There are several important sources of toxic metals in the marine environment that the Bermuda government has recently prevented from continuing to enter our coastal waters. Gasoline used to contain lead that was emitted from car exhausts after being burned. Unleaded gas is now required in Bermuda and the BIWI project has been monitoring how the amount of lead already in the coastal environment is changing. Another major change is in the type of paint used on boat bottoms to prevent organisms from fouling or settling on the boat bottoms. Boat owners used to use paints containing TBT (tri-butyl tin) but boat owners now have to use copper- based paints instead.
Researchers have found that inputs of lead into the environment have been effectively controlled by the introduction of lead-free gasoline on the island. The reduction of lead entering the atmosphere has gone from approximately 25,000 tons to 5000 tons on an annual basis. The study indicates that there are still large concentrations of lead in the harbor areas of the inshore waters, mostly associated with the sediments. Shipping activity (we get huge cruise ships as well as small boats) stir up the bottom and introduce this sediment-bound lead into the water column where it can be a source of dissolved lead. The dissolved lead rapidly sticks to the particles in the water column in the well aerated Bermuda waters and is then re-deposited to the sediments. The only "permanent" removal process for this sediment-bound lead is via exchange with "cleaner" seawater from off the reef platform where the lead eventually ends up in the deep sea. Because of this slow removal, the sediments will be a source of lead to the inshore waters for a long period of time.
Copper is toxic in high concentrations to marine organisms, particularly for organisms in the larval stage. This property makes it useful in bottom paint for boats to keep organisms from landing there and slowing down the boat. The sediments and water column in Bermuda have copper in them in the range of 0.51-33 µg/g and 1.7-9.6 nmol/l respectively. The higher concentrations are at, or close to, international target concentrations for sediments and surface waters. This implies that these areas should be monitored for further accumulation of copper. Copper is rapidly cycled through the biological system and the main removal process again is tidal flushing. Because copper does not stick as readily as lead to particles, stopping the input of copper would result in a rapid decrease of copper in the inshore environment. However, since it is used in bottom paints, the marine environment will continue to receive copper input for the foreseeable future.
Tributyl tin (TBT) has been measured at seven stations in Hamilton Harbor. The concentrations have been dramatically reduced from the first study made in 1990 and the subsequent ban on the use of this type of anti-fouling paints. There is still release of organo-tin compounds from the sediments and concentrations are very high (>200ng/g sediment) around the boat yards in the harbor, presumably due to scraping of old paint from boats before the application of the copper based paints. The concentrations in the environment are expected to decrease due to flushing as was the case with the trace metals. Unlike other areas of the world, there are no reported affects of tributyl tin exposure on marine life in Bermuda. Last year analysis of an herbicide (plant killing chemical), Irgarol, was initiated. This compound is being added to copper based anti-fouling paints to boost the effectiveness of such paints. Concentrations of Irgarol were found to be elevated within the harbor area compared to control stations. This represents the first measurement of this compound outside of continental Europe.