Assessing the seasonal variation of lead content in Conocarpus erectus: a case study of an urban megacity

Karachi is a highly urbanised city of Pakistan with thickly populated neighbourhoods having distinct ecological features. The burden of anthropogenic pollution in the city needs an exploration of new and more efficient methods of continuous monitoring of the environment. The study was carried out to assess the level of Lead (Pb) inthe Buttonwood (Conocarpus erectus) plants due to their high availability and low cost in sampling and analysis. Plant samples were collected from locations with different land-uses along a seasonal timeline from pre- to post-monsoon, and analysed after wet digestion by using atomic absorption spectroscopy. Mean lead in plant was 62.274 mg/kg with a standard deviation 30.392 mg/kg. The highest mean lead was found 82.589 mg/kg and the lowest mean lead was 47.21 mg/kg for the monsoon season. It was observed that Lead content of the plant was increased after the monsoon. Analysis of variance confirmed the spatial variation in metal concentration for three different seasons. Cluster analysis was also applied to check the variation in land-use. The lead in plants was found associated with the impact of urbanisation on land-use pattern change. Pb absorption level in Conocarpus erectus in different land use area was: High traffic and industrial > High traffic > Low traffic and industrial > Petrol pumps > Commercial > Vegetated and pumps > Vegetated.