An Investigation on Source-Specific Health Risks Associated with Metals Present in Clouds over Hilly Regions in Indian Subcontinent

Entrance of metals in any form through any pathway causes significant damage to human health.  The present study quantifies probabilistic health risk for carcinogenic and non-carcinogenic metals entering through inhalation, ingestion, and dermal routes within the human body for different age groups (children and adults). Water soluble metals (major metals; Na, Ca, K, Al, Mg, and trace metals; Fe, Zn, Sr, Ni, Cu, Mn, Cr, Ba, and Cd,) present into clouds over hilltop sites of the Western Ghats (Mahabaleshwar) and Eastern Himalayas (Darjeeling) situated at the entrance and final destination of monsoonal clouds over Indian Subcontinents are measured using ICP-OES. pH of cloud water is found to be alkaline in nature over both measurement sites. Clouds contain two times higher total soluble metal concentration (TMC) over Mahabaleshwar than that of Darjeeling. Analysis of enrichment factor and PCA suggest road dust, contributes maximum to the loading of metals into the clouds while desert dust coming from Arabian deserts contribute more to the initial clouds found in Western Ghats and fossil fuel influences maximum to the Himalayan clouds. Heavy metal pollution index (HPI) is found to be 14.8 over Mahabaleshwar and 22.6 over Darjeeling indicating relatively higher polluted clouds over Darjeeling due to higher concentrations of toxic metals like Cd and Zn emitted from fossil fuel combustion and road dust. Inhalation of polluted clouds containing higher concentrations of toxic metals like Cd, Cr, Mn, and Ni are the most potential threat to non-carcinogenic diseases. Cd is most dominating metal in clouds over Darjeeling, mainly coming from fossil fuel combustion, and has two folds higher HQ values than the Mahabaleshwar. Cr emitted from industrial waste has the highest carcinogenic health risk factor for children and adults over Mahabaleshwar (3.2×10^-7, 2.3×10^-7) than that of Darjeeling (2.1×10^-7, 1.5×10^-7). The present study suggests that clouds contain major metals like Na, Ca, Al, etc., mainly coming from marine sources and desert dust over the Arabian Sea and nearby continental regions while entering to Indian Sub-continental region, and later contaminated with trace metals like Cd, Cr, Cu, Ni, etc. emitted from vehicular emissions, industrial waste, and road dust that have greater impact on human health via inhalation pathway responsible for non-carcinogenic and carcinogenic diseases.