Monitoring of organotin compounds in seawater using semipermeable membrane devices (SPMDs) - tentative results

The impact of anthropogenic pollutants on the marine ecosystem is related to the concentrations experienced by the biota in the seawater and the resulting concentration in the organism. Results from monitoring of pollutants in water samples provide snapshots that can be high or low depending on a wide range of variables. To provide more integrated information, semipermeable membrane devices, SPMDs, have been used to monitor different organic pollutants. In this survey, SPMDs were used to monitor organotin compounds in the marine environment. Time-integrated sampling using SPMDs and direct water sampling was carried out at six stations in the inner Oslofjord, Norway. The sample work-up procedure for both water and SPMDs was based on direct derivatisation using NaBEt4 and simultaneous extraction with an organic solvent. Analysis was performed using a gas chromatograph equipped with an atomic emission detector. The results show that SPMDs do accumulate organotin compounds from the water phase. Both tributyl- (TBT) and dibutyltin were detected in all of the analysed membranes while no monobutyltin was found. Levels found in SPMDs range from <1 to 220 ng Sn SPMD-1. Water concentrations range from 0.4 to 10 ng Sn L-1. An investigation of relative levels of TBT showed a similar concentration gradient in the inner Oslofjord using either direct water sampling or passive sampling by SPMDs. As the membranes are able to accumulate the organotins from the water it will be possible to locate lower concentrations than with direct analyses of water samples.