A research has discovered that there are high levels of sulphur in the foliage of plants and soil samples collected along the Superhighway near Karachi. As the distance from the road increases, the levels of sulphur decrease. Traffic density in the city of has increased greatly in recent years. Most vehicles are faulty and emit smoke on the roads. Auto emissions are responsible for variation in atmospheric temperature, atmospheric relative humidity, light intensity, wind velocity and soil temperature in the city. Sulphur is more injurious in the form of acid rain, which may cause environmental intoxication. At low concentration, plants can utilise atmospheric SO2 as sulphur nutrient.
But when its concentration reaches above a certain level, it becomes toxic to plants and reports to produce various physiological and biochemical changes in plants. Researches have been conducted on sulphur accumulation in soil. A decrease in net photosynethetic rate in tomato plants was found after fumigating them with SO2. Plant damage after SO2 fumigation was also reported. The leaves of the three most dominant species – Calotropis procera, Prosopis juliflora and Senna holosericea – were collected from 4.5, nine and 13.5 metres away from the Superhighway near Karachi.
Surface soil samples were also collected from the same distance. The leaves of these species were oven dried for 24 hours at 80°C and then carefully grinded. A total of 0.2-gm of dry plant material was digested with HNO3 and perchloric acid in a fumigation chamber.
The amount of sulphur in the leaves of the three plants collected from three different distances was determined. It was highest in all samples collected from a distance of 4.5 meters from the highway, whereas, reverse was the case at a distance of 13.5 meters from the highway except with little discrepancy.
The concentration of sulphur in the leaves of Calotropis procera was 159 mg kg-1 at 4.5 metres distance and decreased with increasing distance from the super highway. The level of sulphur in the leaves of Calotropis procera was significant between 4.5 and nine metres and 4.5 and 13.5 meters, respectively. The sulphur concentration in Prosopis juliflora also decreased with the increase in distance, but at the 13.5 metres distance from the highway, a little higher concentration was recorded than that of the nine meters distance. However, the results were not significant.
In the case of Senna holosericea, there was not much difference in the total sulphur concentration of leaves in the sample collected from different distances. The soil analysis of available sulphur demonstrated a highly significant difference between the samples collected from various distances from the super highway. The highest available sulphur was recorded at 4.5 metres from the highway, whereas at the other two distances, the sulphur was low. A similar study was also conducted in the centre of the city. It was found that there is a relatively high amount of total sulphur in the foliage of Ficus bengalensis, Eucalyptus and Gauicum offininale and available sulphur in the soil at different points in the city.
In the control area, relatively lower levels of sulphur were recorded. In the present study, the levels of sulphur in plants and soil were not as great as was observed in the study conducted in the city. The levels of sulphur along the Superhighway are less because of low traffic density in comparison with the MA Jinnah Road and Gurumandir in the city’s centre. The other factor could be the dispersion of atmospheric pollutants including sulphur to a longer distance because of less interference from the multi-storied buildings in the area. The city’s centre, including the MA Jinnah Road and Gurumandir is a density populated area, with multi-storied buildings along the roads that ultimately stop the dispersion of pollutants to a longer distance due to low wind speed.
A correlation was found between the total concentration in foliage of the plants and the level of available sulphur in soil. This shows that the higher levels of sulphur in plants and soil particularly near the highway are due to the emissions from the auto vehicle activities.
