KARACHI: Female snails at the Gadani Ship-breaking Yard
have been found to have developed male sex organs due to exposure to a
highly toxic chemical used in ship paints, a recent study of Karachi
University’s Centre of Excellence in Marine Biology has showed.
Scientists
have warned that the chemical contamination might have been introduced
in the food chain and affecting human population.
Titled ‘Study
of imposex in coastal waters of Pakistan: TBT toxicity at Gadani
Ship-breaking Yard’, the research has been carried out by Safia Hassan
under the supervision of Prof Ghazala Siddiqui.
According the
study, two bio-indicator species of gastropods (snails), Thais bufo and
T. rudolphi, collected from the Gadani Ship-breaking Yard in Balochistan
showed 100 per cent imposex (masculinisation of female snails in
response to exposure to certain marine pollutants).
“Tributyltin
(TBT) presence and elevated levels of testosterone were recorded in the
species’ examination. This indicates that the ship-breaking yard is
contributing to organotin (chemical compounds) contamination in marine
environment and affects the aquatic organisms despite global ban on
their usage in antifouling paints,” the study says.
(An
antifouling paint is a specialised coating that is applied to the hull
of a vessel to slow down the growth of marine organisms that attach to
the hull and can affect performance and durability of the boat or ship)
Imposex
in gastropods, according to the study, is induced mainly by TBT and
also by its sister compound triphenyltin (TPhT), both considered the
most toxic biocide ever introduced in the sea.
“TBT disturbs the
normal homeostatic relationship between free and esterified testosterone
and increases the free testosterone levels as the species is more
exposed to the chemical. TBT exposed imposex snails have elevated levels
of testosterone, which is an endocrine dysfunction and is responsible
for imposex,” it says.
The compounds of TBT and TPhT, according
to the study, can be degraded by solar radiation, bacterial
biodegradation or biological decomposition to their metabolites, such
as, dibutyltin (DBT), monobutyltin (MBT), diphenyltin (DPT), and
monophenyltin (MPT).
“The chemicals released from the paint enter
the water column and are finally accumulated in sediments present in
and around harbours and along shipping lanes. These chemicals in the
water column or sediments are taken up by marine organisms and finally
enters the food chain,” it points out.
TBT-based paints, the
study says, have been in use as antifouling agents for a long time as
they are inexpensive and effective as compared to other antifouling
agents. Their use became widespread in the 1970s with the development of
self-polishing copolymer paints.
However, as researches highlighted their toxic effects, their application was banned in the late 1980s in many countries.
“Despite
the ban, many countries have been experiencing decades of unrestricted
use of TBT. To overcome this problem a global ban on the use of TBT from
2003 onwards was introduced which included the removal of all existing
coatings of paints containing TBT by 2008.
“The decision was
taken by the International Maritime Organisation (IMO) in 2001 and was
implemented in many countries. However, there is no check on organotins
released by recycling of old ships at ship-breaking yards,” it says.
On
ship-breaking yards, the study highlights that the world’s largest
ship-breaking yards are situated in China, Pakistan, India, Bangladesh
and Turkey, which account for 95pc of the global ship-recycling industry
over the last three decades.
The ship-breaking industries in
these countries dispose of large quantities of hazardous materials,
including organotin, into the marine environment without any
pre-treatment.
In Pakistan, it says, Gadani Ship-breaking Yard
has been in operation even before the country’s independence in 1947.
“Although Gadani ranks as the world’s third largest ship-breaking yard,
it ranks first due to its efficiency in terms of duration required to
break a ship. There is a paucity of information on the environmental
contamination due to ship recycling at Gadani and the studies are mostly
focused on grease, oil, and bacterial contamination with very little
attention on contamination due to chemical compounds and heavy metals,”
it says.
Speaking to Dawn, Prof Ghazala Siddiqui said that the
phenomenon of imposex had been earlier documented in nine species of
gastropods by a team of KU marine experts in 1993 in the Manora Channel.
“There was a gradual decline in the incidence of imposex in the
following years as countries started rejecting TBT use following the IMO
ban. No case of imposex was recorded in the Manora Channel in 2008,”
she said.
Explaining how the chemical contamination might be
affecting marine biodiversity and the food chain, she said: “There is
evidence that extreme cases of imposex have led to a decline in the
snail’s population as females are unable to lay eggs. When one species
starts disappearing or completely disappear from the ecosystem, the
number of other species
they feed on starts increasing, thus causing harm to biodiversity.
Similarly, humans are also exposed to the imposex
risk through the food chain and exposure to contaminated water. The
scale and nature of the problem can be determined
by examining the testosterone levels in women,” she said.
According
to Prof Siddiqui, gastropods are eaten in many countries and the
species was chosen for the specific research because it shows visible
structural (imposex) changes when they are exposed to TBT even in low
concentration.
“There is a need for more studies to understand ecological issues in play at ship-breaking yards and industries.
Second,
the government should take notice of TBT contamination and implement
ways to tackle it as it carries huge risks for the people employed at
places where old ships are handled and dismantled,” she concluded.
Published in Dawn, September 4th, 2014
