In Situ and Laboratory Studies on the Fate of Specific Organic Compounds in an Anerobic Landfill Leachate Plume, 2. Fate of Aromatic and Chlorinated Aliphatic Compounds

The transformation of specific organic compounds was investigated by in situ and laboratory experiments in an anaerobic landfill leachate pollution plume at four different distances from the landfill. In a previous paper (Part 1, also published in this issue) we described the in situ microcosm and laboratory batch microcosm experiments performed focusing on redox conditions, microbiology and the fate of 7 phenolic compounds. In this paper we present the results on the fate of 8 aromatic compounds and 4 chlorinated aliphatic compounds. Nitrobenzene was transformed at all distances from the landfill in methanogenic, and Fe(III)-and NO3-reducing conditions. Toluene was transformed slowly in one out of three in situ experiments at the distance of 250 m from the landfill in the Fe(III)-reducing part of the plume after a lag phase of ~ 3 months. Benzene, o-xylene, p-dichlorobenzene, o-dichlorobenzene, naphthalene and biphenyl were not transformed at any of the investigated distances from the landfill, neither in in situ nor in laboratory experiments. In the methanogenic part of the aquifer 2 m from the landfill, 1,1,1-trichloroethane, tetrachloromethane and tetrachloroethene were transformed in in situ experiments while trichloroethene was not. Lag phase periods were up to 40 days for 1,1,1-trichloroethane and up to 100 days for tetrachloroethene. No or only short lag phases (<10 days) were observed for tetrachloromethane. Tetrachloromethane was furthermore transformed at distances of up to 250 m from the landfill in Fe(IIl)-reducing conditions but not in NO3-reducing conditions at 350 m from the landfill. Abiotic processes apparently contributed to the transformation of tetrachloromethane. A local variation in the transformation of the chlorinated aliphatic hydrocarbons was observed at 2 m from the landfill. In general, good accordance with respect to compound transformation was observed between in situ and laboratory experiments, but in a few cases more compounds were transformed in in situ experiments than in the corresponding laboratory experiments.