A 200 year record of atmospheric cobalt, chromium, molybdenum, and antimony in high altitude alpine firn and ice

High altitude cold snow and ice cores from midlatitude mountain ranges have been used very little to obtain historical records of environmental contam ination by heavy metals. Co, Cr, Mo, and Sb have been measured by DF-ICP-MS -MCN (double focusing inductively coupled plasma mass spectrometry with mic roconcentric nebulizer) in various sections of a 140 m snow/ice core drille d at a high altitude location near the summit of Mont Blanc in the French-I talian Alps. The bottom of the core is older than 200 years. It gives the f irst snow and ice time series for these metals of high environmental intere st for the post Industrial Revolution period. Measured concentrations range from 26 to 433 pg/g for Co, from 8 to 469 pg/g for Cr, from 0.2 to 50 pg/g for Mo, and from 0.2 to 109 pg/g for Sb. For all four metals, concentratio ns in recent snow are found to be, on the average, significantly higher tha n concentrations in ice dated from before the middle of the 19th century. T h ere are however differences in the timing and the amplitude of the observ ed increases from one metal to another. Mo shows the greatest increase (x16 ), followed by Sb (x5), and Co and Cr (x2-3). Contribution from natural sou rces is, on the average, limited except for Mo in ice dated from before the middle of the 19th century. For recent snow, contribution from oil and coa l combustion is the dominating source for Co, Mo, and Sb. For Cr, on the ot her hand, the most important contribution is from iron, steel, and ferroall oy industries.