Organotin compounds (OT compounds)
Organotin or OT compounds comprise a group of man-made chemicals, which are toxic particularly to marine organisms. The biggest sources of OT compounds dissolved in water bodies are antifouling paints used on ships and boats (tributyltin or TBT, and triphenyltin or TPhT). People can be exposed to these compounds through eating fish. No maximum level has so far been specified in food legislation for OT compounds in fish.
The largest deposits of OT compounds are found in the sediments of harbour and shipyard sites, where also fish show higher OT levels than on open seas and lakes. In lake fish the levels are only one tenth of the levels of sea fish and in farmed fish the levels are even lower. The accumulation and depletion rates of OT compounds vary in the environment and in the human body. In favourable conditions, i.e. in a cold and dark environment, they can persist for several years.
The most significant adverse effects of OT compounds include disturbances in hormonal functions as well as immunotoxic effects, such as reduced resistance. TPhT is also a central nervous system disruptor. In Finland, the average total daily intake is about 3.2 ng per kilogram of body weight, i.e. about one percent of the tolerable daily intake estimated by EFSA (TDI = 250 ng/kg bw). The TDI value has been calculated for the sum total of tributyltin and dibutyltin, triphenyltin and dioctyltin, because immunotoxicity is the most significant adverse effect of all these compounds.
The intake of organotin compounds is minor for the average consumer, but can approach the TDI value for high-level consumers (80 g of fish every day from contaminated areas): 157 ng and 120 ng per kilogram of body weight per day for men and women, respectively.
- TBT and TPhT were previously extensively used in ship bottom paints for their antifouling properties.
- Owing to their toxicity to micro-organisms, OT compounds have also been used as protective substances for wooden materials and paper, albeit to a lesser extent.
- The use of OT compounds in antifouling paints is nowadays prohibited.
- OT compounds are still used to e.g. improve the thermal and light resistance of PVC materials (monobutyltin and dibutyltin as well as dioctyltin).