Anthropogenic osmium in rain and snow reveals global-scale atmospheric contamination

Osmium is one of the rarer elements in seawater, with typical concentration of approximate to 10 x 10(-15) g g(-1) ( 5.3 x 10(-14) mol kg(-1)). The osmium isotope composition (Os-187/Os-188 ratio) of deep oceans is 1.05, reflecting a balance between inputs from continental crust (approximate to 1.3) and mantle/cosmic dust (approximate to 0.13). Here, we show that the Os-187/Os-188 ratios measured in rain and snow collected around the world range from 0.16 to 0.48, much lower than expected (>1), but similar to the isotope composition of ores (approximate to 0.2) that are processed to extract platinum and other metals to be used primarily in automobile catalytic converters. Present-day surface seawater has a lower Os-187/Os-188 ratio (approximate to 0.95) than deep waters, suggesting that human activities have altered the isotope composition of the world's oceans and impacted the global geochemical cycle of osmium. The contamination of the surface ocean is particularly remarkable given that osmium has few industrial uses. The pollution may increase with growing demand for platinum-based catalysts.