Monitoring of Butyltin Compounds in the Aquatic Environments of the Philippines

A comprehensive perspective of Butyltin (BTs) contamination and its possible implications on the marine and coastal environments of the Philippines is presented using green mussels, marine mammals and skipjack tuna as bioindicators. BTs were detected in mussels from all the sampling locations investigated as part of the monitoring surveys under the Asia-Pacific Mussel Watch (APMW) Program conducted in the late 1990s. The BTs detected in green mussels collected in 1994, 1997 and 1998 from various aquaculture and coastal sites in the country were suggestive of considerable widespread pollution by BTs in the coastal waters. Among BTs, TBT was detected at all locations at relatively higher concentrations, whereas the concentrations of DBT and MBT were found to be at lower residual concentrations. This could be indicative that green mussels have limited abil- ity of metabolize TBT to DBT and MBT. It could also be suggestive of recent TBT inputs into the aquatic environments and the presence of sources along the coastal waters. Concentrations of BTs (MBTDBTTBT) in green mussels were reported up to 790 ng g � 1 wet weight in a site where intensive maritime activities are occurring. Mussels from rural areas contained TBT at lower proportions indicating that TBT usage as antifouling agents is minimal. Tolerable Average Residue Level (TARL) for seafood in the Philippines was estimated at 173 ng g � 1 wet weight for an average person weighing 60 kg. Concentrations of TBT or the sum of TBT and DBT in some green mussels analysed revealed that some values exceeded TARL level, which could suggest that hu- mans consuming this seafood from areas with high BTs contamination could be at risk from elevated exposure to BTs. BTs were likewise detected in skipjack tuna collected from the offshore waters of the Philippines, suggestive of the widespread contami- nation even in offshore waters. Considerable BTs levels (up to 220 ng g � 1 wet weight), with high percentages of BTs in total tin (∑Sn: inorganic tinorganic tin) were noted in the liver tissues. This finding indicates that the anthropogenic BTs represent the major source of Sn accumulation. On the other hand, relatively low concentrations of BTs were found in the liver of cetaceans from the coastal waters of the Philippines, which ranged at 42-98 ng g � 1 wet weight. Significantly lower hepatic BT concentra- tions in cetaceans in tropical waters were noted compared with those inhabiting temperate waters proximal to developed na- tions. This result could imply that, at present, usage of BTs in the Philippines is still minimal.