Fogo volcano (Cape Verde) 2014-2015 eruption: dust characterization and impacts on environment and human health

Fogo (Fogo island, Cape Verde Republic) is the youngest and most active volcano of the archipelago. The last eruption occurred in 2014–2015. Aiming at studying dust emissions and transport during the eruption period and assessing their impact on air quality and human health, a mineralogical and chemical characterization was undertaken in outdoor dust from all over the island, as well as in the lava resulting from this event. Air quality monitors were used to obtain concentrations of atmospheric particulate matter (PM) and gaseous pollutants. The mineralogical constitution of the samples was analysed by X-ray diffraction and Electron Microprobe, while the chemical characterization was performed through X-ray Fluorescence Spectrometry and ICP-MS. The volcanic rock was found to be tephritic to basanitic, with high potassium content. Several minerals were identified, such as titanian augite with ilmenite, basaltic hornblendes, pyrrhotites, apatites, pyroxenes, basaltic hornblendes and hematites. Concentrations of the particulate matter inhalable fraction (PM10) exceeded the 24-hour mean of 50 μg/m3 recommended by the World Health Organization. Nevertheless, total volatile organic compounds (TVOCs) showed levels lower than the worrying range. The highest levels of CO2 were recorded in more populated villages and farthest from the volcano. The Pollution Load Index (PLI) for outdoor dust collected on rooftops was always above 1, suggesting enrichment, with higher values in the dust size fraction < 63 μm. In the same way, the Contamination Factor pointed to high enrichment of As, Ni and Pb, and very high enrichment of Cd in the same size fraction. The Noncarcinogenic Hazard Quotient and Hazard Index estimated for Children suggest that health problems may arise. The Carcinogenic Risk, for all size fractions, was above the target risk. The element that most contributed to the global risk was As, followed by Pb and Co. Ingestion was the main exposure route for all size fractions. The dust size fraction that represented the highest risk was < 63 μm, mostly due to the As concentration.


Introduction
Volcanic eruptions cause hazardous effects on the environment, climate, exposed population's health, and are also associated with the deterioration of social and economic conditions of surrounding inhabitants [1]. A volcanic eruption is both an international pollutant source and an extended hazard. Natural hazards, such as volcanic eruptions, can be stressful events once are violent natural disasters that impose a threat to human health, as well as to livestock, and can affect global climate [2]. The unfavorable effects of a volcanic eruption depend on the distance, magma viscosity, volcanic ash and gas concentrations. Hazards near volcanic eruptions include toxic volcanic tephra, which can cause problems in the respiratory system, eyes and skin, as well as disposal of materials on soils and water supply contamination [3].
Apart from the immediate life-threatening hazards following a volcano eruption, several other health risks are associated with populations living close to an active volcano [4]. Short-term exposure to volcanic gases can trigger asthma attacks and has been related to respiratory morbidity and mortality and increased irritation of the respiratory tract [5]. Particle deposition in the lung varies with particle diameter [6]. Other possible impacts include ocular and/or skin alterations. Volcanic dust hazards vary with particle mineralogy, chemical concentration, size and morphology. These characteristics depend on the types of eruptions and volcanoes. It is not possible to generalize about the toxicity of volcanic products harmful to humans. The aims of the present study were to: (a) model mineral dust emissions and transport during the eruption period and their impact on air quality; (b) characterize outdoor dust collected during the 2014-2015 Fogo volcano (Cape Verde) eruption; (c) monitor PM, CO2, CO and TVOC concentrations during the eruption, and (d) understand the impact of the volcanic products on human health.

Materials and methods
Study area: Fogo island (Cape Verde; Fig. 1b) is located in the Atlantic Ocean, 800 km from the northwestern African coast. The Cape Verdean archipelago origin is linked to hotspot magmatism, with melts predominantly alkaline silica-undersaturated of basanitic to tephritic composition, also occurring phonolites and carbonatites [7]. Fogo is an active stratovolcano with a maximum altitude at Pico do Fogo (~2,829 m above sea level (asl)). According to Larrue et al. [8], Fogo island is covered by young volcanic rocks of Quaternary age. The collapsed caldera is located in the center of the island [9], with ~8 km in diameter. This collapse gave rise to a caldera scar, locally called Bordeira, with a vertical wall with maximum ~1000 m high and a flat area of ~35 km 2 (~1700 m asl), locally called Chã das Caldeiras, where 2 villages (Bangaeira and Portela) were destroyed during the 2014-2015 eruption (Fig. 1c). This eruption occurred along a SSW-NNE fissure on the eastern flank of Pico Novo (Fig. 2), with the formation of four eruptive craters, emission of gases, pyroclasts and lavas. The eruptive style of the strombolian type began with an explosive phase characterized by the release of gases and pyroclasts, forming an eruptive column with ~6 km high [10]. First lava flows of pahoehoe type changed later to aa lavas. Three eruptive craters with strombolian emissions (gas explosions, pyroclasts and lavas) were formed, with two further lava fronts developed in direction of the destroyed Bangaeira and Portela villages, previously evacuated.
External dust storm events occurred during the 2014 Fogo eruption, causing air quality deterioration. Usually, mineral dust and sea salt are the main contributors to the Cape Verdean aerosol mass [11], with PM exhibiting a strong seasonal trend, with lower values in summer and maximum concentrations in winter due to the outflow of mineral dust from North Africa [12]. Within the framework of CV-DUST (Atmospheric aerosol in Cape Verde region: seasonal evaluation of composition, sources and transport) research project [13], in Praia region (south of Santiago island), it was observed that, in 2011, the daily concentrations exceeded the air quality guidelines proposed by the World Health Organization [14] for PM2.5 and PM10 in 20 and 30% of the days. Moreover, annual PM2.5 and PM10 values were also above guidelines. Sampling and air quality monitoring: During the eruption event, for each sampling location (Fig. 1c), outdoor dust samples were collected from the rooftops of private houses using new plastic brooms and shovels. Each sample was georeferenced and preserved in polyethylene bags until laboratory processing. In the laboratory, samples were dried (< 40 ºC), homogenized, sieved (< 2 mm) and partially pulverized to < 170 µm in a mechanical agate mill for chemical analysis. The thoracic fraction of particulate matter (PM10) was collected by low volume sampling (2 L/min) using a Deluxe pump (model 224-PCMTX8) from SKC (Dorset, UK) connected to a size-selective head, also from SKC, equipped with 37 mm quartz filters. The pump was powered by a battery and included a run time programmable unit, a constant pressure controller and a low flow adaptor. Continuous measurements of temperature (T), relative humidity (RH), carbon dioxide (CO2), carbon monoxide (CO) and total volatile organic compounds (TVOCs) with a 5-min resolution were performed with an IQ-610 Air Quality Probe (Gray Wolf® monitor). A DustTrak DRX 8533 aerosol real time monitor from TSI (also with 5-min resolution) was used for simultaneous monitoring of PM1, PM2.5, PM4, PM10 and total suspended particulate matter (TSP). Additionally, two fresh lava samples were collected in the 2 directions of the lava flow, N and S (Fig. 1c). During the sampling campaign, informal dialogs were kept with local population, asking about habits and health outcomes before and during the eruption. Respiratory problems, nose and throat irritation with severe coughing and breath difficulty, eye irritation and skin allergies were reported. Also, nervousness and extreme anxiety episodes were communicated by the population as a consequence of the eruption. Granulometric analysis: Outdoor dust < 2 mm fraction was subject to wet sieving to quantify and analyze separately different size fractions: [-∞, 63[, [125, 63[, [250, 125[, [500, 250[, [500, 1000[ and [1000, 2000[ µm. The granulometric distribution of the dust fraction < 106 µm was determined at the University of Aveiro, Portugal, using an X-ray grain size analyzer (Micromeritics® SediGraph III Plus). This technique is based on the sedimentation theory (Stokes' law) and the absorption of X-radiation (Beer-Lambert law). Chemical analysis: Outdoor dust and lava samples were submitted to multielement analysis at the ACME Analytical Laboratories, which is an ISO 9002 Accredited Lab (Vancouver, Canada). A sample of (b) (a) 0.5 g was leached in hot (95 °C) aqua regia (HCl-HNO3-H2O), and concentrations were determined by Inductively Coupled Plasma Mass Spectrometry (ICP-MS) for Al, As, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, P, Pb, Si, Ti, Zn (detection limits of Cd < 0.1 mg kg −1 ; Co, Pb < 0.15 mg kg −1 ; As, Cr, Cu, Ni < 1 mg kg −1 ; Zn < 1.5 mg kg −1 ; Mn < 2 mg kg −1 ; Fe, Mg < 5 mg kg −1 ; P < 10 mg kg −1 ; Al, Ca, K, Na, Si, Ti < 20 mg kg −1 ). XRD analysis: Mineralogy was determined by powder XRD (LNEG, Portugal) using a Phillips/Panalytical powder diffractometer, model X'Pert-Pro MPD, equipped with an automatic slit. A Cu-X-ray tube was operated at 50 kV and 30 mA. Data were collected from 2 to 70º 2θ with a step size of 1º and a counting interval of 0.02 seconds. Electron microprobe analysis: The mineralogical characteristics were determined using backscattered electron imaging (BSE) in an electron microprobe JEOL 8500-F (LNEG, Portugal). The operating conditions obtained for the backscattered electron imaging were 15 kV excitation voltage and 30 nA beam current. Morphology and semi-quantitative chemical analysis: PM10 sampled on quartz filters and outdoor dust collected on rooftops were analyzed at UA with a Hitachi S-4100 scanning electron microscope (SEM) coupled to a Bruker Quantax 400 Energy Dispersive Spectrometer (EDS) to assess the morphological, granulometric and semi-quantitative chemical properties of the particles. The identification of inorganic insoluble particles was performed using a mix of protocols for each particle [15]. Precision and accuracy of analyses and digestion procedures were monitored using internal standards, certified reference material and quality control blanks. Results were within the 95% confidence limits. The relative standard deviation was between 5% and 10%. Modeling mineral dust emissions and transport: The CHIMERE chemistry-transport model [16], forced by 3-D meteorological fields simulated by the WRF model, was used in this study to model the mineral dust cycle over North Africa. This model was previously used over this geographical region with reasonable results since it was able to correctly reproduce the atmospheric dust load and surface concentrations from the daily to the seasonal timescales [17]. The model applied includes only mineral dust and biogenic emissions, i.e., only non-anthropogenic emissions, excluding the volcano. It considers processes that drive the main phases of the dust cycle: saltation and sandblasting for emissions calculations, horizontal advection, and vertical transport, including advection and mixing. Two nested domains were considered (CVd1 and CVd2; Fig. 1a) covering the main dust source areas in North Africa, with horizontal resolutions of 0.5° and 0.175°, respectively. Eight vertical layers were used extending from the surface up to 500 hPa. The simulations were performed in time slices of 24 consecutive hours, each new period being initialized by the previous one, being the concentrations continuous in time. Spin-up runs, relative to the 10 days prior to the period of interest, were used to initialize the model. The GOCART global model climatology [18] was used to set the boundary conditions for the larger domain simulation. Enrichment index (Ei): Ei was calculated by averaging the ratios of elemental concentrations to the lava elemental mean concentration and divided by the number of elements set to assess enrichments in dust samples. An Ei > 1.0 indicates that, on average, the elemental concentration is above the standard level, and that anthropogenic input may have contributed to elemental enrichment [19]. Enrichment Factor (EF): EF is a useful tool to determine the degree of anthropogenic enrichment. EF is calculated by EF = (element/Fe)sample / (element/Fe)lava. Iron was selected as reference element for geochemical normalization once its natural concentration tends to be uniform [20]. EF classes are: EF < 1 no enrichment, EF < 3 minor enrichment, 3 < EF < 5 moderate enrichment, 5 < EF < 10 moderately severe enrichment, 10 < EF < 25 severe enrichment, 25 < EF < 50 very severe enrichment, and EF > 50 extremely severe enrichment.
Potential Ecological Risk Index (PERI): PERI is defined as the sum of risk factors, defining a potential ecological risk of an element in each sample: PERIi is the Potential Ecological Risk Index for each sample (i), EFi the monomial potential ecological risk factor, CFi the contamination factor, and TF the heavy metal toxic-response factor for each element [21]. Reference values of igneous rock types, soil, freshwater, land plants and land animals were as proposed by Bowen [24]. The PERI classification is as follows: PERI < 150 Low, 150 ≤ PERI < 300 Moderate, 300 ≤ PERI < 600 Considerable, and 600 ≤ PERI Very High Ecological Risk.
Non-carcinogenic and carcinogenic risk assessment: Human health risks were calculated taking into consideration that residents, both children and adults, are directly exposed to dust through three main pathways (a) ingestion, (b) inhalation and (c) dermal absorption. PM10 (particles < 10 µm) are more relevant in inhalation processes, nevertheless, coarser sizes are decomposed in the gastrointestinal track. The carcinogenic and non-carcinogenic side effects for each element were computed individually, considering reference toxicity levels for each variable, as extensively described in RAIS [25]. For each selected potentially toxic element (As, Cd, Cr, Co, Cu, Pb, Mn, and Zn) and pathway, the non-cancer toxic risk was estimated by computing the Hazard Quotient (HQ) for systemic toxicity (i.e., non-carcinogenic risk). If HQ > 1, non-carcinogenic effects might occur once exposure concentration exceeds the reference dose (RfD). The cumulative non-carcinogenic hazard index (HI) corresponds to the sum of HQ for each pathway and/or variable. Similarly, HI > 1 indicates that non-carcinogenic effects might occur. Carcinogenic risk, or the probability of an individual to develop any type of cancer over a lifetime as a result of exposure to a potential carcinogen, was estimated by the sum of total cancer risk for the three exposure routes. A risk > 1.00E−06 is classified as the carcinogenic target risk, while values > 1.00E−04 are considered unacceptable [25].    The model suggests that the source regions that mostly affect the surface Cape Verdean air quality are located over Mauritania (Sahara Desert). In Fig. 4 it is possible to comprehend, with more detail, the evolution of surface concentrations within the inner domain (CVd2), during the first identified dust storm. The emission of dust in the Mauritania hotspots was intensified between December 9 and 11. In this period, dust was transported westwards with maximum surface PM10 concentrations being reached around December 12. Aerosol optical thickness (AOD) values (Fig. 5b), registered in the AERONET site of Capo Verde in Sal Island during the same periods, highlight the extent of long-range transport of dust from the African continent.

PM, CO2, CO and TVOCs
Regardless sampling location, both PM10 and PM2.5 concentrations largely exceeded the 24-h daily mean stipulated by the European Air Quality Directive 2008/50/EC and recommended by the World Health Organization [14] of 50 µg/m 3 . Highest concentrations were registered in Covatina, directly impacted by one of the two active lava flows. Lowest concentrations, but still above 100 µg/m 3 , were measured outside the eruption area, on the north-east to the south-west flanks of the volcano (Ponta Verde, Monte Grande and Cova Figueira). In the three monitoring sites closest to the eruption (Monte Beco, Chã and Covatina), PM10 accounted for 65 to 69% of total suspended particulate (TSP). This means that almost 70% of the inhaled particles can pass beyond the larynx and ciliated airways. The percentage of thoracic particles increased to 92 to 96% at other locations, suggesting that small villages and towns within the caldera were strongly impacted by coarse ashes made of tiny fragments of jagged rock, minerals, and volcanic glass, which tend to settle out first. Finer particles remain in the plume and stay airborne while being transported over long distance. The alveolar size fraction encompassed between 51 and 79% of the thoracic particulate mass. The lowest PM2.5/PM10 mean ratio was registered in Covatina, near the caldera headwall, whereas the highest value was monitored in Ponta Verde, a settlement in the northwestern part of the island outside the crater rim. All the locations outside the Bordeira scarp presented PM1/PM2.5 ratios in the 0.92-0.94 range. PM2.5 comprised higher proportions of ultrafine particles (97-98%) in the vicinities of the volcano. In São Filipe, the island capital, a Cape Verdean aerosol monitor station (15 min. resolution) was installed between November 28 th 2014 and February 15 th 2015, the eruption time-lapse. Although some problems with equipment and energy (days 30 November for PM10, 28 November to 6 December for PM2.5 and 15 to 19 December for both PM2.5 and PM10), data was collected. Figure 6 shows that the mean PM10 24-hour concentration guideline [14] was largely exceeded. Maximum daily mean concentration was registered in December 13 th (383 µg/m 3  µg/m 3 (24-h mean). A PM2.5 maximum of 107 µg/m 3 was measured in January 7 th (Fig. 7). The maximum concentration peaked at 123 µg/m 3 in January 7 th 2015 between 2:30 and 5:50 am. Concentrations of PM10 and PM2.5 above the guidelines may represent a risk to the human health and are consistent with the volcanic eruption time-lapse and the Sahara Desert dust intrusions (section 3.1).  TVOCs include non-methane hydrocarbons (NMHC) and oxygenated NMHC. Considerable discomfort and headaches are likely if levels fall in the range of 1.2-10 ppm [26]. Only Monte Beco, and sporadically Achada Furna, reached levels close to the lower limit of the worrying range (Fig. 8). There are no enforceable limits for TVOC concentrations, i.e. there is no legal threshold. Much higher VOC concentrations, varying between 2.89 and 35.3 ppm, have been reported by Varshney and Padhy [27] for 13 sites in Delhi, India. However, much lower levels, in the ranges 7-173 ppb and 10-285 ppb in the summer and fall, respectively, have been registered in Los Angeles, California [28]. Concentrations are highly variable, depending on the emission sources, dispersion conditions and atmospheric stability. It has been shown that VOCs from fumaroles mainly consist of C2-C5 alkanes and relatively high concentrations of aromatics (benzene and toluene) and C2-C3 alkenes (mainly propene and isobutene) [29]. The main mechanism for the production of alkanes is likely related to pyrolysis of organic-matter bearing sediments that interact with the ascending magmatic fluids. Alkanes are then converted to alkene and aromatic compounds via catalytic reactions (dehydrogenation and dehydroaromatisation, respectively). However, a biogenic origin for the light hydrocarbons cannot be ruled out [30]. It is expected that sulfur and halogen-bearing gaseous compounds, not measured as TVOCs, are dominant in the volcanic plume. Moreover, it should be taken into account that the volcanic plume is ejected at high altitude. Emissions from lava and the fraction of the volcanic plume that reaches the ground suffer dilution by strong winds and changes of their direction. Thus, VOCs may originate, at great extent, from other local sources, other than the volcano. These include natural sources, such as vegetation, and anthropogenic sources, which include emissions from biomass burning, solvent usage and road transport.
The average CO2 concentrations (Fig. 8) ranged from 445 ppm at Monte Beco (1908 m asl) to 570 ppm at Campanas de Baixo (453 m asl). The highest levels were not registered near the volcano, but rather in more populated villages. CO2 concentrations around 415 ppm have recently been recorded at the remote observatory near the summit of Mauna Loa, at an altitude of 3400 m asl, which is well situated to measure air masses that are representative of very large areas. CO2 mixing ratios have been found to be higher in many urban centers worldwide compared to adjacent rural locations, phenomenon known as an "urban CO2 dome" [31]. These higher mixing ratios are due in part to local traffic emissions. For example, Widory and Javoy [32] measured CO2 concentrations in air samples collected from various locations in Paris, its suburbs and the surrounding open countryside. These data sets revealed that near-surface atmospheric CO2 concentrations throughout the country outside Paris averaged 415 ppm, while values in the city sometimes reached as high as 950 ppm. The CO levels were always close to the detection limit. Due to ejection at high altitude and atmospheric dilution, concentrations of gaseous pollutants seem less affected by the eruption than particles. Ash and gases can be transported either aggregated or separated in the atmosphere. Vertical separation occurs due to the eruption style or by different sedimentation velocity of ash and gases, and horizontal separation due to wind shear [33].

Ambient PM10 and outdoor dust samples from rooftops
The ICP-MS chemical analysis of outdoor rooftop dust (< 2 mm fraction) and fresh lava samples revealed similar median elemental concentration profiles (Fig. 10). Nevertheless, dust samples from individual locations potentially more impacted by Saharan dust intrusions (NE region) presented higher contents of Fe, Al, Si and Ca than lava. These elements are representative of quartz and other oxides (e.g., FeO2), carbonates (e.g., CaCO3) and aluminosilicates (e.g., feldspar, clay minerals), characteristic of the Sahara Desert [37]. Minimum   The Total Granulometric relative Distribution (TRD, <2 mm) of outdoor dust samples suggested a predominance of particles with diameter < 250 µm (~56 %), followed by the size fraction > 125 and < 250 µm (~30 %). In two locations, other fractions prevailed: (a) Corvo, with a dominant fraction in the size range 250 -500 µm (~55 %); and (b) Cisterno, in the interior of the island, with a prevailing fraction between 63 -125 µm (~55 %). Among the collected samples, Mosteiros was the village whose dust presented the largest representation of the granulometric fraction < 63 µm (~11%). According to Li et al. [38], the fine fractions (< 150 µm) are the ones that most adhere to human skin, especially children with hand-to-mouth behaviors, being more likely to be ingested and dissolved, accessing the gastric system. Inhalable particles < 10 µm (PM10; Fig. 10) represented 33 to 93 % of the 63 µm fraction, also suggesting an external PM source. PM10-bound constituents and morphology can cause breathing problems and irritation to the respiratory system, while PM4 can reach deeper regions of the respiratory track. In turn, PM2.5 can reach alveoli and induce asthma and even heart attacks, being especially disturbing in children and people with pre-existing health conditions [39]. To humans, fresh volcanic ashes might represent a higher hazard than mineral dust, due to morphology and chemical coatings. Sharp volcanic minerals were identified in outdoor dust by SEM analysis, together with less sharpen Fe rich particles, with Sahara Desert as possible source (Fig. 11). In Monte Beco several CaF2 particles were found. The PM10 samples collected on quartz filters (Fig. 12) revealed the presence of sea salt [NaCl]. In S. Filipe, the capital of the island and with more traffic, soot particles were also identified. Minerals identified by XRD analysis in lava and outdoor dust samples, in different size fractions, are summarized in Table 1.  Fogo island inhabitants, particularly those living in Chã das Caldeiras, are exposed to air deterioration, especially during eruptions and Sahara dust intrusions. Eyes and respiratory tract irritation were reported, not only during the 2014-2015 volcanic eruption, but also previously. Dental and bone problems on the interviewed inhabitants were described, conceivably related to Finhalation (dusts and gases) and ingestion (hand-to-mouth, food and drinking water). Association between fluorides geochemistry and health is well studied [e.g., 40,41,42]. Fluoride metabolism varies with solubility, structure, reactivity, and release of F − ions. In humans, the main Fabsorption path is the gastrointestinal tract, by inhalation and ingestion (drinking and diet), with 80-90% of consumed F − absorbed within 30 minutes [43]. Nevertheless, the Fcontent varies with individual uptake and excretion. Usually, 45-60% of the ingested Fis excreted in urine, with the rest recirculated into the plasma or deposited into the bones [44]. The island population is strongly dependent on agriculture, livestock and groundwater. Waters for drinking and cooking are obtained by rainwater harvesting, dug wells and deep bore holes. Agriculture products and livestock are exported to other islands of the archipelago. The volcanic expelled products contribute to inhalation and ingestion of dust and gases in excess, but also through consumption of food and water enriched in potentially toxic elements.

Ecological and human health impact
For the calculation of different indexes, mean concentrations of lava samples were used as background values, to understand the external sources of dust enrichment. Two sets of variables were studied: (a) (c) (d) major elements -Al, Ca, Fe, K, Mg, Si, and Ti; and (b) elements potentially linked to anthropogenic sources -As, Cd, Co, Cr, Cu, Mn, Ni, Pb, and Zn. Three size fractions were selected (< 63, 63-125 and 125-250 µm), once particles with diameter < 250 µm are considered to adhere to hands and may be ingested by hand-to-mouth behaviors [45]. The group of major elements, linked to the Fogo volcano geochemical composition, suggests a small contribution from external sources. The Enrichment Index (Ei; Table 2) was slightly over 1, with a maximum of 1.5 for the dust fraction sized 125 -250 µm of Ponta Verde. These results are confirmed by the Contamination Degree (CD), Pollution Load Index (PLI) and Potential Ecological Risk Index (PERI), which enabled to classify all locations with a low-grade enrichment, although Ponta Verde presented higher results. The Geoccumulation Index (Igeo), Enrichment Factor (EF) and Contamination Factor (CF) also showed a low external contribution in all samples and fractions, with slightly higher Mg concentrations that in lava samples.   The Enrichment index for a set of elements with a potential link to anthropogenic sources (Table 3) suggest the contribution of an external source to the dust samples, irrespective of the size fractions.   (Table 4) of all size fractions was above the target value of 1.00E−6. However, regardless of the samples, the risk was always < 1.00E−4. Arsenic was the element that most contributed to the risk, accounting for 86.2 to 95.8 % of the total, followed by Pb (1.7 to 9.7 %) and Co (1.1 to 10.6 %). Ingestion was found to be the main exposure route for all dust size fractions, representing 78.5 to 87.3 % of the total risk posed by the three exposure routes. The finest size fraction (< 63 µm) was the one with the highest risk, mostly due to As, whose concentrations accounted for 91.4 to 95.5 % of the total. The lowest total risk value was found in Monte Grande, located in the interior of the island, for the 125 -250 µm size fraction, while the highest was observed in the < 63 µm fraction of Ponta Verde.

Conclusions
Modeling of long-range transport of mineral dust between mid-November 2014 and January 2015 pointed out Mauritania (Sahara Desert) as the main external dust mineral source affecting the Cape Verdean air quality, highlighting the intrusion of dust from continental Africa. PM10 and PM2.5 concentrations largely exceeded the guidelines suggested by the World Health Organization, in line with the volcanic eruption time-lapse and the Sahara Desert dust outbreaks. The levels of Total Volatile Organic Compounds (TVOCs) were below the worrying range. The highest levels of CO2 were recorded in more populated villages and not next to the volcanic eruption craters. The chemical analysis of lava samples revealed a SiO2 content indicative of basaltic type with high melt temperature, low viscosity and gas content. This volcanic rock is tephritic to basanitic, with high potassium content. Several minerals were identified, such as titanian augite with ilmenite, basaltic hornblendes, pyrrhotites, apatites, pyroxenes, basaltic hornblendes and hematites. Outdoor dust and fresh lava samples revealed similar median elemental concentrations, with high contents of Fe, Al, Si and Ca. The granulometric distribution of outdoor dust was dominated by particles with diameter < 250 µm, followed by the size fractions > 125 and < 250 µm. The finest particle sizes (< 250 µm) are the ones that most adhere to human skin. The PM10 inhalable fraction represented the highest percentage of the dust sizes < 63 µm, factor that can potentiate breathing problems and irritation to the respiratory tract. Fogo inhabitants exposed to air deterioration reported irritation of the respiratory tract and eyes. Dental and bone problems were also described, possibly related to inhalation of F -, present either in dust or in gaseous form, and ingestion (hand-to-mouth, food and drinking water). The island population is strongly dependent on agriculture, livestock and groundwater. The volcanic expelled products likely contributed to inhalation and ingestion of dust and gaseous pollutants in excess, but also through consumption of food and water enriched in potentially toxic elements. According to the Enrichment Index (Ei), Contamination Degree (CD), Pollution Load Index (PLI) and Potential Ecological Risk Index (PERI), calculated based on the content of Al, Ca, Fe, K, Mg, Si, and Ti, all locations were classified with a low-grade enrichment. The Geoccumulation Index (Igeo), Enrichment Factor (EF) and Contamination Factor (CF) showed a low external contribution to all samples and size fractions. The Enrichment Index for elements with a potential link to anthropogenic sources (As, Cd, Co, Cr, Cu, Mn, Ni, Pb, and Zn) suggested the input of external sources to all size fractions. The Geoaccumulation Index pointed out a small external contribution to all size fractions and elements, with values indicating that dust samples were moderately to heavily enriched by these metal(loid)s. In addition, the Enrichment Factor suggested a moderate enrichment in the size fraction < 63 µm. The same results were obtained with the Contamination Factor, which pointed out to high contamination of As, Ni and Pb, and very high contamination of Cd. The Pollution Load Index presented values above 1 in all samples, categorizing dust as polluted. Higher PLI values were found in the size fraction < 63 µm. The Potential Ecological Risk Index also enabled to include all samples < 63 µm in the "extreme risk" group. The Non-carcinogenic Hazard Quotient and the Hazard Index from the exposure of children to elements through ingestion were above 1, suggesting that non-carcinogenic health outcomes might occur, since concentrations were higher than the reference doses. The Carcinogenic Risk associated with all dust size fractions was above the target risk of 1.00E-06. Arsenic was the element that most contributed to the global risk, followed by Pb and Co. Ingestion was found to be the main exposure route of dust-bound metals in all size-segregated fractions. The size fraction < 63 µm was the one representing a higher risk, mostly due to the concentration of As. It is known that the total concentration of potentially toxic elements can overestimate the risk for humans. To understand the bioaccessible fraction (BAF) in lungs, gastric and gastrointestinal phases of the outdoor dust, the Artificial Lysosomal Fluid (ALF) and Unified Bioaccessibility Method (UBM) assays are being done. Also, the edible plants most consumed in the island are being analyzed and BAF being estimated.