Judith Hebelen Rodriguez1

Eduardo Daniel Wannaz1

Marıa Luisa Pignata1

Andreas Fangmeier2

Jurgen Franzaring2

1Faculty of Physical and Natural

Sciences, Multidisciplinary Institute of

Plant Biology, Section Pollution and

Bioindicators, National University of

Cordoba, Cordoba, Argentina2Institute of Landscape and Plant

Ecology, Plant Ecology and

Ecotoxicology, Universitat Hohenheim,

Stuttgart, Germany

Research Article

Fluoride Biomonitoring around a Large AluminiumSmelter Using Foliage from Different Tree Species

In order to study the pollution gradient in the vicinity of a large aluminium production

facility in Patagonia (Argentina), a passive biomonitoring was performed employing

foliage from three tree species. Primary scope was to identify pollution gradients and to

select suitable tree species which can be used as biomonitor plants in the study area.

Therefore, leaves of Eucalyptus rostrata, Populus hybridus and different needle ages of Pinus

radiata were collected at different distances from the industry and the fluoride con-

centration was analysed in washed and unwashed samples in order to determine the

amount of external fluoride. Washing reduced the F-concentrations by 24, 39 and 51%

on average in E. rostrata, P. hybridus and P. radiata, respectively, indicating that species-

specific characteristics determine the accumulation and wash-off of dust-associated

fluorine. F-concentrations varied from 6 to 3652 ppm F in unwashed samples indicating

a steep pollution gradient in the study area. The influence of F-emissions was discern-

ible in all samples up to a distance of 3500 m from the smelter. E. rostrata accumulated

more fluorine than the other species at equal distance from the emission source. The

present study confirms that aluminium smelting results in high F deposition in the

study area. Establishing a biomonitor network around large emitters is suitable and

feasible to evaluate the efficiency of air control measures.

Keywords: Eucalyptus; Fluoride bioindication; Patagonia; Pinus; Populus

Received: October 20, 2011; revised: May 10, 2012; accepted: May 21, 2012

DOI: 10.1002/clen.201100584

1 Introduction

Among pollutants emitted into the atmosphere, fluoride com-

pounds belong to the most phytotoxic. The gases HF and SiF4 are

one to three orders of magnitude more toxic than other air pollu-

tants [1]. Because plant foliage is effectively scavenging atmospheric

pollutants many studies have used different plant species as bio-

monitors of airborne fluoride [2–6]. The most suited biomonitors are

species that are relatively tolerant to F because an inverse relation-

ship between the degree of sensitivity and fluoride accumulation has

often been reported [1, 7]. Biomonitoring may also be regarded as an

effective tool for detecting potential health risks to animals and

humans in the vicinity of sources of fluoride, taking into account

that grazing is the main uptake route for fluoride in dairy cattle and

that the consumption of fluoride contaminated food has been shown

to be associated with dental and skeletal fluorosis [8]. Although it has

been reported that background concentrations in most plant species

range from 1 to 10 mg g�1 [9], this range may vary according to

geographical and climatic conditions of the study area [1]. Due to

the increasing industrialisation fluoride emissions have increased

globally. Nevertheless, emission control is restricted to sporadic

investigations and is often insufficient to identify and avoid harmful

effects on the environment [2, 10]. Numerous reports in relation to

fluoride pollution in the vicinity of aluminium industries have

indicated extensive damage to the vegetation [3, 6, 11–13]. During

the aluminium smelting process, fluoride is emitted into the atmo-

sphere in gaseous and particulate forms. While gases are absorbed

through the stomata of leaves F containing particulates are depos-

ited on the leaves from which large amounts may be washed off

again by precipitation [3].

One of the largest aluminium production plants of South America

is situated at the Atlantic coast of Patagonia (Argentina). Some

ecological implications of the industrial activity in this area had

been described in the early 1980s, when the production capacity was

about 140 kt year�1 [14–17]. In recent years, the plant production

expanded up to c. four times (CNV, accessed 20.09.2010) although

environmental monitoring studies are still scarce. The Al-industry

has its own system of fluoride monitoring in air at various points in

the city (Aluar, accessed 01.03.2012). Although, the maximum emis-

sion limits in air are set to 16 mg m�3 HF, values approximately forty

times higher than those reported for air quality limits set in many

countries to protect sensitive plant species [18–20]. In this paper we

report on a study of the air quality performed in the vicinity of the

described smelter in Patagonia. Primary scope was to identify pol-

lution gradients and to select suitable tree species which can be used

as biomonitor plants in the study area.

Correspondence: Dr. J. Hebelen Rodriguez, Faculty of Physical andNatural Sciences, Multidisciplinary Institute of Plant Biology, SectionPollution and Bioindicators, National University of Cordoba, Av. VelezSarsfield 1611, X5016CGA Cordoba, ArgentinaE-mail: jrodriguez@com.uncor.edu

Abbreviations: EC, electrical conductivity; SLA, specific leaf area

Clean – Soil, Air, Water 2012, 00 (0), 1–5 1

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2 Materials and methods

2.1 Study area and sampling

The study was performed in the city of Puerto Madryn in the Chubut

province (Argentina) in the vicinity of a aluminium production

plant. The city is located on the west coast of the Golfo Nuevo

and has a population size of about 57 000 inhabitants (INDEC,

accessed 01.08.2010). However, this number doubles during the

summer holidays because the place is one of the most important

resorts in Patagonia and the country. The continental area is charac-

terised by semiarid conditions, with a mean annual precipitation of

238 mm year�1 and an average annual temperature of about 13.68C(CENPAT, accessed 01.08.2010). The topography of the area is nearly

flat and strong south-westerly winds from the continent to the sea

dominate throughout most of the year. The climatic conditions prior

to leaf sampling (January to February 2010) were characterised by a

mean temperature of 20.58C, a cumulative precipitation of 24.6 mm,

a relative humidity of 43%, a global radiation of 7580.8 Wh m�2 day

and south-westerly winds of 19 km h�1 (CENPAT, accessed

01.08.2010). The vegetation is characterised by small shrubs and

subshrubs [21], therefore the city has been forested with tree species

like pine, eucalyptus and poplar, which have been indicated as

suitable biomonitors of fluoride [1, 13]. Leaves of Eucalyptus rostrata

Schlecht., Populus hybridus L. and needles of Pinus radiata D. Don were

collected, when present, at forty sampling points in the vicinity of

the aluminium factory in the third week of February 2010 (Fig. 1).

Samples consisted of 150–200 leaves or needles and were randomly

collected in each sampling site from a single tree according to the

standardised method after VDI [22].

2.2 Plant analyses

In order to address the quantity of surface deposited fluorine,

washed and unwashed leaves and needles were considered in the

F analyses separately. For the washing procedure, leaves and needles

were washed in 500 mL PE flasks with 200 mL deionised water and

shaken for 5 min. The fluoride analysis followed the method

described in VDI [23] and was based on an alkali melt. Fluoride levels

were determined with an ion-sensitive electrode (ISE F 800 DIN, WTW

Weilheim, Germany) coupled to a ionometer (Inolab pH/Ion 735

WTW Weilheim, Germany). Further details on these analyses are

described in Franzaring et al. [4]. The calibration was made using NaF

standard solutions. To assure the quality of the fluoride analyses a

certified standard was used. In addition to the F-analyses, leaf area

and fresh and dry biomass were determined so that specific leaf area

(SLA) (only determined for P. hybridus and E. rostrata) and dry matter

contents of the leaf samples could be calculated.

Figure 1. Fluoride concentrations (ppm) in unwashed leaves of eucalypt, poplar and unwashed pine needles from the current and the previous season.Rectangle represents the location of the aluminium smelter in Puerto Madryn (Patagonia).

2 J. H. Rodriguez et al. Clean – Soil, Air, Water 2012, 00 (0), 1–5

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2.3 Water analyses

Fluoride analyses were also performed in the solutions that resulted

from the washing of a known quantity and number of leaves.

Twenty-five milliliters of these water samples were mixed with

the same volume of total ionic strength adjustment buffer (TISAB,

WTW Weilheim, Germany). Water samples and standards were

measured with the fluoride-sensitive electrode as specified above.

Furthermore, pH and electrical conductivity (EC) of the solutions

were determined using a pH meter (Altronix TPX II) and an EC-meter

with a glass electrode (Oakton WD-35610).

2.4 Statistical analysis

A regression analysis was performed in order to determine the

relationships between the accumulation of fluoride and distance

from the emission source. In addition, in order to compare signifi-

cant differences between linear regression models for washed and

unwashed samples for each species, and between different pinus

needle ages, the data were analysed contrasting the linear regression

models. All analyses were performed using Excel and InfoStat

software.

3 Results

In the unwashed samples, F concentrations ranged between 6 and

3652 ppm in the deciduous tree species (Tab. 1), while they varied

between 11 and 405 ppm in the conifer (current needles, Tab. 2).

Whereas leaf properties were not addressed in pine, mean leaf size,

dry matter content and SLA were determined in eucalypt and poplar

leaves. These parameters had to be measured in order to calculate

fluoride contents per leaf area. As can be seen in Tab. 1, poplar (mean

leaf size of 35 cm2/leaf) has larger leaves than eucalypt (mean leaf

size of 17 cm2/leaf) on average and the lower SLA in the latter species

indicates that leaves in E. rostrata are much more compact. Latter is

also confirmed by the higher dry matter content in leaves of eucalypt

as compared to poplar. Leaf size, density and dry matter content did

not show strong variation in the study area and were unrelated to

fluoride emissions. E. rostrata showed higher values of F by leaf area

compared to P. hybridus (Tab. 1).

Highest concentrations of fluoride were determined in leaves of

E. rostrata, which were taken from trees close to the emission source

(Fig. 1). In addition, all species showed a steep pollution gradient in

relation to the distance from the industry (Fig. 2). At a distance of

>5000 m for E. rostrata and P. radiata and >3500 m for P. hybridus,

background levels of 10–15 ppm were no longer exceeded (Tab. 1).

Table 1. Leaf properties and fluoride concentrations determined in E. rostrata and P. hybridus

Species Descriptivestatistics

Drymatter (%)

Leaf size(cm2 plant�1)

SLA(cm2 g�1)

Unwashed(ppm)

Washed(ppm)

Washing water(ppm) (pH/EC)

F�

(mg cm�2)Reduction bywashing (%)

E. rostrata Mean 50 17 68 614 555 53 (6/40) 9 24

F¼ 197.81���

N¼ 17 Minimum 50 7 40 12 7 16 (6/18) 0.2 4Maximum 60 33 85 3652 3654 131 (7/78) 47 64SD 4 8 11 1057 1032 33 (0.2/17) 14 22

P. hybridus Mean 43 35 115 31 18 13 (6/76) 0.26 39

F¼ 26.72���

N¼ 13 Minimum 33 16 91 6 4 5 (6/22) 0.06 23Maximum 49 65 147 108 61 19 (7/249) 0.74 54SD 5 16 19 29 16 3 (0.2/60) 0.21 13

‘SLA’ refers to specific leaf area, ‘EC’ to electric conductivity (mS cm�1) and ‘SD’ to standard deviation.F-statistic and probability values in each row are the results of the contrast between linear regression models of washed and unwashedsamples for each species (ns, not significant, �p< 0.05, ��p< 0.01, ���p< 0.001).

Table 2. Fluoride concentrations in unwashed and washed needles determined in current and 1 year old needles of P. radiata and chemical parameters

measured in the washing water

Needle age Descriptivestatistics

F� unwashed(ppm)

F� washed(ppm)a)

F� washingwater (ppm)a)

pH washingwatera)

EC washingwatera) (mS cm�1)

Reduction bywashinga) (%)

2009–2010 Mean (N¼ 19) 98 52 33 7 100 51

F¼ 94.64���

Minimum 11 4 14 6 21 16Maximum 405 162 88 7 448 100SD 110 54 19 0.3 93 21

2008–2009 Mean (N¼ 13) 412 n.d. n.d. n.d. n.d. n.d.Minimum 29 n.d. n.d. n.d. n.d. n.d.Maximum 1789 n.d. n.d. n.d. n.d. n.d.SD 412 n.d. n.d. n.d. n.d. n.d.

F-statistic and probability values in each row are the results of the contrast between linear regression models of washed and unwashedsamples (ns, not significant, �p< 0.05, ��p< 0.01, ���p< 0.001).a) Parameters only determined in 1 year old needles. ‘EC’ refers to electric conductivity, ‘SD’ to standard deviation and ‘n.d.’ to not

determined.

Clean – Soil, Air, Water 2012, 00 (0), 1–5 Fluoride Biomonitoring Using Foliage from Different Trees 3

� 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.clean-journal.com

Washing the leaves reduced the F content by 51% on average in

pine needles, while in the poplar leaves the F content was lowered by

39% after washing. In contrast, only 24% of the accumulated F could

be washed off on average from the Eucalyptus leaves (Tab. 1). In

addition, through contrast analyses, significant differences between

regression models of washed and unwashed samples for all species

were observed (Tab. 1). The fluoride concentration in the washing

water corresponded to the amount of F washed, whose values reflect

the difference between the F concentration in unwashed leaves

minus the F concentration in washed leaves. With regard to

the pH values, no significant difference was found in the washing

water from different species, but for EC the highest values were

observed in P. radiata and the lowest in E. rostrata (Tabs. and 2).

Furthermore, the comparison between the F concentrations in

P. radiata needles from different ages showed significant higher

values (F¼ 218.1, p< 0.0001) in the older needles with F concen-

trations being four times greater than in the current years needles

(Tab. 1 and Fig. 3).

4 Discussion

The highest values found in this study by far exceed the maximum

background levels for plants and animal feed [9, 13, 24, 25] but no

information was available on potential health risk to animals and

humans by the deposition of F in the study area, so it cannot be ruled

out that emissions from the smelter could indeed be harmful to the

environment and animal health. According to the literature, F values

found in this study are among the highest that have ever been

described, whereas Vike [13] reported maximum values of

2400 ppm F in leaves of B. pubescens close to aluminium smelters

in Norway. Lee et al. [26] report values >5000 ppm in native plant

species in the vicinity of ceramic industries in Taiwan.

Overall, very high F-concentrations were found in all species in the

vicinity of the emission source, indicating a steep fluoride concen-

tration gradient in the air along the main wind direction (SW) in the

months prior to monitoring. Although not all the species were found

in the same monitoring sites, differences in relation to the mass and

area-based F concentration were found among the species P. radiata,

E. rostrata, P. hybridus, showing lowest concentrations in the latter.

This could be due to specific differences in growth habit and leaf

properties between the species, which determine the uptake of

atmospheric pollutants and the amounts of pollutants that may

be washed off. Moreover, the comparison between P. hybridus and

E. rostrata identifies the latter as a more efficient bioaccumulator of F

by leaf area.

During 2 months prior to the leaf collection (January to February

2010) rainfall was not significant. The comparison between

unwashed and washed samples suggests that at precipitation

amounts in the study area fluoride concentrations could be reduced

in the species studied, however, there were no significant differ-

ences. In addition, measurements of the reduction of fluoride by

washing showed the highest values in Pinus needles and the lowest

values in Eucalyptus leaves, which was supported by the high and low

EC values in the washing waters of pine and eucalypt, respectively.

These results indicate a strong association of particulate fluoride

attached to the leaf surface, suggesting that species-specific charac-

teristics determine the accumulation and removal of pollutants.

Apart from the leaf area other factors like the presence of hairs,

epidermal features including the structure of wax crystals may

determine the accumulation of air pollutants on plant surfaces. It

Figure 2. Fluoride pollution gradient in the study area expressed as fluoride concentration in unwashed (full lines) and washed (dashed lines) leaves ofE. rostrata and P. hybridus and needles of P. radiata in relation to the distance from the emission source.

Figure 3. Fluoride pollution gradient in the study area expressed as fluorideconcentration in unwashed current needles (dashed lines) and 1 year oldneedles (full lines) of P. radiata in relation to the distance from the emissionsource.

4 J. H. Rodriguez et al. Clean – Soil, Air, Water 2012, 00 (0), 1–5

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may also be hypothesised that the excretion of sticky secondary

compounds may favour the adsorption of particulates and partly

explain why eucalypt has a higher accumulation efficiency. Probably

the large amount of extracellular fluids excreted by Eucalyptus leaves

as described by Goodger et al. [27] relates to the higher chemical

affinity of deposited dusts. Finally, the comparison between differ-

ent needle ages of Pinus showed much higher fluoride concentrations

in the oldest leaf organs, reflecting a greater accumulation of fluo-

rides upon the longer exposure time.

The analysis of F concentrations in leaves confirmed a significant

pollution gradient with the highest fluoride content in samples

collected in the vicinity of the emission source. In the comparison

among species, E. rostrata showed the highest values of fluoride

accumulated which is due to the foliar characteristic such as mass

and area as well as a higher capacity of retention on leaf surfaces. The

impact of the smelter show that this is severe in an area close to the

source of up to four kilometres, but the effects decrease at a greater

distance. Further studies in relation to the environmental and

human health should be carried out, investigating the F concen-

trations in the natural steppe vegetation and in vegetables and fruits

that are used for consumption.

Acknowledgments

This work was funded by the Ministry of Science, Technology and

Productive Innovation (Ministerio de Ciencia, Tecnologıa e

Innovacion Productiva, MINCyT) of Argentina and the

International Bureau (IB) of the Federal Ministry of Education and

Research (Bundesministerium fur Bildung und Forschung, BMBF) of

Germany, Cooperation Project No. AL0802. The first author J. H.

Rodriguez was suported by a scholarship of Consejo Nacional de

Investigaciones Cientıficas y Tecnicas (CONICET). The authors are

grateful to Msc. Ana Marıa Beeskow (CENPAT, CONICET) for provid-

ing advice in the identification of tree species. Mr. S. Weller is

thanked for language revisions.

The authors have declared no conflict of interest.

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