european journal of soil science, june 2006,

8/14/2019 European Journal of Soil Science, June 2006,

1/19

Trace element distributions in soils developed in loessdeposits fromnorthern France

T . S T E R C K E M A N a , F . D O U A Y b , D . B A I Z E c , H . F O U R R I E Rb , N . P R O I X d , C . S C H V A R T Zb & J . C A R I G N A Ne

aENSAIA-INPL/INRA, Laboratoire Sols et Environnement, BP 172, 54505 Vandoeuvre-le`s-Nancy Cedex,

bISA, Laboratoire Sols et

Environnement, 41, rue du Port, 59046 Lille Cedex, cINRA, Unite de Science du Sol, BP 20619, 45166 Olivet Cedex, dINRA,

Laboratoire dAnalyses des Sols, 273, rue de Cambrai, 62000 Arras, and eCNRS, Centre de Recherches Petrographiques et

Geochimiques, 15, rue Notre Dame des Pauvres, 54501 Vandoeuvre-le`s-Nancy, France

Summary

A pedo-geochemical survey was carried out in the Nord-Pas de Calais region (France) on soils developed

in loess deposits. Total concentrations of Al, Fe and 18 trace elements, as well as common soil

characteristics, were determined in samples from 52 surface and 97 deep horizons developed in these

loess deposits. The Pb isotopic composition was determined in two sola. The composition of deep

horizons, compared with that of the upper continental crust, with that of horizons developed from 21

other sedimentary rocks from the region and with that of loess from various parts of the world, confirms

that loess from the Nord-Pas de Calais region derives from multi-recycled and well-mixed ancient

sedimentary rocks. Correlation analysis shows that least mobile (i.e. ionic potential (Z/r) is between 3

and 7) geogenic elements (Bi, Co, Cr, Cu, In, Ni, Pb, Sn, Tl, V, Zn) are associated with the fraction


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few decimetres to about 20 m. The origin of the loess material

of western Europe is still controversial. It has been proposed

that these aeolian sediments were derived locally from

paleoestuaries bordering the English Channel. Alternative

models favour the role of shallow marine shelves that

emerged during glacial times. In either case, a reworking of

Tertiary sediments during the Pleistocene era seems to be

required before the aeolian deposition (Gallet et al., 1998).

Our work deals only with soils developed from typical loess

(Jamagne et al., 1981), excluding those developed in the

transition zone where loamy aeolian formations are mixed

with sand.

In the Nord-Pas de Calais, the development of soils issuing

from loess is quite slight. Soils developed in this recent mate-

rial are attributed to luvic BRUNISOLS or NE OLUVISOLS,

according to the Re fe rentiel Pe dologique (AFES, 1998) or to

Cambisols or Haplic Luvisols according to the WRB (ISSS,

1998). Under forest, the soils are often designated as luvic

BRUNISOLS OLIGOSATURE S or as oligosaturated

NE OLUVISOLS.

The luvic BRUNISOLS are distinguished by incipient clay

illuviation, leading to the formation of a structural horizon

with some clay coatings (St horizon). The NE OLUVISOLS

are characterized by a typical BT horizon, resulting from

marked clay illuviation. The St and BT horizons are brown

to yellow brown (Munsell: 10YR 4/4 to 10YR 4/6), with a

loamy to loamy-clayey texture, and a distinct prismatic and

polyhedral structure. The C horizon generally appears between

0.8 m and 1.2 m. It can be distinguished from the St and BT

horizons by its yellowish colour (Munsell: 10YR 5/6), its

smaller clay content and the absence of structure. The soil

parent material is often calcareous and designated as Cca.

An S or SC horizon may be observed between the BT (or St)

horizons and the Cca horizon. The sola may be truncated as a

consequence of water erosion.

In soils developed in a relatively shallow loess stratum over-

lying an impermeable material (such as clayey Tertiary depos-

its or residual clay with flints), signs of temporary water

excess may appear at depths of less than 0.5 m. When the

loess deposit is thicker, the soils show better natural drainage

and less distinct hydromorphic features appear at greater

depths.

The main use of the loess soils is intensive cultivation for

various crops (cereals, sugar beet, potatoes, vegetables, etc.).

Some of them are under permanent grassland and a very small

portion under forest.

Canche

Authie

Aa

Lys

Scarpe

Esc

aut

Sam

bre

Lille

Valenciennes

Holocene deposits

Loamysandy transition zone

Sands zone (thin mantle)Sands zone (thick mantle)

Loess zone (thin mantle)

Loess zone (thick mantle)

FranceBelgium border

50km

Dunkerque

Calais

Boulogne

Figure 1 Map of the superficial Pleistocene deposits of northern France, adapted from Paepe & Somme (1970).

Trace elements in loess soils 393

# 2006 British Society of Soil Science, European Journal of Soil Science, 57, 392410


3/19

Sampling

Sampling sites were far from potential contamination sources

(industrial plants, busy roads, houses, etc.). There were 38 sites

under cultivation, 11 under permanent grassland and three

under forest. All the horizons were sampled, in soil pits. The

sola were described according to the Pedological Information

System (STIPA, 1982). The horizons were sampled starting at

the bottom of the solum, to avoid contaminating the horizons

to be sampled. A steel blade was used to detach about 1 kg of

soil material, which was poured into a polypropylene bag.

Analysis

In each solum, samples from three horizons were analysed: the

surface organo-mineral horizon (LA horizon for cultivated

soil, A horizon for other soil uses), the C horizon and a

horizon situated between the previous ones, a BT, S or SChorizon. In one solum situated under forest and another one

under cultivation, all the horizons were analysed for the deter-

mination of the lead isotope ratios.

Methods of analysis are presented in Table 1. Quality con-

trol was based on internal control samples whose mean and

uncertainty values were known. For each parameter, a control

sample was analysed every 1520 samples. The total contents

of trace and major elements were determined for batches of

3040 samples. Three blanks, two internal control samples and

two certified samples (GBW 7401 and GBW 7402) in triplicate

were inserted into each batch. Moreover, in each batch two

samples were analysed twice and two others were analysed

thrice. At the INRA Soil Analysis Laboratory, where the

analyses were performed, all the parameters, except Bi, In,

Mo and Sn contents, are controlled by national or interna-

tional inter-laboratory comparisons. The frequency of these

comparisons is one sample a month for the pedological para-

meters (BIPEA, 2000) and four samples every 3 months for

major and trace elements (Van Dijk et al., 2001). The resultswere expressed on a dried soil basis, after deduction of the

moisture content.

Lead isotope ratios were determined using a magnetic sector

and multicollector inductively coupled plasma mass spectro-

meter (MCICPMS) (White et al., 2000) after aqua regia

extraction and lead separation by anionic exchange chromato-

graphy (Manhe` s et al., 1980).

Data processing

Frequency distributions, correlation matrices, principal com-

ponents analysis (PCA) and multiple linear correlations wereperformed using the STATISTICA software (StatSoft, 2002).

Data below the quantification limit were replaced by values of

half this limit (Holmgren et al., 1993; Sanford et al., 1993).

Results and discussion

Soil characteristics

The frequency distributions of nearly all the parameters mea-

sured in the deep horizons are only slightly skewed (data not

shown). Therefore, the data can be reasonably used in regres-

sion analysis without transformation. The particle-size distri-

bution fits that of typical loess as given by Jamagne et al.

Table 1 Methods of analysis. The standards refer to those published by AFNOR (Paris)

Parameter Principle Standard

Pretreatment Drying at room temperature, sieving to 2 mm, grinding to 0.250 mm for total dissolution NF ISO 11464

Residual moisture content Weighing the test portion before and after heating at 105C NF ISO 11465

Particle-size distribution Sedimentation (050 mm) and sieving (>50 mm) NF X31-107

Organic carbon Dry combustion or sulfo-chromic acid oxidation (when CaCO3 >50 g kg1) NF ISO 10694,

NF ISO 14235

Total carbonates Measurement of the volume of CO2 released after reaction with HCl NF ISO 10693

pH pH of a water suspension NF ISO 10390

CEC Percolation of a 1.0 mol l1

ammonium acetate solution, pH 7 NF X31-130Exchangeable cations Extraction with a 1.0 mol l1 ammonium acetate solution, pH 7 NF X31-108

Total Al, Bi, Cd, Co, Cr, Cu, Calcination followed by a HF HClO4 digestion at 180C. Determination by ICPOESa NF ISO 14869-1

Fe, In, Mn, Mo, Ni, Pb, or ICPMSb

Sb, Sn, Tl, V, Zn

Total Hg Digestion by a sulfo-nitric acid mixture at 60C. Determination by CVAFSc INRA methode

Total As and Se Digestion by a sulfo-nitric acid mixture containing V2O5. Determination by CVAASd INRA methode

aICPOES, inductively coupled plasma optical emission spectrometry.bICPMS, inductively coupled plasma mass spectrometry.cCVAFS, cold vapour atomic fluorescence spectrometry.dCVAAS, cold vapour atomic absorption spectrometry.eSterckeman et al. (2002a).

394 T. Sterckeman et al.



4/19

(1981): dominance of coarse silt, and coarse silt to fine silt

ratios are always above 1 and often above 2 (Table 2).

Relationships between trace elements and major mineral

components

The positive correlations of numerous trace element contents

with lutum, Al and Fe contents suggest that trace elements are

specifically associated with phyllosilicates and with iron oxides

and hydroxides of the finest fraction (Table 3). This is sup-

ported by the fact that, in the lutum fraction of two deep

horizons, Sterckeman (2004) found mainly smectites, chlorite

and illite, together with goethite. In the >2 mm fractions, he

found chlorite, micas and feldspars whose content decreased

with increasing fraction size. The quartz content increased

with the fraction size, the >50 mm fraction containing more

than 800 g kg1 quartz. This composition could explain the

negative correlations of trace element contents with the coarse

fraction content, as quartz acts as a diluent of the carryingphases.

In the deep horizons, the correlation between Al and Fe

explains about half of the variance of Bi, Cr, Cu, In, Ni, Pb,

Sn, Tl and Zn contents and about 80% of that of V (Table 3).

It also explains the variance of As, Co, Mo and Sb, but at a

rather smaller level (about 15% to 35%). It does not explain,

or only slightly, that of Cd, Mn, Hg and Se. More or less close

Table 2 Physico-chemical characteristics of the soil horizons from the Nord-Pas de Calais loess deposits (median values)

Horizon type

Variable Unit LA or A BT S, SC or C Cca Subsoil

Cultivation

Size (n) /horizon 38 33 26 11 70

Thickness /cm 20 15 20 20 20

Lutum (


5/19


6/19

Table3

Linearcorrelationcoefficients

betweenvariablesmeasuredinthesoilhorizonsfromtheNord-PasdeCalaisloessdep

osits.Coefficientssignificantlydifferentfromzero(

0.05)

areinboldtype.Coarsefraction(202000mm)isthesumofcoarsesiltandsands

Lutum

Finesilt

Coarsesilt

Finesand

Coarsesand

Coarsefraction

OrganicC

pH

CaCO3

CEC

Al

Fe

Mn

Surfacehorizons

Lutum

1.00

0.23

0.6

7

0.4

7

0.20

0.7

7

0

.00

0.23

0.2

7

0.5

6

0.81

0.8

2

0.05

Finesilt

0.23

1.00

0.3

0

0.8

0

0.3

5

0.8

0

0

.24

0.26

0.22

0.24

0.37

0.4

3

0.4

7

Coarsesilt

0.6

7

0

.30

1.00

0.09

0.2

7

0.6

2

0

.12

0.17

0.3

0

0.2

9

0.58

0.6

7

0.3

1

Finesand

0.4

7

0

.80

0.09

1.00

0.4

2

0.8

1

0

.31

0.17

0.16

0.4

3

0.49

0.5

4

0.24

Coarsesand

0.20

0.3

5

0.2

7

0.4

2

1.00

0.3

5

0

.12

0.07

0.25

0.20

0.28

0.08

0.08

Coarsefraction

0.7

7

0

.80

0.6

2

0.8

1

0.3

5

1.00

0

.16

0.03

0.02

0.5

1

0.75

0.7

9

0.3

4

OrganicC

0.00

0.24

0.12

0.3

1

0.12

0.16

1

.00

0.7

5

0.24

0.7

8

0.27

0.17

0.5

4

pH

0.23

0.26

0.17

0.17

0.07

0.03

0.7

5

1.00

0.5

8

0.4

2

0.27

0.20

0.3

4

CaCO3

0.2

7

0.22

0.3

0

0.16

0.25

0.02

0

.24

0.5

8

1.00

0.03

0.07

0.04

0.00

CEC

0.5

6

0.24

0.2

9

0.4

3

0.20

0.5

1

0

.78

0.4

2

0.03

1.00

0.21

0.3

1

0.4

2

Al

0.8

1

0

.37

0.5

8

0.4

9

0.2

8

0.7

5

0

.27

0.2

7

0.07

0.21

1.00

0.8

6

0.3

8

Fe

0.8

2

0

.43

0.6

7

0.5

4

0.08

0.7

9

0

.17

0.20

0.04

0.3

1

0.86

1.00

0.4

2

As

0.4

0

0.03

0.2

8

0.19

0.10

0.2

7

0

.23

0.13

0.13

0.3

6

0.23

0.3

6

0.11

Bi

0.2

7

0

.39

0.09

0.5

1

0.14

0.4

3

0

.69

0.4

8

0.13

0.6

3

0.10

0.21

0.19

Cd

0.07

0.3

3

0.07

0.19

0.3

6

0.17

0.4

2

0.3

8

0.2

7

0.2

9

0.08

0.05

0.17

Co

0.5

0

0

.35

0.6

0

0.3

3

0.16

0.5

4

0

.56

0.4

7

0.15

0.18

0.68

0.7

6

0.7

7

Cr

0.7

1

0

.36

0.6

5

0.3

6

0.14

0.6

8

0

.37

0.3

7

0.06

0.13

0.78

0.8

5

0.5

0

Cu

0.04

0.22

0.19

0.3

0

0.16

0.12

0

.05

0.02

0.13

0.06

0.01

0.01

0.09

Hg

0.01

0.26

0.06

0.11

0.25

0.17

0

.56

0.26

0.16

0.4

3

0.33

0.25

0.6

3

In

0.4

2

0

.42

0.22

0.5

6

0.14

0.5

4

0

.70

0.4

1

0.03

0.7

4

0.22

0.3

1

0.24

Mn

0.05

0

.47

0.3

1

0.24

0.08

0.3

4

0

.54

0.3

4

0.00

0.4

2

0.38

0.4

2

1.00

Mo

0.12

0.25

0.03

0.3

7

0.07

0.24

0

.79

0.6

0

0.21

0.6

2

0.04

0.01

0.3

8

Ni

0.7

7

0.20

0.6

0

0.3

3

0.09

0.6

1

0

.41

0.4

7

0.2

8

0.09

0.86

0.8

1

0.4

4

Pb

0.10

0.08

0.09

0.01

0.2

9

0.12

0

.64

0.4

2

0.03

0.3

9

0.35

0.23

0.4

9

Sb

0.02

0

.30

0.09

0.3

9

0.05

0.21

0

.79

0.5

4

0.12

0.5

7

0.23

0.12

0.3

6

Se

0.02

0.21

0.09

0.2

8

0.02

0.13

0

.91

0.6

9

0.19

0.6

8

0.29

0.13

0.5

1

Sn

0.11

0.19

0.12

0.06

0.3

6

0.06

0

.38

0.14

0.23

0.3

3

0.12

0.07

0.3

6

Tl

0.4

3

0

.45

0.20

0.5

2

0.4

1

0.5

6

0

.24

0.15

0.10

0.3

6

0.48

0.3

8

0.02

V

0.7

0

0

.42

0.6

4

0.4

7

0.03

0.7

1

0

.03

0.08

0.05

0.3

6

0.65

0.8

6

0.3

6

Zn

0.4

0

0.15

0.4

1

0.00

0.4

2

0.15

0

.22

0.25

0.3

0

0.06

0.34

0.3

9

0.23




7/19


8/19

Table4

AveragecompositionofsoilhorizonsfromNord-PasdeCalaisloessdepo

sitsandsedimentaryrocks(medianvalues)

,ofloessfromFrance,GreatBritain,Germ

any,Spitsbergen,

Kansas,Argentina,ChinaandNewZe

aland(Worldloess,medianvalue)andofu

ppercontinentalcrust(UCC,meanvalue)

Nord-Pasde

Calais

Loess

Surfacehorizons

Deeph

orizons

21othersedimentary

parentmaterialsa

Worldloessb

UCC

Unit

LACultivation

AGrassland

AForest

BT

S,SCorC

Cca

All

Surfacehorizons

Deephorizons

Value(n)

T&Mc

Wd

Ge

Size

/horizon

38

11

3

47

39

11

97

219

390

Al

/gkg

1

41.2

41.0

37.6

52.6

50.1

42.0

50.3

35.0

36.9

65.2(75)

80.4

77.4

72.2

Fe

20.6

20.1

18.2

29.1

26.6

22.5

27.4

20.5

23.8

31.5(75)

35.0

30.9

39.9

As

/mgkg

1

8.5

9.0

10.0

10.6

9.7

8.4

10.0

8.0

7.6

1.5

2

4.4

Bi

0.16

0.15

0.30

0.17

0.15

0.14

0.16

0.17

0.12

0.127

0.123

0.23

Cd

0.41

0.33

0.15

0.13

0.11

0.12

0.12

0.40

0.10

0.098

0.102

0.079

Co

9.2

8.8

4.7

11.5

10.6

10.0

11.1

9.0

8.5

11.4(54)

10

11.6

17

Cr

54

55

44

68

65

54

65

51

57

56(42)

35

35

80

Cu

15.8

14.8

13.7

14.3

13.9

11.6

13.6

13.6

9.3

13.0(42)

25

14.3

32

Hg

0.065

0.061

0.174

0.031

0.020

0.020

0.024

0.061

0.022

0.056

0.0123

In

0.038

0.041

0.062

0.045

0.041

0.037

0.041

0.038

0.031

0.05

0.061

Mn

642

627

302

593

519

450

523

427

276

620(75)

600

5

27

774

Mo

0.53

0.49

0.93

0.53

0.48

0.44

0.50

0.53

0.43

0.14(7)

1.5

1.4

0.78

Ni

20.5

19.1

12.9

28.6

28.6

23.4

27.8

18.8

20.1

19.5(39)

20

18.6

38

Pb

30.3

32.7

71.6

19.2

17.8

15.1

18.6

29.4

14.6

16.0(71)

20

17

18

Sb

0.65

0.76

1.82

0.57

0.61

0.50

0.55

0.71

0.45

0.2

0.31

0.3

Se

0.22

0.29

0.65

0.13

0.06

0.05

0.10

0.29

0.17

0.05

0.083

0.15

Sn

2.17

2.27

3.20

2.09

2.01

1.65

2.02

2.01

1.46

3.6(18)

5.5

2.5

1.73

Tl

0.46

0.44

0.51

0.51

0.48

0.41

0.50

0.39

0.36

0.75

0.75

0.47

V

59

64

53

75

72

58

72

58

64

66(42)

60

53

98

Zn

66

68

47

58

54

43

55

67

44

55(42)

71

52

70

aFromSterckemanetal.(2002a):limes

tones,chalks,shales,marls,clays,sandsan

dmixedfaciesfromPrimary,Secondary,TertiaryandQuaternaryeras.

bFromLeRiche(1973),Tayloretal.(1983),Galletetal.(1996,1998),Dingetal.

(2001),Jahnetal.(2001)andYokooetal.

(2004).

cFromTaylor&McLennan(1995).

dFromWedepohl(1995).

eFromGaoetal.(1998).




9/19

the Cd content is less in surface horizons under forest com-

pared with those under permanent grassland and cultivation.

This is consistent with the hypothesis of an exogenous Cdinput in the surface horizons varying with soil use (see next

section).

In the deep horizons, Cd is positively and closely correlated

with Mn and organic C, while it shows few correlations with

other soil characteristics, contrary to the other trace elements.

Considering the absence of link between Cd and organic C in

the surface horizons, and that Cd is known to generally show

little association with organic matter in soil (Adriano, 1986;

Alloway, 1995), the positive correlation between Cd and

organic C in the deep horizons could be a consequence of a

physical link between Cd and Mn, the latter being also asso-

ciated with organic C.

Enrichment of surface horizons

In the deep horizons, close linear correlations exist between the

contents of various trace elements and those of Al or Fe (Table 5).

These relations have the general form:

TEDH aMEDH b; 2

where [TE] represents the concentration of a trace element (in

mg kg1), [ME] the concentration of a reference major element

(Al or Fe, in g kg1), DH indicates that the content refers to

deep horizons, and a and b are the parameters of the linear

regression (least squares method).

If we consider that [TE]DH represents the trace elementcontent of the original soil parent material, i.e. the pedo-

geochemical background (PGB) content, this can be estimated

in any surface horizon ([TE]PGB/SH) assuming that:

TEPGB=SH aMESH b; 3

where SH indicates that the content refers to a surface horizon.

This assumption is possible because there is generally no sig-

nificant contamination with Al and Fe in soils. In the case of

Cd, Hg and Se, which show no correlation with Al or Fe, the

mean content of the deep horizon was taken as [TE]PGB/SH

(Table 5). For Mn, Co was taken instead of Al or Fe.

Subtracting [TE]PGB/SH from the actual trace element contentof the surface horizon ([TE]SH) gives the enrichment (ETE) of the

surface horizon, relative to the soil parent material (Figure 6),

expressed in mg kg1 or in percentage of [TE]PGB/SH.

The bivariate diagrams (e.g. Figures 4a and 6) indicate that the

surface horizons are enriched with all the trace elements deter-

mined, except Co, Cr and Ni. In absolute values (mg kg1) and

without distinguishing between soil use, enrichments with Mn,

Zn, Pb, Cu and V are the greatest (median from 172 mg kg1 to

3.32 mg kg1) (Table 6); the smallest are Se, Mo, Tl, Hg, Bi

and In (from 0.11 mg kg1 to 0.003 mg kg1). When

expressed relative to the pedo-geochemical background, the

Lutum

Al

Fe

Co

Cr

Ni

V(15)

0.8 0.9 1.0

0.2

0.1

0.0

0.1

LutumV(15)

FS

CS

FSa

CSa

org CSe(4).

pH

CaCO3

CEC

AlFe

Mn

Cd(1)

CoCr

Cu(5)

Ni

Pb(3)

Zn(7)

Mo(11)

Sn(9)

Sb(6)

Tl(12)

Bi(10)

In(14)

As(13)

Hg(2)

1.0

1.0 0.5 0.0 0.5 1.0

0.5

0.0

0.5

1.0

PC1: 32.03%

PC2:23.71%

org. C

Pb(3)Sn(9)

Sb(6)

Hg(2)

Se(4)

0.5

0.6

0.6 0.5 0.4 0.3 0.2 0.1

0.7

0.8

0.9

Figure 3 Principal components analysis of the variables measured in surface and deep horizons from loess deposits. FS, fine silt; CS, coarse silt; FSa,

fine sand; CSa, coarse sand. The surface enrichment ranking number is in parentheses.




10/19


11/19


12/19

estimated from the correlation between the isotopic ratio and

1/[Pb] in the horizon under forest (Figure 9). The results do

not vary significantly whatever the isotopic ratio used and are

close to the mean isotopic composition of the French

industrial Pb emissions and of the main lead ores (Monna

et al., 1997).

In forest soils, the enrichments calculated by the two meth-

ods are close. In the OF horizon EPb/Al is 120.3 mg kg1,

Table 6 Estimated enrichment of the soil surface horizons from the Nord-Pas de Calais loess deposits with 15 elements

All soil uses All Cultivation Grassland Forest

Median 5th percentile 95th percentile Median 5th percentile 95th percentile Median

/mg kg1 /% of the pedo-geochemical background /g m2

As 0.91 1.01 3.89 10.6 13.6 49.8 0.18 0.18 0.17 0.21

Bi 0.030 0.005 0.128 24.8 4.7 99.3 0.005 0.005 0.005 0.009

Cd 0.26 0.09 0.52 220.4 75.3 434.8 0.080 0.085 0.050 0.001

Cu 4.26 0.45 13.43 44.1 4.0 126.9 0.9 1.0 0.8 0.2

Hg 0.035 0.011 0.159 106.4 33.7 482.2 0.009 0.010 0.006 0.007

In 0.003 0.002 0.020 7.6 5.3 66.9 0.001 0.001 0.000 0.002

Mn 172 17 348 37.1 4.7 83.5 47.3 49.8 34.7 2.2

Mo 0.10 0.00 0.39 22.9 0.3 99.3 0.022 0.029 0.022 0.030

Pb 14.93 6.20 48.67 94.6 42.7 337.4 4.0 4.6 3.4 2.4

Sb 0.22 0.03 0.90 42.8 5.8 196.2 0.069 0.071 0.053 0.071

Se 0.113 0.038 0.373 94.2 32.0 311.2 0.029 0.029 0.030 0.024

Sn 0.51 0.18 2.20 28.9 10.4 139.8 0.11 0.12 0.11 0.08

Tl 0.049 0.001 0.117 11.6 0.1 31.6 0.012 0.015 0.009 0.006V 3.32 2.84 12.97 6.6 4.8 22.2 0.6 0.6 1.1 0.2

Zn 18.66 4.42 38.50 41.0 11.1 87.2 5.6 6.5 3.6 0.3

Lutum

FS

CS

FSa

pH

Al

FeECd

0.9 0.8

0.1

0.2

0.3

org. C

ECuEPb

EMo

ESn

ESb

EBi

EIn

EAs

ESe

0.4

0.5

0.6

0.7

0.8

0.5 0.4 0.3 0.2 0.1

EHg

Lutum

FSCS

CSa

org. C

pH

CaCO3CEC

Al FSaFe

ECuEPb

EZn EV

EMo

ESn

ESb

ETl

EBiEInEAs

EMn

EHgESe

ECd

1.0 0.5 0.0 0.5 1.0

1.0

0.5

0.0

0.5

1.0

PC1: 40.11%

PC2:16.40%

Figure 7 Principal components analysis of the characteristics and enrichments [expressed as ln(mass or cmol by m2)] of the surface horizons from

loess deposits. FS, fine silt; CS, coarse silt; FSa, fine sand; CSa, coarse sand; EXX, enrichment with element XX.




13/19

Table7

ContentandisotopiccompositionofPbinthehorizonsoftwosolafrom

theNord-PasdeCalaisloessdeposits

Horizon

Depth/cm

Pb/mgkg

1

208

Pb/206Pb

207Pb/206Pb

206Pb/207Pb

208Pb/204Pb

207Pb/204Pb

206Pb/204Pb

Solumundercultivation

LA

024

42.4

2.0726

0.83990

1.1906

2

38.570

15.630

18.609

BT1

2

445

19.3

2.0417

0.81930

1.2205

6

38.957

15.632

19.080

BT2

4

585

18.6

2.0408

0.82000

1.2195

1

38.950

15.650

19.086

BC

8

5100

20.2

2.0382

0.81987

1.2197

1

38.960

15.672

19.115

C1

10

0130

17.6

2.0522

0.82315

1.2148

5

39.054

15.665

19.031

C2

13

0160

17.2

2.0468

0.82247

1.2158

5

38.967

15.658

19.038

C3ca

16

0180

15.6

2.0499

0.82720

1.2088

9

38.764

15.643

18.910

Solumunderforest

OF

03.5

131.7

2.1042

0.86321

1.1584

7

38.051

15.610

18.084

A

3.58.5

113.5

2.0991

0.85837

1.1649

9

38.199

15.620

18.197

Esg

8.537.5

19.9

2.0451

0.82061

1.2186

1

39.049

15.669

19.094

SCg

37.577.5

18.0

2.0513

0.82124

1.2176

7

39.141

15.670

19.081

Cg

77.5150

16.6

2.0511

0.82341

1.2144

6

38.964

15.642

18.997

Qualitycontrol

NBS981Pb

referencematerial

2.1

677

0.91484

1.09308

36.725

15.499

16.942

Twostandard

deviations(n

17)

0.0

001

0.00004

0.00005

0.008

0.003

0.004

Referencevalues(SE)

2.1677

2

0.91483

7

36.722

8

15.498

3

16.941

2




14/19

whilst EPb/IR is 120.6 mg kg1. In the A horizon, EPb/Al is

99.8 mg kg1, whilst EPb/IR is 92.3 mg kg1. In the LA hor-

izon, EPb/IR is 17.3 mg kg1, i.e. about 36% less than EPb/Al

(27.1 mg kg1). When using a greater 206Pb/207Pb ratio (here

1.175), as suggested by the relationship between this ratio and

1/Pb (Figure 9), EPb/IR becomes 26.5 mg kg1. Figure 9 sug-

gests that, at least under forest, the 206Pb/207Pb ratio of the

exogenous Pb could increase with depth, which could reveal a

variation in exogenous Pb composition (and origin) with time.

Semlali et al. (2001) found the 206Pb/207Pb of exogenous Pb to

increase with depth in a French Andosol. This could be the

consequence of the greater206

Pb/207

Pb of lead depositedbefore petrol lead deposition (Farmer et al., 1996, 2002).

This might explain why the estimated isotopic composition

of anthropogenic Pb in the LA horizon is different from that

in the OF and A horizons (for instance a greater 206Pb/207Pb

ratio), as the LA horizon results from mixing by ploughing of

horizons deeper than those of the forest A horizon. However,

it cannot be excluded that the exogenous Pb could be partly

different in forest soils to that in cultivated soils, because of

different sources or interceptions of the fallout. Nevertheless,

it is reasonable to consider that the Pb enrichment in the

surface horizons is completely due to exogenous, mostly

anthropogenic, input.

Comparison with continental crust and other sedimentary

deposits

The composition of the loess horizons is close to that of thehorizons developed in 21 other sedimentary parent materials

from the Nord-Pas de Calais, particularly when comparing the

deep horizons which can be considered to be uncontaminated

(Table 4). This composition is not so very far from the average

composition of loess deposits from various places in the world

(Argentina, China, France, Germany, Great Britain, Kansas,

New Zealand, Spitsbergen) calculated from the results of var-

ious researches. A close agreement is also found when compar-

ing the composition of the Nord-Pas de Calais loess horizons

with those of the upper continental crust (UCC), though this

varies according to the authors (Taylor & McLennan, 1995;

Wedepohl, 1995; Gao et al., 1998). This is consistent with theconclusion reached by Taylor et al. (1983) and confirmed by

Gallet et al. (1998), that the average composition of the upper

continental crust can be obtained from aeolian deposits as well

as from fine-grained clastic sediments.

Enrichment factors (EF) of the loess deep horizons were

calculated for all the elements, using the classical formula

(see for instance Shotyk et al., 2003):

EF EDH=REDH=EUCC=REUCC; 7

where REis one of the reference elements, here Al and Fe, and

UCC refers to the upper continental crust.

0.75

0.80

0.85

0.90

0.95

1.00

1.05

2.00 2.05 2.10 2.15 2.20 2.25 2.30

208Pb/206Pb

207Pb/206Pb

Soils, Germany, surface horizons

Soils, Germany, deep horizons

Pb in gasoline, average, France

Industrial emissions, average,France

Aerosols, N-PdC

Peat bogs, Norway

Pb ores, Australia, Idaho, Canada

Loess, N-PdC, cultivation, LA

Loess, N-PdC, forest, OF

Loess, N-PdC, forest, A

Loess, N-PdC, deep horizons

European Standard Lead Pollution(Haack et al., 2003)

Figure 8 Relationship between 207Pb/206Pb and208Pb/206Pb in horizons from two sola in loess

deposits and in other samples (references in the

text). N-PdC, Nord-Pas de Calais.

Under foresty=1.1424x+1.1531R2=0.96

1.15

1.16

1.17

1.18

1.191.20

1.21

1.22

1.23

0 0.03 0.05 0.07

1/[Pb] / mg1kg2

206Pb/207P

b

Cultivation

Forest

Figure 9 Relationship between 206Pb/207Pb and 1/[Pb] in horizons

from two sola on loess deposits.




15/19

Enrichment factors using the composition of UCC from Gao

et al. (1998) are closer to 1 than the EF based on the data from

Taylor & McLennan (1995) and Wedepohl (1995) (Figure 10).

Whatever the REand the UCC composition used, the loess soils

from the Nord-Pas de Calais appear richer in As and Sb than

the upper continental crust, and also seem to be slightly

enriched with Cd. When based on the values from Taylor &

McLennan (1995) and Wedepohl (1995), the EF indicates a

slight enrichment with Bi, Cr, Ni and Se, which is not confirmed

by the EF based on the data from Gao et al. (1998).

The enrichment factors have also been calculated using the

average composition of world loess as a reference (Figure 10).They indicate no or only slight enrichment of the Nord-Pas de

Calais loess compared with the available data, except for Mo.

However, the reference data for Mo come from only one loess

deposit of Great Britain (Le Riche, 1973), analysed with a

method which may not be comparable to the methods used

in the other more recent work. The relative composition of

loess from the Nord-Pas de Calais is close to that of the other

loess from distant parts of the world. Again, this is consistent

with the fact that loess is a representative sample of the con-

tinental crust, more or less diluted with quartz and carbonates.

Their ionic potentials make As, Cd, Mo and Sb relatively more

mobile (less conservative) elements (Goldschmidt, 1958; Pedro

& Delmas, 1970), susceptible to accumulation in sedimentary

rocks. This may be why loess appears enriched with these

elements in comparison with UCC.

Bivariate diagrams give a generally positive correlation

between Al and Fe in the various loess deposits. However,Fe/Al ratio varies according to the location of the deposit

(Figure 11). Loess deposits from the Nord-Pas de Calais,

together with those from France and southwestern Germany

(Kaiserstuhl), appear to be slightly richer in Fe than those

from the rest of the world. Whatever the deposit, the

0

5

10

15

20

25

30

35

40

45

50

30 40 50 60 70 80 90 100

Al / gkg1

Fe/gkg1

Nord-Pas de Calais

France

Great Britain

Germany

Spitsbergen

Kansas

Argentina

China

New Zealand Figure 11 Relationship between Fe and Al con-

tents in loess deposits from Nord-Pas de Calais,

France, Great Britain, Germany, Spitsbergen,

Kansas, Argentina, China and New Zealand

(see Table 4 for sources).

0

1

2

3

4

5

6

7

8

9

10

11

12

Al Fe As Bi Cd Co Cr Cu Hg In Mn Mo Ni Pb Sb Se Sn Tl V Zn

EFAl

UCC, Taylor & McLennan, 1995

UCC, Wedepohl, 1995

UCC, Gao et al., 1998

World loess depositsSedimentary rocks from N-PdC

Figure 10 Average enrichment factors (EFAl) of

elements in deeper horizons from loess deposits,

against different materials, using Al as reference

element. UCC, upper continental crust; N-PdC,

Nord-Pas de Calais.




16/19

correlations between Fe and Al show negative y-axis inter-

cepts, indicating an impoverishment in Fe. This could be the

consequence of sedimentary differentiation and the moderate

chemical weathering undergone by the loess protoliths (Gallet

et al., 1998). These differentiation and weathering processes

might have been slightly weaker in northwestern Europe thanin the other parts of the Earths surface.

There is often a close correlation between Al and most of the

trace element contents in the loess deep horizons from the

Nord-Pas de Calais (Table 4). In the other loess deposits, the

correlation is generally not as good and does not fit that found

in the Nord-Pas de Calais horizons (Figure 12a). However,

several trace element contents from the various deposits corre-

late with Fe more uniformly, as if there were a unique relation-

ship between the Fe and TE of the loess from various regions

of the Earths surface. Figure 12(b) illustrates this phenom-

enon in the case of Zn and is similar to that observed for Co,

Cu, Pb and V. These elements behave more like Fe than Al

and could be more associated with iron (oxy-)hydroxides than

with phyllosilicates. Chromium content appears to be more

closely correlated to Al than to Fe (Figure 13). In this case, as

well as in the case of Ni and Sn, loess from Argentina, Kansas,

Spitsbergen and New Zealand does not fall along with the

correlations with Al or with Fe. This connects with the Nd

and Sr isotopic compositions measured by Gallet et al. (1998),

which clearly distinguished the Argentinean loess from the

other deposits they studied. The rare earth elements and theisotopic results from these authors indicate a significant con-

tribution of young Andean volcanic rocks to the Argentinean

loess deposits, whereas multi-recycled and well-mixed ancient

sediments are the principal sources for the other loess deposits.

Note that the New Zealand loess rests upon two eroded vol-

canoes of basaltic composition (Taylor et al., 1983).

The manganese content clearly does not correlate with that of

Al or Fe because of its great mobility (Pedro & Delmas, 1970).

However, Mn varies similarly in the different loess deposits. No

data were available about the As, Bi, Cd, Hg, In, Sb, Se and Tl

contents of loess from the other parts of the world. If loess

deposits from the Nord-Pas de Calais are considered to derive

from sedimentary rocks similar to those found in this region, EFs

based on these sediments average composition show that loess is

not enriched with As, Sb and Cd, nor with any other element.

0

10

20

30

40

50

60

70

80

90

30 40 50 60 70 80 90 100

Zn

/gkg1

Zn/gkg1

Fe / gkg1

AI / gkg1

(a)

0

10

20

30

40

50

60

70

80

90

10 15 20 25 30 35 40 45

Nord-Pas de Calais

France

Great BritainGermany

Spitsbergen

Kansas

Argentina

China

New Zealand

(b)

Figure 12 Relationship between Zn content

and (a) Al content, (b) Fe content in loess

deposits from Nord-Pas de Calais, France,

Great Britain, Germany, Spitsbergen, Kansas,

Argentina, China and New Zealand (see Table

4 for sources).




17/19

They show an impoverishment in Se, due to the large Se content

in some peat horizons fromthe region (Sterckeman etal., 2002a).

These results suggest that the ratios between trace element

contents and those of Al or Fe in deep loess horizons from

northern France (Table 8) give an acceptable characterization

of the pedo-geochemical background of soils developed in

most sedimentary rocks from northwestern Europe.

Conclusions

In the north of France, the contents of the least mobile ele-

ments in the deep horizons of soils from loess deposits are

close to those in the upper continental crust. In contrast, loess

appears to be enriched with mobile elements, such as As or Cd.

The composition of Nord-Pas de Calais loess is close to that of

loess from other parts of the world (the rest of France, Great

Britain, Germany, Spitsbergen, Kansas, Argentina, China,

New Zealand). However, whatever the mobility of the element,

the average composition of the loess from the Nord-Pas de

Calais is closer to that of the 21 other sedimentary rocks of the

region than to that of the loess from the rest of the world. Our

results highlight the fact that, to some extent, loess composi-

tion reflects the composition of the various rocks it is derived

from, which can be slightly different from those of the upper

continental crust.

In the deep horizons, Bi, Co, Cr, Cu, In, Ni, Pb, Sn, Tl, V and

Zn are associated with phyllosilicates and, probably even moreclosely, with iron oxy-hydroxides of the fine fraction. This is

suggested by the correlation of these element contents (except

Cr and Sn) with Fe, which is closer than that with Al, when

considering the loess deposits from the rest of the world. More

mobile elements such as As, Cd, Hg, Mn, Mo, Sb and Se seem

less or unassociated with these carrying phases. Cadmium, as

well as Co, seems to be particularly linked to Mn. The distribu-

tion of trace element/Al or trace element/Fe in loess could be

used as an estimate of the background contents for soils devel-

oped from most of the sedimentary materials in the north of

France and also in northwestern Europe.

0

20

40

60

80

100

120

140

160

180

30 40 50 60 70 80 90 100

Cr/gkg1

Cr/gkg1

Fe / gkg1

AI / gkg1

(a)

(b)

0

20

40

60

80

100

120

140

160

180

10 15 20 25 30 35 40 45

Nord-Pas de Calais

France

Great Britain

Germany

Spitsbergen

Kansas

Argentina

China

New Zealand

Figure 13 Relationship between Cr content and

(a) Al content, (b) Fe content in loess deposits

from Nord-Pas de Calais, France, Great

Britain, Germany, Spitsbergen, Kansas,

Argentina, China and New Zealand (see Table

4 for sources).




18/19

Surface horizons are enriched with exogenous input of all the

trace elements examined, except Co, Cr and Ni. Isotopic com-

position demonstrates that Pb enrichment is almost totally due

to human contamination through atmospheric fallout fromvarious emission sources. Enrichments with Cd, Cu, Mn and

Zn are greater in cultivated soils than in forest soils.

Enrichments with Pb and with Cu, Hg, Mo, Sb, Se and Sn are

due mainly to human contamination through atmospheric fall-

out. Humic substances seem to act as a sink for all these

exogenous elements.

Acknowledgements

We gratefully acknowledge the financial support of the Conseil

Re gional du Nord Pas de Calais and of the Ministe` re de

lAme nagement du Territoire et de lEnvironnement.

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[Element]/[Al] [Element]/[Fe]

Element Arithmetic mean Median 5th percentile 95th percentile Arithmetic mean Median 5th percentile 95th percentile

Al 1.00 1.00 1.00 1.00 1.86 1.85 1.71 2.08

Fe 0.54 0.54 0.48 0.59 1.00 1.00 1.00 1.00

As 0.20 0.20 0.14 0.23 0.36 0.36 0.27 0.44

Bi 0.0033 0.0033 0.0027 0.0039 0.0061 0.0060 0.0051 0.0071

Cd 0.0024 0.0024 0.0013 0.0038 0.0046 0.0046 0.0023 0.0072

Co 0.22 0.22 0.19 0.27 0.41 0.40 0.35 0.49

Cr 1.30 1.29 1.16 1.43 2.42 2.42 2.18 2.74

Cu 0.27 0.27 0.22 0.31 0.50 0.50 0.41 0.58

Hg 0.0007 0.0005 0.0002 0.0027 0.0012 0.0009 0.0004 0.0052

In 0.0009 0.0009 0.0007 0.0010 0.0016 0.0016 0.0014 0.0019

Mn 10.6 10.8 6.0 16.3 19.8 19.9 10.8 28.8

Mo 0.010 0.010 0.008 0.012 0.019 0.019 0.015 0.022

Ni 0.56 0.56 0.46 0.65 1.03 1.03 0.86 1.23Pb 0.37 0.37 0.33 0.42 0.69 0.68 0.59 0.82

Sb 0.011 0.011 0.008 0.014 0.021 0.021 0.015 0.026

Se 0.0024 0.0021 0.0010 0.0051 0.0044 0.0038 0.0017 0.0099

Sn 0.040 0.040 0.036 0.044 0.075 0.074 0.067 0.082

Tl 0.010 0.010 0.009 0.011 0.019 0.018 0.016 0.021

V 1.43 1.43 1.29 1.55 2.65 2.65 2.44 2.85

Zn 1.09 1.09 0.97 1.21 2.04 2.03 1.73 2.39




19/19

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