Coastal Marine Environment Sustainability - Sustainable Practices in Geoenvironmental Engineering - page 286

aquatic animals in the irst level of the food chain serving the human population, and
unreported or undiagnosed (underdiagnosed?) poisoning of the affected population.
8.4.6 Organic Chemical Contaminants
8.4.6.1 Organotins
Other than from direct, and indirect discharge of land-based industrial waste contami-
nants and leachates from waste piles, some hazardous substances enter the marine envi-
ronment through direct contact and use, such as organotins used as antifoulants for ships,
quays, buoys, etc. Organotins are compounds of tributyltin (TBT). They are highly toxic
chemicals comprising of tin combined with organic molecules. They are used not only
as antifoulants, but also as wood preservatives, slimicides, and biocides. In the context
of a coastal marine environment, organotins are used essentially as biocides to prevent
the buildup of barnacles and algae. They are self-polishing co-polymers and generally
have a service life between 3 to 5 years—meaning that they have to be reapplied to the
marine structures at the end of their service lives. They are poisonous to marine life
including whales, dolphins, seals, ish, and sea birds. Linley-Adams (1999) reports that
concentrations in bottlenose dolphin liver from the U.S. Atlantic and Gulf Coasts found
in the period between 1989 and 1994 ranged from 110 to 11340 ng/g wet weight. He fur-
ther reports on the presence of organotins in sea otters in California waters and harbor
porpoises in Turkish coastal waters in the Black Sea. TBT has been reported to result in
the development of imposex, a pseudo-hermaphroditic condition in female gastropods
(snails) at ng/L levels of concentration (Horiguchi et al., 1994). The U.K. guideline pro-
vides 0.002 μg/L of TBT for sea water quality, and 0.008 μg/L for seawater quality for tri-
phenyltin (TPT) guideline. The Canadian environmental guideline for seawater quality
is 0.001 μg/L for TBT.
TBT can enter the marine environment through (a) leaching of the antifoulant paints,
(b) during application of TBT as an antifoulant, and (c) when the paint is removed from the
pieces of equipment painted with the antifoulant. The degradation of TBT is relatively slow
in sediments. The half-life of TBT in sediments has been reported to be approximately 2.5
years (de Mora et al., 1995), whereas it is only a week or so in marine waters (Seligman et
al., 1988). Since 1990, their use have been banned for all vessels in certain countries (Japan,
Australia, and New Zealand), and in some other countries, their use have been restricted
to vessels with lengths greater than 25 m. The IMO (International Maritime Organisation)
in 2001 adopted the International Convention on the Control of Harmful Anti-Fouling
Systems—a convention that prohibits the use of harmful organotins as antifoulants. The
Convention came into effect at the beginning of 2003 for all ships and was expanded to
include all loating platforms, loating units, loating production and storage units at the
beginning of 2008.
8.4.6.2 Chlorinated Organic Microcontaminants
Chlorinated organic microcontaminants have been accumulating in sediments and sea
animals for many years. These contaminants are highly toxic and direct or indirect inges-
tion of these will be life-threatening. The particular group of chemicals known as CDDs
(chlorinated dibenzo- p -dioxins) is perhaps the one that has gained the most attention and
concern, since it is known to enter the geoenvironment and into the marine environment
from many sources. Of the more than 70 chemicals that make up the CDDs, the one known