To obtain a better understanding of the unusual accumulation of organic matter in tropical volcanic soils in the West Indies, humic and fulvic acids were extracted with 0.5 N NaOH under N2 from four surface and two subsurface horizons of four such soils from the island of Dominica and degraded by KMnO4 oxidation of unmethylated and methylated materials. The oxidation products were fractionated by solvent extraction and chromatographic methods and 52 compounds were identified on a gas chromatography–mass spectrometry–computer system. Major oxidation products (identified as esters and ethers) were benzenecarboxylic, phenolic and aliphatic mono- and dicarboxylic acids. Smaller amounts of n-alkanes, furan derivatives and dialkyl phthalates were also identified. The major chemical structures detected in the tropical volcanic humic and fulvic acids were aromatic rings substituted by: (a) three to six C atoms; (b) one OCH3 group and three, four and six C atoms; and (c) two OH groups and one, two, three and five C atoms. Judging from the qualitative and quantitative distribution of the major oxidation products, the chemical structure of tropical volcanic humic and fulvic acids did not appear to differ significantly from that of humic and fulvic acids extracted from soils from widely differing climatic zones. We were unable to detect any effect of depth of sampling or soil pH on the chemical structure of the humic materials extracted from the tropical volcanic soils.
Long-term pollution by chlordecone of tropical volcanic soils in the French West Indies: A simple leaching model accounts for current residue
