arsenic in soil and vegetation of contaminated areas in southern tuscany_italy

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Arsenic in soil and vegetation of contaminated areas in

southern Tuscany (Italy)

F. Baronia , A. Boscagli b, L.A. Di Lella a , G. Protanoa , F. Riccobonoa,*

a Dipartimento di Scienze Ambientali, Sezione di Geochimica Ambientale, University of Siena, Via del Laterino 8, I-53100 Siena, Italy b Dipartimento di Scienze Ambientali, Sezione di Botanica, University of Siena, Via Mattioli 4, I-53100 Siena, Italy

Received 27 February 2003; accepted 16 June 2003

Abstract

Arsenic contents of soils and higher plants were surveyed in two former Sb-mining areas and in an old quarry once used for

ochre extraction. Total As in the soils ranged from 5.3 to 2035.3 mg kg 1, soluble and extractable As from 0.01 to 8.5 and from

0.04 to 35.8 mg kg 1, respectively. The As concentrations in the different fractions of soil were correlated significantly or very

significantly. Sixty-four plant species were analyzed. The highest As contents were found in roots and leaves of Mentha

aquatica (540 and 216 mg kg 1, respectively) and in roots of Phragmites australis (688 mg kg 1). In general, the As contents

of plants were low, especially in crops and in the most common wild species. In the analyzed species, roots usually showed the

highest content followed by leaves and shoots. Arsenic levels in soils and plants were positively correlated, while the ability of

the plants to accumulate the element (expressed by their Biological Accumulation Coefficients and Concentration Factors) wasindependent of the soil As content. Comparison with the literature data, relationships between the As contents in plants and

soils, and biogeochemical and environmental aspects of these results are discussed.

D 2003 Elsevier B.V. All rights reserved.

Keywords: Arsenic; Plant accumulation; Mining area; Soil contamination

1. Introduction

The average arsenic content in the Earth’s crust

(clarke) was estimated by Greenwood and Earnshaw(1984) to be as high as 1.8 mg kg 1. A rather similar

value of 1.5 mg kg 1 was suggested by Wedepohl

(1970) for igneous rocks on the basis of the average

values of granites, basalts and gabbros. Decidedly

higher As values were detected in sedimentary rocks

and a value as high as 13 mg kg 1 (Wedepohl, 1970)

appears appropriate for clayey rocks such as shales.

Since As accumulates during weathering and translo-

cation in colloid fractions, its concentration is usually

higher in soil than in parent rocks (Yan-Chu, 1994). Innature, the element is a fundamental constituent of the

sulfide mineral arsenopyrite (FeAsS), as well as the

minerals lollingite (FeAs), realgar (AsS) and orpiment

(As2S3).

The anthropogenic contribution to As contents of

superficial geochemical environments is also impor-

tant (Nriagu and Pacyna, 1988; Pacyna et al., 1995).

In some cases, mining activity is directly involved in

the release of huge stocks of arsenic into superficial

environments (Murdoch and Clair, 1986).

0375-6742/$ - see front matter D 2003 Elsevier B.V. All rights reserved.doi:10.1016/S0375-6742(03)00208-5

* Corresponding author. Fax: +39-577-233945.

E-mail address: [email protected] (F. Riccobono).

www.elsevier.com/locate/jgeoexp

Journal of Geochemical Exploration 81 (2004) 1–14



Arsenic exists in soil mainly as pentavalent (AsV)

arsenate (AsO43), which mak es up 90% of dissolved

As species in aerobic soils (O’Neill, 1995), or as

trivalent (AsIII

) arsenite (AsO2

). The latter representsthe most environmentally dangerous form of As.

The chemical similarity of arsenate to phosphate

and the high affinity of arsenite with sulfhydryl groups

of enzymatic and structural proteins are the ultimate

reasons for arsenic toxicity to living organisms.

The arsenate anion is rather easily chemisorbed by

soil colloids and, deriving from the strong arsenic acid

H3AsO4, adsorbs most effectively at low pH. Conse-

quently, arsenate mobility is quite low in acidic soils,

especially where high contents of clay or metal oxide

are involved. Conversely, in alkaline soils, As may be

mobile in the soluble Na-arsenate form (McBride,

1994). Thus, adsorption of arsenate onto soil particles

is dependent on various parameters, but mostly pH.

According to Elkhatib et al. (1984), the pH, the

redox conditions and the Fe-oxide content in soil are

the most important features controlling AsIII adsorp-

tion. The element has a rather long residence time in

soils (from 1000 to 3000 years; Bowen, 1979) and

tends to be enriched into top horizons by cycling

through vegetation, atmospheric deposition and sorp-

tion by soil organic matter (Alloway, 1990). Its

availability for uptake by plants is affected by severalfactors, such as the source, chemical speciation and

soil parameters (pH, Eh, organic matter and colloid

contents, soil texture and drainage conditions; Eisler,

1994; Mitchell and Barr, 1995).

The mobility of arsenic in aqueous solutions in-

creases in the trivalent oxidation state (Hermann and

Neumann-Mahlkau, 1985). However, the conversion

of AsV to AsIII appears rather slow, even under

strongly reducing conditions, as suggested by obser-

vations on a range of redox and pH environments

(Masscheleyn et al., 1991).In terrestrial plants, arsenic uptake is largely spe-

cies specific and arsenic concentrations in plant tis-

sues generally cannot be related to those in the soils

(O’Neill, 1995). In this regard, it is relevant for human

health that As levels in edible plants are usually low,

even when they grow on contaminated soils (NRC,

1977; MAFF, 1982).

Kabata-Pendias and Pendias (1984) reported that

the As background for terrestrial plants growing on

uncontaminated soils ranges from 0.009 to 1.5 mg

kg 1 on a d.w. basis. Some species of the genus

Agrostis growing on contaminated soils have been

found to accumulate and tolerate high As levels: up to

6640 mg kg 1

d.w. in the old leaves of A. canina and A. tenuis (Porter and Peterson, 1975), 1350 mg kg 1

in Agrostis stolonifera (Porter and Peterson, 1977a),

1900 mg kg 1 in Agrostis castellana and 1800 mg

kg 1 in Agrostis delicatula (de Koe et al., 1991; de

Koe, 1994). Pseudosuga taxifolia, Pityrogramma cal-

omelanos and Pteris vittata growing on soils of

mineralized or contaminated areas were even more

able to accumulate As, showing cont ents of 8200,

8350 and 7526 mg kg 1, respectively (Warren et al.,

1968; Ma et al., 2001; Visoottiviseth et al., 2002).

Aquatic plants such as Ceratophyllum demersum,

Egeria densa and Potamogeton pectinatus accumu-

lated arsenic up to 1160, 1120 and 4990 mg kg 1,

respectively, without any apparent damage (Dushenko

et al., 1994; Robinson et al., 1995). In contrast,

wetland plants a ppear unable to accumulate As to

the same extent (Otte et al., 1990; Qian et al., 1999).

The highest concentrations have been found in Spar-

tina alterniflora (550 mg kg 1) by Carbonell et al.

(1998) and in Eichornia crassipes (500 mg kg 1) by

Zhu et al. (1999).

Arsenic is not an essential element for plants, and

once it is taken up, usually only a small proportion istranslocated to the epigeal parts. The result is the

following concentration gradient: roots>stems>leaves.

Nevertheless, concentrations up to 2000, 22,630 and

8350 mg kg 1 were found in foliage of Agrostis

ecotypes, P. vittata and P. calomelanos, respectively,

by Porter and Peterson (1975, 1977a,b), Ma et al.

(2001) and Visoottiviseth et al. (2002).

Inside the plant cell, the two most common chem-

ical species (arsenite and arsenate) strongly induce

phytochelatin synthesis, which has an important role

in detoxification (Schmoger et al., 2000).This paper deals with the impact on vegetation of

As diffusion into the environment related to different

forms of historical mining activities.

2. The study areas

Since the pre-Roman Age, southern Tuscany has

been one of the few important mining districts in Italy.

Epithermal deposits of Hg and Sb were intensely

F. Baroni et al. / Journal of Geochemical Exploration 81 (2004) 1–142



exploited until the 1970s. These intensive mining and

smelting activities produced huge quantities of waste

materials which, in the absence of any reclamation,

still release toxic heavy elements into the surroundingenvironment (Protano and Riccobono, 1997; Protano

et al., 1998). Since As is a minor but ubiquitous

constituent of the epithermal mineral assemblage of

these ores (Riccobono, 1993), this element also con-

tributes to the overall pollution of the mining areas.

High resolution geochemical maps of southern Tus-

cany (Protano et al., 1998, 1999) have shown that

strong, extensive As anomalies are present in various

areas of this region where base metal and Sb– Hg

epithermal deposits were exploited in the past.

In addition to the abandoned mining and smelting

areas, other situations with severe arsenic contamina-

tion are known from this region. In the Mt. Amiata

volcanic massif area in the southeastern corner of the

region, there are numerous deposits of yellow-brown

ochre, employed as a dye since the Etruscan Age and

intensely exploited until very recently. These deposits

consist of horizons (3–4 m thick) belonging to the

sedimentary sequence of Quaternary lacustrine basins.

The ochre exhibits extremely high arsenic contents,

ranging (if expressed as As2O3) from 0.59% to 9.04%

by weight (Cipriani et al., 1971). Such high figures are,

at least in part, due to the diffuse presence of ironarsenates (most probably poorly crystalline FeAsO4

2H2O or scorodite).

Fig. 1 shows the location of the three areas of

southern Tuscany (with expected anomalous As con-

tents in the soil) where we chose to investigate the

transfer of this element from soil to plant species.

Area A is in the Sb-mining district of the Tafone

Valley in the Monti Romani area (Protano and Ricco-

bono, 1997; Baroni et al., 2000a). The most important

antimony mines of the region were active there,

together with a plant for Sb-ore smelting and the production of antimony trioxide.

Area B refers to the old antimony mine of Cetine di

Cotorniano near the town of Siena, which was mainly

exploited in the period between the two World Wars.

More than half a century after closure, the mine dumps

and the roasting-plant area are now largely colonized

by several herbaceous plant and shrub species.

Area C is located in the volcanic massif of Mt.

Amiata near the town of Castel del Piano (Grosseto

County). A quarry was active there for the exploita-

tion of an extensive ochre horizon. The central and

deepest part of the quarry is now occupied by a very

small lake, while the surroundings are colonized by

wild vegetation.

The general geology and lithological features of

areas A and B are not identical but rather similar. APaleozoic metamorphic basement, mainly composed

of quartzites and metasandstones, is unconformably

covered by a Triassic succession. The lowest carbon-

ate member (Cavernous Limestone) of the Mesozoic

sequence was widely affected by strong hydrothermal

alterations, which mostly produced limestone siliciza-

tion, and hosts stibnite (Sb2S3)-rich ore bodies.

Area C lies on the lava flows, mostly riodacitic in

composition, present on the western slope of the

inactive Mt. Amiata volcano. The ochre horizons are

Fig. 1. Location of the study areas in southern Tuscany (see text).

F. Baroni et al. / Journal of Geochemical Exploration 81 (2004) 1–14 3



often interlayered with very thin clayey and diatomite

levels, sometimes bearing lenses of yellow opal

(Cipriani et al., 1971). Analyses of ochre samples

revealed very high contents of iron (up to 65% Fe byweight) and arsenic (up to 9% As expressed as As2O3

by weight; Cipriani et al., 1971). The genesis of these

As-rich ochre horizons has still not been satisfactorily

explained. However, according to Carobbi and Rodo-

lico (1976), both inorganic and organic processes

were involved in the formation of this quite peculiar

type of rock.

3. Sampling surveys

Plant and soil samples were collected in 1996,

1997 and 1998 from the three localities described

above. Wild plant species were usually sampled,

except in area A where specimens of cultivated plants

were also collected.

Sampling was carried out in area A in the sur-

roundings of the small lake in the open pit of the old

Tafone Mine and along a length of the Chiarone

stream where mining works were intensive. In this

area, six sampling sites were established (S1–S6). S1

and S2 were located in cultivated fields, S3 in a

vegetable garden, S4 in an old field, S5 on minedumps and S6 at a mineral processing tailing pond.

In area B, plant specimens were collected from the

dumps and from the area used to roast sulfide miner-

als. In area C, plant species were sampled from the

slopes of a quarry and from adjacent pastures.

Plant and soil samples were collected according to

the following criteria. Cultivated plant species were

selected to represent the ones most commonly sown in

the sampling areas. Wild species were selected on the

basis of thei r potential use as phytoremediators,

according to their:

– adaptation to adverse edaphic conditions

– large biomass allocation in the above-ground part

– fast maximization of above-ground biomass

– frequency in the field

At least three specimens of each selected species

were collected for analysis at each sampling site. In

species where roots were difficult to collect, only the

shoots were collected.

From four to nine soil samples, representative of

the top 20 cm, were collected at each site.

The nomenclat ure of the plant species is according

to Pignatti (1982).

4. Materials and methods

4.1. Analysis of plant tissues and soil

Plant material was carefully washed in tap water

and then processed in an ultrasonic cleaner to remove

soil particles. This was followed by a rinse with

acidified deionized water (HCl 3%) and a final rinse

with ultra-pure water.

Absorbing (roots) and non-absorbing parts of

plants (leaves, shoots, inflorescence, etc.) were usual-

ly separated in order to obtain information about the

species’ ability to transfer As. In some species,

especially those of Gramineae, the leaves and shoots

were analyzed together because of the difficulty in

separating them. The plant material was oven-dried at

40 jC to constant weight, then pulverized. About 0.5

g of dry matter was digested with a Milestone micro-

wave lab-station (Ethos 900) after addition of 5 ml

HNO3 and 2 ml H2O2 (Baker ultra-pure reagents).

Soil samples were air dried, sieved through a 2-mmmesh and pulverized in an agate mortar. They were

then subjected to acid digestion for determination of

total As content: 1 ml HF + 2 ml HNO3 + 2 ml HCl + 1

ml HClO4 were added to 200 mg of powdered soil and

the mixture was processed with an Ethos 900 lab-

station. An estimate of the phytoavailable As content

was obtained by both pure water and gentle acidic

extraction. Water extraction was performed by adding

100 ml of ultra-pure water to 40 g of soil and shaking it

for 24 h; acidic extraction was carried out by adding

200 ml of a 0.43 mol solution of acetic acid to 5 g of soil and shaking it for 16 h (according to the procedure

of Ure et al., 1993). Polyethylene bottles were used to

collect and store the solution after the extraction.

Atomic absorption determination of As contents

was carried out with a Perkin-Elmer 5000 AAS,

equipped with FIAS, employing the hydride genera-

tion method. Working standards for chemical analyses

were prepared from Perkin-Elmer stock solutions.

Reference standards were SV-M (soil) from the Insti-

tute of Radioecology and Applied Nuclear Techniques




(IRANT), Kosice (Slovakia), 2709 San Joaquin soil

from NIST, BCR 60 (aquatic plant) from the Bureau

of Reference of the EU and GBW-07603 (bush

branches and leaves) from the Institute of Geophysicaland Geochemical Exploration of Langfang (China).

Accuracy of the analytical results was within 7%.

The cation exchange capacity (CEC) was deter-

mined by the compulsive exchange procedure sug-

gested by Gillman and Sumpter (1986); extractable

phosphorus was measured by UV – Visible spectro-

photometry (Hach DR-4000) following the Hach

8190 method; the pH was measured in deionized

water (soil/water ratio = 1:2.5 w/v). Organic matter

contents were estimated through the percentage loss

in weight after ignition at 375 jC for 16 h in a furnace

(Storer, 1984).

4.2. Data analysis

The analytical results were used to check the

relationships between: (i) total, soluble and extract-

able soil arsenic; (ii) soil and plant As contents.

Two coefficients, Biological Absorption Coeffi-

cient (BAC) and Concentration Factor (CF), were

also considered. The former is the ratio of plant

arsenic to total soil arsenic (Edwards et al., 1998),

while the latter is the ratio of plant arsenic to solubleor extractable arsenic in the soil. The CFs for soluble

and extractable soil arsenic were designated as CFsol

and Cf extr , respectively. Relationships were identified

with the non-parametric Spearman Rank Correlation

Coefficient.

The ability of the plant species to translocatearsenic from the roots to shoots was also tested. The

palatability of each plant species to livestock (primar-

ily to sheep, the most common livest ock in the study

areas) was consider ed according to Daget and Pois-

sonet (1971) and Sostaric-Pisacic and Kovacevic

(1974).

5. Results

5.1. Soils

In the Tafone–Chiarone district (area A), the total

arsenic contents in soils of the cultivated and unculti-

vated fields averaged from 5 to 40 mg kg 1 d.w. The

mine dumps and the tailing ponds showed mean values

of 266 and 1226 mg kg 1, respectively (Table 1).

However, the arsenic content was highly variable,

ranging from 1.3 to 55 mg kg 1 in the fields, from

38to899mgkg 1 in the dumps and from 2 to2466 mg

kg 1 in the tailings. Similar contents were found in the

soils above the mine dumps of area B and high values

were recorded in the quarry slopes and the pastures of area C, where a mean content exceeding 2000 mg kg 1

and a range from 1037 to 3133 mg kg 1 were found.

Table 1

As content and some edaphic parameters of soils (meanFS.E.). In each column, the values followed by the same letter are not significantly

different (Tukey test; p < 0.05)

Sampling

sites

As (total)

(mg kg 1)

As (soluble)

(mg kg 1)

As (extractable)

(mg kg 1)

Organic matter

(%)

pH Pavailable

(mg kg 1)

CEC

(meq/100 g)

Area A

S1 (n = 4) 14.60F 1.00a 0.01F 0.01a 0.10F 0.03a 4.37F 0.66a 5.8F 0.2a 0.13F 0.07a 5.34F 1.39a

S2 (n = 4) 5.30F 2.17b 0.01F 0.01a 0.08F 0.03a 4.82F 0.80a 5.5F 0.1a 0.15F 0.05a 5.51F1.08a

S3 (n = 4) 39.90F 2.85c 0.02F 0.01a 0.04F 0.02a 5.25F 1.27a 5.4F 0.3a 0.18F 0.12a 5.97F 0.42a

S4 (n = 5) 40.00F 3.81c 0.02F 0.01a 0.08F 0.02a 4.59F 0.30a 5.0F 0.1a 0.11F 0.10a 5.19F 1.54a

S5 (n = 9) 265.60F 88.26cd 0.01F 0.01a 0.66F 0.23b 3.03F 0.40ab 7.3F 0.2ab 0.14F 0.03a 5.83F 1.54a

S6 (n = 6) 1225.60F 351.70d 0.04F 0.02a 1.50F 0.33c 1.68F 0.39b 7.2F 0.5ab 0.11F 0.02a 4.06F 0.96a

Area B

(n = 4) 372.83F 77.25 0.03F 0.02 0.52F 0.18 3.06F 0.55ab 8.2F 0.6b 0.08F 0.04a 5.49F 1.63a

Area C

Quarry slopes (n = 4 ) 753.82F 34.55a 1.82F 0.27a 7.60F 0.91a 2.80F 0.22ab 5.8F 0.7a 0.97F 0.89bb 6.04F 0.59a

Pasture (n = 4) 2035.32F 297.12b 8.48F 1.40b 35.80F 2.98b 5.05F 1.41a 6.2F 0.9ab 0.83F 0.39bb 6.66F 1.04a




Water-soluble arsenic gave figures from 2 to 5

orders of magnitude lower than the total As values.

In area A, the mean value (for each sam pling site)

varied from 10 to 40 Ag kg 1

(see Table 1), while thetotal range was from 2 to 70 Ag kg 1. In area C, the

water-soluble arsenic content was very high, especial-

ly in soils of pastures (mean: 8.5 mg kg 1).

There was a rather similar pattern for acid-ex-

tractable arsenic. The As contents reached the high-

est values in C but the extractable fraction still

represented a very small aliquot of the total As

(0.1–1.8%).

A relationship between As contents was only

evident in the case of fields (cultivated and old),

particularly between total and soluble As (r = 0.921;

p < 0.01; n = 17). However, when the high variability

of the data (the coefficients of variation averaged

53%) was smoothed by considering the mean of each

sampling site, the soluble and extractable fractions

were correlated with the total contents (r = 0.887 andr = 0.862, respectively; p < 0.01; n = 9), and a relation-

ship between the soluble and extractable fractions also

appeared (r =0.680; p < 0.05; n =9).

According to SISS (1985) criteria, only the soil of

the area A tailing ponds (S6) can be considered poor

in organic matter (Table 1). The pH was acidic in the

fields of area A (S1–S4) and area C, while it was

neutral or alkaline in the mine wastes of areas A (S5–

S6) and B, respectively.

All sampling sites showed very low levels of avail-

able phosphorus in the soil, as well as low cation

exchange capacities (CEC). The correlation analysis

Table 2

Sampling area A. Arsenic content in crops and vegetables of cultivated sites (S1, S2, S3) and in plant species growing in the old field S4

(meanF S.E.; mg kg 1)

Sampling sites and

plant species

Leaves Leaves and

shoots

Shoots Roots Flowers and

inflorescences

Fruits and

seeds

S1

Zea mays < 0.02 0.03F 0.02

Triticum aestivum < 0.02

S2

Helianthus annus 0.04F 0.01 0.03F 0.02 Medicago sativa 0.04F 0.03

S3

Lactuca sativa 0.13F 0.11

Solanum melangena 0.11F 0.09

Cucurbita pepo 0.23F 0.12 0.23F 0.11

Capsicum annuum 0.27F 0.18 < 0.02

Lycopersicon esculentum 0.07F 0.03 < 0.02

S4

Rubus ulmifolius 0.86F 0.19 0.21F 0.19

Sonchus asper 0.11F 0.05 1.24F 0.73

Medicago hispida 0.62F 0.14 1.14F 0.27

Bromus hordeaceus < 0.02 0.53F 0.17

Bromus madritensis 0.04F 0.02 0.22F 0.09

Helichrysum italicum 2.53F 1.99 1.05F 0.05 0.31F 0.12

Phalaris coerulescens 0.54F 0.09 5.14F 1.42 < 0.02

Avena fatua 0.44F 0.15 6.21F 2.37 0.04F 0.01

Achillea ageratum 6.95F 1.72 0.47F 0.31

Brassica napus 0.19F 0.13 0.02F 0.01 0.34F 0.26

Lupinus albus 2.54F 1.79 0.81F 0.13 2.89F 0.95 0.44F 0.17

Urospermum dalechampii 0.07F 0.06 2.20F 1.14 0.24F 0.81

Coleostephus myconis 0.62F 0.21 0.04F 0.03 13.25F 3.71 0.59F 0.09

Rumex crispus 0.48F 0.33 < 0.02 0.05F 0.01 0.29F 0.11

Anchus italica 1.39F 0.74 0.09F 0.02 0.79F 0.26 0.69F 0.30




showed that the As contents of soil (total, soluble and

extractable) were independent of CEC, pH, content of

available phosphorus and organic matter. All the

edaphic parameters were also independent of eachother.

5.2. Arsenic contents of plant species

In total, 64 plant species were sampled, 59 of them

in the Tafone–Chiarone district (area A). The plant

species were mostly Dicotyledons (54), Compositae

(15), Leguminosae (12) and Gramineae (9), tap-rooted

(42), perennial (41) and herbaceous (54), largely as a

result of the sampling criteria. Some species, such as

Achillea ageratum, Dactylis hispanica, Helichrysum

italicum, Inula viscosa, Medicago sativa, Plantago

lanceolata and Silene vulgaris, were collected in two

or more sampling sites.In area A, crops and vegetables sampled at sites S1,

S2 and S3 showed very low As concentrations,

sometimes below the limit of instrumental detection

(Table 2). In the old field (S4), plants had As contents

of 1–2 mg kg 1 or less and only the weed Coleos-

tephus myconis showed slight accumulation, with 13

mg kg 1 of arsenic in its roots (Table 2). Only 5 ( P.

lanceolata, Mentha aquatica, Galactites tomentosa,

C. myconis and A. stolonifera) of the 34 plant species

sampled on the mine dumps (S5) had at least 10 mg

Table 3

Sampling area A. Arsenic content in plant species growing on mine waste dumps S5 (meanF S.E.; mg kg 1)

Plant species Leaves Shoots Leaves and shoots Roots Inflorescences Seeds

Achillea ageratum 1.81F 0.52 0.07F 0.04 0.70F 0.19 3.32F 0.73

Plantago lanceolata 9.35F 1.70 62.18F 9.74

Mentha aquatica 216.35F 19.36 37.44F 9.26 540.16F 23.08

Galactites tomentosa 4.40F 1.62 1.15F 0.07 16.18F 3.21

Silene vulgaris 5.82F 1.09 2.54F 1.74 6.68F 2.76

Coleostephus myconis 10.85F 4.52 2.40F 0.08 22.83F 5.29 4.50F 1.08

Sylibum marianum 5.19F 2.07 2.16F 0.49 5.53F 0.99

Trifolium pratense 0.50F 0.13 0.08F 0.03 4.46F 1.72

Conyza bonariensis 7.70F 3.28 2.54F 0.72 4.00F 1.37 Dorycnium hirsutum 3.11F 0.09 3.24F 1.04 2.81F 0.15

Melilotus officinalis 0.67F 0.27 0.13F 0.05 0.86F 0.17

Lepidium campestre 1.44F 0.35 0.15F 0.07 1.22F 0.29 0.12F 0.04

Dipsacus fullonum 0.24F 0.09 0.09F 0.02 5.36F 0.77

Reichardia picroides 1.51F 0.68 0.72F 0.28 0.83F 0.25

Ranunculus velutinus 2.14F 0.88 0.44F 0.13 2.35F 0.86

Sinapis arvensis 1.67F 0.41 0.06F 0.02 0.44F 0.08

Hedysarum coronarium 0.47F 0.15 0.37F 0.11 0.66F 0.24

Inula viscosa 2.97F 1.31 0.06F 0.04 0.24F 0.06

Hypericum perforatum 1.23F 0.08 0.87F 0.09 1.12F 0.09

Ulmus minor 0.16F 0.05 0.14F 0.03

Sambucus ebulus 0.59F 0.16 0.97F 0.26 0.79F 0.16

Cistus salvifolius 1.29F 0.37 0.22F 0.07

Trifolium incarnatum 0.38F 0.09 0.89F 0.39 0.21F 0.04

Rosa canina 0.39F 0.21 0.19F 0.05 0.09F 0.04

Dactylis hispanica 0.16F 0.04 < 0.02 0.34F 0.05

Medicago sativa 2.81F1.04 3.34F 0.58

Lotus corniculatus 0.09F 0.07 0.99F 0.15

Sanguisorba minor 0.09F 0.01 0.17F 0.02

Spartium junceum < 0.02

Foeniculum vulgare 0.08F 0.03 3.32F 0.35 2.55F 0.27

Quercus ilex 0.10F 0.03

Quercus cerris 0.05F 0.01 < 0.02

Holoschoenus vulgaris 6.87F 1.73

Agrostis stolonifera 10.13F 1.08




kg 1 of arsenic in their tissues, mostly in the roots

(Table 3). The M. aquatica specimens collected at the

shores of the small lake had rather high arsenic levels,

both in the leaves (mean: 216 mg kg 1) and roots

(mean: 540 mg kg 1).

Almost all the plant species growing in the tailing

ponds were sampled because of the small number

growing at this site. They generally had higher arsenic

contents than plants at the other sampling sites (com-

pare Table 4 with Tables 2, 3 and 5). However, in five

of the nine collected species, the arsenic concentra-

tions were < 50 mg kg 1 and only the roots of

Phragmites australis (mean: 688 mg kg 1) showed

arsenic accumulation.

In the intensively sampled area A, there were low

or very low arsenic contents in most plant species

growing on the mine dumps, slopes and neighboring

dry badlands. This was es pecially true for the above-

ground biomass (Table 6). In this area, I. viscosa and

Dorycnium hirsutum showed slightly higher arsenic

contents than other species.

Plant species common in wet habitats, such as M.

aquatica and P. australis, showed high arsenic con-

tents mostly in roots but also in leaves ( M. aquatica).

The above-ground tissues of the plant species most

palatable to livestock showed very low arsenic con-

centrations, except for the leaves of P. lanceolata (9 –

24 mg kg 1 on d.w.; Table 7).

Table 4

Sampling area A. Arsenic content in plant species growing on mineral processing tailing ponds S6 (meanFS.E.; mg kg 1)

Plant species Leaves Shoots Roots Rhizomes Inflorescences

Achillea ageratum 15.29F 3.94 6.89F 1.64 12.27F 2.71 34.58F 7.03Silene vulgaris 82.77F 25.07 73.64F 25.09 52.46F 5.27


Phragmites australis 3.71F 0.95 1.52F 0.08 688.24F 64.00 5.07F 1.09

Dorycnium hirsutum 33.95F 16.82 54.23F 3.49 16.11F 3.72

Aster squamatus 1.49F 0.07 9.63F 2.19 2.92F 0.81

Atriplex patula 37.63F 14.67 10.44F 3.47 21.91F 7.16

Inula viscosa 47.33F 9.32 5.14F 0.94 5.77F 1.49

Melilotus alba 5.74F 1.07 1.05F 0.05 3.58F 0.85

Table 5

Sampling areas B and C. Arsenic content in plant species (meanFS.E.; mg kg 1)

Sampling area and site Leaves Shoots Leaves and shoots Roots

Area B

Dactylis hispanica 0.06F 0.04 1.74F 0.59

Helichrysum italicum 0.33F 0.18 0.05F 0.04


Cichorium intybus 0.55F 0.21

Calluna vulgaris 0.38F 0.12

Hypericum perforatum < 0.02

Reichardia picroides 0.77F 0.25

Area C

Quarry slopes

Cytisus scoparius 0.96F 0.17 0.67F 0.22

Euphorbia cyparissias 61.3F 10.62 41.42F 7.31

Medicago sativa 1.14F 0.48 2.21F 0.97


Pasture

Silene dioica 176.27F 21.31 3.07F 0.73

Medicago sativa 2.23F 0.74 5.51F1.46




Very low arsenic contents were found in plant

species collect ed in ar ea B (<1 mg kg 1 in almost

all the plants; Table 5) and area C. Exceptions were

Euphorbia cyparissias and P. lanceolata sampled on

the quarry slopes and notably Silene dioica from

pastures, which contained 176 mg kg 1 As in its

leaves.

5.3. Arsenic accumulation and translocation in plants

In general, the ability of the plants to accumulate

arsenic, as expressed by the Biological Accumulation

Coefficients (BACs) and Concentration Factors (CFs),

was independent of the As contents in the soils. These

indices were not correlated with total, soluble or extractable arsenic in soil.

Nevertheless, when the plant part with the highest

As content was considered for each species, there

were significant relationships between arsenic in the

plant tissue and the total, soluble and extractable

arsenic in the soil (r = 0.635, 0.439 and 0.951, respec-

tively; p < 0.001; n = 80).

With the exception of M. aquatica (BAC = 2.03),

the BACs of all the plant species were < 1; in 91% of

them, the BAC was < 10 1 and in 55% < 10 2. The

CFs for extractable arsenic were generally low: < 5 in69% and < 20 in 86% of cases. The highest values

referred to the roots of the two wetland plants M.

aquatica (818) and P. australis (459).

Very high CFsol values were found in M. aquatica

(90,026), P. lanceolata (10,363) and P. australis

(17,206). They were also high in A. stolonifera

(1688), C. myconis (3805), Conyza bonariensis

(1283), D. hirsutum (1356), G. tomentosa (2697),

Holoschoenus vulgaris (1145), I. viscosa (1183) and

S. vulgaris (2069).

Table 6

Arsenic content (mean or range; mg kg 1) in the more common plant species of the main habitats occurring in the sampling area A

Habitats and species Roots Shoots Leaves Shoots and leaves Fruits

Mine dumps and slopes and neighbouring badlands Bromus hordeaceus < 0.02

Bromus madritensis 0.04

Dactylis hispanica < 0.02 0.20

Inula viscosa 0.20 – 6.00 0.06 – 5.00 3.00 – 47.00

Helichrysum italicum 1.00 2.53

Spartium junceum <0.02

Rubus ulmifolius 0.90

Dorycnium hirsutum 3.00 –16.00 3.00 –54.00 3.00 –34.00

Quercus cerris 0.05 < 0.02

Quercus ilex 0.10 3.00

Ulmus minor 0.10 0.20

Lake (ex open mine pit) shores and wet surfaces neighbouring to the tailing ponds

Agrostis stolonifera 10.00 Mentha aquatica 540.16 37.44 216.35

Phragmites australis 688.00 2.00 4.00

Table 7

Sampling area A. Arsenic content (mean or range; mg kg 1) in

leaves and shoots of the most pabular species for livestock

Species Leaves Shoots Shoots and

leaves

Avena fatua 0.40

Bromus hordeaceus < 0.02

Dactylis hispanica 0.20 < 0.02

Hedysarum coronarium 0.50

Lotus corniculatus 0.10

Medicago sativa 3.00

Plantago lanceolata 9.00–24.00

Sanguisorba minor 0.10

Trifolium incarnatum 0.40 0.90

Trifolium pratense 0.50 0.08

Sonchus asper 0.11

Medicago hispida 0.62

Phalaris coerulescens 0.54

Brassica napus 0.19 0.02

Reichardia picroides 1.51 0.72 0.77

Cichorium intybus 0.55




In most of the sampled species, the roots had the

highest arsenic concentration (Tables 2 – 5). The trans-

location of As to shoots was low or very low, with

translocation coefficients (TC) < 2 in 76% of cases.Three species showed enhanced As transport to shoots:

A. ageratum collected in the old field (TC = 14.8), I.

viscosa from the tailing ponds (TC = 8.2) and dumps

(TC = 12.4) of area A and S. dioica collected in the

pastures of area C (TC = 57.4).

6. Discussion

6.1. Relationships between As contents of soils and

plants

When compared to the As contents of soils at

several mining sites, where total As ranged from 2

to 17,000 mg kg 1 and available As from < 1 to 390

mg kg 1 (de Koe, 1994; Bech et al., 1997; Flynn et

al., 2002; Jung et al., 2002; Madejon et al., 2002;

Visoottiviseth et al., 2002), the values of our soils can

be considered intermediate or moderately low. Nev-

ertheless, in some agricultural soils (pasture of area C

and part of the fields of area A), the arsenic contents

exceeded the Italian legal limits, even for garden or

park (20 mg kg

1) and industrial sites (50 mg kg

1;DM 471/99, 1999).

The highest values of soluble and extractable As in

area C can be explained by the highest values of total

As in the soils. However, they may also be influenced

by the likely presence of the iron arsenate scorodite

and its stability relationships driven by Eh–pH con-

ditions (Vink, 1996).

Our results clearly showed that when the concen-

tration of arsenic in the soil was not particularly high

(as in the fields and vegetable garden of area A), its

availability to plants strongly depended on the totalsoil As content. Soluble and extractable As in soils

were positively correlated to the As contents in plants.

This relationship could be perceived throughout the

entire study areas when the mean concentrations for

each sampling site were considered.

This finding agrees with previous results for grass

growing near smelters (Temple et al., 1977), for

Urtica dioica and P. australis growing on experimen-

tal soils (Otte et al., 1990) and for Agrostis species

growing at mining sites (de Koe, 1994). We must

observe, however, that this relationship was not found

in other cases (O’Neill, 1995; Pitten et al., 1999).

Perhaps a parallel change of As contents in plants and

As contents in soils through a gradient can be moreeasily detected when several plant species are sampled

(as in our study).

In contrast, As translocation from the roots to the

above-ground biomass appeared to be under stronger

biological control than As uptake. This could explain

the lack of correlation between As contents of soils

and As concentrations in the epigeal parts. In this

respect, our results strongly agree with the literature

data (Otte and Ernst, 1994; O’Neill, 1995).

When we compared the As contents in our plants

with those sampled at other mining sites by de Koe

(1994), Bech et al. (1997), Jung et al. (2002), Made-

jon et al. (2002) and Visoottiviseth et al. (2002), we

found much lower maximum values (from less than

one-half to less than one-tenth). Since As contents in

our soils were also lower in the most contaminated

situations, a weaker selective pressure can be inferred

or, simply, more effective accumulator plant species

may have escaped our sampling.

Neither the arsenic availability in soils nor its

concentration in plants reflected the differences in

organic matter content, pH and available phosphorus

in soils of the sampling sites. All these factors areknown to affect both bioavailability and plant uptake

of As (Otte et al., 1990; Bhumbla and Keefer, 1994).

Yet in our study, these factors had no apparent

influence.

6.2. Biogeochemical and environmental aspects

Plants contributed very little to the arsenic diffu-

sion, cycling and transfer from soil to biosphere in the

study areas. Both the As concentrations in plant

tissues and the ability of plants to accumulate theelement were low or very low. This was especially so

in the most common crops (corn, lucerne, sunflower,

wheat), in common wild herbs ( Bromus hordeaceus,

Bromus madritensis, D. hispanica, I. viscosa), in the

main chamaephytes ( D. hirsutum and H. italicum) and

shrubby colonizers ( Rubus ulmifolius and Spartium

junceum), as well as in the main components of the

local forest (Quercus cerris and Quercus ilex).

However, species such as M. aquatica, P. lanceo-

lata, P. australis and some others growing on soils




very rich in arsenic (especially in dumps and tailing

ponds of study area A) appeared to be good pumps for

soil As. Their CFs were high or very high, especially

for soluble soil As.A low As concentration in the above-ground plant

biomass decreases the risk of food chain contamina-

tion through grazing. Indeed, with the exception of P.

lanceolata (9–24 mg kg 1 of As in its leaves), this

was the general case for the species most palatable to

livestock. However, P. lanceolata also had As con-

tents below the maximum level (50 mg kg 1) toler-

ated by cattle, sheep and swine (Chaney, 1989). Thus,

plant contamination by As-rich soil particles (or soil

ingestion) could be the main route of As intake by

wild herbivores and livestock, as found elsewhere

(Thornton and Abrahams, 1983; Li and Thornton,

1993).

The As contents found in the edible parts of crops

and vegetables are not cause for concern, since they

were close to or below the instrumental detection

limit.

6.3. Remarks on some plant species

One of the sampled species, S. vulgaris, is well

known for its tolerance to several trace elements, such

as antimony, cadmium, cobalt, copper, lead, nickeland zinc, which are even accumulated or hyperaccu-

mulated (Harmens et al., 1993; de Knecht et al., 1995;

Wenzel and Jockwer, 1999; Baroni et al., 2000b).

With regard to the ability of S. vulgaris to accumulate

arsenic, our data agree with literature reports. Mean

values such as 261 mg kg 1 (Paliouris and Hutch-

inson, 1991) or 637 mg kg 1 (Sneller et al., 1999)

have been reported for soils with soluble As 25–37

times higher than the highest value (tailing ponds) in

our soils. Moreover, our plants had higher As contents

in the shoots than in the roots; this is an important aspect since a substantial As depletion occurs at the

end of the growing cycle when most of the above-

ground biomass is shed.

Rather high As contents were also found in S.

dioica growing in pastures of study area C. However,

in this case, the levels of soluble and extractable As in

the soil were high: 8.5 and 35.8 mg kg 1, respectively.

M. sativa sampled in area C, as well as in the old

fields and mine dumps of area A, behaved as an

excluder.

P. australis, with a mean As content of 688 mg

kg 1 in the roots, 1.5 mg kg 1 in the shoots and 3.7

mg kg 1 in the leaves, clearly confirmed its low

ability to translocate arsenic from root s t o t h eabove-ground biomass (Otte et al., 1990). Reduced

metal transport from roots to shoots appears to be the

usual behavior of the species (see for instance Ye et

al., 1997).

A. stolonifera has been found to be an As accu-

mulator in other mining areas, with contents up to

1350 mg kg 1 (Porter and Peterson, 1975), but this

was not the case in our study (maximum concentra-

tions of 21 mg kg 1 were found). Nevertheless, it

must be stressed that Porter and Peterson also found

extremely high As contents in the soils they studied

(from 8510 to 26,530 mg kg 1).

The ability of M. aquatica to concentrate As and

translocate it to the leaves is rather interesting. There-

fore, its potential use as a phytoremediator could be

assessed.

7. Conclusions

The soil levels of organic matter, available phos-

phorus, pH and CEC had no effect on soil As content

and its bioavailability to plants. Tissues of the 64 plant species generally exhibited an As content positively

correlated to that of the soil. Nevertheless, the As

content in plants was always low, even in the most

contaminated conditions, with two exceptions: M.

aquatica and P. australis. In spite of the long contam-

ination history of the surveyed areas, there is an evident

lack of effective pressure toward As tolerance by the

plant species through accumulation of the element.

With few exceptions, the As concentration was

higher in roots than in leaves and shoots. This

decidedly decreases the risk of food chain contami-nation via herbivores.

Arsenic concentrations were also low in the most

common herbaceous species (crops and wild plants),

in the main chamaephytic and shrubby colonizers and

in the main forest trees. This means that it is likely

that plants play a minor role in superficial geochem-

ical cycling of arsenic. Nevertheless, the arsenic levels

above the legal limits in agricultural soils suggest that

a wider survey of As contents in crops, fodders and

vegetables should be carried out.




Acknowledgements

This paper is a contribution to the research project:

‘‘Dispersion and transfer of metals to the biosphere inmining areas’’, supported by Ministero dell’Universita

e della Ricerca Scientifica e Tecnologica (MURST)

and the University of Siena.

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