Studies on Adsorption and Microbial Degradation of the Pesticides Isopropyl N-(3-Chlorophenyl) Carbamate and 2,4-Dichlorophenoxyacetic Acid in Aqueous Solutions

Citation

Schwartz, Henry Gerard (1966) Studies on Adsorption and Microbial Degradation of the Pesticides Isopropyl N-(3-Chlorophenyl) Carbamate and 2,4-Dichlorophenoxyacetic Acid in Aqueous Solutions. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/1E55-D295. https://resolver.caltech.edu/CaltechETD:etd-06252004-114224

Abstract

The adsorption and microbial degradation in aqueous solution of two selected pesticides, isopropyl N-(3-chlorophenyl) carbamate (CIPC) and 2,4-dichlorophenoxyacetic acid (2,4-D), were studied to better understand the influence of these processes on the persistence of pesticides in natural waters. Based on the experimental results, certain inferences have been made concerning natural water systems. Radioactive tracer techniques were utilized to follow the adsorption and degradation of the two pesticides. Additional information about the disappearance of the phenyl carbon atoms from CIPC adaptation cultures was obtained from ultraviolet spectra.

2,4-D was found strongly resistant to microbial degradation in a liquid medium of mineral salts. Less than 40 percent of the acetic acid portion of the molecule disappeared from solution in six months, even in the presence of additional sources of organic carbon. CIPC was degraded much more rapidly than 2,4-D. The isopropyl segment of the CIPC molecule was completely metabolized. Metabolism of the carbon atoms in the ring structure ceased after 40 to 60 percent of the atoms had disappeared from solution. A partial metabolic pathway for the degradation of CIPC is proposed.

The clay minerals, illite, kaolinite, and montmorillonite, suspended in dilute pesticide solutions adsorbed very little 2,4-D or CIPC. CIPC was adsorbed extensively from water solutions with powdered activated carbon. The equilibrium for the adsorption of CIPC on activated carbon was represented closely by a Freundlich isotherm. The adsorption appeared to involve physical or weak chemical bonding. There was some indication that the adsorption of CIPC on activated carbon in a well-stirred system was diffusion controlled.

The addition of activated carbon decreased the overall rate of degradation of CIPC. It is proposed that the decomposition of CIPC in the presence of powdered activated carbon occurs principally in the aqueous phase or at the interface between the liquid and the exterior surface of the activated carbon. As CIPC is degraded in solution, additional quantities desorb. The adsorption equilibrium of the activated carbon-CIPC system is influenced by the presence of bacterial cells and metabolic intermediates.

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