Trends in TBT Water Column Concentrations at a Marina in Hampton Roads, VA
Status: Though generally declining, the water column concentrations recorded near marinas in Hampton Roads, VA are still high enough to poase a risk to certain Bay organisms such as plankton and mollusks.
Goal: Reduce TBT concentrations to below the applicable state water quality standrad (Virginia's chronic water quality standard for TBT in estuarine watwers is 1 ppt)
- Tributyltin (TBT) is an ingredient in antifouling paints that was commonly
used by boaters to keep boat hulls free of barnacles, algae and other marine
organisms. In time, TBT in the paint leaches from the boats into surrounding
waters. It is still used as an industrial fungicide.
- European scientists were the first to link elevated levels of TBT in the
water with the "balling" of oysters (curling and malformation of the shell into
more of a ball form than a flatter shell).
- In the 1980s, scientists at the Virginia Institute of Marine Science and the
Johns Hopkins University, found TBT to be toxic to certain bay life, such as
plankton and mollusks, and a threat to the creatures that feed on them. This
resulted in VA and MD restricting TBT use in the Bay in the late 1980s and
national legislation (modeled directly on the VA and MD state legislation), in
1988, restricting TBT use in antifouling paints.
- EPA has proposed chronic water quality criteria for TBT of 63 parts per
trillion (ppt) for freshwater and 10 ppt for saltwater. Respective acute water
quality criteria are 460 ppt for freshwater and 360 ppt for saltwater. Chronic
toxicity causes impairment or abnormalities in aquatic life forms; acute
toxicity is lethal. Virginia's chronic Water Quality Standard for TBT in
estuarine waters is 1 ppt. Maryland's chronic Water Quality Standard for TBT is
26.4 ppt in freshwater and 10ppt in saltwater. (1 ppt = 0.001 µg/L)
- Studies in the field showed highest concentrations were near recreational
boat marinas, largely because boats were freshly painted, launched and allowed
to sit at the dock each year. This is why recreational boats were targeted.
- The International commercial fleet still uses TBT, but the ships move almost
all the time, so the leachate has few local effects. It's legal for use on
aluminum hulled boats or commercial vessels over 27M, (about 60 ft), as well as
on motor outdrives and crab pots.
- The Navy can use TBT, but chooses not to.
- For more information contact Kelly Eisenman, Chesapeake Bay Program Office,
1-800-968-7229 or Dr. Mike Unger, VIMS Gloucester Point, VA