Analysis of the total heavy metal content was carried out using method 3051A of the United States Environmental Protection Agency (USEPA, 1998), consisting of a soil sample digestion with HNO3 and HCl in a microwave oven (Milestone Ethos D). Heavy metal content was then determined in the final solutions by FAAS in a Varian SpectrAA-220FS spectrometer with the exception of some samples for Cd, which were analysed by graphite furnace atomic absorption spectrometry-GFAAS. Results were expressed in mg kg-1 dry weight on the basis of soil dried at 105ºC.
The accuracy of the digestion method was checked by analysing a certified reference material (CRM) supplied by the Community Bureau of Reference Sample (CRM 141R, calcareous loam soil). Accuracy was evaluated by calculating the recovery of each metal, based on the mean certified value for CRM 141R [measured concentration (mg kg-1)/mean certified values to aqua regia soluble contents for the CRM 141R (mg kg-1)× 100]. Eight replicates were made of the CRM 141R by microwave-assisted digestion for several days. Recoveries were acceptable for most elements, at 85% to 103%. However, there was a low recovery of Zn(76%), due to Zn retention by some soil components(e.g. silicates) which are moderately resistant to dissolution
with HNO3 and HCl.
Analysis of the total heavy metal content was carried out using method 3051A of the United States Environmental Protection Agency (USEPA, 1998), consisting of a soil sample digestion with HNO3 and HCl in a microwave oven (Milestone Ethos D). Heavy metal content was then determined in the final solutions by FAAS in a Varian SpectrAA-220FS spectrometer with the exception of some samples for Cd, which were analysed by graphite furnace atomic absorption spectrometry-GFAAS. Results were expressed in mg kg-1 dry weight on the basis of soil dried at 105ºC.
The accuracy of the digestion method was checked by analysing a certified reference material (CRM) supplied by the Community Bureau of Reference Sample (CRM 141R, calcareous loam soil). Accuracy was evaluated by calculating the recovery of each metal, based on the mean certified value for CRM 141R [measured concentration (mg kg-1)/mean certified values to aqua regia soluble contents for the CRM 141R (mg kg-1)× 100]. Eight replicates were made of the CRM 141R by microwave-assisted digestion for several days. Recoveries were acceptable for most elements, at 85% to 103%. However, there was a low recovery of Zn(76%), due to Zn retention by some soil components(e.g. silicates) which are moderately resistant to dissolution
with HNO3 and HCl.
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