Trace Elements and Their Variation with pH in Rain Water in Arid Environment

Abstract

Climate change in Kuwait has resulted in temperature fluctuations, frequent dust storms, and noticeable changes in the amount of precipitation. Pollutants released into the atmosphere from various sources affect the chemical composition of rainwater and impact its usability. The present study on rainwater focused on the determination of trace elements, sources, and their variation with respect to change in temperature and pH. The samples were collected from 12 different locations in both industrial and urban regions during significant rain events (n = 31) from November 2018 to March 2019 and samples were analyzed for trace elements in ICP-OES using standard USEPA 200.7 method. The mean concentration of the 16 elements analyzed followed the trend: Co < Cd < Cr < Mo < V<Ni < Pb < As < Se < Fe < Cu < Mn < Zn < Al < Ba < Sr and were inferred to be within the WHO permissible limits of drinking water. The analytical results revealed that Strontium (Sr) had the highest mean concentration (188 μg/L) followed by barium (Ba), aluminum (Al), and zinc (Zn) with mean concentrations of 95.2 μg/L, 30.4 μg/L, and, 16.6 μg/L respectively. The sources of contamination in rainwater were identified by calculating the enrichment factor (EF) using element concentration reported in Kuwait dust and from continental crustal values. EF for Fe, V, Ni, and Cr were below 10, indicating purely crustal sources. Ni, Zn, Cu, and Mn exhibited values between 10 and 100, reflecting industrial sources of contamination. EF for Sr was greater than 100, due to inputs from anthropogenic sources. A strong association between Al and pH along with correlation between Sr, Cr, Cu, Ni, Mo, V, and meteorological parameters was revealed from statistical analysis. Furthermore, pH Redox Equilibrium C programming (PHREEQC) was used to simulate changes in pH and temperature in rainwater to predict the resultant variations in trace element concentrations. There was no significant change observed in pH with rise in temperature, but the concentration of trace elements varied with change in pH. The concentration of V, Cr, and Al were most sensitive to pH variations. The results indicated that industrial emissions, fuel combustion, and dust in Kuwait are the primary sources of Al, Sr, Mn, Zn, and Ba in the rainwater samples. Since, the concentrations of these elements are relatively low, rainwater in Kuwait could be harvested for drinking and domestic purposes and used for recharging aquifers.