Physicochemical and biological characterisation of different dredged sediment deposit sites in France

Environmental Pollution 143 (2006) 106e116 www.elsevier.com/locate/envpol

Physicochemical and biological characterisation of different dredged sediment deposit sites in France Xavier Capilla a, Christophe Schwartz b, Jean-Philippe Bedell a,*, Thibault Sterckeman b, Yves Perrodin a, Jean-Louis Morel b a

Laboratoire des Sciences de l’Environnement a` l’ENTPE, Rue Maurice Audin, 69 518 Vaulx-en-Velin Cedex, France b Laboratoire Sols et Environnement, INPL (ENSAIA)/INRA UMR 1120, 2 avenue de la foreˆt de Haye, BP 172, 54 505 Vandoeuvre les Nancy, France Received 14 June 2005; received in revised form 29 October 2005; accepted 3 November 2005

The term technogenic arthrosols is suggested. Abstract The aim of this work is to determine sediment properties, metal contents and transfers of Cd and Zn from dredged sediments to plants. To this end 10 deposit sites with different contexts were visited in France. The main agronomic characteristics and metal contents for surface soil layers were measured, the plant species present at the sites, such as Brassicaceae and Fabaceae, were listed, and the distribution of their root systems described. Soil characteristics such as available P (Olsen) varied between sites, with values ranging from 0.01 to 0.49 g kg
1. Total contents and enrichment factors were studied, highlighting metal contamination in most of the sites. Despite carrying out principal component analyses, it was not possible to group deposits by age or geographical localisation. However, deposits could be distinguished as a function of proximity of industrial facilities, sediment grain size and carbonate content. Associations between metals were also highlighted: (1) Cd, Pb and Zn, and (2) Al, Cr, Cu and Fe. Consequently, we propose classifying them as technogenic anthrosols. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Anthroposol; Deposit; Trace elements; Sediment; Typology; Vegetation

1. Introduction An integral part of aquatic systems, sediments are formed by deposits, particles introduced into the ecosystem and precipitates formed by biochemical processes in aquatic environments. Numerous chemical substances discharged into the environment accumulate in sediments at the bottom of rivers, canals, lakes and reservoirs as well as in estuaries and on sea beds. Thus, sediments are potentially polluted with different metals and/or organic compounds (Hursthouse, 2001). The damage done to ecology and health by sediment contamination can take many forms. Water quality can be deteriorated by releases and resuspensions (Aguilar and

* Corresponding author. Tel.: þ33 4 7204 7081; fax: þ33 4 7204 7743. E-mail address: [email protected] (J.-P. Bedell). 0269-7491/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.envpol.2005.11.007

Thibodeaux, 2005), population diversity, particularly that of invertebrates living in sediments, may decrease (Sasaki et al., 2005) and leisure activities can be severely affected (Romero, 1999). Furthermore, additional costs are generated by the need to manage materials contaminated during dredging and cleaning (Babut et al., 1999). The contaminants mentioned most frequently in sediment multipollution are metals (Cd, Cr, Cu, Hg, Ni, Pb and Zn), organochlorides and polycyclic aromatic hydrocarbons (PAH) (Babut et al., 1999). Sedimentation can necessitate dredging when it increases the risk of flooding, decreases the navigational depth of waterways (Romero, 1999), and when it represents a proven ecological or health risk (Fontana, 1997). The sediments removed can be left in water, piled or deposited in borrow pits, used in environmental techniques, e.g. for covering dumps (Mohan et al., 1997) and restoring marshes (Ford et al., 1999), or they can be deposited on land. In practice, the 6 million m3 of

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sediments dredged annually from French inland waterways can be broken down as follows between the different sectors: 70% in deposits (in water or on land), 10% used for public works, 7% spread on farmland and 3% in piles, miscellaneous fills and processes (Carpentier et al., 2002). In the case of deposits located near rivers or canals, transfers can occur to the surrounding soil, surface water and groundwater (Bedell et al., 2003a). The organisms concerned are therefore micro-organisms, terrestrial fauna and flora, and aquatic species. Plants can play a role in the fate of the pollutants of contaminated matrixes via their root systems (Adriano et al., 2004), especially since the chemical conditions of the rhizosphere can be very different from those of the rest of the soil (Wang et al., 2001). Different phenomena can be involved, such as fixation and adsorption, or the dissolution of pollutants, for example via a change of pH at rhizospheric level or a physical or chemical change in the sediment. The influence of Fagus sylvatica would be, for example, a decrease of pH, an increase of the concentration in solution of Al3þ ions and a decrease of the concentration of nitrates (Braun et al., 2001; Wang et al., 2001). Also, a mutant of Arabidopsis has a strategy by which it makes its rhizosphere more alkaline in order to decrease the toxicity of Al (Matsumoto et al., 2001). Various studies of in situ dredged sediment deposit sites have been carried out in the United States (Beyer et al., 1990), United Kingdom (Stephens et al., 2001) and Belgium

107

(Vandecasteele et al., 2002a). However, few general studies of these deposit sites have been performed in France. In this study, different French sediment deposit sites of different ages were investigated in order to first determine the main physicochemical characteristics related to metal contamination of the sediments in deposits. The second objective was to identify the vegetation that grows on these sites and determine the transfer of metal contamination to the vegetation. Then, by comparing these data, we attempted to evaluate the evolution of such sites according to their age and localisation. The purpose of this study is to improve the understanding of the transfer mechanisms involved relating to the metal trace elements contained in the sediments deposited. 2. Materials and methods 2.1. Site description Ten terrestrial dredged sediment deposit sites representing different climates and geochemical backgrounds were investigated in different French regions. Four are in the south of France: A, D, H, and I; four in the north: C, E, F, and J; and two are in the northeast: B and G (for details see Fig. 1 and Table 1). Visits were made to the sites during April and May 2003. Initially, profile pits were dug (1  1  1 m3) in areas with homogeneous plant cover. Two or three pits, noted as F1, F2 and F3, were dug at each site. These pits included one on a plot without plant cover (when one existed) and two with plant cover. The root profiles were established and expressed by the presence or absence of roots in the mesh (2  2 cm2) of a grid set against the side of the

Fig. 1. Localisation of dredged sediment deposit sites.

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profile pit examined. Root density was evaluated at a depth of 60 cm. This corresponds to the usual rooting depth observed in agricultural soils. This evaluation was performed by counting the meshes from 58 to 60 cm with at least one root (out of the 30 meshes at this depth). The total density of the first 60 cm was obtained by grouping the observations of the 900 squares from 0 to 60 cm depth.

2.2. Sampling and sample preparation The profiles were described for each pit and the horizons identified and characterised by descriptive criteria, i.e. texture, structure, colour, and compaction. Samples of each horizon were collected. Regarding the surface horizon, samples were taken from the upper layer of the deposits between 0 and 5 cm depth. Twenty samples were collected from an area of about 400 m2 and mixed together to obtain a single composite and representative sample for each site, as described by Tack et al. (1998). The sediments were stored at 4  C from sampling until analysis and measurement. During April and May 2003, individuals of all the plant species present on the sites were sampled and identified. For each of the two dominant species, about 1 kg of biomass of aerial and root parts was collected across the site and mixed together to obtain a single composite and representative sample for each site.

2.3. Chemical and physical analyses Only soils from the upper horizon of each site were analysed by the INRA soil analysis laboratory in Arras. Sediment particle size distribution (five fractions), pH in water (NF ISO 10390), organic C ratio (NF ISO 10694, combustion method) out of total N (NF ISO 13878, combustion method), total calcium (NF ISO 10693), CEC (NF X 31-130), exchangeable bases (contents in Ca, Mg, K and Na exchangeable with cobaltihexamine), plant available phosphorous (Olsen method), total contents (by mineralisation in hydrofluoric acid) in Cd, Cr, Zn and Ni, as well as total conductivity (by a sample with the ratio 1/5 of sediment and water) were determined after drying in air and sieving at 2 mm. Bulk density and total porosity were also measured for the surface layer of each pit. In order to determine bulk density, volumes of 28 cm3 were sampled and weighed after 48 h at 105  C. Total porosity was then calculated, assuming a particle density of 2.6 t m3. Normalisation based on the correlation between the trace elements and naturally occurring elements, Al and Fe, was performed (Svete et al., 2001) to estimate the anthropogenic contribution of the trace element content in the sediments. The enrichment factor (EFy) versus the trace element (y) is defined as follows: EFy ¼ ð½Trace element=½yÞsediment =ð½Trace element=½yÞgeochemical background

anomaly existed or not. Two calculations were performed, one with y ¼ Al and the other with y ¼ Fe. Cross-linking with the total contents obtained leads to the assumption of pollution of anthropic origin. Enrichment into a trace element is highlighted when the corresponding enrichment factor is higher than 1.3 in the case where local geochemical background values are available (Sterckeman, personal communication), otherwise it is higher than 10. Characteristic humidities and especially the water holding capacity of the different soils were determined. The soils were air dried and sieved (2 mm), then saturated with water for 12 h by capillary take-up (Duchaufour, 2001). Pressures of 0.1 and 15 bar, corresponding to pF values (as withering point) of 2 and 4.2, were then applied for 24 h to determine the available water for the plants in the soil (Duchaufour, 2001). The metal contents in the aerial part and roots of the plants were determined as follows. After washing three times with tap water and rinsing three times with deionised water the plants were dried for 48 h at 70  C after which they were crushed in an agate mortar. A sample of 0.5 g of dry matter was then dissolved using a mixture of 8 mL HNO3 and 2 mL H2O2, heated in a CEM type microwave oven (Mars 5). After filtration through ash-free filter paper (Prolabo) (average filtration) and adjustment in a 25 mL phial with HNO3 [0.1 M], the metals were analysed by inductive coupled plasma (ICP) and flame atomic absorption (Zeeman effect) (Zhao et al., 1994). Certified Reference Material (CRM 281 from BCR) and internal control samples were used to check the complete recovery of the dissolution. The total contents of the two metals, Cd and Zn, were determined since they were among the metals most frequently at the source of pollution in the case of sediment deposits, as observed by Vandecasteele et al. (2002a) and in our observations. The bioconcentration factor, which in this case is the ratio between the metal content of the plant and that of the sediment, was then calculated for each plant (Marseille et al., 2000).

2.4. Statistical analysis A principal components analysis (PCA) was performed in order to examine correlations between the different properties measured and identify possible groupings of sites according to their geographic localisation and age. The analysis was performed using the following parameters: metal contents, pH, particle size distribution, organic C, N, carbonate content, CEC, exchangeable bases, P Olsen, conductivity and maximum rooting depth. PCA was also performed on a normalized original matrix composed of 26 columns and 10 lines (the different sites). The columns can be considered statistically dependant variables, making it possible to extract new reduced factors. StatisticaÓ software was used and a threshold of 5% applied. According to the low number of observations, PCA was used as a visual approach for our data in order to synthetise them and highlight differences and/or pertinent parameters if any.

By measuring total Al and Fe contents, the geochemical enrichment factor versus each of these metals was calculated in order to identify whether an

3. Results and discussion

Table 1 Characteristics of the sites visited

3.1. Characterisation of sediments

Code

Date of deposit

Surface area (ha)

Volume (1000 m3)

Origin

A B C

2001 and 2002 2002 1980

1.4 10 11.5

Un 12 120

D E F G H I

1993 1998 2001 1995e1996 1997 1980

Un 600 60 Un Un 13

J

1975

3 8.3 4.5 0.01 5.5 Un Partially removed 8.8

Canal du Rhoˆne/Se`te Moselle, canalised section Canal along a non-ferrous metal foundry Canal du Rhoˆne/Se`te Canal de Lens Scarpe e middle reach Port de Lerouville Canal du Rhoˆne/Se`te Canal du Rhoˆne/Se`te

250

Scarpe e upper reach

Un: unknown.

The observations performed on the pits showed that the deposits were structured. The profiles observed were often composed of layers of different contributions corresponding to different cleaning programmes. According to Mathieu and Pieltain (1997), the sediments studied had different textures varying from sand to average silt and heavy clay, with a prevalence of silty textures (Table 2). The sediments studied had an average pH of 8, varying from neutral to very alkaline, from pH 7 to 9 (Table 2). These values agree with the pH measured by Vandecasteele et al. (2003) for 131 sediment derived soils sampled in Belgium. Average conductivity was 1.2 mS cm
1 and varied from 0.2 to 4.2 mS cm
1. Except for site A, conductivity was in the same region of magnitude as that measured by Vandecasteele et al. (2003) for 131 sediment derived soils

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Table 2 General characteristics and total metal contents of sediments Site

A

B

C

D

E

F

G

H

I

J

Water pH Total conductivity (mS cm
1) Grain size Clay (%) Silt (%) Sand (%) Texture CEC Ca Mg K Na Saturation

8.3 4.17

7.9 0.47

7 2.06

9 0.51

7.2 1.89

7.8 0.74

8.2 0.17

8.8 0.25

8.1 1.64

7.4 0.19

29.5 42.6 27.9 L A-S 16.4 18.06 7.71 1.4 13.63 Saturated

19.9 40.5 39.6 L S-A 16.6 15.91 1.42 0.3 0.12 Saturated

14.6 76.4 9 Lm 13.8 28.60 0.60 0.23 0.05 Saturated

26.2 27.9 45.9 L S-A 19.4 10.72 4.62 2.08 3.15 Saturated

26.2 63.9 9.9 LA 23.6 39.06 0.78 0.38 0.12 Saturated

22.2 56.3 21.5 L A-S 16.6 19.06 0.38 0.32 0.05 Saturated

25.8 29.7 44.5 L A-S 23.1 21.21 0.99 0.42 0.03 0.98

5.2 8.2 86.6 S 2.6 4.14 0.36 0.2 0.06 Saturated

34.2 62.6 3.2 AL 16.3 25.66 3.13 0.18 0.66 Saturated

16.6 74.2 9.2 Lm 20.9 19.21 0.81 0.63 0.05 0.99

Carbonate (g kg
1) Olsen P (g kg
1) Organic C (g kg
1) N (g kg
1) C/N

346 0.108 55.2 1.34 41

58 0.286 33.3 1.54 22

177 0.155 80.9 2.07 39

346 0.311 74.4 3.91 19

120 0.479 111.6 6.82 16

199 0.228 96.2 2.7 36

514 0.090 93.4 2.74 34

309 0.029 39.6 0.22 180

329 0.013 48.8 1.01 48

97 0.491 60.5 4.01 15

Fe (mg kg
1) Al (mg kg
1) Cd (mg kg
1) Cr (mg kg
1) Cu (mg kg
1) Ni (mg kg
1) Pb (mg kg
1) Zn (mg kg
1)

22 300 44 400 1.0 53.1 43.2 24.7 54 106.6

51 800 84 600 3.6 130.9 147.6 88.5 734 963.5

42 800 30 000 5669.4 104.7 437.7 32.8 114 013 76 198

16 100 37 100 2.5 41.3 31.3 18.3 67 117.2

24 800 43 800 7.0 79.9 567.1 47.2 432 1753

19 500 38 800 3.7 62.7 200 36.5 360 1137.6

24 800 37 200 1.1 48.9 35.4 26.9 39 158.3

9900 24 300 0.2 25.2 4.4 10.1 14 28.6

30 400 58 100 0.3 62.1 21.6 37.7 39 88.6

17 400 33 700 14.8 60.3 79.7 29.9 365 876.6

L A-S: clay-sand silt; L S-A: sand-clay silt; L m: average silt; A L: silty clay; L A: clayey silt; S: sand. Texture according to Mathieu and Pieltain (1997).

sampled in Belgium, i.e. from 0.1 to 2.2 mS cm
1. For site A, the high sodium and magnesium contents could explain the high conductivity value of 4.17 mS cm
1. This could be due to the origin of the sediment, since it came from the canal linking the River Rhone with the town of Se`te in which the water is brackish. CEC varied from 2.6 to 23.6 cmolþ kg
1 with a mean value of 16.9 cmolþ kg
1. The contents in the exchangeable bases were such that the absorbent complexes of the sediments were all saturated. Contents in Al, Fe and Mn during extraction with cobaltihexamine were below analytical detection thresholds (respectively, 0.02 cmolþ kg
1 for Al, 0.01 cmolþ kg
1 for Fe and 0.005 cmolþ kg
1 for Mn), except for the Mn in the sample from sediment C, with a content of 0.025 cmolþ kg
1. The carbonate content of the sediments studied permitted their qualification as moderate to very calcareous, a detail also observed by Tack et al. (1996) in sediment deposit sites in Belgium. The average plant available P content (Olsen method) was 0.21 g kg
1 with values ranging from 0.01 to 0.49 g kg
1. Organic carbon ranged from 33.3 to 111.6 g kg
1 with an average of 69.4 g kg
1. These values are in the same range as the values recorded on sediment deposit sites in Belgium by Vandecasteele et al. (2002a), who recorded values ranging from 14 to 62 g kg
1. Nitrogen content ranged from 0.2 (site H) to 6.8 g kg
1 with an average of 2.6 g kg
1. The C/N ratio varied from 15 (site J) to 180 (site H) with an average value of 45. The highest value obtained for site H was due to a very low N content.

Contrasts were observed for total metal contents (Table 2). The values at some sites were 33 000 times higher than the values at others (e.g. Cd), with metal concentrations varying by at least a factor of 1e3. Sediment H appeared to be the least contaminated by metals, whereas sediments C and B appeared to be the most contaminated. Site C is near a non-ferrous metal working plant, which could explain the pollution observed. Excepting site C, the values obtained here were lower than those obtained for a fresh sediment from the lower Scarpe by Vaule´on et al. (2001): 6600 mg Zn kg
1 of sediment and 190 mg Cd kg
1 of sediment. Likewise, the values were in the same region of magnitude as those obtained by Bedell et al. (2003b) for fresh sediments from eastern France: from 145 to 12 220 mg Zn kg
1 DW of sediment and from 0.5 to 7.8 mg Cd kg
1 DW of sediment. Compared to the sediment sampled in Delft (Kelderman et al., 2000), Cd content was lower in our sediment (except site C) and in the same region of magnitude for Zn. In a study carried out in the United Kingdom on two dredged material deposits, total concentrations determined with aqua regia, respectively, were 2.3 and 0.3 mg Cd kg
1, 116.7 and 35.6 mg Cr kg
1, 84.8 and 19.9 mg Cu kg
1, 15 132 and 46 828 mg Fe kg
1, 69.7 and 46 mg Ni kg
1, 22.6 and 45.8 mg Pb kg
1, 320.7 and 540.1 mg Zn kg
1 (Stephens et al., 2001). In comparison, for our 10 sediments, Cr and Fe were in the same region of magnitude, but sites E and C had higher Cd, Cu, Pb and Zn contents. Moreover, sites B, E, F had higher Cu, Pb and Zn contents, while site J in particular

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had higher Cd, Cu, Pb and Zn contents than the sites in the United Kingdom. In Switzerland, the indicative values for soils (Ruling 814.12 on soil degradation, 1998), triggering investigation, are 0.8 mg Cd kg
1 DW, 150 mg Zn kg
1 DW with extraction using HNO3. In France, soils receiving sewage sludge must have contents lower than 2 mg Cd kg
1 DW and 300 mg Zn kg
1 DW (A.F.NOR. NF U 44-041, 1988). If Swiss values are taken into account for Cd and Zn, then only sites H and I were not polluted. According to French values for Cd and Zn, sites A, G, H and I were not polluted. A comparison was made between the sites of the NordePas-de-Calais Region and its geochemical background. For the other sites, comparisons were made with geochemical background values indicated by Wedepohl (1995) for the upper part of the European continental crust. According to these comparisons, all the sites were contaminated. Sites A, G, H and I were slightly contaminated, sites B, D, E, F and J were moderately contaminated and site C was heavily contaminated. The geochemical background values used were 0.26 and 59.7 mg kg
1 for Cd and Zn in NordePas-de-Calais and 0.10 and 52 mg kg
1 for Cd and Zn elsewhere. In our case the enrichment factor versus Al highlighted an anomaly for Cd, Cu, Pb, Ni and Zn contents for sites E, F and J (EF > 1.3) and suspicion regarding Cr (1.3 > EF > 1.1) (Table 3). This high Cr content was confirmed by the calculation of the enrichment factor in comparison to Fe. All the metal contents measured at site C were seen to have increased. Sites A, B, D and G showed an increase in Cd content and a slight increase in Cu content. Cd and Pb contents increased slightly for sites I and H. Sites A, B and G showed slight enrichment in Cr while sites B, G and I were slightly contaminated by Ni. The Pb contents of sites A, D and G were slightly higher, with site B showing higher enrichment with this metal. Sites A, D and G showed a slight increase of Zn content, this increase being greater for site B. All these results were confirmed by the calculation of the enrichment factor in comparison to Fe, except in the case of Cr and Ni for site C. Comparison of the results obtained for the sediments with the contents of the geochemical background of the same sites was better adapted for the sites of NordePas-de-Calais. The

geochemical background values used correspond to the averages measured for 758 soil horizons in this region (Sterckeman, 2004), i.e. 40.5 g kg
1 for Al and 0.26, 57.5, 12.8, 25, 23.2, 59.7 mg kg
1, respectively, for Cd, Cr, Cu, Ni, Pb and Zn, and 24.6 g kg
1 for Fe. For the other sites, the geochemical background values used correspond to the values indicated by Wedepohl (1995) for the upper part of the European continental crust, i.e. 77.4 g kg
1 for Al and 0.10, 35, 14.3, 18.6, 17, 52 mg kg
1, respectively, for Cd, Cr, Cu, Ni, Pb and Zn, and 30.9 g kg
1 for Fe. Furthermore, considerable variability between sites was observed with regard to both the agronomic characteristics of the sediments sampled and their pollutant metal contents. This variability between sites could also be seen regarding the bulk density of the sediments, which varied from 0.45 for site J to 1.17 for site A, and the porosities of the sediments studied (Table 4). This could be linked to the technique used during dredging, since the method of depositing impacts on the porosity of anthropic soils (Beaudet-Vidal et al., 1998). Variability between sites could also be observed regarding the available water for plants of different sediments which varied from 6.4% for site H to 42.5% DW for site J (Table 4). Site H had the lowest water reserve, whereas sites C, E and J had the highest water reserves. Variability within sites could also be observed, for example, regarding bulk density, with variations from 0.5 to 0.8 for site D (data not shown). Particle size distribution inside deposits was heterogeneous. During sedimentation, sand accumulates close to weirs whereas silts are distributed throughout the rest of the deposit (Vandecasteele et al., 2002a; Vervaeke et al., 2001). No differentiation of horizon according to deposit was observed, as the pedological profile was made up of layers of different materials corresponding to the successive phases of deposits. Dredged materials have mostly silty textures, are alkaline and have a high carbonate content, conductivity and C/N ratio. Moreover, metal contamination was detected in these sites. Variability was seen to exist both between sites (inter-site) and within sites (intra-site).

Table 3 Enrichment factor of sediment deposit sites in comparison to aluminium

Table 4 Physical characteristics of surface layers of the deposits and characteristic humidities of the different sediments (in % mass)

Site

Localisation

Fe

Cd

Cr

Cu

Ni

Pb

Zn

Site

A B C D E F G H I J

South Northeast North South North North Northeast South South North

1.3 1.5 2.3 1.1 0.9 0.8 1.7 1.0 1.3 0.9

16.6 32.2 29 437 51.6 25.0 14.9 22.4 5.4 4.3 68.5

2.6 3.4 2.5 2.5 1.3 1.1 2.9 2.3 2.4 1.3

5.3 9.4 46.2 4.6 41.0 16.3 5.2 1.0 2.0 7.5

2.3 4.4 1.8 2.1 1.7 1.5 3.0 1.7 2.7 1.4

5.6 39.5 6634 8.2 17.2 16.2 4.8 2.7 3.1 18.9

3.6 17.0 1723 4.7 27.2 19.9 6.3 1.8 2.3 17.6

Number of pits

Bulk density

Total porosity (cm3 g)

Field capacity

Available water for plant

Water content (during storage)

A B C D E F G H I J

3 3 2 3 2 3 3 3 2 2

1.17  0.06 0.73  0.06 0.65  0.07 0.67  0.15 0.65  0.07 0.73  0.12 0.93  0.12 0.9  0.1 1.1  0.28 0.45  0.21

0.53  0.06 0.7  0.01 0.75  0.07 0  0.06 0  0.07 0.73  0.06 0.63  0.06 0.63  0.06 0.55  0.07 0.85  0.07

33.6 29.7 68 36.3 71.2 60.5 35.8 8.6 34.5 59.5

16.7 17.0 40.5 17.5 39.0 29.1 20.0 6.4 21.5 42.6

24.0 13.5 53.3 26.6 70.8 56.0 35.1 5.3 21.5 48.2

The values in bold type correspond to enrichment factors higher than 1.3 for the sites of NordePas-de-Calais and higher than 10 for the other sites, thus to sites at which pollution is identifiable in comparison to the geochemical background.

Average  standard deviation.

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3.2. Observation of vegetation The list of plant species recorded at the deposit sites shows the presence of different families including, for example, Brassicaceae, Poaceae, Apiaceae, Fabaceae and Aceraceae (Table 5). Moreover, species considered as spontaneous colonisers in the framework of our study were also observed at other sediment deposit sites. These species included Salix sp. (present on half of the sites studied) (Tack et al., 1999), Sambucus nigra (present on one site) (Vandecasteele et al., 2002b), and Urtica sp. (present on five sites) (Vaule´on et al., 2001; Tack et al., 1998). Colonising species such as Rumex sp. and Juncus sp. observed on old, highly polluted mining sites were also present on some of the sites of our study (Freitas et al., 2004). Maximum rooting depth varied considerably according to site (from 21 to 119 cm) as did the percentage of roots reaching 60 cm (from 0 to 58%) and the total percentage of roots present at 60 cm (from 18 to 79%) (Table 6). These parameters are strongly related to the dominant plant species growing on the sites. We can also distinguish sites C, F and J, where Salix sp. are dominant species, from the other sites. Sites I and J had the deepest root systems of all the pits. Site B had the lowest maximum rooting depths, reaching about 20 cm. For sites A and D, the maximum rooting depth always ranged from 40 to 60 cm. The percentage of roots present at 60 cm was nil for 13 of the 26 ditches observed and high for the ditches of site I (40 and 77%). Furthermore, site I had the highest total percentage of roots at 60 cm (79%), while site B had the lowest value (18%). These observations agree with those made by Ragab (1995), who observed that the roots of a meadow grazed by sheep were located in the first 40 cm of soil, and with those of Crow and Houston (2004), who determined a maximum rooting depth of 1.3 m at seven sites planted with willows and poplars. Therefore, the sediment/plant interface or rhizosphere did not have the same volume for all the sites though it was present in each of them. Besides observing variability between sites, mention should be made of intra-site variability regarding maximum rooting depth with, for example, a variation from 24 to 78 cm for site F and from 38 to 120 cm for site G, and regarding the total percentage of roots present at 60 cm with, for site F, variations from 8.2 to 69.4%. This could also be seen in the distribution of vegetation at the different sites (Ernst, 1988), as different zones of vegetation could be identified. At site F, one zone was colonised by Salix sp., another by herbaceous plants and a third zone was sparsely covered by Matricaria sp. Metal accumulation in plant tissues varied considerably from one site to another. However, the Cd content in all the aerial parts of the plants is higher than the threshold Cd levels defined by the European Commission (2001) for cereal grain (0.01 mg kg
1). Thus, in the case of Salix sp., Cd contents varied from 1.5 mg kg
1 DW for site J to 34.5 mg kg
1 DW for site C (Table 7). Cd and Zn contents in the aerial part of Salix sp. of sites F and J were in the same region of magnitude as those observed by Mertens et al. (2001) on sediment deposits in

Table 5 List of plant species identified on the sediment deposit sites Family

Genus of species

Number of site of observations for the species

Salicaceae Urticaceae

Salix sp. Urtica sp.

5

Rubiaceae

4

Lythraceae

Galium aparine and Galium sp. Lythrum salicaria

Asteraceae Boraginaceae

Matricairia sp. Myosotis sp.

3

Asteraceae

Arctium sp., Eupatorium 2 cannabinum and Petasites sp. Carex sp. Iris pseudacorus Rumex sp. Sparganium sp.

Cyperaceae Iridaceae Chenopodiaceae Sparganiaceae Ace´raceae Apiaceae Araliaceae Asteraceae

Acer pseudoplatanus 1 Heracleum sphondylium Hedera helix Tanacetum vulgare, Tussilago farfara, Chardon Betulaceae or Corylaceae Corylus avellana Boraginaceae Symphytum sp. Brassicaceae Arabidopsis sp., Brassica napus oleifera, Cardaminopsis sp. Buddlejaceae Buddleja davidii Cannabaceae Humulus lupulus Caprifoliaceae Sambucus sp., Sambucus nigra Caryophyllaceae Arenaria sp., Lychnis sp., Minuartia hybrida, Silene latifolia Chenopodiaceae Chenopodium sp., Salicornia sp. Convolvulaceae Convolvulus sp. Cornaceae Cornus mas, Cornus sanguinea Cyperaceae Carex paniculata, Carex sp. Dipsaceae Dipsacus fullonum Equisetaceae Equisetum arvense Fabaceae Robinia pseudo-acacia Ge´raniaceae Geranium pyrenaicum Joncaceae Juncus sp. Lamiaceae Glechoma hederacea, Lycopus europeus Onagraceae Epilobium hirsutum Poaceae Arundo donax, Avena sterilis, Hordeum sp., Phalaris arundanicea Renonculaceae Ranunculus repens, Ranunculus sp. Rosaceae Filipendula ulmaria, Potentilla sp., Rubus sp. Salicaceae Populus tremula Solanaceae Solanum dulcamara Tamaricaceae Tamarix sp. Typhaceae Typha latifolia Valerianaceae Valerianella carinata

X. Capilla et al. / Environmental Pollution 143 (2006) 106e116

112

Table 6 Observations of root systems in different ditches and root densities at 60 cm depth Site

Number of pits

Max. depth (cm)

(%) At 60 cm

Total (%) at 60 cm

A B C D E F G H I J

3 3 2 3 2 3 3 3 2 2

39  34 21  18 36  51 50  4 35  7 49  27 72  43 69  34 107  1 119  16

12 00 35 00 00 24  42 11.1  19 8  11 58  26 32  16

27  22 18  15 21  29 52  2 30  9 39  31 60  12 42  10 79  20 49  5

Average  standard deviation.

Belgium, with 1e6 mg kg
1 DW for Cd and from 100 to 700 mg kg
1 DW for Zn with sediment contents of 5.3  5.1 mg Cd kg
1 and 528  365 mg Zn kg
1. It is also in the same region of magnitude as that observed by Vandecasteele et al. (2002b), for Salix alba growing on dredged material deposits and containing less than 0.5 mg Cd kg
1 and from 7 to 112 mg Zn kg
1. Furthermore, for the same plant they measured from 0.3 to 4.5 mg Cd kg
1 and from 89 to 628 mg Zn kg
1. For site C, Cd and Zn contents of the aerial parts were much higher; this is probably due to the highest total contents of the sediment of this site with, for example, 76 200 mg Zn kg
1. Brassica napus oleifera Zn content was lower than that measured by Bernhard et al. (2005) for hydroponic culture and on artificially contaminated soil: about 100 mg Zn kg
1 for the aerial part and from 1 to 20 g Zn kg
1 for roots. The bioconcentration factor (BCF) permits estimating the metal fraction available for the plant considered for the site and classifying plants as a function of their capacity to accumulate metals (Table 7). Site F had higher Cd and Zn availability for Salix sp. than that existing for sites J and C. Likewise, for Urtica sp. site G had higher Cd and Zn availability than that for sites J and E. Once again, variability between

sites is apparent, concerning the status of metals inside the sediment deposits vis-a`-vis the plants. We did not determine every species of plant due to the large variety of sub-species. Moreover, differences in the BCF value do not always imply a difference in plant concentrations (Planquart et al., 1999). In addition, low BCF does not always mean low plant concentrations, as is illustrated in our case, when comparing site C to sites F and J for Salix sp. Either BCF must be calculated with the available concentration in the soil (Planquart et al., 1999) or it must be calculated with soil total concentration. In the latter case, interpretations have to take account of plant concentrations. Urtica sp. for sites E, G and J, Matricaria sp. on site B and Arabidopsis sp. on site C had higher Cd and Zn contents in their upper roots than in their aerial parts; this was the opposite for B. napus oleifera on site D. Lythrum salicaria accumulated more Cd in its aerial parts than in its roots though this was the reverse for Zn. On the contrary, Chenopodium sp. accumulated more Cd in its roots than in its aerial parts, but more Zn in its aerial parts than in its roots. Considerable variations can also be seen between species. Salix sp. accumulated less Cd and Zn than Arabidopsis sp. at site C, whereas Arabidopsis halleri is known to be a hyperaccumulator of Zn (Schwartz et al., 2001). L. salicaria has a greater capacity to accumulate Zn than Urtica sp. in its aerial and root parts. On the other hand, Urtica sp. accumulates more Cd than L. salicaria in its roots, but not in its aerial parts. Salix sp. accumulates more Cd and Zn in its aerial parts than Urtica sp. Apart from the case of Cd at site F, no case of metal hyperaccumulation was identified for Salix sp. These characteristics include an accumulation factor for the aerial parts and a ratio between the metal contents of leaves and upper roots that are both higher than 1 (McGrath and Zhao, 2003). The high Cd and Zn contents observed in the plants remained low in comparison to those contained in sediments. Thus at site C, Arabidopsis sp. had the highest contents with an accumulation factor in the region of 0.1, taking into account the high concentrations of Cd and Zn in the sediment. This high concentration of Cd and Zn tended to reduce BCF.

Table 7 Content in cadmium and zinc of plants sampled from the deposits and the bioconcentration factor Site

Species

Plants content

Bioconcentration factor (BCF)

PA

C D A G B F J C E G J

Arabidopsis sp. Brassica napus oleifera Chenopodium sp. Lythrum salicaria Matricairia sp. Salix sp. Salix sp. Salix sp. Urtica sp. Urtica sp. Urtica sp.

PR

PA

PR

Cd

Zn

Cd

Zn

Cd

Zn

Cd

Zn

609.9  1.39 0.9  0.05 0.2  0.03 0.3  0.03 0.3  0.01 8.5  0.2 1.5  0.1 34.5  1.8
8471  58 54.9  5.32 90.6  1.9 46.9  4.1 39.3  0.05 677.4  20.2 347.54  11.5 1100.9  21.1 43.8  2.7 36.1  6.1 54.7  2.3

622.8  43.6 0.6  0.09 1.7  0.3 0.2  0.05 1.0  0.01 Not sampled Not sampled Not sampled 1.6  0.2 0.4  0.02 0.6  0.02

6259  409 28.4  1.81 55.0  1.6 57.9  5.8 108.5  1.3 Not sampled Not sampled Not sampled 97.7  4.1 50.4  4.4 83.5  2.5

0.1 0.3 0.2 0.3 0.1 2.3 0.1 0.0 0.0 0.2 0.0

0.1 0.5 0.8 0.3 0.0 0.6 0.4 0.0 0.0 0.2 0.1

0.1 0.2 1.7 0.2 0.3 Not sampled Not sampled Not sampled 0.2 0.3 0.0

0.1 0.2 0.5 0.4 0.1 Not sampled Not sampled Not sampled 0.1 0.3 0.1

Plants content in mg kg
1 DW. Aerial parts (PA) and root parts (PR) (standard deviation) (n ¼ 3). lq: Quantification limit. The bioconcentration factor (BCF) is calculated as follows: BCF ¼ metal content in plant/metal content in sediment.

X. Capilla et al. / Environmental Pollution 143 (2006) 106e116

1.0

N P orga C Coarse silt

0.5

Max rooting depth

CEC

Fact. 3 : 14.66%

Plant cover developed on these sites in spite of metal contamination of the sediments deposited. The vegetation observed is various. The root system of the plant cover can reach a depth of 1.3 m, thereby exploring a considerable volume of sediment. The aerial parts of the plants had high metal contents due to the metal pollution present in the sediment. The metal content of the aerial parts differs according to plant species. Site C could be distinguished from the other sites in particular due to high metal contents in the sediment and in the plants present. Considerable variability was also observed both between sites and within the same site. This intra-site variability should be linked to the heterogeneity of textures within a deposit when the sediments form.

113

Cu Calcium

Coarse sand Fine sand Potassium limestone C/N pH

0.0 Clay NiZn Cd Pb Fine Crsilt

Sodium Magnésium

Al Conductivity

-0.5 Fe

3.3. Statistical analysis Two main factors (or axes) explaining 52% of the total inertia on the scatter plot are emphasised (Fig. 2). For the first axis (comparison of correlation coefficients at a threshold of 5% with a Student’s table), the positive axis groups the contributions of sands, pH, the C/N ratio while the negative axis groups those of silts, Ca, Fe, Cr, and Cu. Axis 2 represents 18% of the global data, and the negative axis represents the clay content, Mg and K contents and the CEC. Factor 3 explains 15% of the total inertia of the scatter plot. The corresponding axis (comparison of correlation coefficients at a threshold of 5% with a Student’s table) groups contributions from the agronomic characteristics of the sediments (N, C and P Olsen) and that of Fe on the negative axis (Fig. 3). Analysis of the correlation matrix of the variables highlights correlations between them (comparison of correlation coefficients at a threshold of 5% with a Student’s table). Positive correlations are established between the following variables: 1 e Ca and Cu; 2 e Fe, Al, Cr, and Ni; and 3 e Pb, Cd, and Zn.

-1.0 -1.0

-0.5

0.0

0.5

1.0

Fact. 1 : 33.85% Fig. 3. Projection on plane 1  3 of the variables.

Negative correlations are established between the following variables: 1 e pH and Cr; 2 e pH and Cu; and 3 e carbonate and Cr. Numerous variables are independent. For example, we noted clays and Cr, clays and Cu, coarse silts and Fe, pH and maximum rooting depth. This PCA does not permit establishing relations between the maximum rooting depth and the physicochemical characteristics of the sediment apart from that of independence. However, it should be noted that these characteristics are those of the surface layer only. Nonetheless, plant rooting occurs in underlying horizons which may explain the absence of correlation. The projection of the points representing the different sites on the factorial level highlights the different groups (Fig. 4).

1,0 6 C/N

Pb Cd

5

Coarse sand

Zn

4

Pmax of roots CrCu

Coarse silt Ni Sharp silt

0,0

Calcium

Sharp sand C P N

LimestonepH water Al Conuctivity

-0,5

H

C

3

Fe

Sodium

Factor 2 : 18,21%

Fact. 2 : 18,21%

0,5

2 1

BJ F

G

0 I

-1

E

-2

CEC

D

Potassium Clay

A

-3

Magnésium

-4 -1,0 -1,0

-0,5

0,0

0,5

Fact. 1 : 33,85% Fig. 2. Projection of the main plane of the variables.

1,0

-5

-8

-6

-4

-2

0

2

4

6

8

Factor 1 : 33,85% Fig. 4. Representation of the sites on the main plane.

10

X. Capilla et al. / Environmental Pollution 143 (2006) 106e116

114

Sediment C is very polluted, sediment E has a siltier texture and sediment H has a sandier texture; these are all characteristics that can be distinguished from the other sediments. Sites C and H can also be distinguished due to their low content in clay, Mg and K. Also their CEC is lower than that of the other sites, especially site H. Sediments A and D, which were the most saline, also stood out. The other sediments (B, J, F, I and G) are not statistically distinct from each other. This analysis does not permit distinction according to deposit age or geographic origin. The projection of the points representing the different sites on plane 1  3 highlights different groups (Fig. 5): sediment C is very polluted; sediment H is sandier; and the clayeyesandy characteristics of sediment A distinguish it from the other sediments. Sites C and H also stand out due to their low contents in clay, Mg and K. Also, their CEC is lower than that of the other sites, especially site H. Sediments E and J can also be distinguished due to their higher P Olsen and N contents than the other sediments. Sediments B and I constitute a group with a higher Fe content than that of the other sediments. Sediments F, G and D constitute a group with lower N content than sediments B and I but higher than that of the other sediments. In the evaluation, sediments F and G, on the one hand, and B and I, on the other, can be grouped mainly as a function of their N and P Olsen contents. The other sediments remain isolated, perhaps due to the local histories of the sites concerned. For example, sediment E came from a section of canal located downstream of a sewage plant, giving it different characteristics from the other sediments. Ca and Cu contents in the sediments are positively correlated. Two groups of metals also appear to stand out: Al, Cr, Fe and Ni, on the one hand, and Cd, Pb and Zn, on the other. Consequently, Cr and Ni could be linked with alumino-silicates and iron oxides and are thus likely to be solubilised during changes in oxidoreduction conditions. What is more, Cr and carbonate contents in the sediments are negatively correlated, thus Cr is not linked to carbonate. The first group of metals was also

5 4 J

Factor 3 : 14,66%

3 E

2

F

G

1

D

H

0 -1

I

C

-2

B

A

-3 -4 -5 -8

-6

-4

-2

0

2

4

6

Factor 1 : 33,85% Fig. 5. Representation of the sites on plane 1  3.

8

10

identified by Sterckeman (2004) during a study of the surface horizons of agricultural soils in NordePas-de-Calais in which he noted that the carbonate contained little geochemical Cr. Independence relations between clay and Cr and between clay and Cu lead to the assumption that Cr and Cu are not specifically localised in clays. Cr and Cu can be distinguished once again from Cd and Zn which are found in the finest particles (Vaule´on et al., 2001; Prokop et al., 2003). A correlation between the finest contents and Cr, As, Fe, Al, Mn and Ni contents was, nonetheless, brought to light for fresh sediments from the Seine (Carpentier et al., 2002), likewise for Pb, Cr and Zn for agricultural soils near a metal works (Kaasalainen and Yli-Halla, 2003). Given the independence relation between the coarse silts and Fe, the latter does not appear to be localised specifically in the coarse silts. The ‘‘CdePbe Zn’’ group identified previously is also independent of Ni. In the evaluation, the coarse silts are linked to Fe, the clays are not specifically linked to Cr and Cu, and carbonate is not linked to Cr; however, Cr and Ni are linked to aluminosilicates and iron oxides. It appears possible to distinguish two groups of metals with respect to both positive correlations and independence relations with Cd, Pb and Zn in the first group and Al, Cr, Fe and Ni in the second group. The presence of these metals may be explained by the proximity of the source of the metal. For example, site C is rich in Cd, Pb and Zn and is close to a non-ferrous metal working plant. Casas et al. (2003) highlighted a group of Cd, Cu, Cr and Zn contents in sediments located in a river bed in northeast Spain while Carpentier et al. (2002) found a group of Al, Cr, Cu, Fe, Mn, Ni and Zn in sediments located in the bed of the Seine. These different groups can be explained by the different origins of the metals. Differentiation occurring during drying following the deposit may also be possible. Some authors consider dredged sediment deposits as soils, naming them dredged sediment derived soil (Vandecasteele et al., 2005). This approach is reinforced by the similitude of the approaches formulated, i.e. study by horizon and calculation of enrichment factors. In addition, these deposits are exposed to weather, resulting in pedogenesis processes such as accumulation of organic matter, decarbonation, changes in pH, and mineralogical changes that modify the material initially deposited (Zikeli et al., 2005). Soil can be defined as a major compartment of the biosphere resulting from the interaction between the atmosphere and the most superficial layers of the lithosphere (Ramade, 2002), and which evolves under the influence of the climate and vegetation (Duchaufour, 1995). Thus the term soil groups all the mineral and organic materials of the terrestrial surface potentially capable of supporting plant life (Hollis, 1991). According to this definition, the sediments deposited after dredging are therefore soils. One possible classification of sediments could make use of that proposed by Antonovie (1986), i.e. a specific class called deposol (dredged materials). The sites studied could be distinguished according to their specific localisation (proximity of a sewage plant, industrial activity: sites C and E). Grain size would then permit separating site H from the other sites (sites

X. Capilla et al. / Environmental Pollution 143 (2006) 106e116

A, B, D, F, G, J, I, etc.). Carbonate content could then permit distinguishing different groups such as less calcareous (site B), calcareous (sites J, F and I) and more calcareous (sites A, D and G). According to the World Reference Base for Soil Resources (ISSS/ISRIC/FAO, 1998), sediments displaced by human activity are anthropogeomorphic materials. Moreover, a high C/N ratio, as observed for sediment, is a common feature in anthropic soils (Morel et al., 2005). The more classical term ‘‘fluvisol’’ appears inappropriate here due to the artificial nature of depositing these sediments, with superpositions of dredged materials from different reaches. As a large, though not easily quantifiable, share of these sediments stems from industrial activities, the term technogenic used by Zikeli et al. (2005) could be proposed, which would lead to designating these soils as technogenic anthrosols, with an indication of their carbonate content, texture and origin (dredged material). Soil A would therefore be designated as a calcareous sandy-clayey silt technogenic anthrosol derived from dredged material. 4. Conclusion The sediments are mostly neutral to very alkaline and moderate to very calcareous, with a silt texture. Two groups of metals can be distinguished in the sediments. The first comprises Cd, Pb and Zn while the second comprises Al, Cr, Fe and Ni. Cr and Ni are linked to alumino-silicates and iron oxides, and thus likely to be solubilised during changes in oxidoreduction conditions. The soil characteristics of the sediments deposited permit the development of plant cover, leading to the existence of a rhizospheric area to a depth of 1.3 m. The aerial parts of the plants have high metal contents due to the metal pollution of the sediments. Furthermore, considerable variability was observed both between and within sites. The distinction between sites mainly stems from their immediate environments, followed by their texture and carbonate content. We therefore propose classifying these materials as technogenic anthrosols, a sub-group of anthropomorphic soils. This work could lead to further investigations of other sites in order to develop a typology of sediment deposit sites. Moreover, transfers of materials to the groundwater require evaluation, taking into account the depth of the sediment layer. In these layers, oxidoreduction conditions probably immobilise metals and thus the effect of plants cannot be detected. Acknowledgements The authors would like to thank Ste´phane Colin (Laboratoire Sols et Environnement-INPL (ENSAIA)/INRA) and Marc Danjean (Laboratoire des Sciences de l’EnvironnementENTPE) for their assistance during visits to sediment deposits and digging ditches for pedological purposes. Thanks are also due to Denis Vein for his patience in identifying the plants observed, which also contributed to this study. We are also grateful to the Services de la Navigation du NordePas-de-Calais, Nancy and Palavas and the Service Maritime et de la Navigation du Gard which authorised us to work

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