Atmospheric particulate matter intercepted by moss ...

Chemosphere 176 (2017) 361e368

Contents lists available at ScienceDirect

Chemosphere journal homepage: www.elsevier.com/locate/chemosphere

Atmospheric particulate matter intercepted by moss-bags: Relations to moss trace element uptake and land use Anna Di Palma a, b, Fiore Capozzi a, c, Valeria Spagnuolo a, c, Simonetta Giordano a, c, *, Paola Adamo a, b di Napoli Federico II, via Mezzocannone, 16, 80132 Napoli, Italy Centro Interdipartimentale di Ricerca Ambiente (CIRAM), Universita di Napoli Federico II, Via Universita 100, 80055 Portici, NA, Italy Dipartimento di Agraria, Universita c di Napoli Federico II, Via Cinthia 4, 80126 Napoli, Italy Dipartimento di Biologia, Universita a

b

h i g h l i g h t s

g r a p h i c a l a b s t r a c t

Mosses in bags were used to detect airborne particulate matter (PM). PM number and moss chemical composition are specific to land use. The more the PM counted on mosses, the higher the moss elemental content. Total PM number and moss uptake increase in the order agricultural e urban-industrial sites. Precious metals and REEs could be considered as novel air pollution markers.

a r t i c l e i n f o

a b s t r a c t

Article history: Received 21 December 2016 Received in revised form 13 February 2017 Accepted 23 February 2017 Available online 27 February 2017

Particulate matter has to be constantly monitored because it is an important atmospheric transport form of potentially harmful contaminants. The cost-effective method of the moss-bags can be employed to evaluate both loads and chemical composition of PM. PM entrapped by the moss Pseudoscleropodium purum exposed in bags in 9 European sites was characterized for number, size and chemical composition by SEM/EDX. Moreover, moss elemental uptake of 53 elements including rare earth elements was estimated by ICP-MS analysis. All above was aimed to find possible relations between PM profile and moss uptake and to find out eventual element markers of the different land use (i.e. agricultural, urban, industrial) of the selected sites. After exposure, about 12,000 particles, mostly within the inhalable fraction, were counted on P. purum leaves; their number generally increased from the agricultural sites to the urban and industrial ones. ICP analysis indicated that twenty-three elements were significantly accumulated by mosses with different element profile according to the various land uses. The PM from agricultural sites were mainly made of natural/crustal elements or derived from rural activities. Industrial-related PM covered a wider range of sources, from those linked to specific industrial activities, to those related to manufacturing processes or use of heavy-duty vehicles. This study indicates a close association between PM amount and moss element-uptake, which increases in parallel with PM amount. Precious metals and REEs may constitute novel markers of air pollution in urban and agricultural sites, respectively. © 2017 Elsevier Ltd. All rights reserved.

Keywords: Air pollution PM10 Moss biomonitoring Scanning electron microscope Microanalysis Pollution markers

di Napoli Federico II, * Corresponding author. Dipartimento di Biologia, Universita Via Cinthia 4, 80126 Napoli, Italy. E-mail address: [email protected] (S. Giordano). http://dx.doi.org/10.1016/j.chemosphere.2017.02.120 0045-6535/© 2017 Elsevier Ltd. All rights reserved.

362

A. Di Palma et al. / Chemosphere 176 (2017) 361e368

1. Introduction Particulate matter (PM) is a widespread air pollutant, fundamentally consisting of a mixture of solid and liquid particles suspended in the air (USEPA, 2016) and diverse in terms of physical properties (shape, dimension, density) and chemical composition. Commonly, PM is classified into categories (e.g. coarse, fine and ultrafine particles) on the basis of the particle aerodynamic diameter (WHO, 2005). Particles can either be directly emitted into the air, representing the “primary PM”, or formed in the atmosphere as “secondary particles” from gaseous precursors (e.g. ammonia, sulfur dioxide, nitrogen oxides). Primary PM derive from both natural and anthropogenic sources. Lelieveld et al. (2015) attributed, on a global basis, the main sources of the total PM2.5 (e.g. industrial processes, power generation and use, biomass burning, vehicular traffic and natural sources) in the different continents; for example, they recognized the agriculture as the main source of PM2.5 in Europe. Air pollution due to PM is considered a serious environmental issue as the particulate matter represents an important transport form of heavy metals in the atmosphere (WHO, 2013); metal particulates can deposit on terrestrial and water surfaces and easily bioaccumulate in food chains (EEA, 2013). Particulate matter is recently recognized by the International Agency for Research on Cancer (IARC) as one of the pollutants mostly affecting human health and closely associated with increased cancer incidence (EEA, 2015). Fine airborne particles containing metals, polycyclic aromatic hydrocarbons (PAHs) and other toxic chemicals can increase the natural-cause mortality even at concentrations well below the European annual mean limit value (40 mg m3). The effects of atmospheric particulate on human health are related to both short and long-term exposure and depend in part on PM size. As a general principle, the lower the PM size, the longer the residence time in the atmosphere; indeed, as described in Bargagli (1998), PM below 1 mm are permanently suspended. The inhalable fraction includes particles with a diameter less than 10 mm (PM10); in particular, fine particles (PM2.5), comprising also the ultrafine fraction (diameter < 0.1 mm), have the strongest correlation with mortality. Particles larger than 10 mm have a relatively short lifetime in the atmosphere, rapidly removed by sedimentation processes due to the gravity, and are generally less harmful for humans as they remain mostly entrapped in the upper respiratory tract (Finlayson-Pitts and Pitts, 2000; Kesler and Simon, 2015). The growing awareness of PM related risks justifies the constant monitoring of their concentrations in indoor and outdoor environments (EEA, 2014; UNECE, 2009), but the high costs and technical constrains often hamper an adequate evaluation of airborne particulate load and chemical composition. In this sense, the use of mosses represents a valuable alternative to monitoring stations in order to evaluate qualitatively and quantitatively the PM deposition. Mosses are in fact well-known plants able to absorb water and metal ions over the entire shoot and entrap airborne particles of different nature (Spagnuolo et al., 2017; Tretiach et al., 2011). Their usefulness as biomonitors of inorganic and organic pollutants is given by a huge literature produced in the last decades and some EU funded Projects such as the Biomonitoring Network, coordinated by the UNECE ICP Vegetation Programme (Harmens et al., 2010, 2015) based on the collection of native species, and the EUFP7 project “MOSSclone” aimed at developing a standardized tool for a transplant based technique (Capozzi et al., 2016a; Di Palma et al., 2016). In particular the moss-bag is a versatile approach, consisting in the exposure of mosses inside nylon bags according to a defined procedure and rational design, with the possibility to obtain a wide range of data depending on the experimental procedures applied (Ares et al., 2012; Capozzi et al., 2016a; 2016b).

However, most of the studies concerning the biomonitoring with moss-bags is focused on moss uptake ability, whereas the nature of the PM entrapped by these biomonitors and the relationship with the moss chemical content were scarcely explored so far (Adamo et al., 2008; Giordano et al., 2005, 2010; Tretiach et al., 2011). According to the above considerations, the aims of this work were: 1) to characterize by SEM/EDX in terms of number, size and chemical composition the PM entrapped by the moss Pseudoscleropodium purum exposed in bags in nine urban, industrial and agricultural sites of three EU countries; 2) to relate the PM characteristics to the land use of selected sites; 3) to relate the load and nature of PM found on moss leaves to the moss uptake of metals, metalloids and REEs; 4) to find out potential elemental markers of PM source. 2. Materials and methods 2.1. Moss collection, bag preparation and exposure The moss Pseudoscleropodium purum (Hedw.) M. Fleisch. was collected in an undisturbed area of SE Galicia. Pseudoscleropodium is a monotypic genus with the characters of the species (P. purum); it is a robust pleurocarpous moss indigenous to Europe but now with worldwide distribution. The shoots are up to 15 cm long, with complanate branches, imbricate leaves, very concave, ovateorbicular to broadly ovate with the nerve extending 1/3e1/2 way up leaf. The species was identified on the basis of the diagnostic morphological characters (Smith, 2004) with the aid of a stereomicroscope and a light microscope. The moss shoots were included inside nylon bags (moss weight/bag surface ratio of 10 mg cm2, 2 mm net mesh size) for the transplants. For the experiment, the moss green apical parts (4e5 cm) were selected, then washed with 10 mM EDTA and devitalized by oven-drying at 100 C. The EDTA washing aimed to set free the moss surface exchange sites and the devitalization prevents any effect of moss metabolism on PM (characteristics and chemical composition), thus ensuring exclusively a mechanical and physico-chemical PM interception. More details on the adopted methodology are given in Capozzi et al. (2016b). Moss bags were exposed in triplicate at 4 m above the ground, for 12 weeks during winter 2014 in three EU countries (Austria, Italy, Spain), choosing in each country three sites belonging to different land uses (i.e. urban, industrial and agricultural), for a total of 9 exposure sites. Agricultural sites were green areas with low traffic roads, mainly characterized by crops and cattle farming, located at the outskirts of urban areas and far from industrial activities. Urban sites included residential and commercial areas mainly affected by intensive traffic (passenger cars from 525 to 575 per 1000 inhabitants in Italy and Spain study areas, >575 in Austria (Eurostat, 2015) with population in 2012 ranging from about 100.000 (Santiago de Compostela) to 1.000.000 (Naples) and 1.800.000 (Vienna) inhabitants. Industrial areas included heavy manufacturing plants, as iron and aluminum smelters (Austria and Spain, respectively) and lead battery recycling factory (Italy). After exposure, all moss samples were removed from the nylon bags, dried at room temperature and stored in paper bags before analysis. 2.2. SEM-EDX observations and image analysis The PM profile (morphology, number, size, chemical composition) for each site was defined and used for distinguishing the selected sites, by performing SEM-EDX observations and mass spectrometry analysis. Ten leaves from three to five shoots of postexposure moss materials were detached and mounted on stubs by double sided adhesive disks, coated with carbon and observed under a scanning electron microscopy (SEM; JEOL JSM 5310) in


secondary (SE) and backscattered electron (BSE) modes and analyzed in terms of chemical composition by energy-dispersive Xray spectroscopy (EDX; Oxford INCA). After an overall examination of the leaves, a total of ten representative areas of 100 100 mm for each exposure site were selected (in total 100.000 mm2 per site), observed and the SEM images acquired. The images were examined at a resolution of 1024 803 pixels by ImageJ open source software (Rasband, W.S., U.S. NIH, Bethesda, Maryland, USA, 1997e2012) for counting and size class assignment of the particles, according to their equivalent diameter deq ( 10 mm). Particles with a deq industrial > agricultural sites. 3.2. Particle size distribution In the present study, on the basis of the measured Feret diameters and taking into account the EEA recommendations (EEA, 2015), the counted particles were assigned to four size classes ( 10 mm; Fig. 3). The particles entrapped by moss had a Feret diameter ranging between 0.2 and 47 mm. The majority of the particles fell within the inhalable fraction (approximately 10 mm or smaller) with about 80e85% showing a diameter < 2.5 mm, regardless the land uses. These particles are known to be responsible for adverse human health effects (e.g. Xing et al., 2016). Our findings are similar to the results obtained with particles observation on tree bark (Catinon et al., 2011) and on lichens (Ayrault et al., 2007), showing the very major part of the particles entrapped were smaller than 2.5 mm in diameter. The percentage particle size distribution was similar among land uses with an increasing trend from the agricultural to the industrial sites. Nevertheless, for all size classes, the number of particles counted for industrial and urban sites was respectively 7 and 3 times higher than the number counted for agricultural sites. The particle size is one of the key aspects in order to evaluate the human health risk and to identify the contribution from different pollution sources, since it is related to generation processes of the particles and to their residence time and fate in the atmosphere (Finlayson-Pitts and Pitts, 2000). According to Morawska et al. (2008), the higher frequency of the smaller particles, as observed in our work, suggests a prevailing anthropogenic origin of the particles. 3.3. Particle microanalysis During SEM observations, random EDX microanalyses were carried out on 20 particles found on moss leaves from each exposure site. In general, in all sites microanalysis revealed particles made by Si and Al along with small amounts of K, Fe, Mg, Ca and Na, suggesting a widespread contribution of soil dust (likely in form of silicates, clay minerals and quartz) to airborne PM (Adamo et al., 2011) (Figs. S1aed). Particles made exclusively of Fe or in association with Ni and Cr, likely in a metallic or oxide nature, were

364


Fig. 1. Representative SEM images of the particulate matter observed on moss leaves. a) unexposed moss surface; b,c) agricultural exposure sites; d-f) urban exposure sites; g-i) industrial exposure sites.

Fig. 2. Number of particles counted in the agricultural, urban and industrial sites of Italy (IT), Austria (AU) and Spain (SP).

frequently observed in moss-bags exposed in industrial and urban sites (Figs. S1e and f). In urban areas, iron in association with other elements (Mn and Cr, Cu and Ni) likely suggests a derivation of particles from road dust, diesel engine exhaust, brake wear emissions (Giordano et al., 2010; Samara and Voutsa, 2005; Thorpe and Harrison, 2008). In the Austrian industrial site, the iron smelting likely generated Fe particles (Fig. S1e). In the Spanish industrial site, particles made by Al alone or with Fe, deriving from the Al smelting activities, were found on moss leaflets (Fig. S1g). In the same site,

particles made by S and Fe, or S and Ba, suggest occurrence of sulfite/sulfates such as pyrite and barite (Figs. S1h and i). In the Italian industrial site, particles produced by the process of lead battery recycling and made of Pb alone or in association with Sb and Sn, were observed on moss leaves (Figs. S1j and k). In moss samples exposed in agricultural sites, the frequent associations of S and Cu (Fig. S1l) were assignable to sulfur- and copper-based pesticides, particularly fungicides and bactericides (e.g. Cu sulfate, Cu oxychloride, Bordeaux Mixture), widely used in agricultural practice throughout the world (Moolenaar and Beltrami, 1998). Copper- and sulfur-based fungicides and bactericides are routinely used in conventional as well as organic farming, and studies show that care should be taken in their application for the sake of the plants and to prevent soil and groundwater contamination (Brunetto et al., 2016). Substantial Cu addition to agricultural soils can also occur from the addition of mineral- and organic-fertilizers including organic residues (e.g. pig and poultry manure and organic composts) (Xiaorong et al., 2007; da Rosa Couto et al., 2015). The scanning electron microscope (SEM) equipped with an energy-dispersive X-ray analyzer (EDX) has the potential to be a powerful tool for chemical characterization of single particles. A large number of particles on polished, representative samples should be observed to gain semi-quantitative information (e.g. Sgrigna et al., 2016); otherwise the chemical data are merely qualitative. In our case only qualitative information on chemical composition of observed particles in mosses were obtained based on the adopted procedure of sample preparation and analysis at


365

Fig. 3. Number of particles (a) and percentage of distribution (b) into different size classes ( 10 mm) and land uses.

SEM-EDX. Considering the frequency of the elements in the acquired spectra, a PM element profile per land use class was built up (Fig. S2). Agricultural sites are marked by the presence of Cu, K, Ni, P and S, mostly supplied in consistent amounts as fertilizers (K, P, S) in agro-environments or fungicide (Cu, S) also allowed in organic rek et al., 2010; Mengel, 2006; Sanchez, 2006). agriculture (Koma Nickel can likely derive from gasoline used on farms (Agarry et al., 2014). Urban and industrial sites are characterized by PM frequently made of Cr, Fe and Pb, likely deriving from vehicular traffic (urban sites) and industrial processes (Sanderson et al., 2016; Squizzato et al., 2016; Thorpe and Harrison, 2008). 3.4. Moss uptake Twenty three elements out of the 53 analyzed were accumulated by mosses in more than 60% of the sites (i.e. Ag, Al, Au, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Ge, Hg, La, Mg, Mn, Nb, Pb, Sb, Sn, Y, Zn and Zr). Only these elements were considered for further elaborations aimed to highlight differences among land use scenarios. The elements Be, Bi, Ga, In, Pd, Pt, Re, Ta, Te and W were always below quantification limits (0.001 mg kg1 for Pt, Re and Ta; 0.02 mg kg1 for Bi, In, Pd and Te; 0.1 mg kg1 for Be, Ga and W). The remaining elements (i.e. As, Cd, Cs, Hf, K, Li, Mo, Na, Ni, P, Rb, S, Sc, Se, Sr, Th, Ti, Tl, U, V) were enriched in less than 60% of the sites; in particular, As,

Cd, Cs, Li, Mo, Ni, Sr and Tl were only found significantly enriched in the Italian industrial site. All data on moss uptake are reported in Table S2. The site-specific elemental composition was evaluated by PCA (Fig. 4a and b). Most elements and the total PM number resulted associated positively to Factor 1 explaining 61% of the total variance (Fig. 4b). As shown in Fig. 4a, along Factor 1 a distribution trend was observed from the unexposed T0 (left-hand side of the plot) to the Italian Industrial site (oriented towards the right-hand side) with some overlapping between Agricultural and Urban sites. Zinc, Zr and Y are the sole elements related to the Agricultural and Urban sites (left-hand side of the plot). Along Factor 2, a separation of Austrian from other sites occurs, with B, on one side, and Cr, Y, Mn and Au, on the other side, as the elements contributing more to this factor. However, this trend has to be considered with caution since Factor 2 explains in all only the 14% of the total variance. 3.5. PM load and moss uptake harmonization Combining for each land use scenario the number of particles entrapped by moss and the total element load up-taken by moss (sum of normalized values of the concentrations calculated for all elements, Fig. 5), it is evident that the element load increases from the agricultural to urban and industrial sites, in parallel with the

366


Fig. 4. Principal Component Analysis of the tested sites based on moss uptake considering the absolute number of particles (TOT PM) and the 23 elements significantly accumulated at agricultural (A), urban (U) and industrial (I) exposure sites of Austria (AU), Italy (IT) and Spain (SP). a) Projection of the cases; b) projection of the variables.

increasing number of particles. For each land use, a different set of elements was outlined (Table 1). This likely depends on the different nature (chemical composition, origin) of the PM for each type of land use. The mosses exposed in the rural sites were mainly covered by PM of natural/crustal origin (i.e. Al, Ca, Ce, Ge and La). Aluminum is a main or secondary component of many soil minerals, especially of all the silicates. The lanthanides Ce and La are released into soil by chemical weathering of rocks and minerals, but also drawn from REE-containing phosphate fertilizers and insectofungicides (Carpenter et al., 2015; Kabata-Pendias, 2010). REEcontaining fertilizers are found to have nitrogen fixing capacity, to enhance seed germination, strengthen photosynthetic rate, to enhance respiration and activity of hydrolytic enzymes and plant hormones, and reduce water loss (Wen et al., 2001). Yttrium, outlined as elemental marker mainly of agricultural and urban investigated environments, can be attributed to residues of diesel engine thermal coatings (yttrium-stabilized zirconia) emitted by motor vehicles (Hejwowski and Weronski, 2002; Thorpe and Harrison, 2008). PM derived from sediments and sedimentary rock, particularly clay rich marine sediments and transported by sea salt aerosols, could have been a source of B in the Italy and Spain

Fig. 5. Total element load (sum of normalized mean concentrations) and number of particles entrapped by moss for each land use scenario.

Table 1 Enrichment (median, %) of 23 elements significantly accumulated in mosses of the agricultural, urban and industrial exposure sites. Colored cells indicate the highest % median. Agricultural

Urban

Ag

70

85

Industrial 47

Al Au

200 924

100 2114

102 210

B Ba

367 34

367 62

221 72

Ca Ce Co Cr Cu Fe Ge Hg La Mg Mn Nb Pb Sb Sn

132 312 233 3 30 179 138 27 275 24 26 233 270 168 16

96 219 277 13 116 176 90 21 192 27 28 344 1260 611 73

60 78 339 36 192 278 90 128 90 29 95 400 1383 2058 164

Y Zn

548 53

524 82

123 386

Zr

428

469

157

exposure sites located not far from the coast (Kabata-Pendias, 2010). The precious metals Ag and Au, and Zr were among the elements discriminating the urban sites from the others. Silver and Au are presumably related to bottom ashes produced by municipal waste incineration, electronic items and car components that include circuit boards (Berlizov et al., 2007; Luda, 2011; Muchova et al., 2009). The enrichment in Zr of moss tissue can be linked to PM emissions due to vehicular traffic (i.e. brake lining materials wear) in form of oxide and silicate (Hejwowski and Weronski, 2002; Thorpe and Harrison, 2008). A larger set of elements contributed to the total moss uptake in the industrial sites compared to agricultural and urban ones. For most of the elements enriched in the industrial sites it was hard to


recognize a specific and unique emission source. Apart from the elements linked to the specific activities of the three industrial sites (Fe and Al smelters respectively in Austria and Spain; Pb-battery recycling plant in Italy) resuspension of dusts from wastes and residues of industrial manufacturing processes (Cu, Pb, Sb, Sn and Zn), as well as exhaust and non exhaust emissions linked to heavyduty vehicles (erosion of asphalt and concrete-paved roads eBa, Co, Cu, Sn, Sb, Zne) likely affected moss uptake in this scenario (Berlizov et al., 2007; Gietl et al., 2010; Grigoratos and Martini, 2015; Querol et al., 2010). Mercury naturally occurs in bauxite, used for non-ferrous metals production; other large sources of emissions are represented by cement production (UNEP, 2013). Niobium is employed for several purposes (alloys in engines and rockets, beams and girders for buildings and oil rigs, and oil and gas pipelines, and surgical implants; Kabata-Pendias, 2010; OlivaresNavarrete et al., 2011) and resulted enriched in all scenarios, particularly in the industrial one. While some trace elements are beneficial to biological functions and processes, the intake of others can yield toxic effects (Rembert et al., 2017). With reference to those considered by WHO (2017) as priority pollutants: Cd can damage the kidneys and is carcinogenic to humans (Jarup and Akesson, 2009); Pb affects the central nervous system and increases the risk of cancer (IARC, 2006); exposure to high levels of As on a regular basis causes certain types of skin, lung, bladder, and kidney cancers (ATSDR, 2007); Hg poisoning have been suggested to have associations with some cardiovascular diseases (Virtanen et al., 2005). In Europe air quality target values have been established only for As, Cd, Ni and Pb and most automatic monitoring stations measure the concentrations of particles based on size and not their chemical composition. However, the association of potentially toxic elements in airborne PM and their health dangerous effects represents a crucial aspect to be further investigated and addressed by environmental legislation. Indeed, the USEPA human exposure assessment model takes into account the evaluation of human health risks linked to heavy metals in air particulate matter. Biomonitoring with moss bags represents a valuable adjunct to instrumental monitoring for evaluating the related health risk of PM deriving from associated toxic metals. 4. Conclusions Many studies highlighted the efficiency of moss exposed in bags to retain particulate matter, but only few of them are focused on a morphological/numerical/chemical characterization of particles. This study clearly indicates the close association between the amount of PM entrapped by moss surface and moss elemental uptake. We found indeed, that the more the particles counted on moss leaves, the higher the metal content (i.e. the PM amount was strongly related to elemental content). This result confirms that the uptake by mosses is principally based on passive mechanisms (i.e. depending on the moss surface characteristics such as carboxylic and phenolic groups of the cell wall). PM amount and moss uptake increased from agricultural to urban and industrial scenarios, with a commonly frequent soil dust contribution. Different land uses appear to be associated to the deposition of particle with a specific chemical composition, even if no land use marker can be assumed only on the basis of PM profile. The combination of two approaches, SEM/EDX analysis along with ICP-MS provided complementary results, the first giving precise information on PM number and size, the second indicating element concentrations and chemical markers in the different scenarios. According to our observations, precious metals and rare earth elements could be considered as novel markers of air pollution of urban and agricultural land uses, respectively. Biomonitoring with moss bags may integrate instrumental monitoring in the evaluation of potentially toxic elements

367

in airborne PM and their health dangerous effects. Moreover, the effectiveness of mosses to trap above all fine particles (