VOLATILIZATION OF DIMETHYLMERCURY AND ELEMENTAL MERCURY FROM RIVER ELBE FLOODPLAIN SOILS

It has been shown that an untreated mercury-polluted floodplain soil ( containing 10 mu g/g per dry weight (d.w.) total Hg and 12 ng/g (d.w.) monomethylmercury compounds (MMM)) of the river Elbe in Northern Germ any contains both dimethylmercury (DMM) and elemental mercury (Hg degr ees). This is the first time ever that DMM has been detected in unmodi fied soils. A novel purge and-trap-technique involving a sequential th ermodesorption-separation of the two species after trapping on a carbo n molecular sieve (CMS) has been developed that allows the determinati on of the two species DMM and Hg degrees from aqueous solutions or soi l samples by GC-CVAFS. The compounds' identities as Hg-species were co nfirmed by GC-ICP/MS. A DMM-concentration of 740 pg/g (d.w.) was deter mined in the soil; the Hg degrees-concentration was found to be at lea st four times larger, but could not yet be quantified. Since no precau tions against lasses via evapoartion were taken during sampling and st orage, the original concentrations were probably much higher. Both DMM and Hg degrees are easily purged with N-2 from soils as well as from soil suspensions, indicating that the two species may readily evaporat e from those soils under natural conditions. The amount of DMM determi ned in the soil suspension was significantly lower (80 pg/g (d.w.)) co mpared to that in the original soil sample, suggesting that DMM might not be stable under these conditions. Also, it was shown that in natur al samples, MMM can be converted into DMM in the presence of sulfide, at S-2-levels as low as 100 mu g/g.