International Journal of Environmental Research and Public Health Article Heavy Metals of Santiago Island (Cape Verde) Alluvial Deposits: Baseline Value Maps and Human Health Risk Assessment Marina M. S. Cabral Pinto * and Eduardo A. Ferreira da Silva Department of Geosciences, GeoBioTec Research Centre, University of Aveiro, 3810-193 Aveiro, Portugal; [email protected] * Correspondence: [email protected]; Tel.: +35-196-433-2189 Received: 16 November 2018; Accepted: 17 December 2018; Published: 20 December 2018 Abstract: The chemical composition of surface geological materials may cause metabolic changes and promote endemic diseases (e.g., oncological, gastrointestinal, neurological or cardiovascular diseases). The results of a geochemical survey is presented following the guidelines proposed by the International Project IGCP 259 performed on the alluvium of Santiago Island (Cape Verde) and focused on public health issues. Geochemical mapping is the base knowledge needed to determine critical contents of potential toxic elements and the potentially harmful regions in the planet. This work presents maps of baseline values of potentially toxic elements (As, Cd, Co, Cr, Cu, Hg, Mn, Ni, Pb, V, and Zn) in Santiago alluvium and the assessment of their human health risks. According to the results the Cd, Co, Cr, Ni and V baseline values are above the Canadian guidelines for stream sediments (for any proposal use) and for soils (for agricultural and residential proposal uses) and also above the target values of Dutch guidelines. Hazard indexes (HI) were calculated for children and adults. For children (HI) are higher than 1 for Co, Cr and Mn, indicating potential non-carcinogenic risk. For the other elements and for adults there is no potential non-carcinogenic risk. Cancer risk was calculated for Cd, Cr and Ni exposures, for adults and children, and the results are only slightly higher than the carcinogenic target risk of 1 × 10−6 for adults exposed to Cr by inhalation. However, these results may be underestimated because alluvial contaminants may be indirectly ingested by groundwater and by crop and vegetables consumption. Keywords: potentially harmful elements; alluvial deposits; baseline values (BV), human health risk assessment; Santiago Island; Cape Verde 1. Introduction Geochemical surveys were developed in the last century [1–6] mainly as a means of geochemical prospecting of ore deposits [7,8]. Geochemical databases have been carried out in many regions [9–13], countries [7,14–18], multinational regions [19] and, more recently, continents [20–22], at various scales, ranging from high to very low density (e.g., >1 sample/km2 to 1 sample/10,000 km2, respectively). Geochemical surveys application has expanded to also encompass environmental monitoring, land-use decision support, natural resource management, and medical geology [7,23]. A diversity of sampling media have been targeted by geochemical surveys over time, which includes rock, sediment, soil, alluvium, ground water, surface water, dust, and vegetation [22]. In order to understand the transference, mobility, residence and biogeochemical processes of chemical elements few recent surveys have even targeted several media [24,25]. Geochemical surveys are especially important in developing countries like Cape Verde, where intervention limits for near-surface environment are not yet established. Considering this lack of Int. J. Environ. Res. Public Health 2019, 16, 2; doi:10.3390/ijerph16010002 www.mdpi.com/journal/ijerph Int. J. Environ. Res. Public Health 2019, 16, 2 2 of 12 Int. J. Environ. Res. Public Health 2018, 15, x 2 of 13 2 informationinformation aa high-densityhigh-density (aprox.(aprox. 1/3 km km2) )geochemical geochemical survey survey in in Santiago Santiago Island, Island, Cape Verde archipelago, following the guidelines proposed by the International Geological Correlation Program (IGCP)(IGCP) ProjectProject 259259 [ 1[1],], was was conducted conducted in in order order to to compile compile the the first first environmental environmental geochemical geochemical atlas atlas for thatfor that region. region. This This paper paper presents presents the baselinethe baseline value valu (BV)e (BV) Santiago Santiago Island Island maps maps of some of some potentially potentially toxic elementstoxic elements in alluvial in alluvial deposits. deposits Alluvial. Alluvial deposits deposits are important are important natural natural resources, resources, in particular in particular in areas in ofareas limited of limited rainfall rainfall when weatheringwhen weathering profiles profiles are very are thin very or non-existent, thin or non-existent, being the being most adequatethe most placeadequate for localplace agriculture. for local agriculture. Knowledge Knowledge of the geochemistry of the geochemistry of near-surface of near-surface environment environment is essential is asessential it contributes as it contributes to the improvement to the improvement of the nutritional of the nutritional status of status the population of the population [26,27] and [26,27] helps and to understandhelps to understand the causes the ofcauses some of endemic some endemic diseases dise whichases which can persist can persist through thro outugh the out life the course life course due todue heavy to heavy metal metal exposure, exposure, such such as As,as As, Cr, Cr, Al, Al, Mn, Mn, Pb, Pb, Hg, Hg, Cu, Cu, Co, Co, etc. etc. Some Some elements elements cancan naturallynaturally accumulate onon alluvialalluvial depositsdeposits in in concentrations concentrations that that are are toxic toxic to to the the plant, plant, to to the the animal animal feeding feeding on on it andit and to to humans. humans. The The dispersion dispersion of of these these elements elements in in the the environment environmentis ismainly mainly carriedcarried outout byby water and air,air, which which are are vehicles vehicles linking linking the the inorganic inorganic environment environment to life. to Thelife.inhabitants The inhabitants of Santiago of Santiago Island dependIsland depend on groundwater on groundwater for consumption for consumption and for an agricultured for agriculture and the and flux the water-vegetables-human flux water-vegetables- alsohuman deserve also evaluation,deserve evaluation, because endemicbecause diseasesendemic candiseases be controlled can be controlled with proper with measures, proper ifmeasures, its cause isif wellits cause constrained. is well constrained. Some of these Some potentially of these toxicpotentially elements toxic (PTEs) elements can lead (PTEs) to long-term can lead to carcinogenic long-term andcarcinogenic non-carcinogenic and non-carcinogenic health risks andhealth early risks environmental and early environmental and occupational and occupational exposure to exposure PTEs in differentto PTEs in locales different around locales the worldaround has the been world related has been to oncological related to diseaseoncological and mortality,disease and neurological mortality, orneurological cardiovascular or cardiovascular diseases [28– diseases40], etc. [28–40], The widespread etc. The widespread existence of existence PTEs has of become PTEs has one become of the mostone of serious the most environmental serious environmental concerns around concerns the globearound and the the globe development and the development of efficient and of selectiveefficient chemicaland selective sensors chemical to detect sensors such to potentially detect such toxic potentially elements toxic have elements been a priority have been [41– a48 priority]. [41–48]. This study had the following objectives: (1) present a geochemistry survey of alluvial deposits for thethe studiedstudied metalsmetals andand metalloid;metalloid; (2)(2) definedefine thethe baselinebaseline valuesvalues onon SantiagoSantiago Island;Island; (3)(3) evaluateevaluate thethe environmental risks; and (4) (4) evaluate evaluate the the human human heal healthth risk, risk, in in areas areas naturally naturally enriched enriched with with metals. metals. 2. Settings of the Archipelago of Cape Verde andand SantiagoSantiago IslandIsland The archipelago of of Cape Cape Verde Verde (composed (composed by by 10 10islands—Figure islands—Figure 1) is1 )located is located at the at eastern the eastern shore shoreof the ofAtlantic the Atlantic Ocean, Ocean, 500 km 500 west km from west Senegal’s from Senegal’s Cape Verde, Cape Verde,off the western off the western shore of shore Africa of (Figure Africa (Figure1). Santiago1). Santiago island (991 island km (9912), located km 2), in located the southern in the part southern of the part archipelago, of the archipelago, is the biggest is the island biggest and islandwith half and of with the country´s half of the population country´s population [7]. [7]. Figure 1.1. The Cape Verde ArchipelagoArchipelago andand itsits locationlocation onon Senegal’sSenegal’s westernwestern coast,coast, adaptedadapted from [[7]7] and geologicalgeological cartographycartography ofof thethe islandisland ofof Santiago,Santiago, CapeCape Verde,Verde,adapted adaptedfrom from [ 49[49].]. Santiago Island has a semi-aridsemi-arid climate, with strong winds during the dry season, and a meanmean annual precipitation of of 321 321 mm, mm, mainly mainly due due to to torrential torrential rains, rains, during during the the wet wet season season [50]. [50 It]. has It has215 Int. J. Environ. Res. Public Health 2019, 16, 2 3 of 12 215 km2 of arable area and estimated hydric resources of 56.6 × 106 m3/year