METALS - Marine Pollution: What Everyone Needs to Know - page 83

been developed. For thousands of years ship hulls have been
treated with various substances to reduce fouling. Paints con-
taining copper have been used for many years. Beginning in
the 1940s organotin compounds (organic chemicals includ-
ing tin) were developed, and one of the most effective and
long-lasting is tributyltin (TBT), which is also one of the most
toxic to other organisms.
When marshes were being filled in for development, house-
hold and industrial wastes such as metal cans and paint cans
with pigments that contain metals were a common component
of the fill material. Mercury, cadmium (Cd), lead (Pb), and cop-
per (Cu) from pipes, antifouling paints, and CCA (chromated
copper arsenate)-treated wood bulkheads and pilings were
common contaminants. While copper is essential for some
biological processes and is not generally a concern for human
health, it is extremely toxic to algae and invertebrates, and is
even used as an algicide and molluscicide.
Lead comes in runoff from road surfaces during rain, from
its previous use as a gasoline additive, even though leaded gas
is not used any more. Pb remains in the environment and does
not break down, so some otherwise fairly pristine marshes
have elevated amounts in the sediments as a result of decades
of hunting ducks and other waterfowl with lead shot. Lead
shot contaminates marsh soils, and birds that normally pick
up small pebbles for grit in their digestive system to grind up
seeds can consume the spent shot, sometimes resulting in fatal
lead poisoning.
Other metals that can be environmental problems include
cadmium, chromium, zinc, and copper. Selenium (Se) can be
found in different chemical forms and can bioaccumulate in
animals and cause deformities under some circumstances,
although in other instances it can counteract the toxic effects of
mercury. It affects the immune system, alters genes and dam-
ages the nervous system, and is particularly toxic to develop-
ing embryos. Inorganic mercury and methylmercury (a more
toxic form) tend to be more concentrated in sediments with