Traffic police, auto and taxi drivers are most prone to carbon monoxide (CO) poisoning in Mumbai, concluded a year-long study conducted by the Indian Society of Environmental Science and Technology (ISEST).

Thirty-four traffic junctions in the city were monitored for CO levels using direct reading CO monitors. In all the junctions, the CO values during the time period 7 and 8 am were found to be below 10 ppm, which increased after 8 am to 27-65 ppm.

Bandra recorded the highest figure at 65 ppm while Dadar was at the lowest with 27 ppm. Among others, the reading were: Vile Parle (61), Chembur Naka (54), Kalbadevi (53), Kurla (52), Horniman Circle (48), Elphinstone Road and Masjid Bunder (47) and Worli Naka (45).

As per the National Ambient Air Quality Standards, the eight hour exposure limit for CO is about 2 ppm for residential, rural and other areas. It is clear that the concentrations of CO observed are several times more than the standard limit. Thousands of residents of Mumbai stay close to these junctions and the impact on their health can be imagined.

About 60 per cent of the air pollutants released every day in Mumbai city is by automobiles and of this, CO contributes about 58 per cent. The CO emission by various vehicles in India comes to about 23 lakh tonnes. As part of the vehicular pollution monitoring project, conducted by the ISEST, the measurement of CO in blood samples of traffic police personnel, auto and taxi drivers was also carried out.

According to Dr.P.S. Ramanathan, President of ISEST and a renowned analytical and environmental scientist, more than 500 blood samples, drawn once a week from 10-20 individuals, were analysed for COHb content at Dr Nerurkar's Modern Clinical Laboratory. The CO values ranged from zero per cent to nine per cent in the samples. The number of persons with higher COHb percentage showed a decreasing trend.

According to him, it is necessary to conduct such surveys to assess the occupational hazards due to exposure to CO experienced by these subjects. To correlate the overall impact of such high CO levels on these individuals, one has to take into account various other parameters such as their general health profile, habits such as smoking, drinking etc, and the environs in which they live after their work is over.

The density of CO is the same as that of nitrogen so that it mixes with air and gets homogenously distributed in air. Mumbai ranks among the 15 most polluted cities of the world. There are about 12 lakh vehicles in Mumbai and the number is increasing day by day.

Carbon monoxide, a colourless gas, is a key pollutant emanating from automobiles. The traffic police personnel, taxi and auto drivers who get directly or indirectly exposed to environment polluted by automobiles inhale large concentration of CO in traffic junctions. The affinity of CO to haemoglobin is very high. One of the imperfections of human bodies is that, given a choice between carbon monoxide and oxygen, the protein hemoglobin in the blood will always latch on to carbon monoxide and ignore the life-giving oxygen.

CO is bound to haemoglobin of the blood 245 times more firmly than Oxygen (O2). Which means if a gas mixture of O2 and CO is bubbled through blood in such proportions that half the haemoglobin is combined with O2 and half with CO then the gas mixture must contain 245 volumes of O2 for every volume of CO.

In general, environmental monitoring reports of standard organizations do not reflect the CO concentrations in traffic junctions. Importance is normally given to other pollutants like sulphur dioxide, oxides of nitrogen, particulate matter etc.

Studies on the effect of CO have revealed an effect of -- carboxy haemoglobin (COHb) concentration of about five per cent. In some of the tests like pulse rate, respiratory rate, changes in blood pressure, neurological reflexes etc, significant changes in response have been found after exposure to carbon monoxide. For some of these tests, variations in performance were found at COHb levels well below five per cent, possibly even at levels as low as two per cent.

Effectively, CO can remove oxygen from haemoglobin and cause asphyxia. The mechanism of action for CO is therefore regarded as principally an interference with O2 transport brought about by the combination of gas with haemoglobin. One can estimate the relative magnitude of recent exposure to CO by determining COHb.

The symptoms of acute poisoning depend on the concentration of CO in the inspired air, the duration of exposure, and the age and state of activity of the person exposed. The symptoms of low-level carbon monoxide poisoning are so easily mistaken for those of the common cold, flu or exhaustion that proper diagnosis can be delayed.