Study of the impact perimeter of mining activities of Koniambo SA using atmospheric modelling coupled with lichen biomonitoring
Résumé
Nickel mining in New Caledonia proceeds in opencast mines and naked soils are thus submitted to wind blow and susceptible to be a source of particulate matter. The mining particles generally present a high content in trace element and thus can present a threat for the health and the environment. A new plant and mining site has been created in 2010 in the North of New Caledonia. Once earthwork, excavating works began, PM10 were monitored in three tribes around the mine. PM10 year average in these locations are relatively low (10-20 μg/m3).
Air mass backward trajectories modelling for different PM10 ranges was performed using FLEXTRA and meteorological data provided by ECMWF. Five mines were identified as contributors to PM10 in the sampling stations: KNS, N ́epoui, Poro, Kouaoua and Mon ́eo. Trajectories density maps using these five sources were computed to identify areas potentially impacted by PM emitted by mining activities. As lichens are sensitive to their atmospheric environment, they were used for bioindication. In august 2016 lichens were sampled around Koniambo in more and less impacted areas by air masses originated from mines to analyse trace metal (Ni, Cr, Cu, Co and Zn) as well as Ti metal. The concentrations in metal were normalized by dividing them by the simultaneously measured concentration of Ti to avoid bias linked to the age and species of lichens and compared to trajectory densities.
Cr/Ti, Ni/Ti and Co/Ti were linked to trajectory densities. The proximity of mines and the dominating wind field represent the key parameters in Ni, Cr and Co spreading in the environment.