| Popis: |
The form of mercury present in sediment is of environmental concern, particularly since the availability of inorganic mercury is one of the main factors controlling the methylation of mercury in sediment. A frequently used extractant for determining easily released metal fraction in sediments is dilute HCl which dissolves both oxidized different iron and manganese phases, while for anoxic sediments, iron monosulfides are also extracted. However, extraction techniques using cold HCl to measure the concentration of trace metals associated with sulfide minerals were recently questioned for metals forming poorly soluble sulfides. In the present study, the use of dilute HCl for extraction of soluble mercury from suboxic and anoxic sediments is evaluated. The effect of acid concentration (1-6 M HCl) on the extraction of mercury and on the recovery of aqueous mercury preextraction spikes from sediments containing various amounts of AVS has been studied. The results obtained by using 1 M HCl as extractant indicated that acid-soluble mercury may react with H2S released from AVS phases (e.g. FeS, MnS) and precipitate in the form of HgS. The precipitation of HgS(s) was found to be considerably lower when greater (2-6 M) HCl concentrations were used for Hg extraction. These results suggest that 6 M HCl could advantageously replace 1 M HCl for extracting Hg in the presence of AVS. The difference between HCl-soluble Hg fraction obtained by 1 and 6 M HCl in sediments sampled in pristine (Bay dAutie, France) and contaminated (Kastela Bay, Croatia) marine environments was consistent with the model experiments. |
