Influence of metal oxides in the colorimetric determination of acid volatile sulfide in sediments

The sediment of Lagoa dos Patos‐MS, Brazil, was investigated to verify the influence of metal sulfides and oxyhydroxides of Mn and Fe on the heavy metal availability. The spectrophotometric method of methylene blue was used, with 8 interlinked tubes containing the samples with SnCl2, where N2 was introduced to release the H2S extracted with 6.0 mol L–1 HCl, and trapped in 0.05 M NaOH solution. The influence of SO42–, Mn(IV) and Fe(III) oxyhydroxides was investigated with samples constituted by a mixture of MnO2; Na2SO4; FeCl3, and sediments. The presence of SnCl2 was very important to avoid the interferences of iron and manganese oxyhydroxides. The method of standard addition was applied and the efficiency was (100.8 ± 9.4)%. The ratio among the quantities of metals potentially available and the acid volatile sulfide (AVS) indicate that the system presents small metals availability to the benthic community, by the existence of sulfide capable to immobilize the metal as insoluble sulfide.