Abstract
The levels of several composite elements of two wild plants, namely Euphorbia terracina and Calotropis procera were evaluated. These plant species are quite abundant all year round in the Makkah province of Saudi Arabia. Leaves from the above plants were collected at 5 km intervals from the sides of two stretches, 50 kilometres each, of two motorways between the cities of Makkah and Taif. One of the motorways (Aljabal motorway) is dominated by petrol fuelled passenger and light goods vehicles whereas the other motorway (Assail motorway) has a significant number of diesel fuelled heavy goods vehicles totalling up to 40% of the traffic volume. Instrumental neutron activation analysis (INAA) was employed with different irradiation and counting conditions. The suitability of the two wild plant species for botanical environmental monitors was investigated and the effects of the different vehicular emissions on the concentration levels of 15 elements is discussed. Control samples from rural environment were also collected and analysed in order to provide baseline levels of the elemental concentrations.