The problems that may arise from the presence of sulphur compounds may be summarised as follows:

• The toxicity of the sulphur compounds can be from harmful to highly toxic (e.g. H2S) by inhalation at very low concentrations.
• They can cause severe corrosion even at low concentrations. Some mild steels are corroded at H2S concentrations as low as 10 ppm
• Sulphur compounds can poison catalysts. Many processing facilities have units specifically aimed at removing these sulphur species. Hence it is often important to establish which species are present and at what concentration.
• They are classified as ecotoxins causing problems to aquatic organisms and are a source of acid rain (after hydrocarbon is burned forming SO2).
• Sulphur compounds tend to have foul smelling odour and can cause localised odour problems.