Nickel spreading assessment in New Caledonia by lichen biomonitoring coupled to air mass history.

Lichen biomonitoring and air mass trajectories were used to study the influence of mining activities in the atmospheric dispersion of metallic elements to assess the exposure of the population to dust emitted by mining activities. A map of forward trajectory densities from open mine surfaces throughout New Caledonia was computed and allowed to identify three preferred wind directions (trade wind, bent trade winds and oceanic winds) that could arise in mining particles dispersion all over New Caledonia. Areas where an air quality monitoring would be advisable to evaluate the exposure of the population to the Nickel dusts have been identified. Lichens collected around the industrial mining site KNS and in North Provence of New Caledonia were analysed for their Ni, Co, Cr, Zn and Ti contents. Backward trajectories were simulated from the lichen sampling point using FLEXTRA fed with ECMWF meteorological data, and densities of trajectories having overflown a mine were calculated. Ratio metal/Ti was then plotted as a function of air mass trajectory densities having overflown open pits. A positive correlation between trajectory densities and titanium-normalized metal in lichen for Ni, Co, Cr was highlighted, indicating that mining is a source of dispersion of these metals. For Zn, which is a tracer of fossil fuel or biomass (wood) combustion activity, no correlation was found. Graphical abstract.