The Determination of Acid-Volatile Sulphide in Sediments Using Microwave- Assisted Chemical Vapour Generation: An Alternative to the US EPA Method

Background: Acid-volatile sulphides (AVS) and simultaneously extracted metals (SEM) have been used as sediment quality criteria in both contaminated or non-contaminated sediments. The AVS/SEM model is based on the criterion that metal toxicity is absent when the sum of the acid-labile divalent metal concentrations ([ΣSEM]) is less than the concentration of acid-volatile sulphides ([AVS]) expressed as a molar ratio. Method: The US EPA-recommended method for AVS extraction and determination uses 6 mol L-1 HCl solution for 1 hour and NaOH solution to absorb the H2S generated in the previous step. Sulphide ions can be determined by different procedures, such as gravimetry, spectrophotometry and ion-selective electrode. Results: The aim of this work was the use of microwave radiation as a fast alternative for the generation of H2S. For this procedure, a glass apparatus was developed, adapting a digestion tube that is generally used in a focused microwave oven. The chemical extraction conditions were evaluated. A flow injection analysis (FIA) system was applied to the determination of sulphide. Conclusion: The developed procedure results in a total time for the AVS determination method that is one-tenth of that of the recommended method (12 minutes compared to approximately 2 hours). The results obtained show that AVS was accurately quantified in a range of 1.5 to μ290mol S g-1 sediment (RSD < 13 %). Surficial and core sediment samples from several impacted areas were analysed by both the standard (US EPA) procedure and the developed method, and no significant differences were observed.