The effect of land-use type and climatic conditions on heavy metal pollutants in urban runoff in a semi-arid region

This study examined the effects of land-use changes on heavy metal pollution in runoff in a catchment of Tehran, Iran. Urban runoff samples were collected from six stations, including five various land uses and mixed land uses. The event mean concentration (EMC) was applied to determine heavy metals, including mercury (Hg), arsenic (As), cadmium (Cd), zinc (Zn), lead (Pb), and copper (Cu), in five land uses. Sampling was done during six events with different antecedent dry days (ADDs) during 2019–2020. The result revealed higher heavy metal concentrations in runoff in the industrial land use compared to other land-use types in the catchment. The calculated EMC rates were as follows: EMC Zn > EMC Pb > EMC Cu > EM As > EMC Hg > EMC Cd. This study also found that the maximum and minimum EMCs of heavy metals were associated with rainfall events with 115 and 1 dry days, respectively. In comparison to other heavy metals, mercury and arsenic were at a higher level in runoff as determined by EMC data analysis. In order to minimize the risk of heavy metal contamination of runoff, the relocation of industrial land uses from urban environments to non-urban areas is recommended.