Total gaseous mercury and volatile organic compounds measurements at five municipal solid waste disposal sites surrounding the Mexico City Metropolitan Area

The daily municipal solid waste (MSW) generation in the Mexico City Metropolitan Area (MCMA) is the highest nationwide (∼26000 ton day−1); this amount is discarded in sanitary landfills and controlled dumps. Information about the type and concentration of potential pollutants contained in landfill gas (LFG) from these MSW disposal sites is limited. This study intends to generate information about the composition of LFG from five MSW disposal sites with different operational characteristics and stages, in order to identify their contribution as potential pollutant sources of total gaseous mercury (TGM) and volatile organic compounds (VOCs). Important methane (CH4) contents (>55%) in LFG were registered at three of the five sites, while two sites were found in semi-aerobic conditions (CH4<32%). Only at one site (a closed site), potentially polluting emissions from the LFG were detected, including toluene (∼90 ppm) and other VOCs, and especially high TGM concentrations (1100–1500 ng m−3). At the remaining sites, TGM levels in LFG were between 12.5 and 52.4 ng m−3. The impact of TGM contained in LFG emissions in ambient air was assessed by means of the TGMair/LFG ratio. This quotient indicated that values below 0.2, such as those found at two closed sites with final synthetic covers, could imply better closure practices than places with higher ratios, such as sites with only periodical clay cover. High values of the TGMair/LFG ratio were also related to external TGM sources of influence, as a landfill in operation stage located at a highly industrialized area.