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Sampling of gastropods is being
carried out at the Gadani shipbreaking yard.
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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
Shipbreaking 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 shipbreaking 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 Shipbreaking 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.
Source: dawn. 4
September 2014
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