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892019 1-s20-S0016706114002262-main

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A new adsorption model to quantify the net contribution of minerals tobutachlor sorption in natural soils with various degrees of organo-mineral aggregation

Yan He a Zhongzhen Liu ab Peng Su a Xinquan Shen a Philip C Brookes a Jianming Xu a

a Institute of Soil and Water Resources and Environmental Science Zhejiang Provincial Key Laboratory of Subtropical Soil and Plant Nutrition Zhejiang University Hangzhou 310058 Chinab KeyLaboratoryof Plant Nutrition andFertilizerin SouthRegionof Ministry of Agriculture GuangdongKey Laboratory of Nutrient Cyclingand FarmlandConservationSoil andFertilizerInstitute

Guangdong Academy of Agricultural Sciences Guangzhou 510640 China

a b s t r a c ta r t i c l e i n f o

Article history

Received 15 September 2013

Received in revised form 14 February 2014

Accepted 25 May 2014

Available online xxxx

Keywords

Butachlor

Sorption

SOMndashmineral association

Aggregate size fraction

Quanti1047297ed contribution

The effect of interactions between soil minerals and organic matter as a function of aggregate size on butachlor

sorption was quanti1047297ed in natural soils with various degrees of organo-mineral aggregation The smallest size

clay microaggregates sorbed most butachlor (58 to 71) and the 1047297ne sand fraction sorbed the least (less than

43) When normalized to organic carbon butachlor sorption to the clay microaggregates was even smaller

than to the silt and sand fractions under speci1047297c soil conditions The sum of sorption to the different fractions

was on average above 78 greater than sorption to the bulk soils with the greatest differences in the soils

with relatively higher ratios of clay to soil organic carbon (RCO) This suggests that minerals can physically pro-

tectfavorable sorption sites within soilorganic matter (SOM) and inhibit butachlor sorption by in1047298uencing SOM

physical conformation Comparisons of changes in butachlor sorption coef 1047297cients (both K d and K oc ) in two differ-

ent series of soils with the samemineral components but gradients of total organiccarbon (TOC) andRCO values

also showed that minerals can directly contribute to soil butachlor sorption processes which may be even more

pronounced in soils with relative higher RCOs A new adsorption model was proposed and veri1047297ed to quantify

the net contribution of minerals to butachlor sorption based upon 38 different soils This study has increased

our ability to quantify the positive direct contribution of soil minerals and their negative indirect contribution

through associated effects on SOM physical conformation during butachlor sorption in natural soils

copy 2014 Elsevier BV All rights reserved

1 Introduction

The soil matrixis not simplya mixture of discrete soil organic matter

(SOM) and minerals but is a multi-component and structurally orga-

nized combination of aggregates formed from organo-mineral com-

plexes (Amelung et al 1998 Brady and Weil 2008 Zhou et al 2004)

Therefore better understanding of the associations between SOM and

minerals is required in the study of sorption mechanisms since there

is increasing evidence that measurement of SOM concentrations alone

is insuf 1047297cient to provide reliable indicators of the sorption behavior of

organic pollutants (OPs) in soils Many studies have shown that the as-

sociation of mineralswith SOMmay block sorptive functional groups on

SOM surfaces Therefore the extent of sorption of OPs could decrease

when the con1047297guration of SOM is changed when associated with min-

erals (Feng et al 2006 Garbarini and Lion 1986 Lambert et al 1965

Pusino et al 1992 1994 Salloum et al 2001 Wang and Xing 2005ab)

indicating a negative contribution of minerals to OP sorption by soils

However other studies have also emphasized that the different soil

constituents may complement each another leading to enhanced sorp-

tion by the resultant aggregates (Celis et al 1999 Huang et al 1984

Khan 1980) Recent investigations showed a dual function of minerals

vs SOM for OP sorption in soils such as butachlor (Liu et al 2010) Be-

sides the negative contribution through blocking some sorption sites on

SOM minerals may also positively contribute to OP sorption in speci1047297c

soils (eg those of very lowSOM contents)wheremineralndashSOM interac-

tions are small so that their surface could be highly exposed increasing

the extent of OP sorption (He et al 2011) It was also suggested

that 1) the relative importance of SOM and minerals in butachlor sorp-

tion depends on theratio of clay to soil organiccarbon (RCO) and 2) the

positive contributionof minerals to overallsorption maybecome appar-

ent when RCO values increase to a critical value (Liu et al 2008) These

studies collectively highlight the importance of minerals for OP sorption

in determining the accessibility of sorption sites within the soil matrix

But how the natural association between minerals and SOM affects

the physicochemical nature of soil organo-mineral aggregates and

therefore in1047298uences the sorption of OPs in soils remains uncertain To

answer this question more direct information is required on how

Geoderma 232ndash234 (2014) 309ndash316

Corresponding author

E-mail address jmxuzjueducn (J Xu)

httpdxdoiorg101016jgeoderma201405021

0016-7061copy 2014 Elsevier BV All rights reserved

Contents lists available at ScienceDirect

Geoderma

j o u r n a l h o m e p a g e w w w e l s e v i e r c o m l o c a t e g e o d e r m a

892019 1-s20-S0016706114002262-main


adsorbed OP in bulk soils distributes among their different size aggre-

gates which has different degrees of organo-mineral association

Selecting butachlor (a chloracetamide) as a model OP we exam-

ined its sorption by bulk soils and respective organo-mineral aggre-

gates with contrasting degrees of association of minerals and SOM

The soil organo-mineral aggregates were fractionated by ultrasonic

dispersion in water without chemical pretreatment to minimize

any alteration to their composition or structure Soils were also

treated with hydrogen peroxide (H2O2) to remove SOM to variousdegrees We hypothesized that variation of the physicochemical na-

ture of organo-mineral association in different soil aggregates

would result in corresponding differences in butachlor sorption ca-

pacity of soils as a function of aggregate size We also hypothesized

that minerals could provide sites for butachlor adsorption and

when SOM was removed from soils the original and now largely

SOM free mineral surface would be exposed and so would contrib-

ute directly and positively to butachlor sorption by soils Our objec-

tive was to develop an effective method to quantify the dual roles of

minerals vsSOM in thesorption of OPs such as butachlor in natural

soils with various degrees of organo-mineral aggregation To do this

a new adsorption model was proposed and veri1047297ed to quantify the

net contribution of minerals to butachlor sorption based upon 38

different soils

2 Materials and methods

21 Reagents and soils

Butachlor N-butoxymethyl-2-chloro-2prime6prime-diethylacetanilide (N979

purity) was obtained from the Shenyang Research Institute of Chemical

Industry (Shenyang China) The soils used with a wide range of RCO

values (from 112 to 1432) were seven of the referenced soils used pre-

viously (He et al 2011 Liu et al 2008) They were surface horizons

(0ndash20 cm) of uncultivated soils collected in the Guizhou Jiangsu

Henan Zhejiang Heilongjiang and Guangdong provinces of China The

physicochemical properties of the bulk soils and their fractions are listed

in Table 1 Thechemical properties of butachlor soil classi1047297cation andtheanalytical methods for physicochemical properties of the bulk soils and

their fractions are described in Supplementary information (SI) and

Table S1

22 Aggregate size fractionation of soils

Aggregate size fractionation of the bulk soils was conducted for soils

1ndash5 based on mechanical dispersion (Liu et al 2010) The detailed frac-

tionation procedures are described in SI After fractionation the 1047297ne

sand (20ndash50 μ m) silt (2ndash20 μ m) and clay (b2 μ m) fractions were

freeze-dried and then weighed

23 Treatment of bulk soil samples with H 2O 2

To verify that the adsorption model proposed for calculating the net

contribution of soil minerals to butachlor sorption was quantitative

soils 6 and 7 were treated with different volumes of 30 H2O2 to obtain

a series of soil samples of the same mineral compositions but with dif-

ferent total organic carbon(TOC) contents (Heet al 2006) Thedetailed

steps are described in SI

24 Sorption experiments

Sorption was measured using a batch equilibrium technique

(He et al 2011) In brief approximately 030ndash065 g of freeze-dried

bulk soil andtheir soil fractionswere accurately and separately weighed

into 25-mL centrifuge glass bottles with screw caps and equilibrated

with8 mLof 002 mol L minus1 KCl solution (containing002 NaN3 to inhibit

microbial activity) containing different concentrations of butachlor

Each isotherm consisted of 10 increasing concentrations of butachlor

along a log10 scale ranging from 01 to 16 mg L minus1 each with two repli-

cates One series of vials without butachlor served as a control All sorp-

tion data were 1047297tted to the logarithmic form of the Freundlich equation

The sorption partition coef 1047297cients (K d) and the organic carbon (OC)

content normalized partition coef 1047297cients (K oc) were also determined

The mathematical manipulation of the sorption data is described in SI

25 Building the adsorption model to quantify the contribution of minerals

to butachlor sorption

251 Calculation of the K d of minerals in soils

The K d was assumed to be the sum of the mineraland SOM contribu-tions as follows

K d frac14 K dminusmin thorn K dminusoc eth1THORN

Table 1

Selected properties of bulk soils and their fractions and the distribution of each fraction in the bulk soilsa

Soil samples TOC SSA AO-Fe DC-Fe Wf pH CEC RCO

g kgminus1 m2 gminus1 g kgminus1 g kgminus1 (WW) H2O cmol (+) kgminus1

Soil 1 Bulk soil 250 136 60 246 100 409 105 144

Clay 499 413 130 1051 361

Silt 143 20 22 99 623

Fine sand 47 13 ndash ndash 11

Soil 2 Bulk soil 147 191 47 193 100 512 182 276

Clay 263 331 89 573 406

Silt 48 11 05 51 582


Soil 3 Bulk soil 44 68 18 98 100 836 99 579

Clay 135 263 43 325 254

Silt 27 12 02 61 693


Soil 4 Bulk soil 18 133 07 72 100 428 66 1432

Clay 68 314 08 319 252

Silt 23 27 01 101 612


Soil 5 Bulk soil 45 380 29 250 100 459 97 1241

Clay 67 563 37 883 553

Silt 21 15 02 41 453


a TOC totalo rganic carbon SSA speci1047297c surface area AO-Fe ammonium-oxalate extractable amorphous Fe2O3 DC-Fe dithionite-citrate extractable free Fe2O3 CEC cation exchange

capacity RCO the ratio of clay to total organic carbon Wf the weight percentage of each soil fraction in bulk soil

310 Y He et al Geoderma 232ndash 234 (2014) 309ndash 316

892019 1-s20-S0016706114002262-main


where K d is the overall soilndashwater partition coef 1047297cient K d-min is the

mineralndashwater partition coef 1047297cient and K d-oc is the SOMndashwater parti-

tion coef 1047297cient The latter is calculated from the following equation as-

suming that the behavior of SOM is accurately represented by pure

humic acid (HA) extracted from the same soil

K dminusoc frac14 f oc K oc minusHA eth2THORN

where f oc is the OC content of SOM () and K oc-HA is the sorption parti-

tion coef 1047297cient of pure HATherefore the mineralndashwater partition coef 1047297cient can be obtained

by combining Eqs (1) and (2)

K dminusmin frac14 K dminus f oc K oc minusHA eth3THORN

252 Quantifying the contribution of minerals to butachlor sorption in nat-

ural soils

When K d-min is b0 (indicating the contribution of soil minerals to

butachlor sorption is negative) the contribution rate (CR ) of minerals

was calculated from

CR frac14 K dminusmin

K dminus

K dminusmin

100 eth4THORN

If K d-min is N0 (indicating the contribution of soil minerals to

butachlor sorption is positive) the CR () of minerals was calculated

from

CR frac14K dminusmin

K d 100 eth5THORN

26 Statistical analysis

The data were subjected to be compiled and transformed by using

Microsoft Excel 2003 Statistical analysis was conducted with the SPSS

170 software package CORRELATE and FACTOR procedures Simple

Pearson correlations were used to study the relationship of sorption co-ef 1047297cients with physicochemical properties of soils and different soil

fractions Signi1047297cant and highly signi1047297cant levels are p b 005 and 001

respectively The sorption parameters (including K d-min K d and CR)

for butachlor sorption in soils (38 samples including all bulk and

H2O2-treated bulksamples of the present and previous work) were sub-

jected to principal component analysis (PCA) to separate and ordinate

soil plots Principal components that explained more than 5 of the

total variance were considered to be signi1047297cant The potential depen-

dence of sorption on the TOC and RCO values was further identi1047297ed

using correlation test of signi1047297cant PC scores

3 Results and discussion

31 Carbon distribution and main properties of soil different aggregate fractions

The percentage of total mass recovered in the sum of the three frac-

tions was calculated to evaluate the loss of soil during the size fraction-

ation As it rangedfrom 995 to 1080(mean1028plusmn 186) thesoil

loss during fractionation was negligible But the sum being greater than

100 was unexpected This might be ascribed to the systematic and an-

alytical errors during the physical fractionation procedures However

since it was very close to 100 it was presumed that the in1047298uences

caused by these experimental errors were negligible The following

analysis for carbon distribution in the different soil fractions was then

based on conversion of the total mass recovery to 100

After conversion of the total mass recovery to 100 the clay

microaggregates dominated the carbon distribution in all soils

accounting for more than 528 (mean 681 plusmn 552) of the soil TOC

In contrast approximately 201 to 443 (mean 306 plusmn 517) of

the soil TOC was in the silt fraction and an average of 127 (plusmn057)

wasassociated with the1047297ne sand fractionThesethreefractions also pri-

marily differed from each other in terms of speci1047297c surface area (SSA)

and Fe oxide contents (including amorphous Fe oxide (AO-Fe) and crys-

talline Fe oxide (DC-Fe)) which decreased with increasing aggregate

sizes The greatest concentrations of SSA and Fe oxides were in the

clay microaggregates followed by the silt and then 1047297

ne sand fractionsrespectively (Table 1)

32 Differences in butachlor sorption among different sized soil aggregate

fractions

Typical isotherms for butachlor sorption by bulk soils and their

different aggregate size fractions are given in Fig 1 The sorption of

butachlor increased with increasing solution concentration suggesting

that sorption sites within bulk soils and their fractionswere not saturat-

ed within the concentration range used The differences in concentra-

tions of adsorbed butachlor between the three aggregate size fractions

increased with increasing equilibrium butachlor concentrations (C e)

The isotherms were well 1047297tted by the Freundlich equation across the

entire butachlor concentration range with regression coef 1047297cients (r2)

of more than 097 ( p b 001 n = 10) The Freundlich N values varied

between 073 and 102 (mean 090 plusmn 004 in general less than 1)

and increased in the following order clay (mean 084 plusmn 003) b silt

(mean 088 plusmn 003) b 1047297ne sand (mean 092 plusmn 004) (Table S2)

The relationships between K d values of butachlorand the different C evalues aregiven in Fig 1 Thedata-intensity curvesshowed an in1047298ection

pointthat was concentrationdependent within the C e ofca0ndash1mgL minus1

In most cases the K d values sharply decreased at low C e values and then

approached relative unity in the upper C e range The decrease in K d with

increasing C e was greatest with the clay microaggregates followed by

the silt fraction The 1047297ne sand fraction had a virtually constant K dvalue Thus with increasing aggregate size the decrease in the K d values

with increasing C e values gradually disappeared Since precise compari-

sons between Freundlich K f values could not be made because of their

different units as a result of nonlinearity the linear sorption K d valueswere calculated using values within the linear C e range (Fig 2) (Chen

et al 1999 Clausen et al 2004 He et al 2006) The K d values ranged

from 094 with the 1047297ne sand of soil 4 to 950 with the clay of soil 1

(101-fold difference) Compared with the bulk soils the TOC enriched

clay microaggregates in all soils had greater K d values The TOC de1047297cient

1047297ne sand fractions had smaller K d values while the TOC enriched silt

fractions had smaller equal or greater K d values depending upon soil

conditions Between the mean linear K d values of 1047297ve tested soils

the maximum sorption occurred in the clay microaggregates (mean

value 348 plusmn 177) which was 61-fold greater than the weakest

sorption of the 1047297ne sand fraction (mean value 570 plusmn 220) There-

fore the clay microaggregates adsorbed most butachlor and the

1047297ne sand fraction adsorbed the least Simple Pearson correlations

between physicochemical properties of soils and the different soil frac-tions showed that the K d values were signi1047297cantly correlated with TOC

(r2 = 092 p b 001 n = 20) SSA (r2 = 021 p b 005 n = 15) AO-Fe

(r2 = 076 p b 001 n = 15) and DC-Fe (r2 = 046 p b 001n = 15) re-

spectively The highest TOC SSA AO-Fe and DC-Fe contents in the clay

microaggregates resulted in the highest K d values compared with the

other fractions However when normalized to OCvariations in thesorp-

tion coef 1047297cientsamongsoil fractionschangedas shown by theK oc values

(Fig 2) Unlike K d the greatest K oc values did not occur in the clay

microaggregates The silt and 1047297ne sand fractions also yielded the largest

K oc values under speci1047297c soil conditions (eg with the silt fraction in soil

2and the 1047297ne sand fraction in soil 1 andsoil 5)Further correlation anal-

ysis showed that the K oc valueswere not signi1047297cantly correlated with ei-

therTOC (r2 = 001 p = 0685n = 20) orSSA (r2 = 00025 p = 0844

n = 20)

311Y He et al Geoderma 232ndash 234 (2014) 309ndash 316

892019 1-s20-S0016706114002262-main


The SOM is bonded to minerals in various forms which results in

many distinct organo-mineral aggregates (Garbarini and Lion 1986)

The TOC and nitrogen content degree of aromaticity distribution of

alkyl O-alkyl aromatic and carbonyl groups and thermal stability of

SOM vary among sand silt and clay microaggregates of soils (Carmo

et al 2000 Chen and Chiu 2003 Kolbl and Kogel-Knabner 2004) Usu-

ally thedegree of humi1047297cationthe alkylation of theOC content andthe

aromatic structure increase with decreasing size of the soil fraction

(Chen and Chiu 2003 Kolbl and Kogel-Knabner 2004) Our hypothesisof sorption variation as a function of aggregate size was well supported

by the differences in the linear K d values that increased in the order

1047297ne sand b silt b clay with respect to their sorption capacities for

butachlor (Fig 2)

The generally lower Freundlich N values (less than 1 larger devi-

ation from linearity) together with the decreases in K d values with

increasing C e con1047297rmed that the sorption was nonlinear However

the sorption nonlinearity of butachlor only appeared at the low C erange (Table S2 and Fig 2) The possible causes of isotherm nonlin-

earity of butachlor sorption with low C e values are discussed in SI

The nonlinearity gradually became negligible with the increase in

aggregate size (Table S2 and Fig 2) The smallest sized clay

microaggregates demonstrated the most nonlinearity in most

cases However butachlor sorption by the 1047297ne sand fraction wasnearly linear especially in soil 2 This indicates that the sorption

mechanism of soils for butachlor is highly dependent on the nature

and extent of surface area ultimately exposed which in turn is de-

termined by the degree of association between SOM and minerals

(Celis et al 1999) The different sized soil organo-mineral aggre-

gates differ signi1047297cantly in structure and composition due to differ-

ent degrees of SOMndashmineral associations (He et al 2008 Zhou

et al 2004) Weber et al(1992) suggested that the N valueprovides

an index of site energy distribution (ie the smaller the N value the

more heterogeneous the sorption site) Therefore among the three

aggregate size fractions with the smaller N values the clay

microaggregates may have a more heterogeneous structure than

the silt and 1047297ne sand fractions and so exhibit more pronounced

nonlinearity of butachlor sorption

Soil 2

0 2 4 6 8 10

0

50

100

150

200

250Soil 1

0 2 4 6 8 10

Q e ( m g k g - 1 )

0

100

200

300

400

Soil 3

0 2 4 6 8 10

0

50

100

150

200

Soil 4

0 2 4 6 8 10 12

0

50

100

150

200

250Soil 5

0 2 4 6 8 10

0

20

40

60

80

100

120

140

Soil 1

C e (mg L-1)

0 2 4 6 8 10

K d

( L

k g

- 1 )

0

20

40

60

80

100

120

140

160

Soil 2

C e (mg L

-1)

0 2 4 6 8 10

0

20

40

60

80

100

Soil 3

C e (mg L

-1)

0 2 4 6 8 10

0

10

20

30

40

50

60

Soil 4

C e (mg L-1)

0 2 4 6 8 10

0

20

40

60

160

Soil 5

C e (mg L-1)

0 2 4 6 8 10

5

10

15

20

25

Bulk soil Clay Silt Find sand Fitted curve

Fig 1 Theisotherms andthe partition coef 1047297cients forbutachlorsorption on bulksoilclaysilt and1047297ne sandfractions Q e is theamountof butachlor adsorbedper unitmassof sample K d is

the butachlor sorption partition coef 1047297cient and C e is the equilibrium butachlor concentration Lines are the 1047297tted curves based on the Freundlich model

Soil 1 Soil 2 Soil 3 Soil 4 Soil 5

K d ( L

k g - 1 )

0

20

40

60

80

100

Bulk soil

Clay

Silt

Fine sand


K o c ( L

k g - 1 )

0

20

40

60

Fig 2 The sorption partition coef 1047297cients for butachlor in bulk soil clay silt and 1047297ne sand

fractions at equilibrium concentrations within the linear range K d the sorption partition

coef 1047297cient K oc the organic carbon content normalized partition coef 1047297cient


892019 1-s20-S0016706114002262-main


When normalized to OC butachlor sorption to the clay micro-

aggregates was not always largest Indeed it was less than sorption in

the silt and sand fractions under speci1047297c soil conditions (eg in soils 1

2 5) (see K oc in Fig 2) despite the fact that the clay microaggregates

had the largest SSAs and the SOM had a higher degree of humi1047297cation

This agrees with Huang et al (1984) and Barriuso and Koskinen

(1996) who both measured greater atrazine enrichment in silt com-

pared to clay-size fractions Possibly theSOM in theclay microaggregate

is closely associated withminerals and mineral coatings may evencausesome of the SOM to become blocked or occluded thereby preventing

some part of the SOM matrix from partitioning butachlor In contrast

SOM in the silt or 1047297ne sand which may be more loosely associated

with minerals may be relatively labile so demonstrating higheref 1047297cien-

cy of butachlor sorption The interactions between the clay and SOMde-

creases the availability of surfaces to metolachlor and SOM which is

very closely associated with the clay microaggregates is excluded

from metolachlor binding (Pusino et al 1992)

Correlation analysis showed that signi1047297cant dependence of sorption

capacity on TOC and SSA as indicated by K d was removed when sorp-

tion coef 1047297cients were normalized to OC as indicated by K oc This indi-

cates that in addition to SOM clay minerals and pedogenic oxides

contribute to the sorption of butachlor in soil Torn et al (1997)

suggested that soil minerals control the sequestration and turn-

over of soil OC There were highly signi1047297cant correlations of Fe oxides

(including AO-Fe and DC-Fe) with TOC (r2 = 090 and 050 with AO-

Fe and DC-Fe respectively p b 001 n = 15) and with SSA (r2 = 034

and 074 with AO-Fe and DC-Fe respectively p b 001 n = 15) that oc-

curred Therefore the physical conformation of SOM as altered by spe-

ci1047297c interactionswith clay minerals and pedogenicoxides appearsto be

an important factor in regulating how and to what extent butachlor is

sorbed by different sized organo-mineral aggregates Our 1047297ndings sug-

gest that there are limitations in applying K oc values to calculate sorp-

tion coef 1047297cients without considering the contribution of soil minerals

to butachlor sorption due to their varying effects on SOM Therefore

using calculated K oc values to model butachlor behavior in the soilndash

water interface may result in serious errors

33 The dual function of minerals vs SOM on butachlor sorption in soils

Contributions of different aggregate fractions to butachlor sorption

by soils were calculated as described in SI Sorption mass balances

revealed that the calculated values based on the sum of the adsorbed

butachlor concentrations in each fraction were on average 78

(plusmn48) greater than the measured values in bulk soils The percentage

contributions of the three fractionswere then normalized to a total con-

tribution of 100 (Fig 3) The clay microaggregates accounted for about

58 to 71 of total sorption in bulksoils and about 27 to 41 in the silt

just less than the 43 of total sorption by the 1047297ne sand fraction In

particular the differences between the calculated and measured

values were greater in the soils with relative higher RCO values (egmean +105 for soils 4 and 5 vs mean minus1 for soils 1 and 2)

(Table 1) These further imply that SOMndashmineral associations are im-

portant in in1047298uencing butachlor sorption in soils It also suggests that

soil minerals can indirectly and negatively regulate both the quantity

and the accessibilityof sorption sites for butachlor within or on the sur-

face of SOM through ldquoblockingrdquo or physically protecting them (Feng

et al 2006 Garbarini and Lion 1986 Lambert et al 1965 Salloum

et al 2001) Physical fractionation may expose sorption sites within

SOM that are closely associated with minerals and typically not accessi-

ble inbulk soils (Bonin and Simpson 2007) Consequently although we

did not directly investigate differences in chemical composition and

physical structurebetween the soils and their fractions theobserved in-

creases in the calculated sum of sorption of each fraction compared to

that of bulk soils may be due to theaccessibility of more favorable sorp-

tion sites in soil fractions that became available during aggregate frac-

tionation Furthermore soils with relatively higher RCO values were

considered likely to contain more SOMndashmineral associations Therefore

the ldquoblockingrdquo in1047298uence of minerals on SOMphysicalconformation may

be more pronounced thereby resulting in greater differences after the

soils were fractionated

Differentialremoval of SOMwith H2O2 from soils changed theextent

of butachlor sorption (Table 2) With the depletion of TOC ranging from

343 to12 g C kgminus1 soil insoil6 and from280to 32 g C kgminus1 soil in soil

7 the K d decreasedconsistently from 309 to 49 andfrom 207 to 93re-

spectively (Table 2) However the decreases in K d values were smaller

than expected from the decrease in TOC contents When the sorption

coef 1047297cients were normalized to TOC the K oc increased instead from

112 to 325 and from 262 to 228 in soils 6 and 7 respectively

(Table 2) This suggested that after the SOM was removed from soilsthe K d values decreased but the K oc values increased concomitantly

with decreasing SOM Therefore it was likely that the accessible SOM

rather than total SOM governed the extent of butachlor sorption This

also indicates that in addition to the indirect negative contribution

through in1047298uencing SOM physical conformation the minerals may di-

rectly contribute to the sorption of butachlor by soils and this positive

contribution could be even more pronounced at a lower SOM content

The physical conformation of SOM in the samples after H2O2 treatment

was not directly measured Therefore we can only speculate that the

greater af 1047297nity for butachlor sorption (as indicated by the increased


S o r p t i o n C o n t r i b u t i o n

( )

0

20

40

60

80

100

69

59

716258

4327123205

27

38

273541

Clay Silt Fine sand

Fig 3 Contribution of clay siltand 1047297ne sandfractionsto the sorptionof butachlor in soils

Total contribution was normalized to 100

Table 2Values of K d and K oc for butachlor sorption at the equilibrium concentrations within the

linear range and TOC and RCO ratios of H2O2 treated soilsa

Soil samples K d K oc TOC RCO

L kgminus1 L kgminus1 g kgminus1

6 Black soil

Bulk soil-H2O2-1 3090 901 3430 112

Bulk soil-H2O2-2 1820 1528 1191 322

Bulk soil-H2O2-3 1200 1970 609 629

Bulk soil-H2O2-4 491 4161 118 3246

7 Latosols

Bulk soil-H2O2-1 2066 738 2798 261

Bulk soil-H2O2-2 1951 867 2249 325

Bulk soil-H2O2-3 1775 1521 1167 626

Bulk soil-H2O2-4 929 2903 320 2284

a

Bulk soil-H2O2 bulk soil treated with H2O2 Other abbreviations are as in Table 1


892019 1-s20-S0016706114002262-main


K oc ) was due to the newly formed sorption sites on the soil minerals

which were formedafterthe chemical removal of mineral-bondedSOM

34 Quantifying the indirect and direct contributions of minerals to

butachlor sorption

Our results are based on1047297ve soils and their different sized aggregate

fractions along with our previous 1047297ndings with different kinds of pure

minerals and HAs in addition to different types of natural soils andtheir respective H2O2 treated samples (He et al 2011 Liu et al 2008

2010) This consistently indicated that minerals play an important

role in association with SOM in butachlor sorption in soils

In this study our aim was to develop an effective adsorption model

for quantifying the net contribution of minerals to butachlor sorption in

natural soils with various degrees of organo-mineral aggregation Our

approach was as follows

(1) Quantifying mineral contribution in simpli1047297ed pure systems

Four simpli1047297ed pure systems were proposed simplistically as-

suming that the sorption sites for butachlor were composed of

only one kind of typical soil mineral which contained at least

trace amounts of OC Theminerals included amorphoushydrated

iron oxides (AHOs-Fe) amorphous hydrated aluminum oxides

(AHOs-Al) montmorillonite (Mont) and kaolinite (Kaol) Theldquothresholdrdquo f oc value at which the mineral phase signi1047297cantly

contributes to a measured K d value(approximately 10 of overall

K d Mader et al 1997) wasthen calculated in these four systems

Referring to the K oc data of pure HAs (1781 L kgminus1) reported by

Chiou et al (1998)and Liu et al (2008) (TableS3) andthe K d and

TOCdata of AHOs-Fe AHOs-Al Mont andKaol for butachlorsorp-

tion reported by He et al (2011) (Table S3) the K d-min values for

AHOs-Fe AHOs-Al Mont andKaol in each pure systemwere each

calculated usingEq (3) The fraction of total K d (equal to K d-min +

K d-oc ) due to mineral interactions was plotted as a function of f oc in Fig 4 Thethreshold f oc at which mineral contributions to over-

all K d is measurable occurs at different values of f oc depending on

the mineral phase The threshold f oc values were 11 14 146

and 48 for the AHOs-Fe AHOs-Al Mont and Kaol respectively Itis likely that the stronger the sorption af 1047297nity of minerals for

butachlor the higher the threshold f oc of these minerals Since

an OC content of minerals of over 100 is clearly impossible

the contribution of Mont to the overall K d of butachlor sorption

should always be signi1047297cant Furthermore as the OC content of

different minerals should be generally no larger than 5 (Bradyand Weil 2008) the contribution of natural pure AHOs-Fe

AHOs-Al and Kaol to the overall K d of butachlor sorption would

necessarily be larger than 10

(2) Quantifying mineral contribution in natural soils

The K d-min values for minerals in natural soil systems were calcu-

lated (Table 3) based on Eq (3) The K oc-HA values used for these

calculations were derived from the average butachlor sorption

K oc values (1660 L kgminus1) of four HAs extracted from soils report-

edby He et al (2011) The f oc data of soil samples and the exper-

imental K d data for butachlor sorption in soils used for these

calculations were obtained both in this study (derived from 5

soils both bulk samples and those from physical fractionation

samples) and from data reported by others (21 soils 4 treated

with H2O2 for comparison and 1 with physical fractionationdata for comparison) (Table S3) (Chiang et al 1997 He et al

2011 Liu et al 2008 2010)

The CR of minerals on butachlor sorption for each soil sample

was further quanti1047297ed respectively using Eqs (4) and (5)

(Table 3) For all 26 bulk soil samples the CR of minerals for

butachlor sorption was negative for the soils with RCOs b 60

but positive for soils with RCOs N 60 The only exceptions were

soil 2 and soil 19 (Tables 1 and 2) The CR of minerals involved

in butachlor sorption also changed from negative to positive

after most of the SOM wasremoved from thesoils by H2O2 treat-

ment when their RCO values varied from below (117ndash274) to

above (605ndash1239) 60 (see soils 17ndash20 in Table S3 and

Table 3) Meanwhile the correlation analyses between the CR

values and physico-chemical properties of the 1047297ve bulk soils

-4 -3 -2 -1 0 1

00

02

04

06

08

10

K d - m

i n ( K

d - m

i n + K

d - o c

)

log f oc

AHOs-Fe

AHOs-Al

Mont

Kaol

Fig 4 The fraction of total sorption partition coef 1047297cient (K d) due to mineral interactions

versus log f oc for the sorption of butachlor to typical soil inorganic minerals AHOs-Fe

amorphous hydrated iron oxides AHOs-Al amorphous hydrated aluminum oxides

Mont montmorillonite Kaol kaolinite K d-min the mineralndashwater partition coef 1047297cient

K d-oc the organic matter-water partition coef 1047297cient that can be calculated using (Eq (2))

Table 3

The calculated K d-min values andthe quanti1047297ed dual-effectcontribution rateof minerals on

butachlor sorption by soils

Sorbentsa K d-minb CR ()c Sorbents K d-min CR ()

1 Bulk soil minus1202 minus250 1prime Bulk soil minus315 minus202

Clay minus2476 minus261 2prime Bulk soil 186 111

Silt minus765 minus287 3prime Bulk soil minus690 minus502

Fine sand minus149 minus153 4prime Bulk soil minus306 minus72


Clay minus

1392 minus

283 6prime Bulk soil minus

2731 minus

592Silt 135 131 7prime Bulk soil minus1279 minus313

Fine sand 199 210 8prime Bulk soil minus1622 minus386


Clay minus1512 minus676 10prime Bulk soil minus1577 minus495


Fine sand minus082 minus44 0 12prime Bulk soil minus789 minus255

4 Bulk soil 073 201 13prime Bulk soil minus944 minus459

Clay 1317 540 14prime Bulk soil minus1226 minus290

Silt 367 486 15prime Bulk soil minus1410 minus325



Clay 088 73 Bulk soil-H2O2 202 191


Fine sand 410 563 Bulk soil-H2O2 111 8 6 19

6 Bulk soil-H2O2-1 minus2604 minus457 19prime Bulk soil 541 113

Bulk soil-H2O2-2 minus157 minus86 Bulk soil-H2O2 160 6 6 40

Bulk soil-H2O2-3 189 158 20prime

Bulk soil minus

2355 minus

510Bulk soil-H2O2-4 295 601 Bulk soil-H2O2 781 444

7 Bulk soil-H2O2-1 minus1594 minus435 21prime Bulk soil minus849 minus233

Bulk soil-H2O2-2 minus991 minus337 Clay minus121 minus209

Bulk soil-H2O2-3 249 140 Silt 913 452

Bulk soil-H2O2-4 510 549 Fine sand 031 62

a Abbreviations for the sorbents are as in Tables 1 and 2b K d-min themineralndashwater partition coef 1047297cient The values of butachlor sorption parti-

tion coef 1047297cient of pure HA (K oc-HA 1660 L kgminus1) used to calculate K d-min were referred to

the average butachlor sorption K oc values of four humic acids that were extracted from

soils reported by He et al (2011)c CR the contribution rate () of minerals for butachlor sorption


892019 1-s20-S0016706114002262-main


and their respective fractions showed that the CR values

were not signi1047297cantly correlated with either TOC or SSA Howev-

erthey were correlated with theratio of concentrationsof free to

amorphous Fe oxides (DC-FeAC-Fe values) (r2 = 028 p b 005

n = 15) an index of the degree of soil weathering (He et al

2011) Therefore soil weathering might affect the contribution

of minerals for OPs sorption Since we do not have any direct

evidence to demonstrate how and why soil weathering would

affect the possible reason was speculated as the depletion of SOM and the relative accumulation of soil minerals during soil

weathering development that resulted in the variation of soil

RCO values

Two different series of soils with the same mineral components but

gradients of TOC and RCO values were further used to verify this quan-

ti1047297cation model With decreasing OC (caused by H2O2 digestion) the

RCO values increased from 112 to 322 then to 629 then to 3246 for

soil 6 and from 261 to 325 then to 626 then to 2284 for soil 7

(Table 2) As a consequence the CR of minerals for butachlor sorption

increased correspondingly from minus457 to minus86 then to +158

then to +601 for soil 6 and from minus435 to minus337 then to

+140 then to +549for soil 7 respectively After the RCO increased

above 60 the negative contribution of soil minerals to butachlor sorp-

tion disappeared and the positive contribution became apparent(Tables 2 and 3)

Principal component analysis was conducted on the parameters

(including K d-min K d and CR) for butachlor sorption in soils (including

all bulk and H2O2-treated bulk samples of this and previous work

giving totally 38 samples) (Fig 5) Two principal components

which jointly explained 957 of the total variance were screened and

discriminated between the samples with RCO values greater than

(605ndash3246) and smaller than (65ndash579) 60 Highly signi1047297cant correla-

tions of the scores of 1047297rst principal component (PC1) were found simul-

taneously with theTOC (r2 = 072 p b 001 n = 38) and the RCO values

(r2 = 046 p b 001 n = 38)

Therefore can the dual function of minerals vs SOM on butachlor

sorption in soils be quanti1047297ed With development of the above adsorp-

tion model and veri1047297cation of this model for quantifying the net contri-bution of minerals to butachlor sorption based upon38 different soils as

above the answer may be yes By deducing K d-min through assuming

that the K d was the sum of contributions of mineral ( K d-min) and SOM

(K d-oc ) and that the K d-oc could be accurately represented by pure HA

extracted from the corresponding soils ( f oc times K oc-HA) our calculation re-

sults for the CR values of minerals suggested that the RCO value of 60

below which is negative while above which is positive could be a

critical index for estimating the contributions of different minerals to

butachlor sorption in soils

To better optimize the proposed adsorption model further effort is

necessary to obtain comparisons to include nonpolar compound (eg

polycyclic aromatic hydrocarbon) for which sorption contribution

from minerals is generally negligible In addition as the organic carbon

in soil is highly heterogeneous and comprises various complex organic

macromolecules having extraordinarily strong sorption af 1047297nity for OPs

besides HA the representative K d-oc with a wide spectrum of different

origins including fulvic acid humin black carbon and biochar is also

necessary for further development of more realistic K d-min values

4 Conclusion

Gaps within our knowledge regarding the direct positive contribu-

tion of soil minerals and their indirect negative contribution through

their associated impact on the physical conformation of SOM on

butachlor sorption in soils are discussed Soil fractionation indicated

an aggregate size dependent sorption of butachlor within soil organo-

mineral fractions This was underpinned by large differences in mineral

associated effects on SOM across soil fractions of varying aggregate size

Coupled with butachlor sorption data in 21 soils obtained in previous

studies of ours and others a new adsorption model was built and veri-

1047297ed to quantify the net contribution of minerals on butachlor sorption

based upon 38 different soil samples The critical value of 60 was sug-gested for the RCO to give an improved understanding of the contribu-

tion of minerals to butachlor sorption in contrasting natural soils where

SOM is associated with minerals to various degrees This study repre-

sents a 1047297rst step toward quantitatively identifying the dual impact of

minerals vs SOM as a function of aggregate size during butachlor sorp-

tion in contrasting nature soils

Acknowledgment

This work was 1047297nancially supported by the National Natural Science

Foundation of China (41130532 41322006) and the Fundamental

Research Funds for the Central Universities

Appendix A Supplementary data

Supplementary data to this article can be found online at httpdx

doiorg101016jgeoderma201405021

References

Amelung W Zech W Zhang X Follett RF Tiessen H Knox E Flach KW 1998Carbon nitrogen and sulfur pools in particle-size fractions as in1047298uenced by climateSoil Sci Soc Am J 62 172ndash181

Barriuso E Koskinen WC 1996 Incorporating non-extractable atrazine residues intosoil size fractions as a function of time Soil Sci Soc Am J 60 150ndash157

Bonin JL Simpson MJ 2007 Variation in phenanthrene sorption coef 1047297cients with soilorganic matter fractionation the result of structure or conformation Environ SciTechnol 41 153ndash159

Brady NC Weil RR (Eds) 2008 The Nature and Properties of Soils 14th ed PearsonPrentice Hall Upper Saddle River New Jersey Columbus Ohio

Carmo AM Hundal LS Thompson ML 2000 Sorption of hydrophobic organiccompounds by soil materials application of unit equivalent Freundlich coef 1047297cientsEnviron Sci Technol 34 4363ndash4369

Celis R Hermosiacuten MC Cox L Cornejo J 1999 Sorption of 24-dichlorophenoxyaceticacid by model particles simulating naturally occurring soil colloids Environ SciTechnol 33 1200ndash1206

Chen JS Chiu CY 2003 Characterization of soil organic matter in different particle-sizefractions in humid subalpine soils by CPMAS 13C NMR Geoderma 117 129ndash141

Chen Z Xing B McGill WB 1999 A uni1047297ed sorption variable for environmental appli-cations of the Freundlich equation J Environ Qual 28 1422ndash1428

Chiang HC Yen JH Wang YS 1997 Sorptionof herbicides butachlor thiobencarb andchlomethoxyfen in soils Bull Environ Contam Toxicol 58 758ndash763

Chiou CT McGroddy SE Kile DE 1998 Partition characteristics of polycyclic aromatichydrocarbons on soils and sediments Environ Sci Technol 32 264ndash269

ClausenL LarsenF AlbrechtsenHJ 2004 Sorption of theherbicide dichlobenil andthemetabolite 26-dichlorobenzamide on soils and aquifer sediments Environ SciTechnol 38 4510ndash4518

Feng X Simpson AJ SimpsonMJ 2006 Investigating the roleof mineral-bound humic

acid in phenanthrene sorption Environ Sci Technol 40 3260ndash

3266

PC1657 of variance)

-2 -1 0 1 2

P C 2 ( 3 0 0

o

f v a r i a n c e

)

-2

-1

0

1

2

3

4

RCO lt 60

RCO gt 60

Fig 5 The individual loading values for the1047297rst twoprincipal components of PCA param-

eters for butachlor sorption in soils of this and other work


892019 1-s20-S0016706114002262-main


GarbariniDR Lion LW 1986 In1047298uence of the nature of soil organicson the sorption of toluene and trichloroethylene Environ Sci Technol 20 1263ndash1269

He Y Xu JM Wang HZ Zhang QC Muhammad A 2006 Potential contributionsof soil minerals and organic matter to pentachlorophenol retention in soilsChemosphere 65 497ndash505

He Y Xu ZH Chen CR Burton J Ma Q Ge Y Xu JM 2008 Using light fraction andmacroaggregate associated organic matters as early indicators for management-induced changes in soil chemical and biological properties in adjacent native andplantation forests of subtropical Australia Geoderma 147 116ndash125

He Y Liu ZZ Zhang J Wang HZ Shi JC Xu JM 2011 Can assessing for potentialcontribution of soil organic and inorganic components for butachlor sorption be im-

proved J Environ Qual 40 1705ndash

1713Huang PM Grover R Mckercher RB 1984 Components and particle size fractions in-volved in atrazine adsorption by soils Soil Sci 138 20ndash24

Khan SU 1980 In Wakeman RJ (Ed) Pesticides in the Soil Environment Elsevier SciPubl Amsterdam pp 18ndash29

Kolbl A Kogel-Knabner I 2004 Content and composition of free and occluded particu-late organicmatter in a differentlytextured arableCambisol as revealedby solid-state13C NMR spectroscopy J Plant Nutr Soil Sci 167 45 ndash53

Lambert SM Porter PE Schieferstein RH 1965 Movement and sorption of chemicalsapplied to the soil Weeds 13 185ndash190

Liu ZZ HeY Xu JMHuang PJilaniG 2008 The ratio of clay content to total organiccarbon content is a useful parameter to predict adsorption of the herbicide butachlorin soils Environ Pollut 152 163ndash171

Liu ZZ Ding N Hayat T He Y Xu JM Wang HZ 2010 Butachlor sorption in organ-ically rich soil particles Soil Sci Soc Am J 74 2032 ndash2038

Mader BT Uwe-Goss K Eisenreich SJ 1997 Sorption of nonionichydrophobic organicchemicals to mineral surfaces Environ Sci Technol 31 1079ndash1086

Pusino A Liu W Gessa C 1992 In1047298uence of organic matter and its clay complexes onmetolachlor adsorption on soil Pestic Sci 36 283ndash286

Pusino A Liu W Gessa C 1994 Adsorption of triclopyr on soil and some of its compo-nents J Agric Food Chem 42 1026ndash1029

Salloum MJ Dudas MJ McGill WB 2001 Variation of 1-naphthol sorption withorganic matter fractionation the role of physical conformation Org Geochem 32709ndash719

Torn MS Trumbore SE Chadwick OA Vitousek PM Hendricks DM 1997 Mineralcontrol of soil organic carbon storage and turnover Nature 389 170ndash173Wang K Xing B 2005a Structural and sorption characteristics of adsorbed humic acid

on clay minerals J Environ Qual 34 342ndash349Wang K Xing B 2005b Chemical extractions affect the structure and phenanthrene

sorption of soil humin Environ Sci Technol 39 8333ndash8340Weber JrWJ McGinley PM Katz LE 1992 A distributed reactivity model for sorption

by soils andsediments1 Conceptual basis and equilibriumassessments EnvironSciTechnol 26 1955ndash1962

Zhou YM Liu RX Tang HX 2004 Sorption interaction of phenanthrene with soil andsediment of different particle sizes and in various CaCl2 solutions J Colloid InterfaceSci 270 37ndash46


892019 1-s20-S0016706114002262-main


adsorbed OP in bulk soils distributes among their different size aggre-

gates which has different degrees of organo-mineral association

Selecting butachlor (a chloracetamide) as a model OP we exam-

ined its sorption by bulk soils and respective organo-mineral aggre-

gates with contrasting degrees of association of minerals and SOM

The soil organo-mineral aggregates were fractionated by ultrasonic

dispersion in water without chemical pretreatment to minimize

any alteration to their composition or structure Soils were also

treated with hydrogen peroxide (H2O2) to remove SOM to variousdegrees We hypothesized that variation of the physicochemical na-

ture of organo-mineral association in different soil aggregates

would result in corresponding differences in butachlor sorption ca-

pacity of soils as a function of aggregate size We also hypothesized

that minerals could provide sites for butachlor adsorption and

when SOM was removed from soils the original and now largely

SOM free mineral surface would be exposed and so would contrib-

ute directly and positively to butachlor sorption by soils Our objec-

tive was to develop an effective method to quantify the dual roles of

minerals vsSOM in thesorption of OPs such as butachlor in natural

soils with various degrees of organo-mineral aggregation To do this

a new adsorption model was proposed and veri1047297ed to quantify the

net contribution of minerals to butachlor sorption based upon 38

different soils

2 Materials and methods

21 Reagents and soils

Butachlor N-butoxymethyl-2-chloro-2prime6prime-diethylacetanilide (N979

purity) was obtained from the Shenyang Research Institute of Chemical

Industry (Shenyang China) The soils used with a wide range of RCO

values (from 112 to 1432) were seven of the referenced soils used pre-

viously (He et al 2011 Liu et al 2008) They were surface horizons

(0ndash20 cm) of uncultivated soils collected in the Guizhou Jiangsu

Henan Zhejiang Heilongjiang and Guangdong provinces of China The

physicochemical properties of the bulk soils and their fractions are listed

in Table 1 Thechemical properties of butachlor soil classi1047297cation andtheanalytical methods for physicochemical properties of the bulk soils and

their fractions are described in Supplementary information (SI) and

Table S1

22 Aggregate size fractionation of soils

Aggregate size fractionation of the bulk soils was conducted for soils

1ndash5 based on mechanical dispersion (Liu et al 2010) The detailed frac-

tionation procedures are described in SI After fractionation the 1047297ne

sand (20ndash50 μ m) silt (2ndash20 μ m) and clay (b2 μ m) fractions were

freeze-dried and then weighed

23 Treatment of bulk soil samples with H 2O 2

To verify that the adsorption model proposed for calculating the net

contribution of soil minerals to butachlor sorption was quantitative

soils 6 and 7 were treated with different volumes of 30 H2O2 to obtain

a series of soil samples of the same mineral compositions but with dif-

ferent total organic carbon(TOC) contents (Heet al 2006) Thedetailed

steps are described in SI

24 Sorption experiments

Sorption was measured using a batch equilibrium technique

(He et al 2011) In brief approximately 030ndash065 g of freeze-dried

bulk soil andtheir soil fractionswere accurately and separately weighed

into 25-mL centrifuge glass bottles with screw caps and equilibrated

with8 mLof 002 mol L minus1 KCl solution (containing002 NaN3 to inhibit

microbial activity) containing different concentrations of butachlor

Each isotherm consisted of 10 increasing concentrations of butachlor

along a log10 scale ranging from 01 to 16 mg L minus1 each with two repli-

cates One series of vials without butachlor served as a control All sorp-

tion data were 1047297tted to the logarithmic form of the Freundlich equation

The sorption partition coef 1047297cients (K d) and the organic carbon (OC)

content normalized partition coef 1047297cients (K oc) were also determined

The mathematical manipulation of the sorption data is described in SI

25 Building the adsorption model to quantify the contribution of minerals

to butachlor sorption

251 Calculation of the K d of minerals in soils

The K d was assumed to be the sum of the mineraland SOM contribu-tions as follows

K d frac14 K dminusmin thorn K dminusoc eth1THORN

Table 1

Selected properties of bulk soils and their fractions and the distribution of each fraction in the bulk soilsa

Soil samples TOC SSA AO-Fe DC-Fe Wf pH CEC RCO

g kgminus1 m2 gminus1 g kgminus1 g kgminus1 (WW) H2O cmol (+) kgminus1

Soil 1 Bulk soil 250 136 60 246 100 409 105 144

Clay 499 413 130 1051 361

Silt 143 20 22 99 623


Soil 2 Bulk soil 147 191 47 193 100 512 182 276

Clay 263 331 89 573 406

Silt 48 11 05 51 582


Soil 3 Bulk soil 44 68 18 98 100 836 99 579

Clay 135 263 43 325 254

Silt 27 12 02 61 693


Soil 4 Bulk soil 18 133 07 72 100 428 66 1432

Clay 68 314 08 319 252

Silt 23 27 01 101 612


Soil 5 Bulk soil 45 380 29 250 100 459 97 1241

Clay 67 563 37 883 553

Silt 21 15 02 41 453


a TOC totalo rganic carbon SSA speci1047297c surface area AO-Fe ammonium-oxalate extractable amorphous Fe2O3 DC-Fe dithionite-citrate extractable free Fe2O3 CEC cation exchange

capacity RCO the ratio of clay to total organic carbon Wf the weight percentage of each soil fraction in bulk soil


892019 1-s20-S0016706114002262-main













ural soils



was calculated from


K dminus

K dminusmin

100 eth4THORN



from


K d 100 eth5THORN








































fractions
















































n = 20)


892019 1-s20-S0016706114002262-main













butachlor (Fig 2)























Soil 2

0 2 4 6 8 10

0

50

100

150

200

250Soil 1

0 2 4 6 8 10

Q e ( m g k g - 1 )

0

100

200

300

400

Soil 3

0 2 4 6 8 10

0

50

100

150

200

Soil 4

0 2 4 6 8 10 12

0

50

100

150

200

250Soil 5

0 2 4 6 8 10

0

20

40

60

80

100

120

140

Soil 1

C e (mg L-1)

0 2 4 6 8 10

K d

( L

k g

- 1 )

0

20

40

60

80

100

120

140

160

Soil 2

C e (mg L

-1)

0 2 4 6 8 10

0

20

40

60

80

100

Soil 3

C e (mg L

-1)

0 2 4 6 8 10

0

10

20

30

40

50

60

Soil 4

C e (mg L-1)

0 2 4 6 8 10

0

20

40

60

160

Soil 5

C e (mg L-1)

0 2 4 6 8 10

5

10

15

20

25





K d ( L

k g - 1 )

0

20

40

60

80

100

Bulk soil

Clay

Silt

Fine sand


K o c ( L

k g - 1 )

0

20

40

60





892019 1-s20-S0016706114002262-main
























































































( )

0

20

40

60

80

100

69

59

716258

4327123205

27

38

273541

Clay Silt Fine sand







6 Black soil

Bulk soil-H2O2-1 3090 901 3430 112

Bulk soil-H2O2-2 1820 1528 1191 322

Bulk soil-H2O2-3 1200 1970 609 629

Bulk soil-H2O2-4 491 4161 118 3246

7 Latosols

Bulk soil-H2O2-1 2066 738 2798 261

Bulk soil-H2O2-2 1951 867 2249 325

Bulk soil-H2O2-3 1775 1521 1167 626

Bulk soil-H2O2-4 929 2903 320 2284

a



892019 1-s20-S0016706114002262-main





butachlor sorption















































2011 Liu et al 2008 2010)













-4 -3 -2 -1 0 1

00

02

04

06

08

10

K d - m

i n ( K

d - m

i n + K

d - o c

)

log f oc

AHOs-Fe

AHOs-Al

Mont

Kaol






Table 3









Clay minus

1392 minus


2731 minus


















Bulk soil minus

2355 minus




Bulk soil-H2O2-3 249 140 Silt 913 452







892019 1-s20-S0016706114002262-main












RCO values





















(r2 = 046 p b 001 n = 38)





















4 Conclusion

















Acknowledgment







References














3266

PC1657 of variance)

-2 -1 0 1 2

P C 2 ( 3 0 0

o

f v a r i a n c e

)

-2

-1

0

1

2

3

4

RCO lt 60

RCO gt 60




892019 1-s20-S0016706114002262-main























892019 1-s20-S0016706114002262-main













ural soils



was calculated from


K dminus

K dminusmin

100 eth4THORN



from


K d 100 eth5THORN








































fractions
















































n = 20)


892019 1-s20-S0016706114002262-main













butachlor (Fig 2)























Soil 2

0 2 4 6 8 10

0

50

100

150

200

250Soil 1

0 2 4 6 8 10

Q e ( m g k g - 1 )

0

100

200

300

400

Soil 3

0 2 4 6 8 10

0

50

100

150

200

Soil 4

0 2 4 6 8 10 12

0

50

100

150

200

250Soil 5

0 2 4 6 8 10

0

20

40

60

80

100

120

140

Soil 1

C e (mg L-1)

0 2 4 6 8 10

K d

( L

k g

- 1 )

0

20

40

60

80

100

120

140

160

Soil 2

C e (mg L

-1)

0 2 4 6 8 10

0

20

40

60

80

100

Soil 3

C e (mg L

-1)

0 2 4 6 8 10

0

10

20

30

40

50

60

Soil 4

C e (mg L-1)

0 2 4 6 8 10

0

20

40

60

160

Soil 5

C e (mg L-1)

0 2 4 6 8 10

5

10

15

20

25





K d ( L

k g - 1 )

0

20

40

60

80

100

Bulk soil

Clay

Silt

Fine sand


K o c ( L

k g - 1 )

0

20

40

60





892019 1-s20-S0016706114002262-main
























































































( )

0

20

40

60

80

100

69

59

716258

4327123205

27

38

273541

Clay Silt Fine sand







6 Black soil

Bulk soil-H2O2-1 3090 901 3430 112

Bulk soil-H2O2-2 1820 1528 1191 322

Bulk soil-H2O2-3 1200 1970 609 629

Bulk soil-H2O2-4 491 4161 118 3246

7 Latosols

Bulk soil-H2O2-1 2066 738 2798 261

Bulk soil-H2O2-2 1951 867 2249 325

Bulk soil-H2O2-3 1775 1521 1167 626

Bulk soil-H2O2-4 929 2903 320 2284

a



892019 1-s20-S0016706114002262-main





butachlor sorption















































2011 Liu et al 2008 2010)













-4 -3 -2 -1 0 1

00

02

04

06

08

10

K d - m

i n ( K

d - m

i n + K

d - o c

)

log f oc

AHOs-Fe

AHOs-Al

Mont

Kaol






Table 3









Clay minus

1392 minus


2731 minus


















Bulk soil minus

2355 minus




Bulk soil-H2O2-3 249 140 Silt 913 452







892019 1-s20-S0016706114002262-main












RCO values





















(r2 = 046 p b 001 n = 38)





















4 Conclusion

















Acknowledgment







References














3266

PC1657 of variance)

-2 -1 0 1 2

P C 2 ( 3 0 0

o

f v a r i a n c e

)

-2

-1

0

1

2

3

4

RCO lt 60

RCO gt 60




892019 1-s20-S0016706114002262-main























892019 1-s20-S0016706114002262-main













butachlor (Fig 2)























Soil 2

0 2 4 6 8 10

0

50

100

150

200

250Soil 1

0 2 4 6 8 10

Q e ( m g k g - 1 )

0

100

200

300

400

Soil 3

0 2 4 6 8 10

0

50

100

150

200

Soil 4

0 2 4 6 8 10 12

0

50

100

150

200

250Soil 5

0 2 4 6 8 10

0

20

40

60

80

100

120

140

Soil 1

C e (mg L-1)

0 2 4 6 8 10

K d

( L

k g

- 1 )

0

20

40

60

80

100

120

140

160

Soil 2

C e (mg L

-1)

0 2 4 6 8 10

0

20

40

60

80

100

Soil 3

C e (mg L

-1)

0 2 4 6 8 10

0

10

20

30

40

50

60

Soil 4

C e (mg L-1)

0 2 4 6 8 10

0

20

40

60

160

Soil 5

C e (mg L-1)

0 2 4 6 8 10

5

10

15

20

25





K d ( L

k g - 1 )

0

20

40

60

80

100

Bulk soil

Clay

Silt

Fine sand


K o c ( L

k g - 1 )

0

20

40

60





892019 1-s20-S0016706114002262-main
























































































( )

0

20

40

60

80

100

69

59

716258

4327123205

27

38

273541

Clay Silt Fine sand







6 Black soil

Bulk soil-H2O2-1 3090 901 3430 112

Bulk soil-H2O2-2 1820 1528 1191 322

Bulk soil-H2O2-3 1200 1970 609 629

Bulk soil-H2O2-4 491 4161 118 3246

7 Latosols

Bulk soil-H2O2-1 2066 738 2798 261

Bulk soil-H2O2-2 1951 867 2249 325

Bulk soil-H2O2-3 1775 1521 1167 626

Bulk soil-H2O2-4 929 2903 320 2284

a



892019 1-s20-S0016706114002262-main





butachlor sorption















































2011 Liu et al 2008 2010)













-4 -3 -2 -1 0 1

00

02

04

06

08

10

K d - m

i n ( K

d - m

i n + K

d - o c

)

log f oc

AHOs-Fe

AHOs-Al

Mont

Kaol






Table 3









Clay minus

1392 minus


2731 minus


















Bulk soil minus

2355 minus




Bulk soil-H2O2-3 249 140 Silt 913 452







892019 1-s20-S0016706114002262-main












RCO values





















(r2 = 046 p b 001 n = 38)





















4 Conclusion

















Acknowledgment







References














3266

PC1657 of variance)

-2 -1 0 1 2

P C 2 ( 3 0 0

o

f v a r i a n c e

)

-2

-1

0

1

2

3

4

RCO lt 60

RCO gt 60




892019 1-s20-S0016706114002262-main























892019 1-s20-S0016706114002262-main
























































































( )

0

20

40

60

80

100

69

59

716258

4327123205

27

38

273541

Clay Silt Fine sand







6 Black soil

Bulk soil-H2O2-1 3090 901 3430 112

Bulk soil-H2O2-2 1820 1528 1191 322

Bulk soil-H2O2-3 1200 1970 609 629

Bulk soil-H2O2-4 491 4161 118 3246

7 Latosols

Bulk soil-H2O2-1 2066 738 2798 261

Bulk soil-H2O2-2 1951 867 2249 325

Bulk soil-H2O2-3 1775 1521 1167 626

Bulk soil-H2O2-4 929 2903 320 2284

a



892019 1-s20-S0016706114002262-main





butachlor sorption















































2011 Liu et al 2008 2010)













-4 -3 -2 -1 0 1

00

02

04

06

08

10

K d - m

i n ( K

d - m

i n + K

d - o c

)

log f oc

AHOs-Fe

AHOs-Al

Mont

Kaol






Table 3









Clay minus

1392 minus


2731 minus


















Bulk soil minus

2355 minus




Bulk soil-H2O2-3 249 140 Silt 913 452







892019 1-s20-S0016706114002262-main












RCO values





















(r2 = 046 p b 001 n = 38)





















4 Conclusion

















Acknowledgment







References














3266

PC1657 of variance)

-2 -1 0 1 2

P C 2 ( 3 0 0

o

f v a r i a n c e

)

-2

-1

0

1

2

3

4

RCO lt 60

RCO gt 60




892019 1-s20-S0016706114002262-main























892019 1-s20-S0016706114002262-main





butachlor sorption















































2011 Liu et al 2008 2010)













-4 -3 -2 -1 0 1

00

02

04

06

08

10

K d - m

i n ( K

d - m

i n + K

d - o c

)

log f oc

AHOs-Fe

AHOs-Al

Mont

Kaol






Table 3









Clay minus

1392 minus


2731 minus


















Bulk soil minus

2355 minus




Bulk soil-H2O2-3 249 140 Silt 913 452







892019 1-s20-S0016706114002262-main












RCO values





















(r2 = 046 p b 001 n = 38)





















4 Conclusion

















Acknowledgment







References














3266

PC1657 of variance)

-2 -1 0 1 2

P C 2 ( 3 0 0

o

f v a r i a n c e

)

-2

-1

0

1

2

3

4

RCO lt 60

RCO gt 60




892019 1-s20-S0016706114002262-main























892019 1-s20-S0016706114002262-main












RCO values





















(r2 = 046 p b 001 n = 38)





















4 Conclusion

















Acknowledgment







References














3266

PC1657 of variance)

-2 -1 0 1 2

P C 2 ( 3 0 0

o

f v a r i a n c e

)

-2

-1

0

1

2

3

4

RCO lt 60

RCO gt 60




892019 1-s20-S0016706114002262-main























892019 1-s20-S0016706114002262-main























1-s2.0-S0016706114002262-main

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