Chlorophenoxyalkanoic acids

Acidic or anionic pesticides (e.g., chlorophenoxyalkanoic acids and esters, Asulam, and Dicamba) were reported to be adsorbed by hydrogen bonding onto SPm at pH values below their pKa in nonionized forms through their -COOH and -COOR groups [151-153,157]. 

Smith, A.E. (1978) Relative persistence of di- and tri-chlorophenoxyalkanoic acid herbicides in Saskatchewan soils. Weed Res. 18, 275-279. 

Nine different chlorophenoxyalkanoic acids and esters (Pestanal grade, > 99%, Riedel-De-Haen AG Seelze-Hanover, West Germany) (Table 1) and 10 humic acid (HA) samples of different origin and nature, have been examined in this study. Traditional procedures of extraction, fractionation, and purification were used for the isolation of the humic acids of natural origin (soil, peat, coal, anlaboratory-prepared by oxidative... 

The chlorophenoxyalkanoic acids constitute yet another economically important group of halogenated aromatic hydrocarbons. They are widely used as herbicides to control dicotyledonous weeds. The most important of them are 2,4-D and its propionic and butyric acid homologs, 4-chloro> 2-methylphenoxyacetic acid (MCPA), and 2,4,5>trichlorophenoxyacetic add (2,4,5-T). In all the cases studied, aerobic biodegradation proceeds by removal of the aliphatic side chain with the formation of the corresponding chlorinated phenoL Thus, formation of 2,4 chlorophenol from both 2,4-D and 4-(2,4-dichlorophenoxy)-butyric acid, 4-chloro-o-cresol from MCPA, and 2,4,5-trichlorophenol from 2,4,5-T has been... 

In conclusion, toxic chlorinated phenol intermediates formed during the chemical, photochemical and/or enzymatic degradation of chlorophenoxyalkanoic compounds would temporarily be detoxified when they are incorporated into the humic acid, since their bioavailability and movement into terrestrial and aquatic ecosystems would be greatly reduced. However, the knowledge of the potential toxicity problems which these bound-residues could give rise to in the environment is still very limited. Xenobiotic chemicals incorporated into humic polymers are not really removed from the ecosystem and they may maintain their identity and toxic properties for unknown time spans, eventually causing time-delayed pollution problems, if and when they will be released from humic substances. 

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