Environ Sci Pollut Res DOI 10.1007/s11356-017-8810-2

RESEARCH ARTICLE

Polycyclic aromatic hydrocarbons and polychlorinated biphenyls in soils of Mayabeque, Cuba Dayana Sosa 1 & Isabel Hilber 2 & Roberto Faure 1 & Nora Bartolomé 2,3 & Osvaldo Fonseca 1 & Armin Keller 4 & Peter Schwab 4 & Arturo Escobar 1 & Thomas D. Bucheli 2

Received: 8 December 2016 / Accepted: 13 March 2017 # Springer-Verlag Berlin Heidelberg 2017

Abstract Cuba is a country in transition with a considerable potential for economic growth. Soils are recipients and integrators of chemical pollution, a frequent negative side effect of increasing industrial activities. Therefore, we established a soil monitoring network to monitor polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) in soils of Mayabeque, a Cuban province southeast of Havana. Concentrations of the sum of the 16 US EPA PAHs and of the seven IRMM PCBs in soils from 39 locations ranged from 20 to 106 μg kg−1 and from 1.1 to 7.6 μg kg−1, respectively. While such concentrations can be considered as low overall, they were in several cases correlated with the distance of sampling sites to presumed major emission sources, with some of the concomitantly investigated source diagnostic PAH ratios, and with black carbon content. The presented data adds to the limited information on soil pollution in the Caribbean region Responsible editor: Philippe Garrigues Electronic supplementary material The online version of this article (doi:10.1007/s11356-017-8810-2) contains supplementary material, which is available to authorized users. * Arturo Escobar [email protected] * Thomas D. Bucheli [email protected] 1

Centro Nacional de Sanidad Agropecuaria (CENSA), Apartado 10, CP 32700 San José de las Lajas, Mayabeque, Cuba

2

Environmental Analytics, Agroscope, Reckenholzstrasse 191, 8046 Zurich, Switzerland

3

Department of Environmental System Science, ETH Zurich, 8093 Zurich, Switzerland

4

Swiss National Soil Monitoring Network, Agroscope, Reckenholzstrasse 191, 8046 Zurich, Switzerland

and serves as a reference time point before the onset of a possible further industrial development in Cuba. It also forms the basis to set up and adapt national environmental standards. Keywords Soil pollution . Persistent organic pollutants . Exposure assessment . Stockholm protocol . Country in transition . GC-MS . Soxhlet extraction

Introduction Global emissions of polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) due to anthropogenic activities or natural processes are considerable. The total global atmospheric emission of the sum of the 16 US EPA PAHs (PAH16) in 2007 was 504 Gg per year, with residential/commercial biomass burning, open-field biomass burning (agricultural waste burning, deforestation, and wildfire), and petroleum consumption by on-road motor vehicles as the major sources (Shen et al. 2013). Total global PCB production from 1930 to 1993 amounts to an estimated 1,325,810 t, with Cuban estimates around 130 t (Abo Balanza 2005), and these compounds are predicted to be emitted from primary or secondary sources for decades to come (Breivik et al. 2007). Environmental pollution with these semi-volatile and persistent organic pollutants (POPs) by diffuse or point sources has been the inevitable consequence. Soil acts as a major environmental recipient matrix of POPs, and plants and crop may receive such pollutants via atmospheric deposition (e.g., Bohme et al. 1999) or soil uptake (Fismes et al. 2002; Gao and Zhu 2004; Samsoe-Petersen et al. 2002). Consequently, PAH and PCB concentrations in soils have frequently been reported (e.g., Meijer et al. 2003; Nam et al. 2008b; Wilcke 2000); several countries installed corresponding monitoring networks or conducted more or less extensive monitoring

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campaigns (e.g., Brus et al. 2009; Desaules et al. 2008; Gubler et al. 2015; Holoubek et al. 2009; Maliszewska-Kordybach et al. 2008; Nam et al. 2008b; Rhind et al. 2013; Trapido 1999; Villanneau et al. 2013), and many established regulatory guidance values, which vary widely, though, both in their concentrations and legal terminology (Desaules et al. 2008; Jennings 2012). In the Caribbean countries, such soil monitoring studies for PAHs and PCBs are basically absent, and only a few more recent studies are available for PAHs in Latin America (Barra et al. 2005, 2007; Daly et al. 2007; Ortiz et al. 2012). Concentrations in tropical soils are generally low compared to temperate soils (Wilcke 2000), except when samples are taken in urban areas or close to emission sources (e.g., Ortiz et al. 2012). Cuba, through the National Implementation Plan for the Management of Persistent Organic Pollutants (CITMA 2008) and by ratification, has demonstrated its political will to implement the agreements reached in different international conventions such as the Basel, Rotterdam, and Stockholm that contribute to protecting the health of humans and the environment from damage caused by chemicals. While there are no national regulations on PAHs in soils, which limits the parties’ concern to implement any sustainability program in the exploitation of this resource, for PCBs, there is a national standard that takes in consideration the recommendations made by Canadian Soil Quality Guidelines for the Protection of Environmental and Human Health (CCME 1999; Norma Cubana 2009). Specific studies in different regions of Cuba have reported the presence of POPs in different environmental compartments. Elevated concentrations of the sum of seven Institute for Reference Materials and Measurements (IRMM) PCBs (PCB7) up to 7281 pg m−3 were found in air samples from an urban sampling site in Havana (with nearby commercial ship traffic and petrol refineries) in comparison with other, more background, regions of the Caribbean (Bogdal et al. 2013). Air samples from two oil refineries in Santiago de Cuba and Boca de Jaruco contained PAHs between 10 and 60 μg m−3 (CoraMedina et al. 2011). Total PAHs (PAH16 without naphthalene (NAP) and acenaphthylene (ACY)) in 0.45 μm filtered water samples from Almendares River, Havana, ranged from 836 to 15,811 ng L−1 and were attributed to both petrogenic and combustion sources. With 2784 ng L−1, the geometric mean value of total PAHs was in the same range as for some Chinese rivers, but one to two orders of magnitude higher than for the rivers Seine (France) and Mississippi (USA) (Luis Santana et al. 2015). Polychlorinated biphenyls and organochlorine pesticides (OCPs) in sediments of the Cienfuegos region showed up to 15 ng g−1 of the sum of 11 PCB congeners and up to 13 ng g−1 for OCPs, which are relatively low concentrations compared to other coastal areas (Tolosa et al. 2010). Even lower concentrations close or below detection limits were found in the presumably pristine Gulf of Batabanó (Alonso-Hernandez et al. 2014). Apart from a pesticide and PCB study by Dierksmeier et al. (2002) who used GC-ECD and reported no detects only, to the

best of our knowledge, no data has been published on PAHs and PCBs in Cuban soils. Total organic carbon (TOC) and black carbon (BC) are regarded as key parameters that determine the distribution and availability of POP in the environment (Cornelissen et al. 2005; Koelmans et al. 2006), and correlations between these parameters in soils have repeatedly been reported (e.g., Agarwal and Bucheli 2011a; Liu et al. 2011; Nam et al. 2008a). While organic carbon estimates are provided by the European Soil Data Centre globally, and for Cuba (Hiederer and Köchy 2011), and while organic carbon data exists as part of the soil classification of Cuba (Hernandez Jimenez et al. 2015), actual TOC data seems limited and available only for 22 reference soils from the International Soil Reference and Information Centre (e.g., Chang et al. 1995), as well as from some individual studies from various locations (e.g., Bernal et al. 2015; Chacon Iznaga et al. 2014; Hernández Jiménez et al. 2013; Reyes Rodríguez et al. 2014). However, TOC soil data have not yet been used in relation with POP, and no data at all is available for BC. Mayabeque is a province southeast of Havana (Fig. 1), in which industry and agriculture co-exist at short distances. As such, it is a model province for the whole country and ideally suited to initiate a soil monitoring network in Cuba. It has an area of 3733 km2 and about 381,500 inhabitants in total. The municipality of Santa Cruz del Norte (SC) is most industrialized, with a focus on energy production in the form of electricity (1,520,783 GWh), fossil fuel (1,415,533 t), and gas (874,549 m3). San José de las Lajas (SJ) hosts several secondary sector industries that produce, e.g., wires and cables (31,079 km) or ceramic tiles (195,641 m2). The municipality of Güines (GU) is less industrialized and features, e.g., wood (6557 m3) and charcoal (499 t) production. Jaruco’s (JA) primary industrial activity is textile production (552,000 units). With 113,110 t of vegetables, fruits, meat, and milk, GU presented the largest agricultural production, followed by SJ with 25,340 t, while JA and SC produced less than 10,000 t (all statistical data are provided on an annual basis for 2014 (ONEI 2015b)). The aim of this study was to (i) systematically sample soils of Mayabeque province for the first time, (ii) determine the concentrations of PAH16 and PCB7 therein, (iii) identify possible sources and gradients of pollution, (iv) analyze the results in relation to BC and TOC, and (v) evaluate the gathered data in terms of exposure risks to humans and the environment.

Materials and methods Area under investigation The study was carried out in four municipalities of the Mayabeque province (Fig. 1), with their capital cites SC (23° 09′ 20″ N 81° 55′ 36″ W), JA (23° 02′ 34″ N 82° 00′

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Fig. 1 Area of investigation within the province of Mayabeque, southeast of Havana, Cuba. Soil samples were taken in four different counties: San José de las Lajas (SJ), Santa Cruz del Norte (SC), Jaruco (JA), and Guines (GU). Individual soil sampling sites are marked with a black dot and consecutively numbered (1–39). For a detailed description

of the sites, see Table S1. Presumed major emission sources are marked with a red star. Red capital letters specify emission source types: thermoelectric power plant (A), zeolite production (B), asphalt factory (C), cable industry (D), rum factory (E), paint industry (F), rubber manufactures (G), firebrick production (H), and electrical power transformer station (I)

34″ O), SL (23° 02′ 34″ N 82° 00′ 34″ O), and GU (22° 50′ 51″ N 82° 01′ 25″ O). The area and the number of inhabitants of these municipalities are 379 km2 and 32,576, 258 km2 and 25,000, 593 km2 and 74,186, and 445 km2 and 68,840, respectively. Mayabeque has a humid tropical climate with an annual temperature between 24 and 26 °C and an annual rainfall between 1291 and 1504 mm (Climate 2016; ONEI 2015a). The soil types in SC are dominated by Sialitic Humic Rendzina, subtype red and gray Brown Rendzina (Lopez-Kramer et al. 2012), whereas carbonated brown and ferralitic red soils prevail in the other municipalities (Hernández Jiménez et al. 2013).

cm depth, including the humus layer). Of resulting 100 individual cores, four bulked soil samples were prepared, each consisting of 25 single cores, put in a polyethylene bag, and transported in a cool box to the laboratory. There, the samples were put in paper bags and dried at 40 °C. Afterwards, they were crushed and sieved through a 2-mm mesh and stored in polyethylene bottles at 20–25 °C room temperature. After extended manual shaking, an aliquot of 100 g was gathered and shipped to Agroscope for analysis.

Soil sampling and sample pretreatment Soil samples were collected between January and April 2014 in 39 different sites of the municipalities abovementioned. The main criteria for site selection were that the locations represented a certain gradient of human activities from high to low and that different soil types and land uses were considered. The exact location of the individual sampling sites is indicated in Fig. 1, and further ancillary information is given in Table S1. The soil sampling followed the protocol of the Swiss Soil Monitoring Network (NABO) and is described in detail in Desaules et al. (2008) and Gubler et al. (2015). Briefly, in an area of 10 by 10 m, one subsample was taken for each square meter with a steel gouge auger (3 cm inside diameter, 0–20-

Analysis of PAHs and PCBs The soil samples were analyzed by the Cuban team in the laboratory at Agroscope for PAH16 (i.e., naphthalene (NAP), acenaphthylene (ANY), acenaphthene (ANA), fluorene (FLU), phenanthrene (PHE), anthracene (ANT), fluoranthene (FLT), pyrene (PYR), benzo[a]anthracene (BaA), chrysene (CHR), benzo[b]fluoranthene (BbF), benzo[k]fluoranthene (BkF), benzo[a]pyrene (BaP), indeno[1,2,3-cd]pyrene (IPY), dibenz[a,h]anthracene (DBA), and benzo[ghi]perylene (BPE)) and PCB7 (i.e., #28, #52, #101, #118, #138, #153, #180) as described in detail in earlier papers (Brändli et al. 2006; Bucheli et al. 2004; Desaules et al. 2008; Gubler et al. 2015). Briefly, samples (10 g) were Soxhlet-extracted for 36 h with hexane. Extracts were concentrated to a volume of 1–2 mL with a Syncore Analyst (Büchi Labortechnik AG, Flawil, Switzerland). The concentrated extracts were split in two

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fractions for separate cleanup of PAHs and PCBs. For PAHs, they were cleaned by N,N-dimethylformamide–MilliQ water (9:1, v/v) liquid–liquid partitioning and over water-deactivated silica gel. The PCB aliquots were cleaned over sodium sulfate and deactivated (10% Milli-Q water), potassium hydroxide-impregnated, and sulfuric acid-impregnated silica gel. Indeno[1,2,3cd]fluoranthene (for PAHs) and 1,2,3,4-tetrachloronaphthalene (for PCBs) served as recovery standards and were added to the final extracts immediately before analysis. PAHs and PCBs were separated and detected with GC-MS and quantified using the internal standard method and isotope-labeled extraction standards (i.e., 16 deuterated PAHs, and seven 13C12-labeled PCBs) for each of the target analytes. Thereby, the concentrations in the calibration solutions ranged from 7.5 to 2500 pg μL−1 (corresponding to approximately 0.75 to 250 μg kg−1 soil) and from 5 to 250 pg μL−1 (corresponding to approximately 0.5 to 25 μg kg−1 soil) for individual PAHs and PCBs, respectively. Calibration curves were linear over these concentration ranges. The spike levels of the individual isotope-labeled extraction standards were 20 and 5 μg kg−1 soil for PAHs and PCBs, respectively. For details about the instrumental conditions, we refer to the earlier published literature (Brändli et al. 2006; Bucheli et al. 2004). Additional molecular markers (i.e., coronene (COR), 4-Hcyclopenta[def]phenanthrene (cPHE), cyclopenta[cd]pyrene (cPYR), perylene (PER), and retene (RET)), as well as characteristic ratios of methylphenanthrenes and anthracenes ((mPHE&ANT)/PHE), methylfluoranthenes and pyrenes ((mFLT&PYR)/PYR), and 1,7-dimethylphenanthrene to 1,7dimethylphenanthrene and 2,6-dimethylphenanthrene (1,7-/ (1,7&2,6-)dmPHE), were quantified as described elsewhere (Brändli et al. 2008; Bucheli et al. 2004). Quality control The method detection (MDL) and quantification (MQL) limits of individual PAHs and PCBs were determined by three and ten times the signal over the noise of soil extract chromatograms, respectively, and the corresponding quantified concentrations. They were obtained as median values from 3 to 12 different soil samples (number of replicates vary because of frequent to occasional no detects of some individual analytes). The MDL and MQL of individual PAHs were between 0.01 and 0.68 μg kg−1 and 0.02 and 2.27 μg kg−1, respectively, while for individual PCBs, they ranged from 0.03 to 0.11 μg kg −1 and 0.11 to 0.37 μg kg −1 , respectively (Table S2). Concentrations above MDL but below MQL are highlighted in Tables S3 and S6 but were kept and used as such for further data interpretation. Average extraction standard recoveries of the 16 deuterated PAHs and the seven 13 C12-labeled PCBs ranged from 11 to 43% and from 50 to 91%, respectively (Table S2). Low absolute recoveries of light PAHs in particular were reported earlier already, but such losses were effectively compensated by the use of deuterated

analogs, as indicated by relative recoveries of added native PAHs above 90% (Bucheli et al. 2004). Internal quality control was based on a well-characterized control soil sample of the NABO (KB6), which was repeatedly analyzed together with the Cuban soil samples, and of a blank sample co-analyzed in each series of 10–12 samples. Average blank concentrations were below MQL for all PAHs except for NAP and PHE. These compounds showed an average blank concentration of 0.3 and 0.5 μg kg−1, respectively, which is comparable with, or lower than earlier reported numbers (Bucheli et al. 2004; Desaules et al. 2008). The average blank concentrations of individual PCBs ranged from 0.1 to 0.3 μg kg−1, which is again similar to those provided by Desaules et al. (2008). Possible reasons for the detection of these analytes in blank samples are the likely presence of PCBs in the laboratory building of Agroscope (Desaules et al. 2008) and some cross-contamination with PAHs from biochars, which were frequently analyzed in the same laboratory and contain NAP and PHE in concentrations up to several 100 mg kg−1 (Hilber et al. 2012). The results were not blank corrected. Reproducibility as a measure of method precision over an extended period of time was assessed by replicate analyses of KB6 in different sample series. The corresponding coefficients of variation of individual analytes ranged from 12 to 28% for PAHs (n = 4) and from 5 to 41% for PCBs (n = 3) (Table S2), which is acceptable in the parts per billion concentration range (Kromidas 2000). The PAH concentrations in KB6 obtained by the Cuban team were not statistically different (0.13 < p values <0.99; Table S2) from those quantified by the Swiss team as part of its routine analytical services to the NABO. In addition, regular successful participation in the International Sediment Exchange for Tests on Organic Contaminants (SETOC) of the Wageningen Evaluating Programs for Analytical Laboratories (WEPAL) served as external quality control of the Agroscope laboratory. BC and TOC analysis Black carbon in soils was quantified using the chemo-thermal oxidation (CTO) method adapted for soil by Agarwal and Bucheli (2011b). Briefly, there are three parts to the method: (1) removal of non-pyrogenic organic carbon from the dried (60 °C) and ball ground sample (15–20 mg) in a programmable tube furnace (LOBA 1200-80.600-1-OW with quartz tube 75/ 70 × 10,000 mm from HTM Reetz GmbH, Berlin, Germany) at 375 °C under controlled air flow, (2) removal of inorganic carbonates via acid fumigation for 4 h in a desiccator with 12 M hydrochloric acid, and (3) quantification of residual carbon as BC using a CHN elemental analyzer (Euro EA 3000 Elemental Analyzer, Eurovector SPA, Milan, Italy). Total organic carbon was determined in a similar way but without stage 1 of the BC method. All data were determined in triplicates. The BC MDL was 0.023% (Agarwal and Bucheli 2011b).

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Linear regression analyses in Excel Office 2013 were employed to test dependences of individual compounds, ratios, or sums of selected analytes, and PAH16 or PCB7, on total concentrations, distances to emission sources, TOC, or BC. A non-parametric analysis of variance (ANOVA) with the Kruskal–Wallis method was employed to analyze the differences of PAHs and PCBs among the Cuban and Swiss laboratory teams. The differences were considered to be significant if p values were <0.05. ANOVA analyses were carried out by the software package InfoStat versión 2010 (Grupo InfoStat, FCA, National University of Córdoba, Argentina). All data are presented on a dry weight basis.

Results and discussion PAH concentrations Total concentrations of the PAH16 in the 39 soil samples of Mayabeque ranged from 20 to 106 μg kg−1 (Table S3). Results are given as mean value of duplicate analysis of one of the four subsamples from each site (as relative standard deviations of true quadruplicates were essentially similar to those of multiple analyses of one subsample in similarly gathered Swiss soils (for details, see Desaules et al. (2008); analysis of one subsample should provide representative results). When grouped by municipalities, concentrations in SC (n = 11) and GU (n = 6) were slightly higher (56 and 70 μg kg−1, respectively) than those in JA (n = 10) and SJ (n = 12) (32 and 32 μg kg−1, respectively). However, this does not necessarily reflect a generally higher exposure, but rather owes to the selection of actual sampling sites and the fraction of samples taken close to potential PAH emission sources in any of the municipalities. In comparison with PAHs in soils from other parts of the world, the here-reported concentrations can be considered low. Background concentrations in temperate soils are generally higher than in tropical soils (Wilcke 2000, 2007) and range from 100 to a few 100 μg kg−1 (Desaules et al. 2008; Maliszewska-Kordybach et al. 2008; Wilcke 2000). According to a Polish classification (Maliszewska-Kordybach et al. 2008), we can conclude that soils of Mayabeque can be considered as uncontaminated with PAHs. The PAH16 were dominated by PHE and NAP, which contributed 33 and 21% (median numbers), respectively, to their total concentrations. Heavier PAHs, such as FLT, contributed only 8% (median value) or less. This finding is in accordance with the literature (Daly et al. 2007; Wilcke 2000, 2007), which describes NAP and PHE to dominate in background or tropical soils. Interestingly, the fractions of light and heavy PAHs decreased and increased, respectively, with increasing total PAH concentrations, as illustrated by Fig. 2 with sums of two-ring to three-ring and four-ring to six-ring PAH

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y = 0.7381x - 14.485 R² = 0.9064, p-value = 6.757e-08

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Fig. 2 Sum of light (two to three ring) and heavy (four to six ring) polycyclic aromatic hydrocarbon (PAH) concentrations, respectively, vs. the sum of the 16 US Environmental Protection Agency’s priority PAH (PAH16) concentrations in soils of Mayabeque, Cuba

concentrations. As most combustion sources are dominated by heavier PAHs (e.g., Brändli et al. 2008), this might indicate that such emission sources would be mainly responsible for the more elevated, although still low in absolute terms, PAH concentrations. In the following, we use four different approaches to test this hypothesis: (1) interpretation of source characteristic PAH16 ratios, (2) consultation of further molecular markers and characteristic ratios, (3) spatial distance to possible emission sources, and (4) correlations of PAHs and molecular markers with BC. 1. Source diagnostic ratios of selected US EPA PAHs yielded inconsistent information (Fig. 3): While ANT/ (ANT&PHE) pointed at predominantly petrogenic PAH emission sources, FLT/(FLT&PYR), BaA/(BaA&CHR), and IPY/ (IPY&BPE) were more indicative of pyrogenic ones. Still, these latter ones were inconclusive with regard to the contributing combustion sources: Whereas FLT/(FLT&PYR) pointed at grass, wood, or coal combustion, IPY/(IPY&BPE) suggested a domination of petroleum combustion (Fig. 3). Another ratio BaP/BPE, exhibited a median ratio of 0.8, which would suggest traffic combustion sources to prevail over nontraffic ones (Bucheli et al. 2004). Overall, the observation of inconsistent information from ratios of selected US EPA PAHs in soils is in accordance with earlier similar observations, which were attributed to biases due to environmental fractionation processes (Brändli et al. 2008). 2. Further molecular markers and source characteristic ratios were analyzed, to the best of our knowledge, for the first time in soils of the Caribbean region. The results are compiled in Table S4. The concentrations of the molecular markers cPHE, cPYR, PER, RET, and COR were mostly not correlated with PAH16, indicating that they may not originate from the same emission sources. Perylene concentrations were below MDL in 29 out of 39 samples, which is surprising given the fact that it is produced by diagenetic and natural processes. Retene concentrations were in a similar range as in Swiss soils (Brändli et al. 2008), with highest concentrations in soils with

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Fig. 3 Selected source diagnostic polycyclic aromatic hydrocarbon ratios in soils of Mayabeque, Cuba, indicative of petrogenic and different pyrogenic emissions. ANT/(ANT&PHE) (a), BaA/ (BaA&CHR) (b), and IPY/(IPY&BPE) (c) vs. FLT/(FLT&PYR). ANT anthracene, BaA benzo[a]anthracene, BPE benzo[ghi]perylene, CHR chrysene, FLT fluoranthene, IPY indeno[1,2,3-cd]pyrene, PHE phenanthrene, PYR pyrene

low PAH16. Interpretation of retene data is difficult though, because its formation has been postulated for both wood combustion and traffic emissions (see Brändli et al. 2008, and references therein). In contrast, COR, indicative of hightemperature combustion, but possibly also natural sources, exhibited concentrations that were systematically lower than in Swiss soils (median 1.7 vs. 7.4 g kg−1). With regard to the source characteristic ratios, (mPHE&ANT)/PHE and (mFLT&PYR)/PYR were in the range typical for pyrogenic sources (median, min–max 0.60, 0.29–1.11 and 0.40, 0.07– 1.50, respectively, Table S4). However, the former ratio was

systematically higher than in Swiss soils (median, min–max 0.15, 0.07–0.46 (Brändli et al. 2008)), whereas the latter one was more similar (median, min–max 0.36, 0.22–0.70 (Brändli et al. 2008)). The ratio 1,7-/(1,7&2,6-)dmPHE ranged from 0.26 to 0.79 (median 0.57), with 36 of 39 samples in the petrogenic or mixed combustion source range (0.45–0.7). The median number in Swiss soil was very similar (0.59; Brändli et al. 2008). 3. One of the main sample site selection criteria of this study was to capture possible concentration gradients with increasing distance from potential contamination sources (for source types and their locations, see Fig. 1; for corresponding distances, see Table S1). In several cases, and in support of our hypothesis, it was possible to tentatively identify such gradients, which also were in accordance with the major wind directions. Specifically, this is illustrated in Fig. 4a for a thermo-electric power plant in Santa Cruz del Norte (Fig. 1, source A), an asphalt production plant (Fig. 1, source C), and several locations close to major roads (Table S1, source K). 4. The BC content was quantified in soils of this study because BC is potentially co-emitted with PAHs in case of incomplete combustion and may therefore help to identify the main PAH emitters. The TOC was quantified as well, because under equilibrium conditions, organic matter partitioning of hydrophobic organic pollutants such as PAHs is a key process that determines their concentrations in recipient matrices such as soil. The content of TOC and BC ranged from 1.26 to 4.70% and 0.06 to 0.36%, with a median of 2.37 and 0.14%, respectively (Table S5). The minimum, maximum, and median BC-to-TOC ratio was 0.03, 0.10, and 0.06. Such concentrations of BC correspond very well with numbers found in Swiss background soils (0.04 to 0.48% (Agarwal and Bucheli 2011a)), and such BC/ TOC numbers fit nicely with median values compiled in a review by Cornelissen et al. (2005) (0.04 and 0.06). The BC content in soils of SC was correlated with the sampling site distance to the thermo-electric power plant (Fig. 4b), suggesting that incomplete combustion processes have led to emission of soot-like forms of BC that have been deposited in the vicinity of the facility. No correlations were found between PAHs (individual, as well as for their sum) and any of the parameters TOC, BC (Fig. 5a, b), or BC/TOC, when looking at the whole dataset (n = 39). There are many possible reasons for the absence of any such correlations, which were discussed in detail in Bucheli et al. (2004) already. One of the more relevant one for this study may be that the CTO-375 method used here for BC quantification (Agarwal and Bucheli 2011b) is selective for soot-like BC and does not quantify char-like BC (Hammes et al. 2007). In the case of dominating wood, grass, or coal combustion sources, the actual amount of BC would not be captured and any potential PAH-BC relationship missed. Obviously, this would also hold in the case of prevailing petrogenic PAH sources. Nevertheless, in accordance with

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PAH (and BC) concentrations. Negative correlations were further observed between (mFLT&PYR)/PYR vs. PAH16, and vs. BC, and RET/(RET&CHR) vs. PAH16, and vs. BC (Fig. S3). In line with the preceding interpretation, the former two suggest that higher PAH concentrations predominantly originated from pyrogenic sources, and the latter two specify that liquid fossil fuel combustion prevailed over grass, coal, or wood combustion in these cases. While plausible, this explanation is not supported by further correlations with any of the other PAH ratios, and the above-made reservations regarding the diagnostic potential and reliability of this approach still hold here as well. Overall, from the data evaluation presented above, we have to conclude that a clear-cut source apportionment of the overall low PAH concentrations found in the province of Mayabeque is only partly possible. Most likely, PAHs are emitted from a wide range of different but overall rather minor emission sources, including fossil fuel combustion and biomass burning. Although the presence of local petrogenic emission sources cannot be excluded, there is no evidence that such sources would be responsible for the background concentrations quantified in the here-investigated samples.

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Fig. 4 Concentrations of pollutants in soils of Mayabeque vs. distance of sampling sites to presumed major emission sources. a Sum of the 16 US Environmental Protection Agency’s priority PAHs (PAH16) and b black carbon (BC). c Sum of the seven Institute for Reference Materials and Measurements (IRMM) PCBs (PCB7)

the correlations of both PAH16 and BC with distance to the power plant in SC (Fig. 4a, b) for a subset of the dataset (sites 1 to 22), these two parameters also correlated among each other (Fig. S1). Finally, the source characteristic ratios presented above were also investigated in relation to the total PAH16 concentration and in relation to TOC and BC. Negative correlations were found for FLT/(FLT&PYR) vs. PAH16, and vs. BC (Fig. S2a, b). This could indicate that pyrogenic (as opposed to petrogenic) sources with primarily fossil fuel (as opposed to biomass) would mainly be responsible for the relatively higher

Total concentrations of the PCB7 in soils of Mayabeque ranged from 1.1 to 7.6 μg kg−1, with a median number of 2.8 μg kg−1 (n = 39) (Table S6). Similar to PAHs, SC exhibited the highest concentrations (median 4.8 μg kg−1, n = 11) of the four investigated municipalities, followed by JA (median 3.0 μg kg−1, n = 10), GU (median 2.4 μg kg−1, n = 6), and SJ (median 1.6 μg kg−1, n = 12). Again, such differences are probably mainly caused by site selection criteria and not actual differences in general pollutant exposure. All of these values are two orders of magnitude below the allowable value of 0.5 mg kg −1 according to the Cuba regulation (Norma Cubana 2009). The observed concentrations are similar to those of background soils of Switzerland. The concentrations of PCB7 in over 100 samples, determined by the very same method and in the same laboratory, were between 0.5 and 12 μg kg−1 (median 1.6 μg kg−1) (Desaules et al. 2008). Other soil monitoring studies in Eastern Europe quantified PCB concentrations in the range of a few to a few tens of micrograms per kilogram (Holoubek et al. 2009, and references therein). Meijer et al. (2003) found PCB concentrations in background soils worldwide to spread over four orders of magnitude (0.026 to 97 μg kg−1), with lowest numbers in Greenland and highest ones in mainland Europe. The data in non-contaminated soils from tropical countries is relatively scarce, but the few papers available for Mexico (Javier Perez-Vazquez et al. 2015), Malaysia (Ilyas et al. 2011), and India (Kumar et al. 2013) indicate concentrations (usually as sum of a varying number

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a)

b)

120

100

PAH16 [μg/kg]

100

PAH16 [μg/kg]

120

80 60 40 20

80 60 40 20

y = 4.747x + 37.038 R² = 0.0321, p-value = 0.2753

y = 82.062x + 35.949 R² = 0.0691, p-value = 0.106

0

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d)

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5.0 4.0 3.0

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2.0 y = 0.9046x + 0.7643 R² = 0.2094, p-value: = 0.003404

1.0

y = 18.587x + 0.0711 R² = 0.6371, p-value = 1.158e-09

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Fig. 5 Sum of the 16 US Environmental Protection Agency’s priority PAH (PAH16) concentrations vs. total organic carbon (TOC) (a) and black carbon (BC) (b) content, and sum of the seven Institute for

Reference Materials and Measurements (IRMM) PCBs (PCB7) vs. TOC (c) and BC (d) content in soils of Mayabeque, Cuba

and composition of individual PCB congeners) that are in the same range as reported here. The mean concentration of PCB7 in agricultural soils of Mayabeque (3.1 ± 1.7 μg kg−1) was higher than that reported for the sum of 26 PCB congeners (0.2 μg kg−1) in sediments of the Gulf of Batabano, Cuba, south of this province (AlonsoHernandez et al. 2014). This is in line with several other studies that found PCB concentrations to be higher on a total mass basis in soils than in sediments at the same locations (Holoubek et al. 2007; Quinn et al. 2009; Wong et al. 2009). This finding may generally be attributed to the water saturated conditions in sediments, allowing for faster phase distribution and higher metabolic activities (Quinn et al. 2009). The PCB7 concentrations were dominated by PCB#153 (median contribution 26%), followed by PCB#138 (median contribution 16%) and PCB#180 (median contribution 15%). The same congeners prevailed in Swiss soils, in other European soils (Desaules et al. 2008, and references therein), and in background soils globally (Meijer et al. 2003). While the light PCB#52 remained largely constant with increasing total PCB concentrations, the heavier ones such as PCB#153 increased (Fig. 6). In other words, the fraction of the light congener #52 decreased with increasing total PCB concentration, while the one of the heavier ones #153 and #138 increased. Several reasons may account for this finding. Depending on the

commercial PCB products originally in use, the total stock and relative contribution of individual PCB congeners may vary. According to the Cuban PCB inventory, over 60% of the about 130 t of PCBs ever used consisted of the commercial product Sovtol-10 (Abo Balanza 2005; Velazco et al. 2013), which contained 90% Sovol (Ivanov and Sandell 1992; Velazco et al. 2013). It seems that the relative abundance of PCB#52, #153, and #138 in Sovol was largely similar (Ivanov and Sandell 1992; Kannan et al. 1992; Velazco et al. 2010l 2.5

individual PCB [μg/kg]

PCB#52 2.0

y = 0.3202x - 0.1508 R² = 0.9791, p-value < 2.2e-16

PCB#153

1.5

1.0

y = 0.029x + 0.285 R² = 0.2981, p-value = 0.0003917

0.5

0.0 0.0

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Fig. 6 Polychlorinated biphenyl congener #52 (PCB#52) and PCB#153 concentrations, respectively, vs. the sum of the seven Institute for Reference Materials and Measurements (IRMM) PCB (PCB7) concentrations in soils of Mayabeque, Cuba

Environ Sci Pollut Res

Wyrzykowska et al. 2006; Zabelina et al. 2004). However, lighter PCBs exhibit a higher vapor pressure and are more water soluble than heavier ones, which facilitates environmental distribution, dilution, and also bioavailability of the former ones. Moreover, lower chlorinated biphenyls can more easily undergo aerobic microbial degradation, while higher ones require reductive dechlorination (Borja et al. 2005; Field and Sierra-Alvarez 2008). Consequently, heavier PCBs may, relative to lighter ones, exhibit higher persistence and therefore accumulation. A relationship between concentrations of PCB7 with distance to emission sources was only observed in the case of the thermo-electric power plant in SC (Fig. 4c). In fact, of all the 39 sampling sites, most of the higher end concentrations (4 < PCB7 < 8 μg kg−1) were quantified within 5 km from this location. None of the other sources specified in Fig. 1 exhibited any gradient in PCB soil concentrations. Opposite to PAHs, concentrations of PCB7 were weakly correlated with TOC, and even more strongly so with BC (Fig. 5). Although a bit counter-intuitive at first sight, this may indicate that soot-like BC-emitting and PCB-emitting sources are partly identical, which would favor heavy duty industries over, e.g., traffic or biomass burning as sources for the former. A somewhat similar situation was observed in European background soils, in which PCBs correlated with BC, whereas the sum of PAHs did not (Nam et al. 2008a). In that case, the correlations with TOC were stronger than with BC, though.

Conclusions and outlook PAHs and PCBs are considered environmental pollutants and are part of the POP management plan in Cuba (CITMA 2008). In the present study, we confirmed generally low concentrations of these compounds in soils of Mayabeque, which can therefore be classified as non-contaminated. These results constitute the first report in Cuba for PAHs and PCBs in soils. The data will be communicated to the local authorities (Ministry of Science Technology and Environment of Mayabeque) and will form the basis to (a) establish environmental standards for hitherto non-regulated PAHs in Cuban soils and (b) adapt existing but generic standards for PCBs, by taking into account local tropical conditions. Acknowledgements This work is part of the project BEstablishing a soil monitoring network to assess the environmental exposure to PAHs and PCBs in the province of Mayabeque, Cuba (Soil-Q),^ within the Swiss Programme for Research on Global Issues for Development (r4d programme). We thank the Swiss Agency for Development and Cooperation (SDC) and the Swiss National Science Foundation (SNSF) for financial support. We are further thankful to the Swiss Embassy and the Swiss Cooperation Office in Havana for administrative and logistic assistance. Thanks are also due to various Cuban institutions for their support, the Bland owners,^ and the team of the Analytic Unit of CENSA for their assistance in soil sampling and sample preparation.

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