Ma. Cheney et al., ABIOTIC DEGRADATION OF 2,4-D (DICHLOROPHENOXYACETIC ACID) ON SYNTHETIC BIRNESSITE - A CALORESPIROMETRIC METHOD, Colloids and surfaces. A, Physicochemical and engineering aspects, 107, 1996, pp. 131-140
Abiotic transformation of organic pollutants in soil environments can
contribute significantly to remediation. As a model for the examinatio
n of abiotic remediation, the birnessite-catalyzed degradation of 2,4-
D(dichlorophenoxyacetic acid) and ethyl ether was monitored by calores
pirometric methods, and the products were examined by calorespirometry
, chromatography and electron spin resonance (ESR) spectral analysis.
Birnessite is a common component of many soils. Birnessite (modeled as
the oxide mineral delta-MnO2) is an efficient solid-state catalyst of
the breakdown of organic pollutants. Our results show that 2,4-D and
ethyl ether adsorbed on the surface of birnessite are rapidly oxidized
. Both compounds produce CO2 as a major product, but by somewhat diffe
rent mechanisms. Analysis of the reaction products by high-performance
liquid chromatography shows no accumulation of intermediates. Followi
ng reaction with 2,4-D, but not with ethyl ether, ESR analysis detecte
d Mn2+ extractable into methanol. These experiments show (a) that birn
essite catalyzes the breakdown of organochlorine herbicides, such as 2
,4-D and organic solvents, such as ethyl ether; (b) that CO2 is a majo
r product of degradation for both compounds; (c) that the reaction pro
ceeds via the birnessite-catalyzed oxidation of hydrocarbon structures
, but the 54-D-assisted dissolution of birnessite to produce Mn2+ is a
lso involved in the degradation of organic solvents; and (d) that soli
d-state analysis by calorespirometry allows simple, rapid determinatio
ns of the reaction kinetics of pollutant breakdown.