Environmental Pollution 144 (2006) 308e316www.elsevier.com/locate/envpol

Impact of river overflowing on trace element contamination ofvolcanic soils in south Italy: Part I. Trace element speciation

in relation to soil properties

P. Adamo a,*, M. Zampella a, L. Gianfreda a, G. Renella b, F.A. Rutigliano c, F. Terribile a

a Dipartimento di Scienze del Suolo, della Pianta e dell’Ambiente, Universita di Napoli Federico II, Via Universita 100, Portici, 80055 Napoli, Italyb Dipartimento di Scienza del Suolo e Nutrizione della Pianta, Universita di Firenze, P.le delle Cascine 28, 50144 Firenze, Italy

c Dipartimento di Scienze Ambientali, Seconda Universita di Napoli, Via Vivaldi 43, 81100 Caserta, Italy

Received 26 September 2005; received in revised form 24 February 2006; accepted 3 March 2006

River overflowing adds up soil with Cr-rich sediments which, although chemically low reactive,transfer metal along the soil pore network during water movement.

Abstract

Volcanic soils affected by different numbers of polluted river flooding events were investigated. Chromium and Cu were the major soil con-taminants. Nickel, Fe, Zn and Mn total content never exceeded the Italian mandatory limits. The distribution of Cr and Cu total contents amongstudied soils indicated that only Cr contamination was related to overflowing events. In polluted soils, sequential chemical extractions revealeda preferential association of Cr and Cu with organic forms. A progressive Cr insolubilization with ageing was observed. Significant amounts ofCr and Cu were extracted by NH4-oxalate, suggesting metals association with short-range-order aluminosilicates and organo-mineral complexes.Possible methodological drawbacks in the use of the EU-BCR chemical speciation protocol on volcanic soils are discussed. Micromorphologyand SEM/WDS analyses revealed Cr and Cu enriched silt and clay coatings in surface and subsurface soil horizons, suggesting a transfer ofmetal-rich sediments along the soil pore network with water movement.� 2006 Elsevier Ltd. All rights reserved.

Keywords: Chromium; Copper; Speciation; Metal ageing; Volcanic soil; River flooding; Soil contamination

1. Introduction

The Solofrana river valley (Campania Region, south Italy)is characterised by thick, fertile volcanic soils with moderateto high andic properties. Agricultural and industrial activitiesoccurring in this area have produced a widespread degradationof local natural resources. In particular, tanning plants (w160)operating in the upper valley caused in the past a Cr-enrich-ment of the Solofrana river waters (Basile et al., 1985). Re-cently, a Cr content decline in river waters was observed(Adamo et al., 2001), while the river sediments (De Vivo

* Corresponding author. Tel.: þ39 81 253 9172; fax: þ39 81 253 9186.

E-mail address: adamo@unina.it (P. Adamo).

0269-7491/$ - see front matter � 2006 Elsevier Ltd. All rights reserved.

doi:10.1016/j.envpol.2006.03.006

et al., 2003) and the valley soils still contain Cr concentrationsabove natural background (Adamo et al., 2003). Besides theuse of polluted river waters for irrigation (prohibited since1990), a key role, both in the past and at present time, in theCr enrichment of the valley soils might have been played byrepeated flooding events, due to river embankments weakness,after intense rainfall. About 400 ha of the valley are interestedby overflowing (Consorzio Bonifica Integrale Agro SarneseNocerino, 1996) which release on the adjacent soil 20e30 cm layers of coarse and fine sediments, usually mechani-cally removed by farmers after drying.

Impact of flooding on soil trace metal contamination and itsconsequences on soil biota depend on metal total amount,metals forms and soil properties, such as pH, texture andorganic matter content (Kabata-Pendias, 2004). High metal

309P. Adamo et al. / Environmental Pollution 144 (2006) 308e316

retention capacity of volcanic soils may increase the tracemetal retention time but also might reduce their mobility,attenuating their toxicity over time.

From 2002, a multidisciplinary study was performed in theSolofrana valley focused on soils subjected to flooding events.Objectives of the study are: i) to analyse the main physico-chemical and mineralogical soil properties, ii) to determineCu, Cr, Ni, Zn, Al and Fe total content and speciation, iii)to describe micromorphological features produced by sedi-ment deposition, iv) to analyse soil eubacterial communitiescomposition by PCR-DGGE approach, v) to measure micro-bial biomass, total and active fungal mycelium, and severalsoil enzymes activities. In this paper results concerning ieiiipoints are presented, with emphasis on metal availability in re-lation to andic properties. Some of these data are reconsideredin the second manuscript of this series (D’Ascoli et al., 2006)for interpretation of metal effect on selected soil biologicaland biochemical functions.

2. Description of the area

The Solofrana river valley, located between the towns ofSolofra (NE) and Nocera Inferiore (SW), constitutes the inlandportion of the Sarno plain, located in Campania Region (southItaly) between the volcanic complex of Somma-Vesuvius(NW), the Sarno Mountains (NE), the limestone Lattari Moun-tains (S) and the Tyrrhenian cost (W). It covers an area ofapproximately 3000 ha of cultivated soils originated bypyroclastic material from Somma-Vesuvius colluviated tothe valley (Terribile and Di Gennaro, 1996). The slopes varybetween 1e5% and the elevation from 42 to 150 m abovesea level. The area has a Mediterranean climate regime, withaverage annual temperature of 17.2 �C and average annualrainfall of 1203 mm (Ufficio Idrografico e Mareografico diNapoli, 1960e1995). Field horticulture, orchards and green-house horticulture and floriculture are the main productionsof the valley very intensive agriculture. Land use on the south-ern slope generally consists in terraces with coexisting horti-culture, fruit trees and vineyards, while chestnuts are widelypresent on the north-facing slopes.

3. Materials and methods

3.1. Study areas selection and soil sampling

Combining in a GIS environment land information (soil, hydrology, flooding

and land use maps), three plots of about 700 m2 with the same soil type (Humic

Haplustand, Soil Survey Staff, 1998) were selected for this study: E1 (from

14 �4504700E, 40 �4705700N to 14 �4505400E 40 �4705500N), E2 (from 14 �4504400E,

40 �4705000N to 14 �4505200E, 40 �4704900N), E3 (from 14 �4505000E, 40 �4704300Nto 14 �4504700E, 40 �4704400N). Plots were not cropped by at least 5 years, covered

by spontaneous herbaceous vegetation and affected by different numbers of

flooding events: 1) E1, flooded in 1981; 2) E2, flooded in 1981 and 1993; 3)

E3, flooded in 1981, 1993 and 1998. At the E3 site, flooded again in October

2002, sediments (SED) were sampled soon after the event and before mechanical

removal by farmers. Location of the studied sites is given in Fig. 1. Another site

(C), located in the same area (from 14 �4600000E, 40 �4901600N to 14 �4600800E,

40 �4901500N), but never flooded by the Solofrana waters, was considered as

control soil.

The selection of not cultivated sites was produced in order to avoid the

influence of agriculture treatments on soil microbial activities, biomass and

diversity, covering the trace metals influence.

Soil sampling was carried out in all selected sites following a ‘‘W’’ shaped

sampling scheme. Surface soils were sampled at a depth of 0e10 cm, using

plastic cores and avoiding any pollution in the sampling procedure. For each

study site, five independent subsamples, each composed of 20 soil cores mixed

together, were sampled and kept separate. The samples were stored at 4 �Cand analysed within 20 days after sampling.

E1

E2

E3

0 100 200 300 400 500 m

Fig. 1. Location of selected study sites in the Solofrana river valley. Arrows

indicate overflowing departing location and directions. The areas affected by

floods at different times are shown in different grey gradations. Rectangles

indicate the sampling plots.

310 P. Adamo et al. / Environmental Pollution 144 (2006) 308e316

Pedological profiles P1 and P2 were opened respectively in sites C and

E3. Soil profiles were described and samples from each horizon collected.

Undisturbed soil samples for micromorphology were obtained using Kubiena

boxes.

3.2. Soil properties

Soil samples were air-dried and sieved at 2 mm prior to determinations of

pH(H2O) (1:2.5 soil:water ratio), pH(NaF) (1:50 soil:1N NaF ratio), cation

exchange capacity (CEC) (BaCl2 at pH 8.1), total carbonates, determined by

the Dietrich-Fruehling calcimeter method, (Loeppert and Suarez, 1996),

organic carbon (Walkley and Black, 1934), total nitrogen (Kjeldahl method

in Bremner, 1996), available phosphate by the method of Olsen, available

potassium, by extracting soils with EDTA at pH 4.65 (Lakanen and Ervio,

1971). Particle-size analysis was carried out by the Andreasen’s pipette

method at pH 10 after ultrasonic treatment (20 kHz, 75 W, for 15 min).

For estimation of Al, Fe and Si forms soils were extracted with dithionite-

citrate (Ald, Fed, Sid) according to Holmgren (1967) and with NH4-oxalate

(Alo, Feo, Sio) (0.2 M at pH 3) according to Schwertmann (1964). Al, Fe

and Si contents were analysed in the extracts by atomic absorption spectrom-

etry (AAS).

Mineralogy of the coarse (<2 mm) clay fraction of the control and flooded

soils and of river sediments was determined by X-ray diffraction (XRD) after

treatment with H2O2 and centrifugation (1000 rpm). Ca-saturated oriented

samples were analysed using a Rigaku Geigerflex D/Max IIIC X-ray diffrac-

tometer (XRD), equipped with iron-filtered Co-Ka radiation. The analysis

was also repeated after treatment with glycerol to aid the identification of

smectites and heating at 300 �C to elucidate the nature of the 2:1

phyllosilicates.

3.3. Heavy metal extractions

Total heavy metal content of soil and sediment samples was determined by

acid digestion in a Milestone 900 microwave oven in HF:HNO3 1:5 solution at

600 W for 24 min.

The three-step chemical extraction procedure (0.11 M HOAc, 0.5 M

NH2OH $ HCl, H2O2/1 M NH4OAc), developed by the Measurement and Test-

ing Programme of the European Commission (Ure and Davidson, 2002), fol-

lowed by HF/HNO3 digestion of the residual fraction, was used to fractionate

heavy metal chemical forms.

Metals associated to short-range-order aluminosilicates and amorphous

iron oxides and hydrous oxides and Al associated with humus, were deter-

mined by acid-ammonium oxalate (0.2 M at pH 3.0 and 1:100 extraction ra-

tio), with shaking for 4 h in the dark at 25 �C. The bioavailable pool of Cu

was determined by extraction with 0.005 M DTPA þ0.01 M TEA þ0.01 M

CaCl2 at pH 7.3 (Lindsay and Norwell, 1978).

Soil extraction experiments were done using 1 g of soil in two replicates.

The concentration of Al, Fe, Mn, Cr, Cu, Ni, and Zn in the extracts was deter-

mined by a Perkin Elmer Analyst 700 atomic absorption spectrometer equip-

ped with graphite furnace.

Effectiveness of total and sequential extraction procedures and reproduc-

ibility of data were checked by including one BCR Standard Reference Mate-

rials (CRM 141R and CRM 701) sample of known composition in each

analytical set.

3.4. Micromorphology

Undisturbed soil samples were collected from the P1 and P2 profiles, and

impregnated with a polyester resin (Crystic). A series of thin sections was

then produced according to the procedure of FitzPatrick (1984) and analysed

by Optical Microscopy and by SEM/EDS/WDS. Qualitative elemental analy-

ses were performed by a 5900 LV JEOL SEM, with an EDS SiLi ISIS Oxford

Instrument and INCA software. Quantitative elemental analyses were per-

formed on selected samples by a SEM/WDS Camebax SX50 Cameca Thomp-

son CSF.

3.5. Statistical analyses

All soils samples were analysed separately, thus results are the means �standard deviations of the five independent subsamples collected at each study

site. Results of the laboratory analyses were analysed for descriptive statistics

(mean, median, minimum, maximum, standard deviation, skewness and kurto-

sis) using STATISTICA software package. One-way ANOVA analysis was

performed, using EXCEL Data Analysis program, to assess differences among

the studied sites soils. When the occurrence of significant differences between

means was shown by ANOVA, the differences were tested by the Least Signif-

icant Difference (LSD) test at 95% confidence level.

4. Results

4.1. Soil properties and total heavy metal content

P1 (C, control soil) and P2 (E3, 3 times flooded soil) shortprofile descriptions are given in Table 1. Soils are young vol-canic soils, mainly formed by both colluvium material (fromupslope relieves covered by well developed Andosols) and al-luvial sediments. Soils are deep and homogeneous in structure,texture, colour and degree of soil genesis. In P2 0e20 cm layerrecent carbonate-rich sediments occur.

Major physical and chemical properties of E1, E2, E3 andC soils are reported in Table 2. Soil texture was sandy-loam,with clay content ranging from 160 � 20 (C) to 205 � 32 gkg�1 (E2), with pH values from neutral (7.2 � 0.3) (C) tosub-alkaline (7.9 � 0.2) (E3). Total carbonates ranged be-tween 4.3 � 0.1 (C) and 61 � 25 g kg�1 (E3). Sodium fluoridepH was >10.0 for all soils, indicating the presence of amor-phous material (Shoji and Ono, 1978). All the soils had highorganic C (OC) and N contents. Available K content rangedbetween 896 � 67 (E3) and 1194 � 114 mg kg�1 (E2), andavailable P between 22 � 5 (E2) and 45 � 4 mg kg�1 (E3).

X-ray analysis of clay fraction (<2.0 mm) revealed a similarmineralogy in all studied soils and sediments, with presence of1:1 and 2:1 phyllosilicates, plagioclases and quartz (Fig. 2).1.4 peak collapse to 1.0 nm after 300 �C heating indicatedthe presence of vermiculite. Expansion after glycerol treat-ment, suggested the occurrence of swelling smectites, presum-ably vermiculite-smectite interstratifications. The 1.0 nm and7.0 nm peaks indicated the presence of illite or mica and ofkaolinite or halloysite, respectively.

Based on selective dissolution data, an estimation of poorlyordered soil constituents was made (Table 3). The (Alo-Ald)/Siomolar ratio was in all cases within the allophane range(1.0e2.5) (Dahlgren, 1994), with low allophane content(from 6.4 in C to 7.3% in E3). The active iron ratio (Feo/Fed),suggested the occurrence of a poorly crystalline fraction of Feoxides in soils, whose content according to Childs (1985) was1.5% in C and 1.7% in E1eE2 soils. The oxalate extractableAl plus ½Fe percentage, one of the USDA requirements torecognise andic soil properties (Soil Survey Staff, 1998), is2.2%, with C soil showing a slightly lower value (2.0).

Total metal content of E1, E2, E3 and C soils is reported inTable 4.

In the majority of the analysed soil samples total Cr and Cucontents were higher than the Italian national mandatory limits

311P. Adamo et al. / Environmental Pollution 144 (2006) 308e316

Table 1

P1 and P2 short profile descriptions

Profile Horizon Depth of

lower

boundary

(cm)

Colour

(moist)

Rock

fragments (%)

Structure Texture Consistence

(dry)

Carbonates

P1 (C) Ap 20 10YR 3/2 10 Crumb and fine subangular blocky Sandy loam Soft None

Bw 50 10YR 3/3 5 Fine and medium subangular blocky Sandy loam Soft None

BC1 80 10YR 4/2 10e15 Fine and medium subangular blocky Sandy loam Slightly hard None

BC2 100 10YR 4/2 10e12 Medium subangular blocky Loamy sand Slightly hard Very weak

BC3 110 10YR 4/2 15 Medium subangular blocky Loamy sand Loose None

P2 (E3) A1 10 10YR 3/3 20 Fine subangular and medium

angular blocky

Loam Hard Moderate

A2 20 2.5Y 4/2 3 Fine subangular blocky Sandy loam Moderately hard Weak

Bw1 35 10YR 4/2 1 Fine subangular blocky Sandy loam Moderately hard Very weak

Bw2 40þ 10YR 4/2 1 Medium subangular blocky Sandy loam Moderately hard None

(Cr 150 and Cu 120 mg kg�1) (Italian Ministry of the Environ-ment, 1999). Total Cu was lower in E3 soil (114 � 14 mg kg�1),and increased in soils with less flooding events, with the highestvalue in C soil (229� 17 mg kg�1). In the river sediments totalCu was 97 � 14 mg kg�1. Differently, total Cr was lowest in Csoil (21 � 1 mg kg�1) and increased in soils interested bymore flooding events with 378 � 84 mg kg�1 maximum valuein E3. Total Cr content in soils showed a higher variabilitythan Cu. High values of total Cr were also found in sediments(542 � 175 mg kg�1).

The total content of the other analysed metals did not ex-ceed the Italian national mandatory limits and, with the excep-tion of Fe, was not significantly different among the studiedsoils.

4.2. Heavy metal speciation and availability

Speciation of heavy metals is reported in Fig. 3.In C soil Cu was mainly associated with organic matter

(48%) and reducible and residual fractions (24 and 24%, re-spectively). Soluble, exchangeable or carbonates-bound Cuamounts were negligible (4%). However, in soils subjectedto repeated flooding, Cu speciation was different: residual(40% in E1, E2 and 41% in E3) > organic (25% in E2, 26%in E3 and 37% in E1) > reducible (23% in E1, 31% in E2and 30% in E3) [ HOAc-extractable (3% in E1, E3 and

4% in E2). In sediments, Cu was mainly associated with themineral residue (49%) (not shown).

Speciation of Cr was even more different in control andflooded soils. In C, Cr was mostly found in the residue(90%), with the reducible and oxidizable fractions containingonly 4 and 5% of total Cr. Soluble, exchangeable and car-bonates-bound forms were negligible (1%). In flooded soilsCr residual fraction accounted for 51% in E2, 35% in E1and 23% in E3, and the Cr percentages associated with or-ganic matter increased to 41% in E2, 59% in E1 and 67%in E3. Lower Cr amounts were recovered in the reducible(5e9%) and soluble fractions (z1%). In sediments Cr wasmainly associated with the oxidizable fraction (73%) (notshown).

In control and flooded soils and river sediments no signifi-cant differences were found in speciation of Ni, Fe, Zn andMn, which were mostly concentrated in the residual fraction(Ni z 92%, Fe z 91%, Zn z 56%), whereas the most labilefractions contained about 10% of the total contents, indicatinglow availability of these elements. The high Mn content in thereducible fraction was due to the use of NH2OH-HCl in thisextraction step.

Large amounts of both Cu and Cr were extracted by ammo-nium oxalate from soils and sediments (Cuo 39e63% and Cro

4e66%) suggesting their association with short-range orderedminerals and organo-mineral complexes (Table 5). The highestCuo value was found in C soil. The Cro values increased with

Table 2

Major physical and chemical properties of studied soils

Soil Particle-size fractions (mm) pH H2O pH NaF CEC CaCO3 OC N Kjeldahl P Olsen K EDTA

2000e200 200e20 20e2 <2

g kg�1 cmol(þ) kg�1 g kg�1 mg kg�1

C* 351 � 32 244 � 30 245 � 15 160 � 20 7.2 � 0.3 10.5 � 0.2 33.4 � 2.5 4.3 � 0.1 40.8 � 2.3 2.2 � 0.2 25 � 10 1007 � 87

E1 225 � 42 304 � 93 274 � 40 197 � 76 7.4 � 0.1 10.2 � 0.2 47.0 � 4.0 4.4 � 3.0 48.0 � 4.6 3.4 � 0.3 40 � 3 1006 � 102

E2 331 � 29 253 � 62 211 � 31 205 � 32 7.6 � 0.3 10.7 � 0.3 37.1 � 3.6 12.4 � 5.4 22.8 � 8.2 4.0 � 1.0 22 � 5 1194 � 114

E3 269 � 128 350 � 83 214 � 41 167 � 43 7.9 � 0.2 10.3 � 0.2 38.0 � 3.8 61.0 � 25.5 22.5 � 3.9 2.2 � 1.0 45 � 4 896 � 67

LSD** 9 4 24.6 0.7 0.8

*C ¼ control soil; E1, E2, E3 ¼ soils flooded ones, two and three times respectively. **Least Significant Difference of the means; not indicated when one-way

ANOVA did not show the occurrence of any significant difference between means.

312 P. Adamo et al. / Environmental Pollution 144 (2006) 308e316

soil Cr total content. From 15 to 19% of Cu total content wasextracted by DTPA (CuD) (Table 5).

4.3. Micromorphological analysis

Micromorphology enabled to follow a path of sedimentphysical degradation. In P2 surface horizon, large aggregateswith an internal laminar structure were observed. They werepresumably made by fine alluvial material deposited during re-cent river flooding, In Bw horizons these large aggregates altertowards the formation of round shaped smaller aggregates. Insome of them Fe segregations produced by redox conditionschanges due to water logging were observed.

Thin sections SEM/EDS examination showed in P2 surfacehorizon the clayey aggregates and surrounding soil matrixwere characterized by a similar chemical composition in termsof Si, Al, Fe, K and Ca. Nevertheless, WDS analysis revealedthe clayey aggregates to be enriched in both Cr (38e408 mg kg�1) and Cu (156e330 mg kg�1).

5. Discussion

Solofrana valley volcanic soils interested by river over-flowing were Cr and Cu contaminated. Metal total contentdistribution and metal speciation, along with sediment

0-5 cm

untreated

+ glycerol

300 °C

1.486

I1.006

K, H 0.724

K0.358 nm

I0.501

I, K 0.448 Q

0.426

P0.377

2 9 16 23 302θ

Fig. 2. X-ray diffractograms of the oriented clay fraction (<2.0 mm) separated

from the surface E3 soil. It can be considered representative of all analysed

soil samples. I ¼ illite or mica, K,H ¼ kaolinite or halloysite,

P ¼ plagioclases, Q ¼ quartz.

analysis, suggested different sources of contaminants. Riversediments were particularly rich in Cr and had a relativelylow Cu total content and concurrently the soil interested bythree flooding events had the lowest Cu and the highest Crtotal concentrations. Conversely, higher Cu and lower Crconcentrations occurred in the control soil. Furthermore, totalCr content in flooded soils showed a higher variability thantotal Cu. Therefore, only Cr contamination appears associ-ated with polluted sediment deposition by overflowing,whereas Cu contamination seems to depend on differentsources, presumably past widespread agricultural practicesof Cu-rich material utilization. According with literature(Adamo et al., 2001; Basile et al., 1985), the record of theCr-enrichment of the Solofrana river sediments is a conse-quence of the increased river water metal loading causedby the uncontrolled discharge of tanning plants Cr-containingeffluents and the reduction of Cu concentration in the repeat-edly flooded soils could be interpreted as a ‘dilution’ effectdue to low Cu sediments deposition.

Variability in particle-size distribution, carbonates and or-ganic C content of surface soils was probably due to spatialvariation of hydrodynamic conditions during overflowing,which in turn produced local sorting of sediment and sedimentrelated contaminants. Organic C differences among soilsmight also be due to mechanical removal of sediments andvegetation stands (particularly in E2 and E3).

Despite the variability in Cr and Cu total contents, the Fe,Al, Mn, Ni and Zn contents, the pH values and the mineralog-ical composition of all soils, were very similar, supporting therole of C as a good control soil for Cr contamination.

Sequential extractions show that both Cr and Cu in pollutedsoils were mainly associated with the organic fraction,whereas other trace elements and Fe were found mostly inthe residual fraction. Chromium and Cu amounts associatedwith organic matter increase with the increasing extent ofsoil contamination by these metals, thereby suggesting highconstants values of organic-Cu and organic-Cr complexes(Donisa et al., 1999; McGrath, 1995). Although the high affin-ity of Cr and Cu for soil organic matter is well known(Alloway, 1995), the adopted experimental design allowedthe Cr ageing to be well described. In fact, by consideringthe Cr speciation in river sediments and E3, E2 and E1 soilsas a chronosequence from the first flooding event, it seemsthat Cr undergoes to a progressive insolubilization in about20 years. Particularly, by considering the (HOAc þ OXI)

Table 3

Si, Al and Fe content extractable in ammonium-oxalate (Xo) and dithionite (Xd)

Soil Sio Sid Alo Ald Feo Fed Feo/Fed Feest** Alo�Ald/Sio AM*** Alo þ ½ Feo

% % %

C* 1.10 0.17 1.53 0.16 0.88 1.69 0.52 1.5 1.3 6.4 2.0

E1 1.03 0.18 1.68 0.17 0.97 1.58 0.62 1.7 1.5 6.5 2.2

E2 1.11 0.16 1.72 0.16 1.03 1.49 0.69 1.7 1.4 6.8 2.2

E3 1.20 0.18 1.78 0.15 0.92 1.36 0.67 1.6 1.4 7.3 2.2

Feest ¼ estimated ferrihydrite content, AM ¼ allophane content, Alo-Ald/Sio ¼ Al/Si molar ratio for allophanic materials. *C ¼ control soil; E1, E2, E3 ¼ soils

flooded ones, two and three times respectively. **Feest ¼ 1.7Feo e ***AM ¼ 100Sio /{23.4e5.1(Alo-Ald)/Sio}.

313P. Adamo et al. / Environmental Pollution 144 (2006) 308e316

0

10

20

30

40

50

60

%

Cu Cu

Cr Cr

0

20

40

60

80

100

120

114 (E3) 132 (E2) 151 (E1) 229 (C)

total content (mg kg-1)

total content (mg kg-1)

114 (E3) 132 (E2) 151 (E1) 229 (C)

total content (mg kg-1)

abso

lute

con

tent

(mg

kg-1

)ab

solu

te c

onte

nt (m

g kg

-1)

abso

lute

con

tent

(mg

kg-1

)

0

50

100

150

200

250

300

21 (C) 100 (E2) 188 (E1) 378 (E3)

total content (mg kg-1)C (55) E1 (57) E2 (64) E3 (65)

total content (mg kg-1)C (55) E1 (57) E2 (64) E3 (65)

total content (mg kg-1)21 (C) 100 (E2) 188 (E1) 378 (E3)

0

20

40

60

80

100

%

0

20

40

60

80

100

%

Ni

0

10

20

30

40

50

60

70Ni

HOAc RED RESOXI

Fig. 3. Relation between total metal content and either absolute (left) and relative (% of the total) (right) amounts of Cu, Cr, Ni, Fe, Zn and Mn extracted sequen-

tially (HOAc ¼ HOAc-extractable; RED ¼ reducible; OXI ¼ oxidizable; RES ¼ residual) from C, E1, E2 and E3 soils.

Table 4

Total content (mean � SD) of Fe, Al and heavy metals of the studied soils and sediment (n ¼ 5)

Soil Fe Al Cr Cu Mn Ni Zn

mg kg�1

C* 44 488 � 720 87 732 � 6961 21 � 1 229 � 17 1006 � 90 55 � 5 142 � 8

E1 40 175 � 1274 60 615 � 6664 188 � 31 151 � 9 1169 � 94 57 � 5 139 � 4

E2 40 668 � 1083 71 018 � 3347 100 � 53 132 � 5 1101 � 85 64 � 5 143 � 19

E3 39 454 � 1395 83 940 � 7863 378 � 84 114 � 14 1095 � 78 65 � 10 157 � 18

SED 42 132 � 4063 77 450 � 446 542 � 175 97 � 14 1112 � 111 68 � 10 145 � 10

LSD** 1538 70 16

IG*** e e 150 120 e 120 150

*C ¼ control soil; E1, E2, E3 ¼ soils flooded ones, two and three times respectively. **Least Significant Difference of the means; not indicated when one-way

ANOVA did not show the occurrence of any significant difference between means. ***Italian Ministry of Environment (1999): limits for public, private and res-

idential green areas soils.

314 P. Adamo et al. / Environmental Pollution 144 (2006) 308e316

Fe

0

10000

20000

30000

40000

50000

E3 (39) E1 (40) E2 (41) C (44)

total content (mg kg-1)

abso

lute

con

tent

(mg

kg-1

)

Fe

0

20

40

60

80

100

E3 (39) E1 (40) E2 (41) C (44)

total content (mg kg-1)

%

Zn

0102030405060708090

E1 (139) C (142) E2 (143) E3 (157)

total content (mg kg-1)

abso

lute

con

tent

(mg

kg-1

)

Zn

0

10

20

30

40

50

60

70

E1 (139) C (142) E2 (143) E3 (157)

total content (mg kg-1)

%

Mn

0

100

200

300

400

500

600

700

C (1006) E3 (1095) E2 (1101) E1 (1169)

abso

lute

con

tent

(mg

kg-1

) Mn

0

10

20

30

40

50

60

C (1006) E3 (1095) E2 (1101) E1 (1169)

total content (mg kg-1) total content (mg kg-1)

%

HOAc RED RESOXI

Fig. 3 (continued).

fraction as the available fraction, Cr in this fraction accounts74, 68, 45 and 60% in sediments, E3, E2 and E1 soils,respectively.

The ageing process involved transformation of organicallybound Cr into insoluble Cr, likely operated by soil micro-

Table 5

Content of Cu and Cr extractable in ammonium oxalate (Xo) and of Cu

extractable in DTPA (XD) of the studied soils and sediment

Soil Cuo Cro CuD

mg kg�1

C 144.3 (63*) 0.9 (4) 44.1 (19)

E1 52.4 (35) 65.8 (35) 25.2 (17)

E2 51.5 (39) 28.0 (28) 22.4 (17)

E3 55.6 (49) 225.7 (60) 18.7 (16)

SED 35.9 (37) 359.4 (66) 14.5 (15)

*Percentage of the total content in soil.

organisms and fauna. Evidence of high soil faunal activitywas observed in soil thin sections while the microbial activityin these soils is detailed discussed in the second manuscriptof this series (D’Ascoli et al., 2006). Moreover, despite theincreasing amount of carbonates in flooded soils, the amountof HOAc-extractable metals did not significantly increasesuggesting that the analysed trace metals were not associatedto soil carbonates.

Interpretation of speciation data should also take into ac-count some methodological aspects. Acetic acid may removefrom allophane the Cu2þ chemisorbed forms, breakingmetal-oxide bonds by proton attack (Clark and McBride,1984). Its complexing ability may considerably increase theproportion of Cu removed in the first extraction step as a resultof greater desorption of Cu from organic matter or oxides(Adamo et al., 1996; McLaren and Crawford, 1973). Althoughin soils Cu was mostly associated to organic matter,

315P. Adamo et al. / Environmental Pollution 144 (2006) 308e316

HOAc-extractable amounts were always very small, indicatinga low contribute from soluble organic Cu complexes.

The quantification of the metals associated to soil organicmatter have derived important concern. The H2O2 treatment,applied to remove organic matter prior to ammonium acetateextraction, may degrade clay minerals because of the soilH2O2 slurry acidity (Douglas and Fiessinger, 1971). Therefore,it cannot be excluded that the amorphous clay minerals of thesoils could have been partly dissolved at this step with the re-lease of the associated metals. An overestimation of the metals’organic’ fraction may result. Moreover, oxidising and acidicconditions induced by H2O2 in the presence of residual Mnoxides, could have also oxidized some stable forms of Cr(III)to more mobile oxidized Cr ones (Bartlett and James, 1979).

Based on <2.0 mm clay fraction XRD and on bulk soil se-lective dissolution data, plagioclases, quartz, halloysite/kaolin-ite, illite, vermiculite, smectite, allophane and both crystallineand amorphous Fe minerals occurred in both soil and riversediments. Among clay minerals, the expandable layer sili-cates may have an important role in contaminated sedimentsand soils because they may act as effective Cr sinks. In smec-tites, interlayer adsorbed Cr becomes strongly held by inner-sphere complexation with the siloxane oxygen, increasingthe disorder of the interlayer material (Dubbin and Goh,1994; Dubbin et al., 1995). Possibly, some mineralogical dis-order of smectitic minerals, due to interlayer complexed Cr,could occur in studied soil and sediments and be responsiblefor broad and low intense X-ray peaks (Fig. 2). Interactionbetween smectites and organic matter with formation oforgano-clays would have improved the soil adsorbing capacityfor inorganic contaminants.

The large Cu amounts extracted by DTPA and, for Cr, byammonium oxalate of polluted soils indicate a potentiallymore available Cu and Cr as respect to the not polluted soils.Allophanic minerals of these soils likely retain metals ontocation exchange sites due to the ionization of surface OHand COOH groups at subalkaline pH (Abd-Elfattah andWada, 1981; Clark and McBride, 1984). Oxalic and otherlow molecular weight (LMW) organic acids form a stabilepool of soil organic matter (Stevenson, 1994), resulting fromrhizodeposition and microbial metabolism during organic mat-ter decomposition (Robert and Berthelin, 1994); these organicacids can induce the mobilization of heavy metals throughcomplexation or weathering of soil minerals (Krishnamurtiet al., 1997). The Cu amounts extracted in DTPA were in allcases higher than those commonly found in cultivated neutralItalian soils (Barbafieri et al., 1996), with the highest value(44.1 mg kg�1) measured in C soil.

Soil physical incorporation of river sediments with alter-ation of aggregates to silt and clay size, and coatings occur-rence in subsurface elongated pores was shown by opticalmicroscopy. Trace metals transfer in soil may occur in dis-solved forms, but also in colloidal forms, as contaminants ad-sorbed to colloid surface (Kretzschmar et al., 1999). Colloidshave been identified as metal carriers in groundwater(McCarthy and Zachara, 1989), in rivers and lakes (Buffleand Leppart, 1995) and in landfill-leachates (Gounaris et al.,

1993). SEM/WDS analyses reveal Cu and Cr enrichment inclayey aggregates strengthening the possible risk of metalmigration in soil as solid suspension.

6. Conclusions

Chromium and Cu were the main anthropogenic metal con-taminants in Solofrana river valley soils. A multidisciplinaryapproach based on soils and river sediments pedological, min-eralogical and chemical analyses allowed to distinguish thetwo contaminants different sources, and ascribe Cr contamina-tion to repeated Solofrana river flooding events and the Cucontamination to past intensive agricultural practices.

The chemical speciation data allowed us to describe thechanges of Cr speciation during Cr ageing in soils, althougha possible overestimation of organic bound contaminants andan underestimation of expandable clay minerals bound con-taminants could not be excluded. The important role of allo-phane and swelling smectites in metals retention was alsodescribed. Micromorphology coupled with SEM/WDS analy-ses highlighted evidences of the possible transfer of metal-rich clay size particles as solid suspension along soil porenetwork, associated with water movement.

Acknowledgements

Thanks are due to Dr Bruno Moroni, director of the Agri-culture and Environmental Area of the Consorzio di BonificaAgro Sarnese Nocerino, and to all his staff components whokindly assisted the soil sampling campaign. This paper repre-sents Journal Series No. 103 from DISSPA.

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