Occurrence of Volatile Transition Metal Compounds in Landfill Gas: Synthesis of Molybdenum and Tungsten Carbonyls in the Environment

Evidence for the occurrence of volatile molybdenum and tungsten compounds in the environment is presented for the first time. The gases from three different municipal waste deposits were sampled and analyzed for volatile metal and metalloid compounds by using gas chromatography coupled with inductively-coupled plasma mass spectrometry (GC−ICP−MS). In addition to the known hydrides and methylated compounds of As, Se, Sn, Sb, Te, Hg, Pb and Bi, volatile Mo and W compounds were found in concentrations of about 0.2−0.3 μg of Mo/m 3 and 0.005−0.01 μg of W/m 3 . The isotopic fingerprint of the detected Mo and W from the samples matched perfectly with Mo and W standards. The correspondence of the samples' retention times (GC−ICP−MS) with those of standards provides convincing evidence that Mo(CO) 6 and W(CO) 6 are present in landfill gas. The toxicity and origin of these compounds are discussed.