pollution in Dhaka City
Statistical Metropolitan Area has now extended to more than double the area of
what existed in 1981, and by the end of the century, with a population of 11.2
million, it will rank seventeenth among the mega cities of the world. Unplanned
growth of Dhaka city has already created adverse ecological effects. According
to Asian Development Report 1998, Dhaka is the most polluted city of the world.
is no quantitative air monitoring station in Dhaka but a few scattered studies
show the alarming situation. The Environmental Pollution report ’98 of the
Department of Environment (DoE) describes that Suspended particulate Matter (SPM)
in the air is between 1000 and 2000 microgram, four to five hundred percent
higher than the acceptable level. The size, shape, and density of an airborne
particle determine how long a particle will remain in the atmosphere, whether or
not it will be inhaled, and where it may be deposited in the respiratory tract.
The solubility of a gas determines (in part) whether it will cause upper airway
irritation or pulmonary edema. The particulate material can also absorb gases
(including sulphur dioxide and formaldehyde) on surface.
highest acceptable level of sulphur dioxide (SO2) is 60 microgram per cubic
meter of air. But it has been recorded at 300 to 500 microgram in Dhaka. The
amount of nitrogen is also three times higher than that of normal. Bangladesh
Atomic Energy Commission reports that automobiles in Dhaka emit 100 kg lead, 3.5
tonnes SPM, 1.5 tonnes sulphur dioxide, 14 tonnes hydrocarbon and 60 tonnes
of lead in ambient air of Dhaka city has been marked as world’s record of 463
nanogram (ng-one part per billion) per cubic metre offsetting earlier record of
Mexico city (383 ng) and other cities like Kyoto (49 ng) and Los Angles (70 ng).
Gaseous and particulate emissions moved downwind either by direct absorption on
precipitation or by deposition on surfaces. Many of the pollutants deposited dry
on the surface return to hydrological cycle during the next rainfall as they are
washed from the surface. A local Bangla daily on its March 10, 1997 issue
reports a very high content of lead in fish at Dhanmondi Lake and advices to
stop consuming fish. The University of Engineering (BUET) found 151 to 210 mg
lead per liter in Dhanmondi Lake. It is most likely that most of the wetlands
surrounding Dhaka city are extremely polluted.
average suspended particle leads to particulate matter (PM) rises as high as 227
mg per cubic metre, whereas, according to WHO, annual maximum average value
should range between 60-90 mg per cubic metre.
air pollution is inadequately carried out in Bangladesh due to the absence of
trained personnel and modern laboratory equipment. There is a great concern
about the role of air quality in cancer mortality incidence.
chemical interactions of air pollutants
pollutants are complex mixtures of chemicals solubilised in air, chemicals
solubilised in aerosols and chemical particulate. The general consensus
unscientific literature is that health decreases with increasing air pollution.
Increased human moralities have been associated with the elevated air pollution,
elevating total suspended particles and SO2 by 10 ug/m3 increased mortality by 7
and 5 per cent respectively. High level concentrations both SO2 and SPM is
particularly hazardous to health giving rise to increase mortality and
air pollution, air is the vehicle that conveys pollutants to biota. The
chemistry of the pollutants in air is a dynamic process. For example, SO2
emissions are converted to sulphate, sulphuric acids, ammonium sulphate,
ammonium bisulphate, and when inhaled, these compounds have properties of
particulate. Hydrocarbon pollutants are oxidised and the oxidation products are
important in the production of troposphere ozone.
are produced by ultraviolet light-activated reactions ultraviolet light
activated reactions of atmospheric pollutants. Briefly, nitrogen dioxide (NO2)
when activated by ultraviolet light, undergoes photo oxidation to produce nitric
oxide (NO) and atomic oxygen (O-1). The O-1 combines with diatomic oxygen (O2)
to form (NO2). The O3 is used up by the reaction with nitric oxide to form
nitrogen dioxide. Hydrocarbon pollutants especially olefins and substituted
aromatics, react with oxygen to form free radicals. The free radicals reacts
with nitric oxide to form nitrogen dioxide.
level exposure effects have been done in humans on photochemical products.
Concentrations of 100 ug of photochemical products/m3 causes headaches, 300 ug/m3
is irritating to the eyes, 510 ug/m3 is irritating to the respiratory tract and
produces cough, and 580 ug/m3 produces chest pain. Moralities in Los Angeles
area increase when atmospheric increase when atmospheric photochemical products
reached levels ranging from 0.5 to 0.9 ppm.
is generally short-lived at ground level. But once formed, the reservoir can
replenish O3 at ground level for 2 or 3 days. The toxic effects of O3 in the
lower regions of the respiratory tract increase with increased minute
respiratory volume. Animal and human test exposed to O3 shows pulmonary injury
and pulmonary function decreases ranging from 12.6 to 20.7 per cent. Ozone
comprises the native resistance of the lungs to disease.
of soil and water
around Dhaka is deficient in lime and acidification of soils and water has
crated diverse damage to ecological system. Acidification causes:
· Diminish in organic (humus) content in soil;
· Greater solubility of many metals including aluminum;
· Elimination of fish;
· Essential metals and nutrients are leached out to ground water,
Loss of vegetation.
200,000 motor vehicles ply in Dhaka. In industrial countries lead added gasoline
driven cars are almost disappearing and at the same time these harmful
automobiles are exported to the developing countries in the name of
“reconditioned cars”. In recent years due to reduced tax these cars have
conquered Bangladesh market.
wheelers or two-stroke engine (auto-rickshaws) driven vehicles emit poisonous
gases as these engines have very low efficiency to burn hydrocarbon. Hydrocarbon
such as benzo (a) pyrene are produced by incomplete combustion. bezo (q)
pyrene is classified as a proven
carcinogen which in process encompassing the conversion of normal cells to
neoplastic cells into a tumour. Auto richshaws are also using “processed burn-mobil
oil” in their engines. It is known in industrial countries that recycled old
oils may contain many extremely carcinogen constituents like Polycyclic Aromatic
Hydrocarbon (PAH), Dioxins etc. Besides “local mixtures” with many cheaper
varieties practised in Bangladesh may crate more serous health hazards.
than 80 per cent of the vehicles of the city are totally unfit to run on the
streets. (Department of Environment, 1988). More than 50 per cent of the
vehicles, moving in the city under the shadow of invisible power, have no
authorised papers and they never bother
to have any (a comment of an official of the Bangladesh Road and Transport
plants in and around Dhaka are producing one of the worst hazardous emissions of
this planet. Apart from the destruction of valuable topsoil and palm and bamboo
trees of the country, a highly poisonous mixing procedure has been developed by
the brick-manufactures for the furnace at the cheapest
cost. They use trees, coal of very low quality (more than 10 per cent
sulphur, very high ash content etc.), used types (contain PCB), and used tyres
(contain PCB), and used oil to obtain optimal temperature for burning bricks.
“used oil” is one of the most hazardous wastes that costs million of dollars
for disposal in the industrial countries The
present writer visited (January, 1987) the ship-breaking sites at Patenga,
Chittagong, electrical transformer repairing workshops and old oil selling
centres where a huge amount of old oil of different sources are collected and
sold to brick-manufactures and local grocery shops. Along with old ocean going
vessels a huge amount of hazardous oil is imported from the industrial
countries. The old-oils extracted from transformer oils, hydraulic fluids,
automobiles and the like are sold locally named “Maita Tel” or
“soil-oil” and used in households as insecticide for protecting wood or
metal from rust. Among other hazardous chemicals PCBs are synthesised
derivatives of the compound bi-phenyl, and complex mistures of various isomers
and they are very resistant and stable in environment and do not breakdown over
time when exposed to heat, sunlight, water, and or biological/chemical
reactions. Especially dangerous is PCBs biological persistence. PCBs may remain
in the fat cells of organisms (including man) for the life of the organisms.
PCBs related hazard are:
· PCB’s contain, furans, dioxins, napthalenes (carchinogen)
· Absorbed by skin, respiratory tract and alimentary tract
· Concentrated in lipids
· Concentrated in food chains Chlorine – severe and persistent acne-like rash. Liver damage
· Suppress immune system and nervous system
· Increased growth of cancer
· Birds reduced hatchability and toxicity of the embryo.
Ambient air of Dhaka has become a deadly pollutant reaching a level of all times and it can be declared as one of the worst polluted cities of the world. Eight million vehicles runs in Los Angeles show lead content between 0-70 nanogram (part ber billion) lead content in cubic metre, whereas Dhaka with 200,000 vehicles has been marked as world record of 463 nanogram (one part of a billion). Environmental researchers attribute the pollution to vanishing green trees making way for concrete structures, unabated growth of industries and brick fields in city are, two-stroke engine vehicles and dumping of garbage on roadside.
actions for better air in Dhaka requires:
· Prevention of emission at source
· Use of compressed natural gas (CNG) instead of petrol or diesel
· Motorise vehicle free areas in the city
· Improve mass transport service ban two-stroke engine
· Use of natural gas for burning in the brick-fields.
Source: Observer Magazine, February 9, 2001