Partitioning and solubilities of metals and metalloids in spring rains in Moscow megacity

Abstract

This study obtained the first dataset on the solubilities and partitioning of metals and metalloids (MMs), including Al, As, Ba, Be, Bi, Ca, Cd, Co, Cr, Cs, Cu, Fe, K, Li, Mg, Mn, Mo, Na, Ni, Pb, Rb, Sb, Sc, Se, Sn, Sr, Th, Ti, Tl, U, V, W, Y, Zn, and Zr, during spring rains in Moscow. MM concentrations were determined using inductively coupled plasma mass spectrometry and atomic emission spectroscopy. The metals Ti, Zr, Al, Sn, Fe, W, Th, Li, V, Cs, Bi, and Y were predominant in the insoluble fraction of the rainwater, whilst Sb, Zn, Ca, Cd were prevalent in the soluble fraction. The end of the winter heating season, together with a weaker dilution effect due to lower precipitation in April, caused higher soluble and insoluble MM concentrations in rainwater than those in May. MM solubilities increased with decreasing pH and longer periods of precipitation, and declined with an increase in precipitation intensity, the length of the antecedent dry period, and the content of solid particles in the rainwater. A 20%–50% increase in solubility in acid rains compared to non-acid rains was observed for Y, Pb, U, Be, Na, Ni, Th, Cu, W, Fe, Mg, Cr, Tl, and Ba. Anthropogenic sources contributed significantly to the concentration of soluble MMs (>90% for Sb, Pb, Se, Cd, Zn, Cu, Bi, Ca, Mo, Sc, Ba, As, W, Sr, Mn, Sn, Co, Tl, Ni, and Be). For the insoluble MM, crustal materials were the important contributors. During public holidays in Russia in the first decade of May, an increase in the proportion of insoluble MMs was observed.