rates of 50, 500, 5,000 and 20,000 µg/g of soil (ppm). Degradation of the 2,4-D was measured by ¹⁴CO₂ evolution resulting from the oxidation of uniformly ringlabeled carbon. At an application rate of 500 ppm, all three soils degraded 2,4-D. At 5,000 and 20,000 ppm, degradation occurred in the Webster silty clay loam and Terra Ceia organic soil, but not in the Cecil sandy loam during 80 days of incubation. The degradation rate was generally higher for the formulated 2,4-D than the technical grade material. For the higher 2,4-D concentrations, 5,000 or 20,000 ppm, when extensive degradation occurred, total CO₂ evolution was also greatly stimulated, and the pattern of total CO₂ evolution rate exhibited a two-peak response. Carbon dioxide-carbon (CO₂-C) from the first peak appeared to be mainly from the formulation materials or from the impurities and CO₂-C from the second peak was mainly from 2,4-D-C.

Key Words: pesticides • herbicides • pesticide persistence • microbial degradation • microbial activity • high concentrations • phenoxy acids

¹ Contribution from the Soil Sci. and Food Sci. Dep., Univ. of Florida, Gainesville, FL 32611. Supported by grant no. R803849 from USEPA and by special funds from the Center for Environ. Programs of the Inst. of Food and Agric. Sci. Florida Agric. Exp. Stns. J. Ser. no. 801.

² Assistant Research Scientist, Professor, Associate Professor, and Professor, respectively.

Received for publication July 27, 1977.