United States Office of Water
Environmental Protection Regulations and Standard- August 198"^
Agency C riteria and Standards Diwisior. SCD# 13
Washington DC 20460
Water
vvEPA
SEDIMENT QUALITY CRITERIA FOR METALS: II.
REVIEW OF METHODS FOR QUANTITATIVE
DETERMINATION OF IMPORTANT ADSORBENTS
AND SORBED METALS IN SEDIMENTS
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SEDIMENT QUALITY CRITERIA FOR METALS:
II. REVIEW OF METHODS FOR QUANTITATIVE
DETERMINATION OF IMPORTANT ADSORBENTS
AND SORBED METALS IN SEDIMENTS
Work Assignment 56, Task 4
August 1987
Prepared by:
Everett A. Jenne
Battel1e, Pacific Northwest Laboratories
Richland, Washington
for:
U. S. Environmental Protection Agency
Criteria and Standards Division
Washington, D.C.
Submitted by:
BATTELLE
Washington Environmental Program Office
Washington, D.C.
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ABSTRACT
This report 1s one 1n a series of reports that collectively describe
an approach for establishing sediment criteria for metals. The approach
uses surface complexatlon constants 1n conjunction with estimates of
sorbed metals and the quantities of Important adsorbents to estimate the
equilibrium activity of metals 1n the pore water of sediments. This
estimate of metal activity In pore water will then be used to evaluate the
potential toxicity of the sediments td benthlc organisms.
Predicting the equilibrium concentrations of metals 1n pore waters
and soil solutions requires reliable estlmfttes 6f both the total
quantities of the Important adsorbents and sorbed metals, as well as
estimates of appropriate adsorption constants. Various authors have
concluded that amorphic Fe, cryptocrystalllne Mn, and particulate organic
carbon constitute the Important adsorbents for metals In a large portion
of oxygenated sediments and soils. Many methods have been proposed for
determining the quantities of these adsorbents. Recently, a consensus has
evolved that acidic hydroxy!amine hydrochloride Is the. preferred Ghemlcat
extractant for estimating the quantity of cryptocrystal11fte Hn ox1de£.
Importantly, this extractant also provides an effective means of
estimating quantities of amorphic Fe oxides. Alkaline extractants appear
to be appropriate for estimating the reactive particulate organic carbon
content of sediments.
The extensive literature on the "selective" extraction of trace
metals and metalloids from Individual adsorbents 1n sediments indicates
that none of the available extraction methods will selectively remove
111
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trace metals from Individual adsorbents to the exclusion of other
adsorbents. Similarly, 1t Is exceedingly difficult to selectively
dissolve Individual adsorbents without simultaneously dissolving a
significant portion of another adsorbent(s). This nonselectlvlty of
extraction methods 1s Indicated both by the plethora of published
extraction methods and the variable importance that different studies
ascribe to Individual adsorbents. Because the various acid and/or
reducing extraction methods are known to attack multiple adsorbents, 1
conclude that 1t 1s physlcochemlcally impossible to distinguish among the
quantities of trace metals adsorbed separately by amorphic Fe oxide,
poorly crystallized Mn oxide, and reactive particulate organic carbon.
Nevertheless, the total quantity of sorbed metal may be determined
simultaneously with the quantities of amorphic Fe and poorly crystallized
Mn oxide l>y using the hot addle hydroxylamine hydrochloride extraction
method. An alkali extractant 1s recommended to estimate the quantity of
reactive particulate organic carbon. An experimental effort 1s required
to select between alternative alkali extractants to be used to estimate
the reactive particulate organic carbon, optimize experimental procedures
for the selected extraction methods, determine appropriate adsorption
constants, and validate the approach detailed 1n this report for
determinating sorbed metal concentrations.
1 v
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CONTENTS
ABSTRACT 111
INTRODUCTION 1
BACKGROUND 3
MAJOR ADSORBENTS .... 6
QUANTIFICATION OF AMORPHIC IRON AND CRYPTOCRYSTALLINE MANGANESE ... 10
ACIDIC AMMONIUM OXALATE 10
ACIDIC HYDROXYLAMINE HYDROCHLORIDE 11
OTHER EXTRACTANTS 12
QUANTIFICATION OF REACTIVE PARTICULATE ORGANIC CARBON ADSORBENT ... 15
DETERMINATION OF ADSORBED METALS 17
SELECTION OF METHODS 21
INTERIM EXTRACTION METHODS 22
RATIONALE FOR INTERIM EXTRACTION METHODS 23
OPTIMIZATION OF METHODS 25
REFERENCES . . 27
v
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SEDIMENT QUALITY CRITERIA FOR METALS:
II. REVIEW OF METHODS FOR QUANTITATIVE DETERMINATION OF
IMPORTANT ADSORBENTS AND SORBED METALS IN SEDIMENTS
TNTRODUCTTON
The Criteria and Standards Division of the U.S. Environmental
Protection Agency 1s developing sediment quality criteria for both
nonpolar organic contaminants and metals. These Criteria will be used in
conjunction with water quality criteria to protect aquatic organisms and
the food chain 1n both freshwater and saltwater. The approach selected
for developing sediment quality criteria for metals Involves calculating
the thermodynamic activity of the uncomplexed metal 1n the sediment pore
water and relating this thermodynamic activity to the toxic level of the
metal, which 1s Inferred from the water quality criteria for Individual
metals (Jenne et al. 1986). This approach assumes that the activity of
metals in pore water 1s 1n equilibrium with the sorbed metals and requires
only that the quantity of each important adsorbent (sorption "sink") and,
the quanti ty of sorbed metal s be determined. These data, plus surf act
adsorption constants for tlie individual abluents, are used along with
appropriate algorithm (model) to estimate the activities of metals il nore
water. Th1 s approach separates thruWems of detectntn§ m^tai
aval1abll1ty and evaluating toxlcity. Important!y, the approach relates
sediment quality criteria to the water quality criteria.
Tfils report is one tn aseries of five reports that review the
overall rationale for the approach (J#n«# et a.l. 198$), the available
1
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sorption data for reactive particulate organic carbon (RPOC)^a\ and the
selected adsorption constants for Fe oxidesand both review and
(c)
present recalculations of selected adsorption data for Mn dioxide . The
objectives of this report are to consider the nature and occurrence of the
Important adsorbents, evaluate the published extraction methods for
determining sorbed metals and adsorbents, and select appropriate
extraction methods for further evaluation.
(a) Allen, H. E., and J. M. Mazzacone. 1987. Sediment Quality Criteria
fnr MgtaUf TTT. Review of Data on the Complexatlon of Trace Metal*
bv Particulate Organic Carbon. Drexel University. Submitted by
Battelle, Washington Environmental Program Office, Washington, D.C.
to the U.S. Environmental Protection Agency, Criteria and Standards
Division.
(b) Jenne, E. A. 1987. Sediment Quality Criteria for Metals; TV.
Surface Complex^*"!1 and Ac1d1tv Constants for Modeling Cadmium anH
21 nc onto Tmn Oxides. Submitted by Battelle, Washington
Environmental Program Offjce, Washington, D.C. to the Environmental
Protection Agency, Criteria and Standards Division.
(c) D1 Toro, D. M., and B. Wu. 1987. Sediment Quality Criteria fn-
Metals: V. Review of Data for Determ1n1nn the Intrinsic AH
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pflryrsBOUND
Various approaches are used to Identify segments possessing
anomalous (I.e., geochemlcally Interesting and potentially biologically
dangerous) trace metal contents. These approach Involve size and/or
density separations, various nomination techniques, and/or selective
extraction methods. Metal analyses of «ed1«nt »1« fraction, provide
Information on the distribution of metals as , function of particle size;
however, such analyses are labor Intensive (Jem, et aj. I960: Salomons
and FSrstner 1984). Total metal concentrates wy De-Bowallied to
remove the dilution effect of various primary rtnerals (e.g., quartz).
This normalization technique assume, that all «f the trace metals are
contained In the smaller diameter particleste-fl., <16 *m) art.rwatres
that gram-size analyses be performed on sepjMt. samples' (Be 6n»t 196*).
Alternatively, trace metal analyses may > noml.1z«l to a Bn»ry,
mineral-free basis by using chemical analysis to determine a suite of
primary minerals and computing the trace metal concentrations by assuming
that the primary minerals contain none of the trace metal set Interest
(Thomas and Jaquet 1976). A related normalization technique assumes that
particular solid phases such as SI oxides and/or carbonates contain low
trace metal concentrations and serye as d11uteits. This technique-nay-be
applied, for exam>le, by normalizing the trace metal concentrations to
unit AT concentration (see references cited by Salomons and Forstner
1984).
Chemical extraction has been the. most gewral .approach used to
Identify anomalous trace metal concentrations fcnel -to estimate the
3
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quantities of particular geochemlcal adsorbents. Chemical extraction
methods are used specifically to 1) quantify solid phases Important In
soil classification (McKeague and Day 1966), 2) estimate the quantity of
major adsorbents present 1n soils (Blume and Schwertmann 1969), 3) locate
potential ore deposits by identifying geochemlcal halos in soils and
locally anomalous trace metal concentrations In stream sediments (Chao
1984), 4) Investigate the partitioning of trace metals among various
adsorbents In .sediments, 5) Investigate the cycling of metals (G1bbs 1977)
and radionuclides (Spalding 1985), 6) estimate soil fertilization
requirements and Interpret responses to trace metal fertilization (Miller,
Martens and Lelalny 1986), and 7) evaluate the potential toxicity of
sediment-bound metals to aquatic organisms (D1ks and Allen 1983).
Extensive literature exists on the "selective" extraction of trace
metals and metalloids from Individual adsorbents. This literature
Indicates that even the most selective extraction methods do not remove
trace metals from one particular adsorbent to the exclusion of other
adsorbents. Similarly, selective extraction methods intended to dissolve
an Individual adsorbent frequently dissolve a significant portion of other
Important adsorbents. This nonselectlvlty 1s Indicated by the plethora of
published extraction methods (Appendix 1) and the variable Importance
ascribed to Individual adsorbents 1n various studies. Because the various
methods containing acid and/or reducing agents are known to attack
multiple adsorbents, It 1s probably Impossible to reliably distinguish
between trace metals sorbed by the major adsorbents. For example, the
carbonates of surflclal sediments may contain significant amounts of
metals (Jenne 1977; Tessler, Campbell and Blsson 1980). Thus, the
4
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acidification commonly used to decrease readsorptlon during reductive
dissolution of Mn and/or Fe oxides may dissolve significant quantities of
carbonates and released occluded metals. Using competitive exchange to
quantify the total amount of sorbed metals present 1n sediments (as
opposed to a readily exchangeable fraction) 1s conceptually simple but
quantitatively difficult because of the extended time that may be required
to reach equilibrium (Cutshall et al. 1973). Extended equilibration times
have the disadvantage of allowing precipitation and/or dissolution
reactions to proceed. As discussed in the following section, the
precipitation of oxides (e.g,, Fe or SI), carbonates, or organic carbon on
the surfaces of soil particles tends to armor the Interior of the particle
from pore water. Differing degrees of aggregation and armoring of
sediment particles are expected to yield widely variable times for a given
fraction of the sorbed metals to desorb from different sediments. These
factors probably preclude an accurate estimate of the total quantity of
sorbed metals via partial desorption.
The following sections Identify the major aiisorbents and their mode
of occurrence, review the available method* for determining the amounts of
the major adsorbents, select a provisional set of extraction
methodologies, and provide a rationale for the selected methodology.
5
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MAJOR AnSnRRFNTS
In oxygenated sediments that are not composed primarily of
carbonates, the major adsorbents for metals are the oxides of Fe and Mn,
as well as particulate organic carbon (POC) (Jenne 1968, 1977). Because
the sediment-water Interface is frequently oxidized, the Fe and Mn oxides
may also be Important adsorbents for metals that are present 1n the water
column, even when the sediments are largely anoxic. These three
adsorbents are considered to be major adsorbents because of their 1) large
surface areas that result from their general occurrence as coatings on
minerals and aggregated particles, although they also occur as discrete
particles or aggregates (Nlehof and Loeb 1972; Johnson 1974; Suarez and
Langmulr 1976; Jenne 1968, 1977; Hunter and Llss 1979; Hunter 1980);
2) high reactivity, as Indicated by the extent that other elements are
copreclpltated with and adsorbed onto amorphic Fe and cryptocrystalllne Mn
oxides; and 3) comparatively large surface complexatlo.n constants for
metals as compared to major cations. The Mn oxides that form 1n soils and
sediments are referred to as cryptocrystalllne because of their great
structural disorder that results from extensive substitution by many other
cations (Jenne 1977).
The relative proportions.of amorphic and crystalline Fe oxides (e.g.,
goethlte and hematite) occurring 1n soils varies considerably (McKeague
1967). The same 1s probably true for sediments. Amorphic Fe oxide will
crystallize to goethlte or hematite within weeks to years 1n the absence
of crystal growth inhibitors (Schwertmann, Fischer and Papendorf 1968;
Avotlns 1975). However, the crystallization of amorphic Fe 1s inhibited
6
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by the following: 1) excess salts as compared to dlalyzed preparations
(Gastuche, Bruggenwert and Mortland 1964); 2) low concentrations of
anionic Hgands that form complexes or compounds with Fe, such as
phosphate (Scheffer, Welte and Ludwleg 1957; Krause and Borkowska 1963)
and S1 (Schellmann 1959; Anderson and Benjamin 1985; Aggett and Roberts
1986); and 3) copredpftatlon with fulvic acid (Schwertmann, Fischer and
Papendorf 1968; Kodama and Sehn1tz#r 1977) and dissolved organic
substances 1n general (Kuntze 196$; Schwertraann 1§66). A marked decrease
In the dissolution rate of amorphic ?« oxtde 1rt ethylene
d1 aminetetraacetlc acid (EDTA) occurred aft#r the oxide aged for 4 Weeks
(Aggett and Roberts 1986). These authors also faund that the dissolution
rate decreased only slightly upon aging when the amorphic Fe oxide was
precipitated 1n the presence of and onto «b$®rtat©gfc»pti1e SI g#l. These
results suggest that dissolved S1 1nh1Wt« cryst»in»»tton ©f the amorphic
Fe precipitate.
Although the quantity of crystal 11 ne?Fe and m oxtdes'may excfcedthe
quantity of amorphic Fe and Un oxWts ln ^^ents, other factors tind to-
Increase the relative Importance of the amorphic oxides as adsorbSnts.
Although the surface complexat!on constants for Cd and Zndo- not appear to
be systematically larger for amorphic'Fr^oMdeUhan for goeth1te^a)
(Leckle 1986), the quantity of trace metal sorted per raoleef Feds larger
for the amorphic oxide because the number of sites per unit mass ®f
amorphic Fe is large comparedtothat of well-crystal 11 zed Fe oxides
(a) Jenne, E. A. ana J. M. Zachara. "Factors Influencing the Sorption
of Metals." In Fmt* and Sffljtneni Boanti Cfasmll calmly AajMiittr
Systems, eds. K. L. Dickson, A. W. Mak1 and VI. BrUngs. Pergamon Press (in
press).
7
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(Anderson and Benjamin 1985). The relative adsorption capacities for
cryptocrystal11ne and crystalline Mn oxides Indicate that the number of
sorption sites Is considerably larger for the cryptocrystalline Mn oxides
than for the well-crystallized Mn oxides (Anderson, Jenne and Chao 1973).
The large number of sorption sites associated with poorly crystallized Fe
and Mn oxides, In conjunction with the general occurrence of amorphic Fe
coatings and cryptocrystalHne Mn oxide particles on the surfaces of'
sediment particles (Jenne 1968), suggests that the poorly crystallized
oxide fractions of these two metals are more Important as adsorbents for
trace metals and metalloids than their corresponding crystalline fraction.
The Fe, SI, and A1 oxides and POC "coatings" that form on the
surfaces of soil and sediment particles may occur 1n partially alternating
layers. These coatings tend to Isolate portions of Individual adsorbents
located In the Interior portion of. particles, preventing them from
reacting with dissolved metals In the pore water. Thus, Jenne (1960)
found that days to weeks were required to rehydrate air-drfed coastal
Oregon soils that were high 1n amorphic alumlno-sillcates. The ability of
Fe coatings to limit equilibration of particle Interiors with pore water
1s strongly suggested by the significantly smaller amounts of Al, and
particularly S4, that were dissolved by hot sodium hydroxide 1f the alkali
extraction was performed prior to extracting the soils with d1th1on1te-
cltrate (to remove Fe coatings), as compared to the amount removed If the
d1th1on1te«c1trate treatment 1s carried out first (Jenne 1960).
Similarly, alternating dlthlonlte and hydrogen peroxide treatments
Increased the amount of total d1thlon1te*extractable Fe. These results
suggest that only a portion of each of these adsorbents are available for
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equilibration with dissolved metals. This reactive portion of a major
adsorbent 1s, therefore, the parameter that should be measured to model
the extent of sorption and desorptlon of trace metals 1n sediments. The
amorphic nature of the major Fe adsorbent, the cryptocrystalllne nature of
Mn oxides, and the need to estimate the reactive portion of these oxides
and of the particulate organic carbon (I.e., RPOC) largely precludes using
any physical method for quantifying the reactive portions. Therefore,
chemical extraction techniques must be used. Estimating adsorbent mass by
chemical extraction Involves the dissolution of these oxides >y a major
alteration 1n pH, reduction 1n valence, compilation, or a combination of
these processes.
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QUANTIFICATION OF AMORPHIC IRON ANO CRYPTQCRYSTAI I tmf
The chemistry of Fe and Mn are sufficiently similar that any chemical
extractant used to dissolve amorphic Fe or cryptocrystalllne Mn also
dissolves at least part of the other adsorbent. Thus, the partitioning of
sorted trace metals between these two adsorbents cannot be determined by
extraction techniques. One objective of this review Is to evaluate the
possibility that a single extraction method can be used to estimate the
quantity of both adsorbents. After considering two of the more promising
extraction methods, the advantages and limitations of certain other
extractants are presented.
AfTnTC AMMONIUM OXALATE
Acidic ammonium oxalate 1s the classical extractant used to estimate
the amorphic Fe oxide content of soils and sediments In the presence of
crystalline Fe oxides (Lundblad 1934; Schwertmann 1959, 1964; McKeague and
Day 1966; McKeague, Brydon and Miles 1971). A decrease In Fe oxide
crystal Unity Is generally accompanied by an Increase 1n surface area and
1n the rate of dissolution 1n acidic ammonium oxalate (Karlm 1984).
Although the crystal Unity of precipitated Fe oxides commonly Increases
with time, the crystal Unity of naturally occurring oxides 1s principally
determined by the amount of extraneous copreclpltated elements that are
present 1n the oxides. For example, the amount of Fe extracted Increased
from 47% to 82% of the total amount present 1n a single 2-h acidic
ammonium oxalate extraction, paralleling an Increase 1n the SI content of
ferrlhydrlte from 1.19% to 1.85% (Karlm 1984).
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There are some limitations to using the acidic ammonium oxalate
method for dissolving amorphic oxides of Fe. This extraction method may
only partially remove poorly crystallized Fe oxides, as some ferrfhydrite
remained even after three oxalate extractions (Carlson and Schwertmann
1981). Another disadvantage of this method 1s that crystalline Fe oxides
are partially dissolved. For example, magnetite (Fe304) Is quite
susceptible to dissolution during an acid oxalate extraction (Barll and
Bltton 1967; McKeague, Brydon and Miles 1971; Rhoton et al. 1981;
Borggaard 1982; Chao and Zhou 1983; Walker 1983). Some maghem1t« (ah
Fe203) (Borggaard 1982), and to a lesser degree lepldocrocfte (a^FeOOM)
(Pawluk 1972; Schwertmann and Taylor 1972; Sehwartmann li73), Is also
dissolved. Schwertmann (1973) reported that oxalate extracted a i«i#r
part of organic Fe and presumably dissolves Mn oxides. Another analytical
disadvantage of the acidic ammonium oxalate method 1s the need to carry
out the procedure 1n darkness (Schwertmann 1973)-.
ACTDTC HYnpnyvi amtmp HWMCHLWIVE
The common extractant for cryptocrystalllne Mn oxides Is
hydroxyl amine hydrochloride (NHjjOH'HCl), which 1s a relatively ml Id
reducing agent that has been used at various concentrations and acidities
(Appendix 1). Chao and Zhou (1983) and Chao (1984) have utod1fled the
hydroxyl amine method, originally developed by Chester and Hughes (1967)
for the dissolution of Mn oxides, to Include the dissolution of amorphic
Fe ox1 des. The modi f 1 ®d method 41 swlved Teas than 18. of the crystal 11 ne
Fe oxides that were pretfnt and provided estimates of amorphic Fe that are
similar to those obtained uslns the acidic aiBuoiturn oxalate method. Thus,
11
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this method appears preferable for simultaneously determining poorly
crystallized Fe and Mn oxides.
The necessity of acidic conditions 1s a limitation of both the acidic
ammonium oxalate and hydroxylamine methods because of the Increased
analytical effort required to adjust the pH during the extraction and the
possible dissolution of additional absorbents. Luoma and Bryan (1981),
using the 0.1H NH^H^HCI plus O.OltL HNO3 method of Chao (1972), noted that
carbonates 1nthe sediment caused the pH to increase. The partial
dissolution of carbonates 1s undesirable for two reasons. A pH Increase
may allow sorted metals that are released from oxide and RPOC absorbents
to be partially readsorbed onto other sol Ids (Rendell, Batley and Cameron
1980). To avoid this problem, Thompson-Becker and Luoma (1985) titrated
the hydroxylamine hydrochlorlde-sedlment suspension back to pH 2 after
adding sediment to eliminate the effects of variable pH among samples.
The second reason that the attack on carbonate minerals is undesirable Is
that the carbonates may be Important adsorbents 1n some sediments.
However, there are no satisfactory means to avoid acidic conditions In the
hydroxylamine method.
OTHFR fxtpaetants
Numerous other extractants are sometimes used to remove poorly
crystallized Fe and/or Mn oxides from earth materials. Sodium acetate at
pH 5 (Jackson 1956) has been used to remove Mn oxides from soils and
sediments (e.g., Lion, Altraann and Leckle 1982). The advantage of this
extraction method 1s that 1t 1s rather mild. However, the lack of
specificity of'acidic sodium acetate for poorly crystallized Mn oxides 1s
12
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Indicated by its frequent use to remove carbonates from earth materials
(Appendix 1). Thus, the use of sodium acetate does not appear to have
merit 1n comparison with hydroxylamine hydrochloride.
Sodium dlthlonlte, plus citrate to complex dissolved metals, 1s the
method generally used to estimate the total oxldlc Fe and Mn content of
earth materials. The disadvantages of extracting with dlthlonlte to
quantify poorly crystallized Fe and Mn are that 1) the dissolution rate 1s
so rapid that time variations 1n mixing and during phase separation cou.1 d
result 1n significant differences 1n the amount of crystalline Fe oxides
dissolved; 2) the very low redox potential results in the dissolution of
crystalline Fe and Mn oxides,* 3) the extractant contains relatively high
levels of metal Impurities, although the metal Impurities can be removed
(Jenne, Ball and Simpson 1973); and 4) sulfides may form during the
extraction process and result In the precipitation of a portion of the
trace metals as sulfides (Tessler, Campbell andBlsson 1979).
Interestingly, the dlthlonlte plus citrate extraction method 1s
Ineffective 1n dissolving magnetite (McKeague, Brydon and Miles 1971;
Walker 1983).
Complexlng agents are occasionally used to estimate the quantity of
amorphic Fe oxide 1n sediments and soils. For example* EDTA was used at
an alkaline pH (9 to 10.5) to determine amorphic Fe (Borggaard 1981).
Less Fe was removed over a 3- to 8-month period using this method than 1n
a 2-h extraction, 1n darkness, with 0.211 ammonium oxalate solution at pH
3.0. Another complexlng agent, 0.1M tiron (d1-sodium salt of
catecholdlsulphonlc acid), was recommended by Blermans and Baert (1977)
for the simultaneous dissolution of amerpfcic Fe, Al, and S1 (pH 10.5 at
13
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80°C for 1 h). The tlron method dissolved up to 13% of the glbbslte
(AT(OH)3) present but little of the crystalline Fe oxides. Thus, the
combination of the 1) extended reaction periods-required by the EDTA
method, 2) use of EDTA for carbonate and calcium sulfate removal (Bodlne
and Fernalld 1973; Chao 1984), and 3) high pH conditions with probable
extraction of other adsorbents (e.g., RPOC and amorphic alumlnoslHcate)
suggest that these complexlng agents have no advantages over hydroxylamine
hydrochloride for estimating the quantity of amorphic Fe and
cryptocrystalUne Mn absorbents 1n sediments.
14
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ntlANTTFTCATTON OF REACTIVE PARTICULATE ORGANIC CARBOM AOSORRFNT
Luoma and Bryan (1981) obtained similar estimates of RPOC using U
NH4OH and 0.1H NaOH extractants 1n their study of a sediment from a
British estuary. These authors simultaneously maximized the extraction of
both Cu and POC from one of their sediment samples. They estimated the
quantity of extracted organic carbon by using absorbance measurements at
640-nm. The 640-nm absorbance measurement was calibrated by repeatedly
precipitating the organic substances at a low pH and then weighing the
residue. The amount of RPOC 1n their estuarine sediments was estimated to
range from approximately IX to 231 of the POC.
Jenne (1984) and Zachara et al. (19^6) used hot 0.5H KOH and ltl KOH,
respectively, with 30-m1n extraction periods to estimate RPOC in sediments
and soils (Table 1). Using 0.511 KOH -bn four river sediments, Jenne (1984)
found total POC contents ranging from 0.015% to 0.034% and RPOC contents
ranging from 60% to 76% of the POC. For subsoils developed on parent
materials ranging from Colorado oil shale (bituminous dolomite) to
alluvium, Zachara et al. (1986) found that the estimated RPOC ranged from
23% to 79% of the total POC. Potassium hydroxide was used 1n both of
these studies to minimize dissolution of layer alum1no-s1l1cates (Dudas
and Harward 1971). Strong alkali 1s the extractant of choice because
other extractants, such as acids (Schnltzner and Skinner 1968) or
phosphates (Luoma and Bryan 1981), generally extract relatively small
quantities of POC. Thus, any extractants other than strong alkalis are
expected to underestimate the RPOC component of sediments. There 1s one
potential limitation to the alkali extraction method for estimating RPOC.
15
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In sediments with significant silica armoring, the dissolution of silica
may release additional POC, resulting 1n an overestlmatlon of the RPOC.
Table 1. Total and Reactive Particulate Organic Carbon Determined by
Combustion and Extraction with Potassium Hydroxide, Respectively
POC
RPOC
RPOC/
Extractant
(X)
(%)
POC
Material
Jenne (1984)
(«)
0.5M KOH
0.034
0.024
0.71
25-46 ft
0.5U KOH
0.025
0.019
0.76
75-85 ft
0.5H KOH
0.015
0.009
0.60
30-41 ft
0.5M KOH
0.016
0.012
0.75
85-95 ft
Zachara et al. (1986)(b)
Lorlng, Typlc Fragludalf, 8x2
horizon
Elk, Ultlc Hapludalf, C horizon
Ooront, Ultlc Hapludalf,
C hor1zon/res1d1um
Westmorland, Ultlc Hapludalf,
B2t horizon
Vebar, Typlc Haploboroll, C2
horizon and below
Zahl, Typlc Arglboroll, C2
horizon and below
Anvil Points, unconsolidated
material overlying aquifer
Ft. Martin, unconsolidated
material overlying aquifer
Vernlta, wind-sorted sand
(a) Columbia River flood plain samples collected at the specified depth
and dry sieved to <425 /*m.
(b) The <2-mm fraction of various subsoils.
(c) Contains undecayed roots,
id) Soil formed from oil shale.
(e) Contains coal fragments.
(f) Calculation not meaningful.
1.0M
KOH
0.24
0.19
0.79
1.0H
KOH
0.22
0.16
0.73
1.0(1
KOH
0.26
0.19
0.73
1.0H
KOH
0.20
0.13
0.65
1.0U
KOH
0.35
0.15
0.43
1.0H
KOH
1.21(e)
0.41
0.34
1.0M
KOH
0.58(d)
0.16
0.28
l.Ofcl
KOH
0.74(f)
0.17
0.23
1.0M
KOH
0.02
0.04
(f)
16
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DETERMINATION OF AfKORRFn MFTAI S
Three chemical processes are usea to estimate the quantity of sorbed
netalsr 1) competitive exchange by dissolved 1ons, 2) complexatlon by
dissolved ligands, and 3) selective dissolution of adsorbents.
Many sets of extraction methods have been proposed for partitioning
trace metals between the "exchangeable" fraction (i.e., metals adsorbed
onto external surfaces) and the fraction absorbed (I.e., metals In the
Interior of particles) by various adsorbents (Appendix 1). Two of the
classical sets of extraction methods are those of Chester and Hughes
(1967) and G1bbs (1977). Chester and Hughes (1967) used addle
hydroxylamine to release absorbed trace metals plus associated Fe from
cryptocrystalUne Mn oxides, and acetic acid to dissolve Fe oxides and
release absorbed trace metals. G1bbs (1977) used magnesium chloride to
extract sorbed metals, d1th1on1te to release absorbed metals from Mn and
Fe oxides, and hypochlorite to release metals associated with RPOC.
Exchangeable metals were historically considered to represent the
sorbed metal compartment and were determined by competitive exchange with
salts, such as ammonium acetate (Appendix 1). However, ammonium acetate
partially dissolves poorly cry$tall1zed carbonates and cryptocrystalUne
Mn oxides (Chapman 1965; Jackson 1965) and solublUzes some RPOC, thereby
releasing sorbed metals from these solid phases. More recently, magnesium
chloride has been used to displace exchangeable metals (e.g., G1bbs 1977;
Campbell et al. 1985). However, Mg Is a relatively weak competitor for
Cd and Zn on goethlte, a-FeOOH (BallstleM awl Murray 1982). Thus,
alkaline earth and alkali cations may not displace all the metals adsorbed
17
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onto external sites. Because first-transition metals are specifically
adsorbed (at least when the fraction of sites occupied 1s small) onto
sites that may differ 1n adsorption energetics (Benjamin and Leckle 1981),
any two competitive adsorption methods will desorb different amounts of a
given metal, even 1n the absence of the partial dissolution of particular
adsorbents.
Complexlng agents are another class of extractants used to estimate
the quantity of sorbed metals. The quantity of a metal removed from
Individual adsorbents by a complexlng agent within a given time period
will vary with the following: the extent of aggregation and armoring of
particles, the difference between the association constants of the metal-
conplexlng agent and metal-adsorbent complexes, the complexlng llgand
concentration, and the number of absorption sites on the adsorbent.
Consequently, multiple extractions and extended extraction times will be
required when using complexlng agents to determine the total quantity of
metals sorbed by the major adsorbents.
A variety of acids of several different strengths have been widely
used to correlate "bloavallable" metal fractions with the metal content of
organisms associated with the soil or sediment. Acids have minimal
selectivity for the various adsorbents since they may remove metals from
sediments, both by competitive exchange and by partial dissolution of
adsorbents. Recently, hydrochloric acid has become the acid of choice.
Luoma and Bryan (1982) found that the quantity of metals extracted with IN.
HCl correlated better with the metal burdens of two benthlc organisms than
did the metal concentrations determined using five other extraction
methods. Some Investigators who use hydrochloric acid Include a neutral
18
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salt to minimize readsorptlon of elements sNuch as Sr (Spalding 1985),
although alkali metals are largely Ineffective 1n preventing adsorption of
divalent metals onto high-energy sites (e.g., Wahlberg et al. 1965).
Adsorption resulting from complexation reactions at external surface
sites 1s rapid and occurs In time periods ranging from minutes to tens of
minutes for clays (Brown 1964) and oxides (Benjamin 1978). However, with
the possible exception of highly crystallized oxides (e.g., a-Al203) and
certain nonaggregated -clay minerals (Brown 1964), most sediments (Malcolm
and Kennedy 1970) and oxides of Mn, Fe, Al, and S1 generally exhibit a
significant "time-dependent" component of sorption (Benjamin 1978). The
rates of adsorption (and presumably of desorptlon) vary between fresh and
aged oxide precipitates (Lljklema 1980) and probably with particle size.
The equilibrium time allowed by various investigators varies from 2.5 h^
to weeks (Cutshall et al. 1973). Tbe time-dependent component of
adsorption probably results from the slow diffusion of metals into the
absorption sites on the Interior of aggregates and/or particles. The
commonly observed curvilinear portion of sorption versus time curves
(e.g., Loganathan and Burau 1973) 1s postulated to result from a decrease
In the amount of the element sorbed per unit time. This decrease occurs
because of the longer time periods required for an adsorbate to
equilibrate with sites that are progressively more remote from the bulk
solution. Desorptlon rates measured 1n the laboratory may be slower than
measured sorption rates because the concentration gradients are generally
(a) Thels, T. L. and L. W. Kaul. "Rate Studies on the Sorption of
Inorganic Ions at the fieothlte-Water Interface." In ACS Symposium
Series. Surface Processes In Aqueous Geoc-hwnl stryr ed. J. A. Davis
(1n press).
19
-------
lower during desorptlon than during sorption experiments. These
observations Imply that, depending on diffusion restrictions, short but
fixed-time desorptlon procedures will extract variable portions of the
sorbed metals present 1n sediments. The lengthy time period required to
reach desorptlon equilibrium might be largely avoided 1f the entire
quantity of reactive amorphic Fe and cryptocrystalUne Mn 1s solublllzed,
as discussed In the following section.
20
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SF» FCTTON OF METHOBS
Partitioning the quantity of metals adsorbed onto external sites
(I.e., the "exchangeable" or "readily available" fraction of metals) from
those adsorbed onto Internal sites Is a qualitative process and Is
inherently dependent on the fractionation method used. This dependency
exists because of a probable gradation 1n structural properties between
external and Internal sorption sites; variation 1n selectivity for a given
metal on a given adsorbent; and variation 1n the rates of diffusion
between external and Internal sites, which depends on the mlrreralogy and
the extent and nature of armoring of sediment particles. Acetate salts,
which were classically used to extract exchangeable metals, solublHze
some Mn oxides and RPOC. Ammonium does not appear to effectively displace
trace metals from sites on the exterior surfaces of metal oxide.
Magnesium also competes rather weakly with trace metals such as Cd and Zn
sorbed onto goethlte, and Its use may therefore underestimate the quantity
of metals sorbed on external sites of oxide adsorbents.
The use of a series of selective extractants to fractionate absorbed
trace metals among Individual adsorbents appears to be highly qualitative.
Extractants that use the processes of complexatlon or combined hydrogen
exchange and dissolution provide minimal selectivity because of their
attack on multiple adsorbents. At this time, any extractant proposed for
Mn oxides will also solublHze a fraction of the amorphic Fe, and those
extractants that are addle also, at least partially, dissolve carbonates.
21
-------
Because of the major limitations of the existing extraction methods
in fractionating trace metals among the major adsorbents, an alternative
approach must be used, such as simultaneously determining the total amount
of metals sorbed by the three most generally Important adsorbents and the
quantities of poorly crystallized Fe and Mn adsorbents. The Importance of
the attack of an acidic extractant on carbonates, with the accompanying
release of occluded trace metals, must be addressed experimentally.
INTERIM EXTRACTION MFTHfin^
Two Interim methods are selected for further evaluation and
optimization. The acidic hydroxylamlne hydrochloride method 1s selected
as the best available extractant for simultaneously estimating the
quantities of metals sorbed by amorphic Fe, cryptocrystalUne Mn, and
RPOC. This extraction method will also be used to estimate the quantities
of the amorphic Fe.and cryptocrystalUne Mn adsorbents. The hydroxylamlne
extraction method of Chao and Zhou (1983), as used by Jenne (1984), 1s
described below:
Prepare a solution that 1s 0.25M with respect to
hydroxylamlne hydrochloride and 0.25M hydrochloric acid
Place 95 mL of this solution 1n 100-mL stoppered Erlenmever
flasks, bring temperature to 50°C, and add 0.400 g on an
air-dry basis, of either moist or air-dry sediment' Place
the flask 1n 50°C water-bath shaker for 30 m1n. Cool the
solution for 10 rain In a cold water bath, separate the
phases using a high-speed centrifuge, and filter the
supematent through Q.22-/m membrane Into a 100-ml
volumetric flask. Bring filtrate to volume with delonlzed
water. Make dilutions as needed with 2% HC1. Note that 1f
the sediment Is enriched 1n Fe and/or Mn oxides, the solid-
to-sediment ratio may need to be reduced. The
reproducibility of the extractions Is increased if smaller
grain size fractions and/or a larger sample mass are used.
22
-------
Hot potassium hydroxide Is selected as the Interim method to estimate
the RPOC. The method of Jenne (1984) 1s described below:
Bring 100 mL of 0.5J1 KOH to Incipient boll 1n a 400-ml
stainless steel beaker. Add 0.50 g of a1r-dry sediment and
continue heating with stirring for 30 m1n. Place beaker 1n
a cold water bath, and add 100 ml of cold distilled water to
cool. Separate phases In a high-speed centrifuge, decant
Into 250-ml volumetric flash and bring to volume with
distilled water. Analyze dissolved organic carton 1n a
carbon analyzer (Inductive heating, Infrared measurement of
C02) or spectrophometrlcally (Luoraa and Bryan 1981) .
RATIONALE FOR TNTFPTM FXTRArTTON METHODS
The discussion In earlier sections suggests that sorbed metals could
be determined by the same extractant used to quantify the amorphic Fe and
cryptocrystalllne Mn adsorbents. This approach 1s possible 1f the trace
metals sorbed by RPOC are also recovered 1n this extract because of mass
action displacement by the high solution concentrations of ferrous Iron
and hydrogen.
The use of the reactive quantity of amorphic Fe and cryptocrystalllne
Mn (and RPOC) adsorbents 1n conjunction with the total sorbed metal to
calculate metal activity 1n pore water assumes that the sorbed metal
content 1s relatively constant throughout an Individual adsorbent, whether
the adsorbent 1s present as coatings or particulates. The available data
that address this point are so limited that Information on Fe-S1
precipitates Is Included 1n the following discussion. Warnant, Martin and
Herblllon (1981) found a nearly constant moiar ratio of sorbed Cu to
amorphic Fe (I.e., 5 to 10 x 10~3) 1n several German soils. Using the
Chao and Zhou (1983) hydroxylamine method, Jenne (1984) found a relatively
constant ratio of extracted Fe to Mn 1n four samples of Columbia River
terrace sediment. Orange-colored floccules recovered from the bottom of a
23
-------
Japanese lake contained a surprisingly constant Fe:Mn:S1 mass ratio of
1.0:1.4(±0.3):3.1(*0.1), where the plus or minus values Indicate the range
of the four, observations (Kato 1969). The ubiquity of S1 1n the
weathering cycle suggests that SI Is a ubiquitous component of Fe and Mn
oxides 1n sediments. The available laboratory Information Indicates that
incorporating SI into amorphic Fe oxide.by aging the fresh Fe precipitate
1n glass beakers had little effect on the adsorption strength of Co., Cu,
or Zn, but did Increase the amount of Cd adsorbed (Anderson and Benjamin
1985). These findings suggest that the successive layers of the amorphic
Fe component of these particular soils and sediment samples are reasonably
homogenous. Importantly, the adsorption of Np by four Columbia River
fluvial-glacial sediments was satisfactorily modeled, assuming amorphic Fe
to be the dominant adsorbent (G1rv1n 1984). The amount of amorphic Fe
adsorbent was estimated using the hydroxylamine extraction method (Jenne
1984).
The selection of the hydroxylamine method 1s based upon the following
factors: 1) the method 1s reported to effectively discriminate against
crystalline Fe oxides, 2) the quantities of both amorphic Fe and
cryptocrystalllne Mn are obtained with one extraction, 3) the amorphic Fe
and cryptocrystalllne Mn fractions are dissolved rapidly enough (about
1 h) for laboratory efficiency but slowly enough to permit ready
discrimination between amorphic and crystalline fractions, 4) the possible
presence of multiple Fe or Mn subfractlons of varying crystal Unity can be
evaluated by curve stripping or equat1
-------
dissolution. The major significant limitation of this method 1s Its
acidity, which 1s needed to provide for recovery of released trace metals,
but will attack carbonates.
Strong alkali 1s the only available extractant with the potential to
estimate the RPOC adsorbent 1n sediments. The choice of the stronger
alkali 1s based on the extensive use of sodium hydroxide to extract the
fulvlc and humlc acid fractions from soils and sediments, and Its use 1n
estimating the quantities of amorphic alum1nos1l1cates (Langston and Jenne
1964). The choice of potassium hydroxide 1r preference to sodium
hydroxide 1s based on the decreased alteration of layer alumino-s111cates
by potassium as compared to sodium hydroxide (Dudas and Harvrard 1971).
However, applying the proposed approach (Jenne et al. 1986) to a wide
range of sediments may requlre estimating the quantity of amorphic
al um1 nos111 cates and perhaps the el ay ml neral s, also. Amorphl c
alumlnosl 11 cates are likely to be an Important adsorbent 1n-sediments
derived largely from source materials that are -high 1n volcanic ashv In
addition, 1n sediments that have sufficiently low redox potentials to have
caused the dissolution of poorly crystallized Fe and Mn oxides, amorphic
alumlnosl 11 cates may be a major adsorbent. Alteration of layer alumino-
slUcates by the alkali extractant 1s a consideration because the general
application of the proposed approach for delevoplng sediment criteria for
metals (Jenne et al. 1986) may ultimately require consideration of layer
alumlnosl11cates as adsorbents.
25
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OPTIMIZATION OF METHODS
Additional research Is required to optimize these methods and
establish their adequacy as part of the process for developing metals
criteria for sediments. The optimum pH for oxide dissolution and recovery
of sorbed metals, the extent of pH control during extraction, and the
soHd-to-solutlon ratio needs to be evaluated for the hydroxylamine
method. The extent of dissolution of crystalline Fe oxides should be
Included 1n the evaluation of the hydroxylamine method. The pH of the
extraction method Is particularly Important because buffering due to
carbonates and other solid phases may vary markedly between sediments.
The amount of carbonate minerals dissolved during evaluation of the
hydroxyalamine extraction method needs to be determined either from the
C02 evolved or from the decrease 1n total Inorganic carbon 1n the samples.
Adequate evaluation of the carbonate problem may require a review of
existing information on the trace meta.l content of the carbonates of
various sediments.
Refining the RPOC extraction method requires a comparison between
potassium and ammonium hydroxide extractants, optimization of alkali
normality, and examination of sol1d-to-solut1on ratios. Examining the
organic carbon-to-s1Hca ratios 1n the extracts of the variable time
extraction series may Indicate the extent to which the dissolution of
silica coatings 1s responsible for the release of POC. These data will
assist In evaluating the optimum extraction time.
Further evaluation of the selected methods must Include a range of
extraction times to ensure that the quantity of the sorbed metal that 1s
extracted represents the entire reactive portion of amorphic Fe,
26
-------
cryptocrystalllne Mn, and RPOC adsorbents, and does not Include an
appreciable quantity of crystalline Fe and Mn oxides nor of POC Isolated
from pore waters.
27
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33
-------
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34
-------
APPENDIX 1. "Selective Extractants" Used to Partition Metals Among the Various
Presumptive Adsorbates
Exchangeable oj^j
Absorbate Target
Non matrix
Non matrix
Non matrix
Non matrix
Fe(0H)j(A)
Fe(OH)3(A)
Al, Fe and SI
oxides
Fe oxides(A)
Oxides,
carbonates
Fe oxides(A)
Fe oxides(A)
Al and Fe oxides
Mn oxides
Fe oxides(A)
Fe oxides(C)
Sulfides
Matrix
Extractant
(b)
HNO3 + HC1
HC1
NH20H-HC1 + HOAc
EDTA
EDTA
(HH4)2C204
Tiron
70-90 2 h
0.2N
0.1N
0.175* + 0.100N
1-4 H
0.25M + 25X
0.25M ~ 0.25M
31
0.1N ~ 0.01N
0.25M * 0.25M
7 4.75
4N + 7 + ?
roam
70-90
70-90
4.4-10.& room
room
3.0
9.5-11.0 '80-100
1.0
overnight
2 h
2 h
h - Months
2 (i -.Months
25-60 ain
4 h
room and 92 30 mln
70 4 h
50 and 70 1/2 - 2 hr
92 15 - 60 nin
roon 30 min
70
50
92
30 min
30 min
20 ain
?
Solid:Soln<<,)
1:100
5:100
1:100
1:100
1:10 - 1:1000
1:250
1:250
1:250
1:250
1:250
7
?(e)
7(e)
j(«)
?(e)
Sample . .
Quantity* *
1 9
5 g
1 9
1 9
1
Reference
0.100 g
0.100 g
0.100 g
0.100 g
'0.100 g
J
7(e)
?(e)
?
-------
APPENDIX 1. (contd)
Exchanyeable or
Absorbate Target**'
Exchangeable
Exchanyeable
Carbonates
Mn and Fe oxides
Organic
Fe oxides
Organ)cs, sulfides
Fe oxides
Silicates
Exchangeable
Exchangeable, Mn,
oxides, carbonates
Exchangeable,
Carbonates. Hn and
Fe oxides
Organics, sulfides
Ferrihydrate
Extractable
Extractable
Extractant
(b)
CuS04
HgCI2
NaOAc
NH20H-HC1 + hno3
H202 + NH40Ac
HH20H>HCI + HOAc
H7O9 * HNO3 ~ 50* + 0.0;
Nh4 acetate + HNO3 IN * 61
HH20H-HCI * 25X HOAc 0.25H + 251
Concentration^) pH
0.05M
IN 7
IN 5
0.1N + 0.01N 2
301 » 1 H
IN + 25%
SOX + 0.025M ¦»
Tenp-CC) Tt«e
HF*aqua regi a+HCl
HOAc
NH20H*C) ~ HNO3
HOAc
HNO3
(nh4)2c2o4 + h2c2o4
HNO3
HCI
7-tcon+lOX
IM
0.1M ~ 0.01M
IN
0.01N
0.2H ~ 0.2M
Con
IN
3.0
0.1
rood
rooM
room
85
96
dryness
rooa
75
room
1-3 uk
1 h
5 h
30 Bin
,b h
6 h
? ~
30 aln
4 h
?
2 h
30 Bin
90 ain
7
2 b
?
2 h
Soltd:Soln(d>
LaMl
7
7
?(e)
?(e)
jle)
?
-------
APPENDIX 1.
Exchangeable or
Absorbate Target I®'
' Extractant^)
Concentration'c)
PH
Temp.CC)
Extractable
HOAC
2SS
2.2
Extractable
(NH^)2O4 + H^C^0^
0.4N * 0.4N
3.3
Extractable
nh2oh>hci ~ hno3
0.1N ~ 0.01N
2
Extractable
NH40AC
IN
7
Extractable
Ha^P^O?
0.1N
10
Organic
nh4oh
IN
.1
0.1N
11.6
room
Organic
NaOH
12
Surface coatings
S20i2 ~ C6HS073
0.29M + 0.56H
3.0
80
Surface coattngs
Na2S204 +
Na3C6Hs07 ~ NaHC03
0.S7H ~ 0.3N ~
1M 7.0
70
80
Surface coattngs
NH20H>HCI + HOAc
1H ~ 25*
TOOK
Fe oxides
HH20H-HC1 ~ HCI
0.25M ~ 0.25H
1.0
room
Fe oxides
(NH4)2C204 +
0.113H ~ 0.087H
3.0
room
Fe oxides
. (nh4)2c2o4 + h2c2o4
0.113N ~ 0.087H
3.0
room
Exchangeable
Hg(N03)2
1H
Organic
NaOCl
5.3X
8.5
100
Mn oxide
nh2oh*hci
0.1H
2.0
Fe oxide'*)
NH20H*HC1 + HCI
0.25M + 0.25M
SO
Fe oxide^
(nh4)2c2o4 + h2c2o4
0.2M * 0.2H
3.0
100
Carbonates
HCI + KC1
0.1 H + 0.5M
Nn oxides
nh2oh*iici + hno3
0.1M + 0.01M
(contd)
Ti«e'd'
Solid:Soln(d)
(g/nl)
Sample
Quantity1"'
Reference
2 h
1:30
2 ml
Luoma and Bryan (19H1)
2 h
1:30
2 ml
Luoma and Bryan (19B1)
30 nin
1:10
2 Ml
Luoma and Bryan (1981)
2 h
1:30
2 Ml
Luoma and Bryan (1981)
2 b
7
2 Ml
Luoma and Bryan (19U1)
1 wk
1:15
4 ml
Luona and Bryan (1981)
1' Mk
1:15
4 Ml
Luoma and Bryan (1981)
Thomas-Becker and
Luoma (1985)
3 h
7
?
Halo (1977)
IS atn
7
1
Halo (1977)
4 h
7
7
Halo (1977)
16 h
1:250
0.10 g
Ross et al. (19U5)
4 h
1:40
0.25 g
HcKeague (1978),
Ross et al. (1985)
4 h
1:250
0.1 g
Ross et al. (1985)
2 h
1:4
10 g
Sins (1986)
30 mtn
+20 Ml
(b)
Sims (1986)
30 ntn
1:10
5 g
Sins (1986)
30 Bin
+50 al
-------
APPENDIX 1. (contd)
Exchangeable or
Absorbate Target'*)
Extracting)
Concentration^
pH
Temp. CC)
Ti«e
3.2M ~ 201
2
85
2 h
+8 nl
(e)
Tessier et al. (1979,
1981)
Fe oxfdes(A)
hn2oh»hci t HNO3
0.1H ~ 0.01N
2.0
30 Kin
1:50
?
Thomson-Becker and
Luoma (1985)
Fe oxides(C)
(nh4)2c2o4 + h2c2o4
0.2M ~ 0.2M
3.3
2 h
?
?
Thomson-Becker and
luoma (1985)
Matrix
hno3 ~ h2so4
Con ~ con
roan
2 h
>1:25
?
Thomson et al. (19BO)
Matrix
HCi
O.SN
roan
2 h
>1:25
7
Malo (1977),
Thomson et al. (19B0)
Matrix
HOAc
25*
2.2
roon
2 h
>1:25
7
Lortng (1976),
Thomson et al. (1980)
Matrix
(nh4)2c2o4 ~ h2c2o4
0.4N + 0.4N
3.3
rooa
2 h
>1:25
1
Schwertmann (1964),
Eaton (1979),
Thomson et al. (1980)
NH20II*HC1 * HNO]
O.IN + 0.01N
2.0
roaai
30 min
>1:25
?
T
Thomson et a). (1980)
Chao (1972)
NH2OH-HC\ ~ HMOj
NaP2Oy
O.IN
10
room
2 h
>1:25
?
Thomson et al. (1980)
nh2oh-hci + hno3
DTPA
O.OON
7
roon
2 h
>1.25
?
Thomson et al. (1980)
nh2oii-hci ~ hno3
NaOH
O.IN
12
roon
1 wk
>1:25
?
Luoma and Bryan (1970)
Thomson et al. (1980}
nh2oii«hci + hno3
NH40Ac
IN
7
roon
2 h
>1:25
?
Thomson et al. (1980)
Organic
NaOCl + Na2S204
~ Na3C6H50?
?
8.5
?
?
?
Gibbs (1977)
-------
APPENDIX 1. (contd)
Exchangeable or .
ftbsorbate Target**'
Matrix
Surface Coattng
Exchangeable
Carbonates, oxides,
sulfides
Organic
Exchangeable
Matrix
Extractant
(b)
LiBOj ¦» HHOj
Na2S204 + NijCjHjOj
MgCl2
NH2OH-HCl
h2o2
CaCI2
HF + HC104
Concentration
7
7
IN
0.1M
30%
0.5M
5:1
(c)
_E!L
7.0'
2
2.5
S.O
Temp.CC)
1000
Time^
7
7
7
7
7
5 days
7
olid:Solntd'
(9/*')
10
Quantity^
?
7
7
7
7
30
7
Reference
Gibbs (1977)
Gibbs (1977)
Gibbs (1977)
Soloman and DeGroot (1978)
So)Oman and DeGroot (1973)
Suarez and Langmuir (1976)
Tessier (1980)
(a) (A) and (C) signify amorphic and crystalline states, respectively, matrix • silicate Minerals, and non matrix ¦ extractable fraction.
(b) Chemical composition and names of extractants are as follows:
Formula
Name
nh2oh*hci
hydroxylaaine hydrochloride
w?~3
citrate
c2o4"z
oxalate
acetate (OAc")
p2o7-
pyrophosphate
w
dithionite
HZCIQ^i^OgNg•2H20
EDTA (ethylenediaminetetraacettc acid)
Ci3H230.013
OTPA (diethylenetrlaminepentaacetic acid)
c6o8h4"
Tiron (di-sodium- salt of catecholdisulphonic acid)
(c) Concentrations are indicated in the same order as the extractants in the preceding column, -7 • concentration not given, con
X • concentration in volume percent.
(d) 7 * value not given
(e) Solid from previous extraction added to specified volume.
(f) Tessier et al. (1979).
(g) Tessier et al. (1981).
concentrated.
------- |