Structural and chemical characterization of copper, iron and manganese complexes formed by paleosol humic acids

0146-6380/88 $3.00+ 0.00 Copyright © 1988 PergamonPress pie

OrganicGeochemistry1987 Org. Geochem. Vol. 13, Nos 4-6, pp. 1145-1152, 1988 Printed in Great Britain. All rights reserved Advances in

Structural and chemical characterization of copper, iron and manganese complexes formed by paleosol humic acids NICOLA SENESIt and GILBERTO CALDERONI2. qstituto di Chimica Agraria, Universit~ degii Studi di Bad, Via Amendola n.165/A, 70126-Bari, Italia 2Dipartimento di Scienze della Terra, Universit/t "La Sapienza", P. le A. Moro, 5, 001(X)---Roma, Italia Abstract--Highly-purifiedhumic acid (HA) samples extracted from five paicosols collected in Southern Italy, ranging in radiocarbon age from about 14,000 to 29,000 yr BP, were analysed b)' Inductively Coupled Argon Plasma Optical Emission Spectrometry (ICAP-OES), Infrared, (IR) and Electron Spin Resonance (ESR) spectroscopy for their total contents and chemical forms of some transition metals. The HAs contained appreciable amounts of indigenous copper (500-1000 ppm) and iron (300-1400 ppm), and very low amounts of manganese (1-12 ppm). The ESR spectra indicated the presence in all of the paleosol HAs examined of inner-sphere, square-planar complexes for Cu E+ ions, bound prevalently by oxygenated functional groups of the HA, and octahedrically and/or tetrahedrically coordinated Fe3+ ions to HA-functional groups of various nature. The ICAP-OES, IR and ESR spectroscopic analyses showed that all the HAs were able to bind metal ions, added either singularly or simultaneously, in high amounts and in the order Fe > Cu>>Mn. The HA functional groups that were involved in the additional metal-binding were primarily carboxylic and phenolic OH groups. All of the metal-HA complexes formed showed a high stability against intense water-washing, whereas they were only partially stable against exhaustive acid-treatment (proton-exchange). Metal ion-complexed forms exhibited an extended but differentiated reversibility toward exchange with a different metal used as counter ion. In general, the paleosol HAs examined, despite their different ages, contained indigenous metal complexes of similar structural and chemical properties and showed substantially similar behavior in their residual metal-binding capacity and properties, closely-resembling those of HAs from soils and soil fungi. Key words: paleosols, humic acids, metal/complexes, copper/complexes, manganese/complexes, ICAP-OE spectrometry, IR spectroscopy, ESR spectroscopy

INTRODUCTION Paleosols (buried or fossil soils), interbedded in stratigraphic series of Quaternary age erupted tuffa, pumices and ash, are widespread in the major volcanic areas of the Italian peninsula and islands. The genesis of paleosols is mainly related to the environmental conditions (i.e. climate, vegetation cover, parent rocks, etc.) under which they developed, whereas their burial was caused by recurring volcanic activity. Significant amounts of the primitive organic matter, and particularly humic materials, of paleosois were preserved over years due to the physicochemical, biological, climatic and geologic conditions to which the soils were subjected during burial and diagenesis (Stevenson, 1969; Calderoni and Schnitzer, 1984a, b). Despite the numerous investigations carried out in the last two decades on naturally occurring and synthetic humic substances, relatively little attention has been devoted to humic substances from fossil soils. In the present study we used humic acids (HAs) isolated from a stratigraphic sequence of five paleosols, interbedded within volcanoclastic rocks in the Island of Procida, Southern Italy, and ranging

iron/complexes,

in age from about 14,000 to close 29,000yr BP (Calderoni, 1970; Alessio et al., 1971, 1973, 1976; Nonno, 1973). The same paleosol HAs (PHAs) have been previously characterized by measurements of C-14 ages and 13C/12C ratios (Alessio et al., 1976), by their structural and chemical properties (Calderoni and Schnitzer, 1984a) and their distribution of different N-forms (Calderoni and Schnitzer, 1984b). The primary purpose of this investigation was to examine the effect of burial on the distribution, chemical structure and properties, and stability of indigenous (naturally-occurring) PHA complexes with some transition metal ions, including copper, iron and manganese. An additional objective of this work was to obtain information on the residual binding capacity of PHAs for metal ions, and on metal-ion exchange properties of metal-PHA complexes. Metal binding properties play a very important role in the diagenesis of humic materials, i.e. their preservation against microbial attack, their mineralization and chemical alteration, their transport and leaching phenomena, etc., over geologic time (Stevenson, 1969; Schnitzer and Kodama, 1977). MATERIALS AND METHODS

Paleosol samples *Author to whom correspondence should be addressed. 1145

The paleosol samples originated from the Island of

1146

NICOLA SENESI and GILBERTO CALDERONI

modern soil

0 (not considered) 9 ~'.,;"0. o/.~r' o 0. , 0 .-

.. ;',. ";'...'. - . - .:.¢.:::. ; . . . " :..

...:. :. Fig. 1. Location of the Island of Procida where the paleosols were collected.

m

Procida, which is located in the Tyrrhenian Sea, a b o u t 3 km from the coast o f Campania, facing the Phelgrean Fields (Fig. 1). Samples were collected at the place n a m e d Sancio Cattolico, on the N E coast, close to the h a r b o r o f the island, where a 30 m high cliff exposes six paleosols interbedded within pyroclastic rocks. The stratigraphic column in Fig. 2 shows the sequence and the thickness (m) o f the different volcanoclastic units along with the position (numbered) o f the sampled paleosols. Detailed information on the geology o f this area has been published by R i t t m a n (1951) and Di G i r o l a m o and Stanzione (1973). The age, along with the main characteristics o f the paleosols used in this study are listed in Table 1. Isolation

of humic

0

E

Fig. 2. Stratigraphic column of the sampled outcropping showing the sequence of paleosols (1-5). On the left side is reported the thickness (m) of the volcanoclastic units.

BP which were isolated and investigated previously by Calderoni and Schnitzer (1984a, b). F o r the extraction and purification o f the HAs, the procedure r e c o m m e n d e d by the International Humic Substances Society was used, as described previously (Calderoni and Schnitzer. 1984b). Elemental composition, oxygen-containing functional group distribution and ash content o f the five purified P H A s are summarized in Table 2 and have been previously discussed (Calderoni and Schnitzer, 1984a).

acids

The five P H A s used in this study are the same P H A s , ranging in age between 14,000 and 29,000 yr

Table l, Age and some characteristics of paleosols Sample No.

Radiocarbonage (yr BP)"

Depth from surface (m)

Soil thickness(cm)

pHh

% C~

I

14,100 _+ 150

l0

2 3 4 5

19,620_+270 22,330 _+290 25,200 + 400 28,850 + 860

15 20 23 30

60 45 30 30 50

8.5 8.1 7.9 7.6 ~.6

1.04 1.10 0.96 1.05 1.23

"Ages were measured on PHAs (Alessio et al., 1976). bAfter Calderoni and Sehnitzer (1984a). Table 2. Elemental composition"~, major oxygen-containingfunctional group distributiona,b, ash content~'~, and total copper, iron and manganese contents of purified PHAs C H N Sample No. % 1 60.80 2.30 2.04 2 59.95 2.47 2.48 3 59.57 2.43 1.53 4 61.17 2.34 1.77 5 60.90 2.12 2.57 "From Calderoni and Schnitzer(1984). bOna moisture and ash-free basis. COn an air-dry basis.

O

34.60 34.83 36.22 34.46 34.12

COOH

6.6 6.5 6.2 6.1 6.0

OH meq/1 4.0 5.6 5.4 5.4 5.8

Tot. acid.

10.6 12.1 11.6 11.5 ll.8

Ash % 0. I 1 3.40 <0.10 0.80 2.20

Cu

Fe

501 i,007 990 785 988

ppm 523 1,412 327 418 408

Mn


Metal complexes of paleosol humic acids

1147

Untreated PHA (O)

HzO-wa~i~ t UCa

OCw

I

I

r,oa% t r e a ~

I

ItlO-we~ng

UCaFw

I

I

NCl-leacNng

UCaFa

I

I

I

Cua÷- ustumtion I I I HlO-washlng HCI-lesching I

Fe3.- saturation I I I HlO-w~h. Ha-kmc~

'-wlmlh.

1

OFa

UFw

] Mna+-treatrnent

I

I H/D-wash.

1 UCaMw

I HCl-leach. HaO-wash.

' U2Ma

I

MnZ~turatlon

I r l H:O--wash. H~-baeg

l UMw

HaO-wuh.

' UMa

I Cua+treltmemt

f I.hO-mm~.

1 UCFMw

I

I ~-kmck H/0-wash.

'

UCFMe

I

H:O- wash. HCI -leack

1 UMaCw

I ( ~ a ÷ * I ~ * * 1~2 + ) - m r maCim

HaO-wash.

' UMaCa

FeS+-tr ~eatmeat I HaO-wash.

1 UMaFw

HCl-leack HzO-wash.

'

UMaFa

Fig. 3. Comprehensive scheme of treatments performed on each PHA sample.

Preparation of metal ion-PHA complexes Portions (200 mg) of the untreated PHAs (U) were placed into fritted-glass funnels and then saturated with 0.1 M solutions (40ml) consisting of (a) Cu(CIO4)26H20(C), (b) FeCI3(F), (c) MnCI2(M), and (d) Cu(CIO4)26H20 + FeCI3 + MnCI2 (CFM). The products obtained were divided into two portions which were washed exhaustively with distilled water (UCw, UFw, UMw, and UCFMw) or with 0.1 M HCI solution (UCa, UFa, UMa, and UCFMa) until a negative Cu 2+, Fe 3+, or Mn 2+ test was obtained in the washing solutions. The acid-treated portion was then washed with distilled water until free of CI- ions. In a successive set of preparations, aliquots (200mg) of the acid-treated Cu 2+- and Mn 2+saturated PHA (UCa and UMa) were treated with either Fe a+ or Mn 2+ ion solutions (40 ml), and either Cu 2+ or Fe 3+ ion solutions (40 ml), respectively. The products obtained were then washed partly with water (UCaFw and UCaMw, UMaCw and UMaFw) and partly with 0.1 M HC1 and water (UCaFa and UCaMa, UMaCa and UMaFa), until negative metalion and CI- tests were obtained. All of the products were air-dried (-..<40°C) before analytical determinations were made. A comprehensive scheme of the treatments performed is shown in Fig. 3.

Total metal ion analyses Total copper, iron and manganese were measured by an Inductively Coupled Argon Plasma Optical Emission Spectrometer (ICAP-OES) Jarrel-Ash Atocomp 800 Series, on 4 M HNO 3 digests of the PHAs and their metal complexes. Wavelengths used and estimated instrumental detection limits were respectively: copper, 324.75nm, 0.010mg/1; iron, 259.94 nm, 0.005mg/l; manganese, 257.61nm, 0.005mg/l. The presence of vanadium was also checked in the untreated HA digests, but this metal

was always below the instrument detection limit (< 0.010 mg/I).

Infrared analysis Infrared (IR) spectra were recorded with a Perkin-Elmer model 399B IR spectrophotometer using KBr pellets obtained by pressing, under vacuum, uniformly prepared mixtures of I mg sample and 400 mg KBr (spectrometry grade), with precaution taken to avoid moisture uptake.

Electron spin resonance analysis Electron spin resonance (ESR) spectra were obtained at liquid nitrogen temperature (77 K) as the first derivative of the absorption signals for solid samples packed in ESR quartz tubes. A Bruker ER-200D spectrometer operating at an X-band frequency with a 100 kHz magnetic field modulation and a microwave frequency of 9.22 GHz was used. A microwave attenuation of 13 db and a modulation amplitude of 6.3 G were used throughout the measurements. The g-values and the hyperfine coupling constants IA I (cm-l 10-4) are the physical parameters of chemical interest that can be derived from the experimental spectra according to standard equations given by Wertz and Bolton (1972). The physical significance of these parameters and the structural and chemical information they can provide about metal ion-organic complexes in humic materials have been recently reviewed (senesi and Sposito, 1984; senesi and Steelink, 1987). RESULTS AND DISCUSSION

Total metal contents The PHAs contain appreciable amounts of copper and iron, whereas indigenous manganese contents are very low (Table 2). Iron seems to predominate in the youngest PHA samples (1 and 2), whereas copper is present in comparatively higher amounts in the oldest

1148

NICOLA

SENESI and

,.e

~'~_-~ Z~

J

....

~#~

eL

g-

z6 < ~b

e~ et

vvvvv~

~

8

E

g

e~

o

LL

GILBERTO

CALDERONI

PHAs (3-5). These metals are strongly bound by the organic matrix in the highly-purified PHA samples, which have been subjected to repeated treatments with H C I - H F solutions until the ash content remained constant (Calderoni and Schnitzer, 1984a). Total Cu, Fe and Mn contents determined in the different metal-saturated PHA samples Nos 1 and 5 are reported in Table 3. Data measured for metalsaturated PHAs 2, 3 and 4 being all comparable to those of samples 1 and 5, are not shown. The data show that: (a) the indigenous (naturally-occurring) metal content of the PHAs are only partially replaced upon treatment with an excess of a different metal ion; (b) the PHAs examined, despite their different age, have a similar, high residual binding capacity toward each of the interacting three metal ions used; (c) the total amount of metal retained after exhaustive water-washing of PHAs saturated with a single metal ion is much larger than the portion stable against intense acid treatment, especially in the case of Mn; (d) when the three metal ions are simultaneously reacted with the PHA, the amounts retained after acid-treatment are only relatively smaller than those held against water-washing, especially for Fe; and (e) the amounts of Fe retained by PHAs both after water- and acid-washings is higher than that of Cu, which in turn is higher than that of Mn. The Cu, Fe, and Mn contents determined in the PHA samples Nos 3 and 4 after treatment of the acid-stable metal-saturated PHA with a different cation are listed in Table 3. Data shows that Mn 2÷, and far more Fe 3÷, besides replacing to some extent acid-stable Cu 2+ ions from the PHA, are significantly adsorbed in forms which display high and low stability against water-washing and acid-treatment, respectively. Furthermore it appears that Cu 2÷ ions exchange-properties toward acid-stable Mn2+-satu rated PHA are similar to those described above, whereas Fe 3÷ ions seem to be able to extensively replace Mn -'÷ ions from PHA without being additionally retained in high amounts, even in forms stable to water-washing. These results show that metal-retention capacity, water- and acid-stability of the adsorbed metal forms, and metal-exchange reactivity of PHAs are similar for the different age PHAs studied. In addition, similar results have been obtained in studies of metal complexing properties of soil and fungal HAs (Senesi and Sposito, 1987; Senesi et al., 1985, 1986, 1987a, b). These observations all imply that the burial of HAs for various lengths of time has not appreciably affected their general metal-binding behavior.

Infrared analysis The IR spectra of the PHAs examined are very similar to one another in their peculiar absorptions (Calderoni and Schnitzer, 1984a) and strongly resemble those of soil HAs (Schnitzer, 1978). A typical IR spectrum for PHAs No. 6 is shown in Fig. 4(a). Briefly, the major absorption bands are as follows:

Metal complexes of paleosol humic acids I

i

I

I

I

(J z I-

z

4000

l

3000

I

I

I

2000 1600 1200

J

600

W A V E N U M B E R (cm -1 )

Fig. 4. IR spectra of PHA No. 6: untreated (a), Cu2+-saturated, water-washed (b) and acid-leached (c); (Cu 2+ + Fe 3+ + Mn2+)-saturated, water-washed (d), and acid-leached (e). IR spectra for PHA No. 4: acid-leached Cu2+-saturated (f), Mn2+-exchange products, water-washed (g) and acid-leached (h), Fe3+-exchange products, waterwashed (i) and acid-leached (j).

3420 cm- 1, strong (hydroxyls of various types, mainly H-bonded); 2920cm -1, weak (aliphatic groups); 1710 cm-], strong (carboxyl and carbonyls); 1610era -l, strong with a broadening toward lower wavenumbers (aromatic rings, carboxylate, etc.); 1390 cm- 1, medium (carboxylate); 1200 cm- 1, strong, broad (carboxyl, phenols and other oxygencontaining functional groups); and 800, 760, 740era -1, medium-weak (aromatic rings and aliphatic groups). The IR spectra confirm the general structural and functional similarity of the studied PHAs and their abundance in free carboxyl and other oxygenated functional groups (carbonyls, phenols,

1149

alcohols, ethers, etc.; compare with data in Table 2). This result points, therefore, to a high potential capacity of PHAs for binding metal ions. In fact, marked variations are observed for peculiar absorptions in the IR spectra of the different metal ionsaturated and/or exchanged PHAs, compared to the IR spectra of untreated PHAs, whereas no appreciable differences are apparent between similarlyprepared metal ion-complexes for the various PHA samples examined. Representative IR spectra of water-stable metal ion-PHA complexes [Figs 4(b) and 4(d)] are characterized by a marked decrease in intensity of the bands at 1710 and 1200 cm- ~ (mainly carboxyls), together with a reduced absorption at 3420 cm-1 (hydroxyls). These variations are always associated with a strong increase in IR absorptions at about 1600 and 1390 cm- ~ (carboxylate). The results clearly indicate the extended conversion of carboxylic, and secondarily phenolic groups, to carboxylate and phenolate groups, upon reaction of PHA with any metal ion. This suggests, therefore, a high involvement of acidic PHA-functional groups in the binding of metal ions. On the other hand, IR spectra very similar to those of the corresponding untreated PHAs are observed for acid-treated Cu 2+- and especially for Mn 2+saturated PHAs [Fig. 4(c)], whereas IR spectra of acid-treated Fe 3+- and (Cu 2+ + Mn 2+ + Fe3+)-PHA complexes [Fig. 4(e)] exhibit variations similar to those previously discussed for water-stable metal PHA complexes of any kind. These results, in agreement with the findings after Hoering (1973), point out that only Fe 3+ ions may be largely retained by PHAs in forms stable also to intense proton-exchange. By reverse it appears that the corresponding Cu 2+- and Mn2+-complexes are extensively disrupted by acidtreatment, which result is a restoration of the free carboxyl and phenolic groups of the PHA. Similar behavior is observed in the IR spectra of metalsaturated PHAs which have been exchanged with the proper metal ion and then washed with water or HCI [Figs 4(f)-4(j)] with the only exception being samples obtained by Fe 3+ exchange on Mn2+-saturated PHA (see also data in Table 3). All of these observations are in good agreement with the corresponding data previously presented for the total metal content variations in the metal-PHA complexes (Table 3). With respect to their IR properties, again the PHAs studied behave in a similar manner, despite their different ages.

ESR analysis Indigenous metal-PHA complexes. The PHA samples exhibit similar ESR spectra over the wide scan range spanned (8000 G). A representative ESR spectrum is shown in Fig. 5(a) (PHA sample No. 1). The main features are as follows: (a) a sharp resonance at g ~ 2.00 (A), which has been characterized in details for these samples in a previous study and attributed to PHA-organic free radicals of semiquinone nature

1150

NICOLA SENESI a n d GILBERTO CALDERONI

o•

A

U

/

C

D

A

100 G

00G

Fig. 6. ESR spectra (scan range, 2000 G) of untreated PHA No. 1 (U), and of its acid-leached Mn2+-saturated complex (UMa).

A

et al., 1977, 1985, 1986, 1987a, b); and (c) a rigid-limit

UMa

Fig. 5. ESR spectra (scan range, 8000 G) for untreated PHA No. 1 (U), and for its metal complexes. For symbol explanation, see "Materials and Methods" and Fig. 3.

(Calderoni and Schnitzer, 1984a); (b) an asymmetrical line at g = 4.1-4.2 (B), often associated with a tail at lower field (g = 8.2, B') (spectral data listed in Table 4), always observed for HAs of any kind and assigned to inner-sphere, octahedrally and/or tetrahedrically-arranged Fe3+-HA complexes (Senesi

anisotropic spectrum (C) of the "axial" type, showing a relatively well-resolved quadruplet at lower field (gpl) associated with an unresolved line at higher field (g±). This type of ESR spectrum has been often observed in HA samples of various sources and is evidence of a d~2_y2ground-state of Cu 2+ ions held in inner-sphere complexes by HA ligands arranged in a square planar, or distorted octahedral coordination around the central ion, i.e. tetragonal symmetry (Senesi et al., 1985, 1986, 1987a, b). This interpretation and additional information regarding the nature of binding sites for Cu ~+ ions can be derived from the evaluation of the ESR spectral parameters (glt[Air[, g i ) referred in Table 4 and calculated from enlarged experimental spectra (scan range, 2000 G) of the type shown in Fig. 6(a). In any ease the spectral parameters are consistent with Cu 2+ ions coordinated in sites involving 3 oxygen and 1

Table 4. ESR spectral data for indigenous Fe 3+- and Cu2+-PHA complexes Fe 3+ (Res. 8 ° B ' )

Cu 2+

Sample No.

g

AH (G)

g'

g"

I 2 3 4 5

4.10 4.12 4.12 4.12 4.11

64 64 75 56 64

8.2 8.2 ----

2.282 2.281 2.279 2.281 2.283

I All[ g± (10 4cm ~) 176 176 174 176 176

2.064 2.063 2.063 2,064 2.064

Ligands 30, 30, 30, 30, 30,

IN IN IN IN IN

Metal complexes of paleosol humic acids nitrogen atoms (Table 4). This implies a large participation of oxygen-containing functional groups (i.e. carboxylate and phenolate) and, secondarily, of nitrogen-containing groups of the PHA molecules in the binding of Cu 2+ ions. In general, ESR results indicate the presence of geometrically and chemically well-defined Fe 3+- and Cu2+-complexes, indigenous of the structure of the PHAs and which have survived the intense purification procedure that these HAs have been subjected to. No ESR evidence for the presence of Mn2+-PHA complexes was observed, probably because of the very low amount of indigenous Mn present in the purified PHAs examined. The most important difference between the ESR spectra of PHAs and those of soil and fungal HAs is the absence in the former spectra of vanadyl-HA complex resonances which have been often observed in the latter ones (Senesi et al., 1985, 1987b).

Laboratory-prepared metal-PHA complexes. The ESR spectra of any water-washed metal ionsaturated PHA and of acid-leached Fe 3÷- and (Cu :+ + F e 3+ +Mn2+)-PHA complexes are dominated by intense unresolved broad peak(s), overlapping the residual rigid-limit Cu 2+ spectrum observed in the untreated PHA samples [Figs 5(b)-5(d)]. These results are ascribed to extended polar interactions arising from the excess paramagnetic metal ion(s) present in multivariate forms in the metal-PHA products obtained under these conditions (Senesi et al., 1986, 1987a). This does not allow, therefore, for any interpretation of the type of metal-PHA complexes that are formed. The ESR spectra are, however, in agreement with the results of the total metal content and IR analysis, thus confirming the extended capacity of PHAs to retain high amounts of added metal ions in forms which are stable to intense water-washing. Acid-leached Cu 2+- and Mn2+-saturated PHAs show relatively well resolved ESR patterns featuring the formation of well-defined complexes of these metals with the reacting PHAs [Figs 5(e) and 5(f)]. The high gll and g± values and the low hyperfine coupling constants IAiil(gll=2.327, IAIII= 164cm -1 10 -4 and g. = 2.075) calculated for Cu 2÷saturated PHA complexes [Fig. 5(b)] are consistent with prevailing 4 0 binding sites for Cu 2+ ions. This indicates a higher involvement of oxygenated functional groups of PHAs in the complexation of additional Cu 2+ ions. The ESR spectra of Mn2+-saturated PHAs [Fig. 5(f)] are characterized by: (a) a poorly-resolved rigid-limit spectrum of residual Cu 2+ ions (C) showing spectral parameters similar to those calculated for the indigenous Cu2+-PHA complexes; and (b) an isotropic hyperfine pattern of six lines with slightly different spacing, typical of Mn :+ ions (D). The spectroscopic splitting factor, g = 2.005, and the hyperfine coupling constant [Ai,ol = 89 x 10-4cm -~

1151

_.J

UMa

/ f

°! UklaFa

D

Fig. 7. ESR spectra (scan range, 8000 G) of acid-leached Mn2+-saturated PHA No. 3 (UMa), of its acid-leached Cu2+-exchange products (UMaCa) and Fe3+-exchange products (UMaFa). calculated from the enlarged spectra of the type shown in Fig. 6, are consistent with the presence of six oxygen ligand atoms (supplied by carboxylate, phenolate, carbonyl and alcoholic functional groups of PHA, and by water molecules) arranged in a distorted octahedral environment around the Mn 2+ ion and bound principally by electrostatic forces (Senesi and Sposito, 1987). Thus manganese is expected to be relatively mobile and can in fact be almost completely displaced by exchange reactions with Cu 2+ or Fe 3+ ions (see data in Table 3 and foUowing discussion). The ESR spectra of the PHA complexes obtained after exchange-treatment with a different metal ion of the preliminary metal-saturated-PHAs, add some useful information to the knowledge of the metal ion-exchange properties of PHAs. In particular, the ESR spectra confirm the more or less extended reversibility of the metal ion adsorption/desorption reactions by PHAs. For example, a comparison of the spectra in Fig. 7 shows that Cu 2+ ions are able to replace Mn 2+ ions from Mn2+-PHA complexes more extensively than Fe 3+ ions can (see also data in Table 3). A comparison of ESR spectra shown in Fig. 8 suggests that Fe 3+ ions are more efficient than Mn 2+ ions in displacing Cu 2+ ions from their PHA complexes (see also data in Table 3). Thus, ESR analysis data confirm the existence of similar indigenous metal ion complexes in PHAs and the similar residual binding capacity of PHAs toward

1152

NICOLA SENF.Sland GILBERTOCALDERONI

UCa B

D

I

t

300~L

5OOO

Fig. 8. ESR spectra (scan range, 8000 G) of acid-leached, Cu2+-saturated PHA No. 4 (UCa) and of its acid-leached, Fe3+-exchange products (UCaMa).

added metal ion, furnishing unique information on the chemical and geometrical structure of m e t a l P H A complexes. In addition, E S R spectra confirm the different stability against water-washing, protonexchange, and metal-exchange of the complexes formed and the extended reversibility of metal ion-exchange reactions by PHAs. In conclusion, sample age seems to have a little effect on the amounts, chemical and geometrical form, stability and exchange properties of both naturally-occurring and laboratory-prepared Cu 2+-, Fe 3+-, and M n 2 + - P H A complexes. In addition, metal binding properties and metal complexed forms of P H A s seem to be substantially similar to those of H A s from other sources, i.e. soils and fungi. Acknowledgements--The authors are grateful to Professor G. Sposito, Department of Soil and Environmental Sciences and to the Department of Chemistry, University of California, Riverside, for permitting the use of the Bruker ESR spectrometer. Gratitude also is expressed to Mr G. Bradford and Mr K. M. Holtzelaw for the analyses of total metal in the humic acid samples.

REFERENCES

Alessio M., Bella F., Belluomini G., Cortesi C., Improta S. and Tuff B. (1971) University of Rome carbon-14 dates IX. Radiocarbon 13, 395-411. Alessio M., Bella F., lklluomini G., Calderoni G., Cortesi

C., Improta S. and Turi B. (1973) University of Rome carbon-14 dates X. Radiocarbon 15, 165-178. Alessio M., Bella F., Belluomini G., Calderoni G., Cortesi C., Improta S. and Turi B. (1976) University of Rome carbon-14 dates XIV. Radiocarbon 18, 321-349. Calderoni G. (1970) Datazioni di alcuni livelli umificati intercalati nelle piroclastiti dei Campi Flegrei (Campania) con il metodo del radiocarbonio. Thesis, Institute of Geochemistry, University of Rome, Italy, 125 pp. Calderoni G. and Schnitzer M. (1984a) Effects of age on the chemical structure of paleosol humic acids and fulvic acids. Geochim. Cosmochim. Acta 48, 2045-2051. Calderoni G. and Schnitzer M. (1984b) Nitrogen distribution as a function of radiocarbon age in paleosol humic acids. Org. Geochem. 5, 203-209. Di Girolamo P. and Stanzione D. (1973) Lineamenti geologici e petrologici dell'Isola di Procida. Soc. Ital. Mineral. Petrol. Rend. 29, 81 125. Hoering T. C. (1973) A comparison of melanoidin and humic acids. Ann. Rep. Geophys. Lab. Carnegie Inst. 682-690. Nonno U. (1973) Datazioni con il metodo del radiocarbonio di alcuni livelli umificati dell'Isola di Procida (Campania). Thesis, Institute of Geochemistry, University of Rome, Italy, 120 pp. Rittman A. (1951) Cenni sulla geologia di Procida. Soc. Geol. Ital. Bull. 70, 533-544. Schnitzer M. (1978) Humic substances: chemistry and reactions. In Soil Organic matter (Edited by Schnitzer M. and Khan S. U.), Chap. 1, pp. l~a0. Elsevier, Amsterdam. Schnitzer M. and Kodama E. (1977) Reactions of minerals with soil humic substances. In Minerals in Soil Environment (Edited by Dixon J. B. and Weed S. B.), Chap. 21. Soil Science Society of America, Madison, Wisconsin. Senesi N. and Sposito G. (1984) Residual copper (II) complexes in purified soil and sewage sludge fulvic acids: an electron spin resonance study. Soil Sci. Soc. Am. J. 48, 1247-1253. Senesi N. and Sposito G. (1987) Manganese (II) complexation by humic acids from soils and soil fungi. Proc. 6th Int. Conf. Heavy Metals in the Environment, New Orleans, September 15-18. CEP Consultants, Edinburgh. Senesi N. and Steelink C. (1987) Application of ESR spectroscopy to the study of humic substances and their interactions with organic xenobiotics and metal ions. In Humic substances H, Structure and Complexation Reactions (Edited by Hayes M. H. B., MacCarthy P., Malcolm R. L. and Swift R. S.). Wiley, New York. In press. Senesi N., Gritiith S. M., Schnitzer M. and Townsend M. G. (1977) Binding of Fe 3+ by humic materials. Geochim. Cosmochim. Acta 41, 969-976. Senesi N., Sposito G. and Martin J. P. (1985) Complexation of some transition metal ions in soil humic acids: an ESR study. Proc. 5th Int. Conf. Heavy Metals in the Environment, Athens, September 10-13, pp. 478-480. CEP Consultants, Edinburgh. Senesi N., Sposito G. and Martin J. P. (1986) Copper (I1) and iron (III) complexation by soil humic acids: an IR and ESR study. Sci. Tot. Environ. 55, 351-362. Senesi N., Sposito G. and Martin J. P. (1987a) Copper (I1) and iron (III) complexation by humic acid-like polymers (melanins) from soil fungi. Sci. Tot. Environ. 62, 241-252. Senesi N., Sposito G. and Martin J. P. (1987b) Intrinsic copper iron and vanadyl complexes in humic acid-like polymers (melanins) from soil fungi: an IR and ESR study. Proc. 7th Int. Syrup. Environmental Biogeochemistry, Viterbo-Roma, September 8-13, 1985. Nijhoff, Amsterdam. In press. Stevenson F. J. (1969) Pedohumus accumulation and diagenesis during the Quarternary. Soil Sci. 107, 185-193. Wertz J. E. and Bolton J. R. (Eds) (1972) Electron Spin Resonance: Elementary Theory and Practical Applications, 497 pp. McGraw-Hill, New York.