Atmospheric aerosol analysis close to the mining area of Aljustrel (SW of Portugal)

Mining activities are associated with dust emissions and increased contaminant levels in the environment, due to excavation, crushing and transportation of ore and the generation of a high amount of polluting wastes. Therefore, it is crucial to study the particulate matter in these areas to understand their impacts on nearby urban areas and populations (Csavina et al., 2012). Analysis PM₁₀ samples collected near the active mining area of Aljustrel (SW Portugal) allowed to do an individual characterization and to investigate the contaminants levels and aerosols sources. In Aljustrel, the exploitation of volcanogenic massive sulphides (VMS) deposits has been done since pre-Roman times, releasing great quantities of mine wastes, which have contaminated the soils (Candeias, et al. 2011). Now the exploitation is done underground, but even so, the ore processing plant releases dust, which is transported by wind to the village.

The PM₁₀ samples were collected in two points at the southeast of the ore processing plant. The sampling was done in two periods July 10-17 and November 1-10 of 2018. Two different techniques were used: SEM-EDX for the individual characterization and ICP-MS for the elemental concentration of 11 elements (Ca, Na, Fe, Mn, As, Cd, Cu, Sb, Pb, and Zn). PM₁₀ mass concentration observed was 20 to 47 µg m^-3 (July) and 4 to 23 µg m^-3 (November) which is lower than the limit of 50 μg m^-3 established in the European Directive (Directive 2008/50/CE of May 21). The individual characterization of 2006 particles by SEM-EDX shows the presence of oxides (17%) and sulphides (10%) in the aerosols, and the elements Na, Si, Fe, S, Al and Cu are those with the most representativeness in all the analyzed particles. The Principal Component Analysis (PCA) allowed to distinguish the main sources of aerosols. Five factors were extracted (72% of the total variance of the data): CP1 is defined by O, Al, Si and Fe, the geogenic elements; CP2 is defined by As and Pb, CP3 is defined by S, CP4 defined by Cu and Zn; and finally, the CP5 defined by Mn. These factors are related to the ore minerals. The ICP-MS results indicate that daily elemental concentration in the samples collected in July is higher than in those collected in November, for each element. The elements Fe, Cu, Zn, As, Cd, Sb, Pb have strong correlations (α = 0.05, r > 0.93) and are the main constituents of the ore minerals. Therefore, these elements will have an anthropogenic source. Comparing the concentration of some pollutes (As, Cd, and Pb) with their limits in the European legislation only As exceeds its limit in all samples.

This work was the first study about atmospheric aerosols developed in this area and shows a strong relationship between PM₁₀ analyzed and the ore exploited in Aljustrel, indicating implications in the quality of the air for the resident population. Even if some limits are not exceeded, the continuous exposition over many years is a potential hazard.