Phytomonitoring and NO x pollution around silver refineries

Abstract

In order to assess the impact of NO x pollution on vegetation around silver refineries, the present study was undertaken in Varanasi, India, during the period January to December 1994. For this purpose, the five most common plants at all sites, Ficus religeosa, Syzium jambolana, Azadirachta indica, Cassia fistula, and Mangifera indica, were selected as test plants. Five study sites were selected around silver refineries. A control site, BHU, was also selected outside the city in the northern direction at a distance of about 10 km. Responses to nitrogen oxides of plants, such as foliar injury symptoms, changes in chlorophyll, carotenoids, sugar, ascorbic acid, protein, and nitrogen content were measured. The NO x concentrations were high in the immediate vicinity of the silver refineries. There also exists a positive and significant relationship between the concentrations of NO x and foliar injury, protein, and nitrogen content in plants. The levels of foliar injury, chlorophyll, carotenoid, sugar, and ascorbic acid were found to decrease, and the amounts of protein and nitrogen were found to increase in comparison to plants growing at a control site. The magnitude of such changes was greatest in F. religeosa. The study suggests that the differential sensitivity of plants to NO x may be used in evaluating the air pollution impact around emission sources, and M. indica plants can be used as an indicator plant for quantifying the biological changes.