Laboratory and field observations of the accumulation of polar organic molecules in clay mineral sealings used in waste disposal sites

Abstract

The composition of the organic matter of a core taken from the clay mineral sealing of the waste disposal site of Geldern-Pont (Germany) after 8 yr of operation has been analysed using GC and GC-MS. Results show that the organic carbon content of the upper part of the sealing which was closest to the waste increased by a factor of 10 when compared with the original unaltered clay. The extractable organic matter from the upper part of the sealing is significantly enriched in long-chain n-alkanes, with a dominance of odd-numbered chain lengths. Long-chain n-alkan-2-ones with a dominance of odd-numbered homologues accumulated in the lower part of the sealing. Two tetracyclic hydrocarbons (des-A-oleanene and des-A-lupane) were present only in the upper part of the sealing close to the dump. Both compounds probably originate from reworking of organic matter in the waste by anaerobic bacteria. Additionally, four Tertiary clays have been percolated in the laboratory with leachate from an industrial landfill over periods of 9 weeks and 19 months. The organic compounds in the seepage waters were primarily phenols, aniline and pyridine derivatives as well as aromatic and alipathic acids. During percolation many of these compounds were apparently microbially degraded in the clays to C 1–C 8 fatty acids. The results indicate that physico-chemical interaction of the clay minerals with organic compounds in the leachate was accompanied by microbial activity within the clays, leading to further conversion of the primary adsorbed organic compounds.