Distribution and ecological effect of mercury in Laogang landfill, Shanghai, China.

Laogang landfill near Shanghai is the largest landfill in China, and receives about 10000 t of daily garbage per day. Samples of topsoil and plants were analyzed to evaluate mercury pollution from the landfill. For topsoil samples, there were significant correlations among total mercury (HgT), combinative mercury (HgC) and gaseous mercury (HgG), and content of total organic carbon (TOC), but, no significantly relationship was found between Hg content and filling time. Hg content changes in vertical profiles with time showed that the average HgT of profiles 1992, 1996, and 2000 was similar, but their average HgG was quite different. HgT was significantly correlated with HgC in profile 1992 and 2000, and HgT was significantly correlated with HgG in profile 1996. HgG/HgT ratio in profile samples decreased in the order of (HgG/HgT)1992 > (HgG/Hg)1996 >> (Hg/HgT)2000. A simple outline of Hg release in landfill could be drawn: with increasing of filling time, degradation undergoes different biodegradation, accordingly, gaseous mercury goes through small, more, and small proportion to total mercury. Distribution of Hg in plants was inhomogeneous, following the order of leaf > root > stem. The highest value of leaf may be associated with higher atmospheric Hg from landfill. Ligneous plants (e.g. Phyllostachys glanca, Prunus salicina and Ligustrum lucidum) are capable of enriching more Hg than herbaceous plants.