Sulphur-based radiotracers for environmental research
The oceans are an important link in the global cycles of many chemical species, including sulphur. Plankton produce dimethylsulphonioproprionate (DMSP) which is then converted to dimethyl sulphide (DMS) and released to the atmosphere. Once in the atmosphere, DMS is converted into sulphur aerosols which influence the Earth's radiation budget and subsequently its climate. The relationship between DMSP and DMS is not well understood. Hence, scientists at the Plymouth Marine Laboratory (PML) undertook an investigation of the mechanisms that produce and destroy DMSP and DMS using radioactive tracers. Building on previous research carried out by American universities, the PML established a protocol for producing high quality sulphur radiotracers based on sulphur 35, specifically 35S-DMSP and 35S-DMS. The procedure involves reactions with amino acids, methylation, ion exchange purification and High Performance Liquid Chromatography (HPLC) techniques. Yields of labelled DMSP are in the order of 5-12 %. In the context of the BASICS project, the radiotracers were used to study DMSP and DMS cycling in the Plymouth Sound and in coastal waters off Spain. The radiotracers, and the techniques PML developed to create them, may be valuable in other applications.
