Ecotoxicology and Environmental Safety 92 (2013) 215–221

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Ecotoxicology and Environmental Safety

0147-65

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n Corr

E-m

hiller@f

journal homepage: www.elsevier.com/locate/ecoenv

Impact of wheat straw biochar addition to soil on the sorption, leaching,dissipation of the herbicide (4-chloro-2-methylphenoxy)acetic acidand the growth of sunflower (Helianthus annuus L.)

Veronika Tatarkova a, Edgar Hiller a,n, Marek Vaculık b

a Department of Geochemistry, Faculty of Natural Sciences, Comenius University in Bratislava, Mlynska dolina G, 842 15 Bratislava, Slovak Republicb Department of Plant Physiology, Faculty of Natural Sciences, Comenius University in Bratislava, Mlynska dolina B-2, 842 15 Bratislava, Slovak Republic

a r t i c l e i n f o

Article history:

Received 15 November 2012

Received in revised form

5 February 2013

Accepted 7 February 2013Available online 6 March 2013

Keywords:

Biochar

Dissipation

Leaching

Pesticide

Soil

Sorption

13/$ - see front matter & 2013 Elsevier Inc. A

x.doi.org/10.1016/j.ecoenv.2013.02.005

esponding author. Fax: þ421 2 60296 217.

ail addresses: tatarkovav@fns.uniba.sk (V. Tat

ns.uniba.sk (E. Hiller), vaculik@fns.uniba.sk (M

a b s t r a c t

Biochar addition to agricultural soils might increase the sorption of herbicides, and therefore, affect

other sorption-related processes such as leaching, dissipation and toxicity for plants. In this study, the

impact of wheat straw biochar on the sorption, leaching and dissipation in a soil, and toxicity for

sunflower of (4-chloro-2-methylphenoxy)acetic acid (MCPA), a commonly used ionizable herbicide,

was investigated. The results showed that MCPA sorption by biochar and biochar-amended soil

(1.0 wt% biochar) was 82 and 2.53 times higher than that by the non-amended soil, respectively.

However, desorption of MCPA from biochar-amended soil was only 1.17 times lower than its

desorption in non-amended soil. Biochar addition to soil reduced both MCPA leaching and dissipation.

About 35% of the applied MCPA was transported through biochar-amended soil, while up to 56% was

recovered in the leachates transported through non-amended soil. The half-life value of MCPA

increased from 5.2 d in non-amended soil to 21.5 d in biochar-amended soil. Pot experiments with

sunflower (Helianthus annuus L.) grown in MCPA-free, but biochar-amended soil showed no positive

effect of biochar on the growth of sunflower in comparison to the non-amended soil. However, biochar

itself significantly reduced the content of photosynthetic pigments (chlorophyll a, b) in sunflower.

There was no significant difference in the phytotoxic effects of MCPA on sunflowers between the

biochar-amended soil and the non-amended soil. Furthermore, MCPA had no effect on the photo-

synthetic pigment contents in sunflower.

& 2013 Elsevier Inc. All rights reserved.

1. Introduction

There is a growing evidence that application of biochars andbiochar-like materials (e.g. activated carbons and ashes) into soilshas many advantages. Because of their long-term stability in soil,biochars may have a potential role in climate change mitigationthrough their ability to sequester carbon and reduce the emmi-sions of greenhouse gases from soil (Sohi et al., 2010; Woolf et al.,2010). It has been shown that addition of biochars to soilimproves soil physico-chemical and biological properties, fertili-zation and thus crop productivity (Jeffery et al., 2011; Laird et al.,2010).

Pesticides applied to soil undergo many partitioning andtransformation processes, from which sorption has been consid-ered as a key soil process for a long time (Wauchope et al., 2002).

ll rights reserved.

arkova),

. Vaculık).

The extent to which pesticides are sorbed by a soil may affectmany other aspects of their behavior in the soil. Sorption, whichcontrols pesticide concentrations in the soil solution, has beenshown to limit soil dissipation of pesticides, their leaching andbioavailability to plants and animals (Alister et al., 2008; Dysonet al., 2002; Hiller et al., 2010). It has been also shown thatbiochar and other biochar-like materials effectively sorb pesti-cides and they are responsible for their increased sorption by soilsamended with these types of organic materials. Various studieshave documented that the increased sorption of pesticides bybiochar- or ash-amended soils may result in a decrease of theirdegradation, desorption, leaching and uptake by plants whencompared to the non-amended soils (Cabrera et al., 2011; Hilleret al., 2009; Xu et al., 2012; Yu et al., 2009), thereby reducingadverse impacts of pesticide residues on the environment and theecosystem functionality. Moreover, toxicity and efficacy of soil-applied pesticides may be also reduced significantly in biochar- orash-amended soils and this is due to high sorption capacity ofbiochars and biochar-like materials (Graber et al., 2011, 2012;Nag et al., 2011; Yang et al., 2006).

T. Veronika et al. / Ecotoxicology and Environmental Safety 92 (2013) 215–221216

Although, the impact of biochar addition to soils on the sorption–desorption and degradation of pesticides has been extensivelystudied in recent years, there are only few studies addressing theleaching and toxicity of pesticides in soils amended with biochars orbiochar-like materials. The central hypothesis was that biochar,when added to agricultural soil, might effectively sorb herbicides,and thus modify other sorption-related processes like leaching,degradation and phytotoxicity of herbicides in soil. To test thishypothesis, a series of laboratory experiments were performed tostudy the sorption and other sorption-related processes of MCPA insoil amended by biochar. The specific objectives of this study wereto (i) determine the ability of wheat straw-derived biochar andbiochar-amended soil to sorb widely used herbicide, (4-chloro-2-methylphenoxy)acetic acid (MCPA), (ii) compare desorption, leach-ing and degradation of the herbicide in biochar-amended soil andnon-amended soil, and (iii) evaluate preliminarily the impact ofbiochar and MCPA addition to soil on the growth of sunflower(Helianthus annuus L.).

Soil used in this study was taken from the Zitny ostrov region(southwestern Slovakia), which is an agriculturally managedregion where phenoxy acid herbicides (MCPA and 2,4-D) arecommonly applied and the most often cultivated plants aremaize, sunflower, cereals, sugar beet and oilseed rape. Moreover,the region is well-known for the largest groundwater resources inCentral Europe. The groundwater table is situated shallow and itranges from 0.5 to 4 m from the soil surface. Hence, groundwaterin the region is susceptible to contamination with herbicides andshould be protected against the contamination. To eliminate therisk of groundwater contamination with herbicides, it is impor-tant to study the effects of agricultural activities such as theapplication of soil amendments on environmental fate of theherbicides.

2. Materials and methods

2.1. Chemicals

Analytical grade MCPA was purchased from Sigma-Aldrich GmbH (Germany).

Its solubility in water at 25 1C is 825 mg L�1 and n-octanol/water partition

coefficient at 20 1C and pH 7 (Kow) is 0.155 (FOOTPRINT PPDB, 2006). Sodium

azide and potassium chloride were of analytical grade and all organic solvents

were of HPLC grade and obtained from Merck (Slovakia, Bratislava). Deionized

water was prepared using a lab water purification system (Milli-Q Integral

system).

2.2. Sorbents

An agricultural soil (Calcaric Fluvisol) was collected from a vegetable field

located near the village of Most pri Bratislave in the Zitny ostrov region, Slovakia

(48108065000N, 17114096500E). The soil was sampled from the upper 15 cm, which

represented A soil horizon, passed through a 2-mm sieve for the degradation

experiment and air-dried and passed through a 2-mm sieve for the sorption–

desorption, leaching, and pot experiments. Soil samples were stored at 4 1C before

use for experiments. The physico-chemical and textural properties of the soil are

given in Table 1. Analyses of the soil properties were conducted by common

standard procedures (Jackson, 1958; Nelson and Sommers, 1996).

Table 1Selected physical and chemical properties of the soil samples.

Sample OCa

(%)

pH CECb

(cmol kg�1)

Sand

(%)

Silt

(%)

Clay

(%)

WHCc

(%)

Soil 1.47 7.91 19.3 29.1 60.1 10.8 45.0

Soilþbiochar 1.90 8.55 – – – – 50.0

a Organic carbon content.b Cation exchange capacity.c Water holding capacity.

Biochar was prepared from wheat straw (Triticum aestivum L.) at a tempera-

ture of 300 1C. Wheat straw was air-dried at 35 1C and then used for the

carbonization process. First, the straw was subjected to carbonization in a sand

bath at 200 1C for 24 h, and subsequently the carbonized residue was charred in a

temperature-programmable muffle furnace. The temperature of the furnace was

adjusted to 300 1C and held for 6 h. The specific surface area of the biochar was

measured by the Brunauer, Emmett, and Teller (BET) nitrogen adsorption method

using a MonosorbTM analyzer (Quantachrome, USA). Ash content of biochar

was determined by weight loss after heating to 1050 1C in air for 4 h. For the

measurement of major inorganic elements (Ca, K, Mg, Na and Si) in biochar, the

sample was digested with a mixture of concentrated H2O2 and HNO3 at a volume

ratio of 1:2.5 and the extracts were analyzed by inductively coupled plasma-

atomic emission spectroscopy (ICP-AES). The contents of C, H and N of the biochar

were determined using an elemental analyzer (Vario EL Element Analyzer,

Germany). Biochar-amended soils (1 wt%) were prepared by thoroughly mixing

soil with accurately weighed wheat straw biochar. This level of biochar in soil is

equivalent approximately to 30 t ha�1 biochar (Sohi et al., 2010).

2.3. Sorption and desorption of MCPA

The sorption experiments were conducted by the batch equilibration proce-

dure. The working solutions of MCPA were prepared by dissolving the herbicide in

an aqueous solution made by adding 0.01 M KCl and 1.5�10�3 M NaN3 to Milli-

Qþ water. Potassium chloride and NaN3 were used to keep ionic strength constant

and prevent microbial degradation, respectively. For pre-equilibration, a prede-

termined weight of each sorbent (3 g of soil and biochar-amended soil, and 0.05 g

of biochar) was mixed with 4 mL of 0.01 M KCl and 1.5�10�3 M NaN3 solution in

10 mL glass centrifuge tubes. After the pre-equilibration for 24 h, 1 mL of MCPA

working solution at each concentration was added into the tubes to reach a final

volume of 5 mL with five or six initial herbicide concentrations ranging from 0.5 to

22 mg L�1. The control samples for each herbicide concentration without soil

were also prepared to account for possible losses of MCPA due to adsorption onto

the glass surfaces, volatilization or microbial activity. The suspensions were

shaken for 24 h in the dark at a temperature of 2371 1C. At equilibrium, the

suspensions were centrifugated at 1160g for 15 min and thereafter at 3000g for

10 min to obtain clear supernatants. A preliminary experiment has shown that

24 h was sufficient for the attainment of sorption–desorption equilibrium.

Desorption of MCPA for non-amended and biochar-amended soils was

determined immediately after sorption with an initial MCPA concentration of

18 mg L�1. After the removal of 2.5 mL of the supernatant, the same volume of

fresh background solution containing no herbicide was added and the tube was

agitated for additional 24 h, centrifuged, and sampled as described above. This

desorption procedure was repeated four times. In each desorption step, the

herbicide concentration in solution is the sum of the remaining solution concen-

tration plus the herbicide amount that desorbed from the solid phase back to the

solution.

Equlibrium concentrations of MCPA in the supernatants were analyzed by

high-performance liquid chromatography (HPLC) with a Hewlett-Packard Agilent

1100 chromatograph coupled to a Hewlett-Packard 1046 fluorescence detector

(FD). The chromatographic conditions were: Lichrosphere 100RP-18 column

(4.6�125 mm2, 5 mm), flow rate of 0.75 mL min�1, sample injection volume of

20 mL, eluent system 50:50 (v/v) acetonitrile/diluted H3PO4 mixture and FD set at

232 nm.

2.4. Leaching experiments

Duplicate glass columns (height of 17 cm and 2.5 cm i.d.) were uniformly

packed with 80 g of soil or biochar-amended soil to a height of 14 cm. Filter paper

and 0.5 cm thick layer of acid washed sand was placed at the bottom of the

columns to avoid soil losses and sand was added also at the top of the soil or

biochar-amended soil. After saturation of the soil columns with distilled water,

2 mg MCPA dissolved in 1 mL HPLC-grade methanol were applied to the top of the

columns, giving an initial MCPA concentration of 25 mg kg�1. To simulate the

worst-case scenario of MCPA leaching in soil, the concentration of MCPA was

higher than its concentration, which would be expected in real soil at the

recommended field dose of MCPA. After evaporation of methanol, the columns

were leached with 180 mL of distilled water for 12 h at 2371 1C. Water was

introduced from the top of the columns into the soil (downward flow) using a

peristaltic pump and the flow rate was adjusted to 0.25 mL min�1. The leachates

were collected at 1 h intervals and analyzed for MCPA concentrations by HPLC.

2.5. Dissipation of MCPA

Two weeks before the start of the experiment, a set of 20 g portions of the soil

samples was placed in the dark at 2371 1C and kept at a soil moisture content of

20% by weight, in glass batches covered with perforated aluminum foil. After this

period, each 20 g portion of the soil samples was spiked with MCPA (1 mL of a

200 mg L�1 MCPA aqueous solution) to obtain an initial MCPA concentration of

T. Veronika et al. / Ecotoxicology and Environmental Safety 92 (2013) 215–221 217

�10 mg kg�1 in soil. To reliably show the impact of biochar on the dissipation of

MCPA in soil and to compare the dissipation data for soil with previously

published studies, the concentration of MCPA in soil used in this study was higher

than that based on the recommended field dose of MCPA. The soil moisture was

adjusted to 70% of the maximum water holding capacity by adding appropriate

amounts of water and weighed. The soils were thoroughly mixed and incubated in

the dark at 2371 1C for a period of 70 d. Incubation periods were 0, 7, 16, 24, 48

and 70 d. To maintain the soil water content constant throughout the experiment,

water was added every other day for evaporation loss if necessary. Duplicate

samples were taken at each incubation period to measure the MCPA concentra-

tions remaining in the soil. The soil samples were dried by flowing air and then

extracted with acetonitrile/acetic acid solution (0.5% acetic acid) in a ratio of 50:50

(v/v) using an ultrasonic system for 2 h. After centrifugation at 3000g for 10 min,

an aliquot of the extract was analyzed by HPLC as previously described. The

extraction recoveries were 85.3% and 87.1% for the non-amended soil and biochar-

amended soil, respectively. All results were corrected with the corresponding

recovery rates to provide accurate amounts of MCPA remaining in the soil

samples.

2.6. Bioassays

Eight seeds of sunflower (Helianthus annuus L., cv. Codicap) per pot were sown

in 340 cm3 polypropylene pots filled with 200 g of non-amended and biochar-

amended soils, and incubated in a growth chamber with a 12-h photoperiod, a

temperature of 26/24 1C (day/night), 75% humidity and 300 mmol m�2 s�1 photo-

synthetic active radiation (PAR) for 7 d. Pots were irrigated with 30 mL of distilled

water every third day during the first week of the incubation. After 7 d of

germination, three representative seedlings were left in each pot. The following

four treatments were prepared and each treatment was performed with four

replicates:

(1)

non-amended soil irrigated with distilled water (control, C)

(2)

biochar-amended soil irrigated with distilled water (B)

(3)

non-amended soil irrigated with aqueous solution of MCPA at a concentration

of 18 mg L�1 (H)

(4)

biochar-amended soil irrigated with aqueous solution of MCPA at a concen-

tration of 18 mg L�1 (BH).

The pots with sunflower seedlings were randomly placed in a growth chamber

and cultivated for additional 28 d. Plants were irrigated with either 30 mL of

distilled water or aqueous solution of MCPA every third day. After 28 d of growth,

plants were harvested and the following plant parameters were determined:

above-ground fresh and dry weights of biomass, the length of hypocotyl and total

length of shoot, and contents of photosynthetic pigments (chlorophyll a, b and

carotenoids). Chlorophyll and carotenoids were extracted from second leaf with

80% acetone and their contents were estimated spectrophotometrically according

to the method of Lichtenthaler and Wellburn (1983).

Fig. 1. Sorption isotherms of MCPA by non-amended soil, biochar-amended soil and

biochar. Desorption isotherms of MCPA for non-amended and biochar-amended

soils are also shown. Symbols represent the measured data and lines are the fitted

Freundlich isotherms. Error bars indicate the standard deviation. Equilibrium

concentration (Ce) is given in mg L�1 and amount sorbed (Cs) in mg kg�1.

2.7. Data and statistical analyses

The measured sorption and desorption isotherms of MCPA for all sorbents

used were fitted to the logarithmic form of the Freundlich isotherm:

log Cs ¼ log K fa=dþna=dlog Ce

where Cs (mg kg�1) is the amount of MCPA sorbed, Ce (mg L�1) is the equilibrium

concentration in solution, Kfa and Kfd (mg1–n kg�1 Ln) are the Freundlich adsorp-

tion and desorption constants, respectively, which represent Cs at Ce¼1 mg L�1

and n is the Freundlich exponent indicative of isotherm curvature. The hysteresis

(H), indicating the irreversibility of the sorption process, was calculated as the

ratio between nd and na, corresponding to the Freundlich desorption and adsorp-

tion exponents, respectively (Cox et al., 1997).

The dissipation of MCPA in soil samples was evaluated by fitting the data to

the first-order kinetic equation in the linearized form:

ln C ¼�k1tþ ln C0

where C and C0 (mg kg�1) are the amounts of MCPA in soil at time t and t¼0

(initial amount), respectively, and k1 (d�1) is the first-order rate constant. The

half-life of MCPA in soil (t1/2, d) was calculated as

t1=2 ¼ ln 2=k1

Analysis of variance (ANOVA) followed by Tukey-HSD as posthoc test was

used to determine differences between bioassay treatments. It was tested for

significance with po0.05 unless stated otherwise. Statistical analyses were

performed using GraphPad Prism version 5.00 for Windows (GraphPad Software,

San Diego, California).

3. Results and discussion

3.1. Biochar properties

The biochar was highly alkaline with the pH value of 10.6 andits specific surface area was 4.59 m2 g�1. The biochar contained5.05 wt% ash and the contents of major inorganic elementsdecreased in the order: K (1.02 wt%)4Si (0.72 wt%)4Ca(0.32 wt%)4Mg (0.13 wt%)4Na (0.02 wt%). The content of C, Hand N of the biochar was 51.7 wt%, 5.13 wt% and 0.64 wt%,respectively. The content of O was calculated by mass balanceand equal to 35.3 wt%. The degree of carbonization of biocharscan be estimated by molar H/C ratio because hydrogen is mainlyassociated with plant organic matter (Kuhlbusch, 1995). Thebiochar had a molar H/C ratio of 1.19, suggesting an increasedfraction of original wheat residue in this biochar. The molar O/Cratio of 0.51 for the biochar also indicated that it was relativelyhydrophilic.

3.2. Sorption and desorption of MCPA

Sorption isotherms of MCPA for non-amended soil, biochar-amended soil and biochar are shown in Fig. 1 and were fitted wellto the logarithmic form of the Freundlich equation with R2 valueshigher than 0.96. The Freundlich exponent values for all sorbentswere close to 1 (na¼1.10, 1.06 and 0.95 for non-amended soil,biochar-amended soil and biochar, respectively), indicating con-stant partitioning of MCPA between sorbent and solution for theconcentration range used. Previously, Chun et al. (2004) sug-gested that the relatively linear sorption of organic compounds bybiochars produced at lower temperatures was due to partition-dominant process into the residual noncarbonized organic-matterphase. Differences in sorption of MCPA among sorbents could becompared using the Freundlich constant as the na values wereroughly equal. The Freundlich constant values for non-amendedsoil, biochar-amended soil and biochar were 0.53, 1.34 and43.65 mg1–n kg�1 Ln, respectively. Based on the Kfa values, wheatstraw biochar and biochar-amended soil had 82 and 2.53 timeshigher sorption capacity than the non-amended soil. This result is

Fig. 2. Percentages of MCPA found in leachates from columns filled with non-

amended soil and biochar-amended soil. Error bars indicate the standard

deviation.

T. Veronika et al. / Ecotoxicology and Environmental Safety 92 (2013) 215–221218

in agreement with the findings of Cabrera et al. (2011) whoobserved an increase in sorption of MCPA by soil amended withvarious biochars. This was attributed to higher carbon contents ofbiochars and their greater surface affinities for the herbicidecompared to soil organic matter. Assuming that the inherentsorption capacity of both the soil and biochar would not changeafter their mixing, the net increase of Kfa value for the soil was0.81 due to the presence of 1.0 wt% biochar. Thus, the contribu-tion from biochar to the overall sorption of MCPA by biochar-amended soil was 60%, indicating the predominance of biocharover soil for MCPA sorption. The predominant role of biochars insorption by biochar-amended soils was observed also for otherpesticides such as isoproturon (Sopena et al., 2012), chlorantra-niliprole (Wang et al., 2012) and acetamiprid (Yu et al., 2011).

Soil pH has been shown to influence the sorption of manyionizable pesticides (Dubus et al., 2001; Kah and Brown, 2006;Thorstensen et al., 2001). The sorption of weak acid herbicides insoils like MCPA is lower at neutral to alkaline pH values than itssorption at acidic pH, particularly if pH is below pKa value ofthe herbicide. However, a change in the sorption of this type ofherbicides is generally negligible at soil pH values exceedinghighly their pKa values (Werner et al., 2013). The pH values of theequlibrium sorption systems were between 7.72–7.89, 8.47–8.60,and 10.1–10.6 for non-amended soil, biochar-amended soil, andbiochar, respectively, depending on the MCPA concentration.Although the pH values varied widely among the differentsorption systems, any influence of pH on the sorption of MCPAis likely only marginal as more than 99.9% of the herbicide occursin the deprotonated anionic form in the test systems. Therefore,the observed differences in MCPA sorption were attributed todistinct properties of the sorbents.

Desorption isotherms shown in Fig. 1 fitted adequately to thelogarithmic form of the Freundlich equation. As seen from Fig. 1,desorption isotherms of MCPA for both non-amended andbiochar-amended soils deviated from the corresponding sorptionisotherms. Lower desorption exponent (nd) values of 0.60 and0.49 for non-amended soil and biochar-amended soil, respec-tively, than the respective sorption exponents (na) were indicativeof positive hysteresis with H values of 0.55 for non-amended soiland 0.46 for biochar-amended soil. The calculated H values werelow and thus led to the relatively high percentages of MCPAdesorbed from non-amended soil (64.2%) and biochar-amendedsoil (55.1%). The results showed that addition of biochar to soildecreased the desorption of MCPA, but the decrease was not solarge as it would be expected based on the adsorption capacity ofthe biochar. This might be attributed to a weak binding strengthsbetween MCPA and biochar components. It is difficult to comparethe desorption results obtained in this study with previousstudies as no data exist about the desorption of phenoxy acidherbicides from biochar-amended soils. However, they wereconsistent with studies that documented a decrease in desorptionof other pesticides from soils amended by biochars (Martin et al.,2012; Sopena et al., 2012; Yu et al., 2010).

3.3. Leaching of MCPA

The percentages of the applied MCPA recovered in the leachatesfrom the soil columns are presented in Fig. 2. In the absence ofbiochar, up to 56% of the applied MCPA was leached through thesoil columns, indicating that MCPA may have a high mobilityin soils. The high mobility of MCPA in soils was reported byHaberhauer et al. (2002) and Socıas-Viciana et al. (1999) with70–99% of the applied herbicide collected in the leachates. Theleaching of MCPA in the biochar-amended soil was significantlylower than that in the non-amended soil and decreased to 35% ofthe applied MCPA. The average maximum concentration of MCPA

in the leachate from biochar-amended soil reached 11.1 mg L�1,whereas its maximum concentration in the non-amended soilleachate was almost two times higher (18.3 mg L�1). The lowerleachability of MCPA in the biochar-amended soil than in the non-amended soil agreed well with the higher sorption of MCPAmeasured in the soil amended with biochar. Jones et al. (2011)also demonstrated that the presence of biochar decreased theamount of simazine leached from soil due to strong bindingcapacity of biochar. The leaching column results with MCPAsuggest that biochar can play a role in preventing the leaching ofacid herbicides from soils, and thus contamination of groundwater.

3.4. Dissipation of MCPA

The addition of biochars and biochar-like materials to soilgenerally decreases pesticide dissipation due to lower pesticideavailability to soil microorganisms induced by the increase insorption (Hiller et al., 2009; Spokas et al., 2009; Yang et al., 2006).On the other hand, an increase of pesticide dissipation in biochar-amended soil was also reported and this was attributed to thestimulation of the microbial activity by the nutrients present inbiochar (Qiu et al., 2009). In this study, the dissipation of MCPA inthe non-amended soil was rapid with only 1.32% MCPA of its initialamount remaining after 24 d (Fig. 3) and a half-life value of 5.2 d.Rapid dissipation of MCPA in topsoils under the similar conditionsas used in this study has been observed by other researchers(Paszko, 2009; Thorstensen and Lode, 2001) and attributed to thepresence of several soil bacteria and fungi, which were identified asefficient degraders of MCPA and other phenoxy acid herbicides(Bollag et al., 1967; Castillo et al., 2001; McGhee and Burns, 1995;Reddy et al., 1997). The dissipation of MCPA in the biochar-amended soil was also rapid within the first 7 d (Fig. 3), but afterthis time slowed down and still 5.6% MCPA remained in the 1 wt%biochar soil after 70 d, resulting in a half-life value of 21.5 d. Thus,the results indicated that the rate and extent of MCPA dissipationin biochar-amended soil were decreased compared to the non-amended soil. The mechanism responsible for the lower dissipationof MCPA in biochar-amended soil was most likely due to the strongsorption affinity of biochar (Sopena et al., 2012), which decreased

Fig. 3. Dissipation of MCPA in non-amended and biochar-amended soils. Lines are

the fitted first-order kinetic reactions. Error bars represent the standard deviation.

Remaining amount of MCPA in soil (C) has units in mg kg�1.

Table 2Measured plant parameter values for different treatments.

Parameter Fresh

weight

(g)

Dry

weight

(g)

Plant

height

(cm)

Hypocotyl

height

(cm)

Chlorophylls

(mg kg�1)

Carotenoids

(mg kg�1)

Treatmenta

C 1.27a 0.16a 17.44a 7.73a 2.39a 0.02a

B 1.66b 0.19a 16.96a 7.37a 1.34b 0.01a

H 0.61c 0.07b 8.92b 5.45b 2.54a 0.02a

BH 1.24ab 0.10b 10.68b 6.08b 1.28b 0.01a

Within columns, means followed by the same lowercase letter do not differ

significantly at p¼0.05.a C¼control; B¼biochar-amended soilþwater; H¼soilþherbicide; BH¼

biochar-amended soilþherbicide.

Fig. 4. Photograph of a typical bioassay illustrating the growth of sunflower

(Helianthus annuus L.) in (a) non-amended soil irrigated with distilled water,

(b) biochar-amended soil irrigated with distilled water, (c) non-amended soil

irrigated with MCPA solution, and (d) biochar-amended soil irrigated with MCPA

solution.

T. Veronika et al. / Ecotoxicology and Environmental Safety 92 (2013) 215–221 219

the concentration of MCPA in soil solution, where the herbicide ismore available to soil microorganisms (Jensen et al., 2004).

3.5. Bioassays

In the absence of MCPA application, sunflower showed anormal growth with no observable growth stimulation by theaddition of biochar to soil as there were no significant differencesin above-ground dry weight of biomass as well as hypocotyl andtotal shoot lengths between the control and the biochar-amendedsoil (Table 2 and Fig. 4). The only significant effects of biocharwere observed on the above-ground fresh weights of biomass andthe contents of chlorophylls a and b, which significantly increasedand decreased (po0.01), respectively, in sunflowers grown in thebiochar-amended soil compared to the control. The decrease ofchlorophyll content was also reported for rice grown in biochar-amended soil and attributed to decrease in nitrogen uptake byplants (Asai et al., 2009). Magnesium is an essential element forthe synthesis of chlorophylls, hence, a decrease of plant-availableMg content in biochar-amended soils as observed by Schulz andGlaser (2012) might be another reason for the lower chlorophyllcontent of sunflowers grown in the biochar-amended soil than inthe control. However, more detailed experiments are needed toexplain the observed decrease of chlorophyll content in

sunflower. The higher above-ground fresh plant weight afterbiochar addition to soil (Table 2) is likely due to positive effectof biochar on water holding capacity of the soil as shown in thisstudy (Table 1).

In this study, sunflowers were irrigated using the MCPAsolution at a concentration of 18 mg L�1. When no dissipationof MCPA in soil is assumed, total concentration of MCPA accu-mulated in the soil systems would be about 25 mg kg�1 during28 d experimental period. Preliminary experiments showed thatthe phytotoxic symptoms on sunflowers occurred also at muchlower concentrations of MCPA. However, differences between thecontrol C treatments and the H treatments were less significantand visible at these lower MCPA levels. Sunflowers grown in non-amended soil and irrigated with MCPA solution (H treatment)were significantly affected by the herbicide at po0.01. In general,hypocotyl and total shoot lengths, and both above-ground bio-mass fresh and dry weights were reduced by �50% compared tothe MCPA-free control (Fig. 4); however, the content of photo-synthetic pigments was not affected when soil was treated byMCPA (Table 2). Sunflowers have been shown to be sensitive tophenoxy acid herbicides. For example, Wall (1996) observed thatsublethal dosages of the related phenoxy acid herbicide 2,4-Dreduced severely sunflower yields in field experiments by morethan 90%. Greenshields and Putt (1958) reported that spray driftof 2,4-D resulted in damage to growing sunflowers.

Results of the Tukey-HSD posthoc comparisons showed that theeffect of biochar addition to soil on the toxicity of MCPA to sunflowerswas significant only for one of the measured plant parameters, i.e.above-ground biomass fresh weight. However, this positive effectmight be related to the higher water holding capacity of the biochar-amended soil, and thus to more effective water uptake by sunflowersrather than to the fact that biochar itself reduced MCPA toxicity.Although, the visual observations of sunflowers indicate that sun-flowers grown in biochar-amended and MCPA-treated soil havesomewhat higher height than those grown in MCPA-treated soilwithout biochar (Fig. 4), the differences were not significant atpo0.05 (Table 2). As it is shown in this study, the efficient sorptionof MCPA by biochar can be suitable for a protection against theleaching of the herbicide to groundwaters, which is of concern inagricultural regions where groundwater table is situated close to thesoil surface. On the other hand, a protective role of biochar at a levelof 1.0 wt% in reduction of the phytotoxic effects of MCPA on

T. Veronika et al. / Ecotoxicology and Environmental Safety 92 (2013) 215–221220

sunflowers could not be confirmed. However, desorption as a reverseof sorption is equally important for the phytoavailability of herbi-cides. If desorption of a herbicide is supressed, concentration in thesoil solution is low, and thus herbicide phytoavailability decreases.Our batch desorption data indicated that the relative amount ofMCPA desorbed from biochar-amended soil (55.1%) was lower thanthat from non-amended soil (64.2%). But, when the desorbedconcentrations of MCPA in solution were compared, no significantdifference between the biochar-amended soil and the non-amendedsoil was observed. In addition to this desorption behavior, MCPAdissipated more slowly in biochar-amended soil than in thenon-amended soil (Fig. 3), and likely a greater amount of herbicideresidue remains in pots with the biochar-amended soil. Thismeans that phytoavailable concentration of MCPA in the biochar-amended soil might be even higher than in the non-amended soil.Despite the higher extent of MCPA sorption in biochar-amended soil(Fig. 1), the phytotoxicity of MCPA against sunflower did not decreaseprobably due to offset of the positive effect of sorption through theelevated persistence and desorption of MCPA in the soil amendedwith biochar.

4. Conclusions

This study showed that the presence of wheat straw biochar insoil could increase the sorption of acid organic compounds such asthe MCPA herbicide. Enhanced sorption of MCPA in the biochar-amended soil resulted in a significant decrease of its leachability insoil columns as well as its dissipation in soil. Therefore, wheat strawbiochar may immobilize to some extent the acid herbicides in soils,and thus protect surface and groundwaters from pollution by theseherbicides and their metabolites. On the other hand, biocharaddition to soil had no stimulative effect on the growth of sunflower(Helianthus annuus L.), and even its presence in soil decreasedsignificantly the content of photosynthetic pigments. Moreover,the phytotoxic effects of MCPA on sunflowers remained unchangedwhen soil was amended by wheat straw biochar. This was probablydue to offset of the positive effect of sorption through the elevatedpersistence and desorption of MCPA in the biochar-amended soil.

Acknowledgments

We thank three anonymous reviewers for their constructivecriticism. This study was financially supported by the ScientificGrant Agency of the Ministry of Education of Slovak Republic andthe Academy of Sciences (VEGA no. 1/0492/11). The authors wishto acknowledge Zoltan Krascsenits for providing wheat straw.

References

Alister, C., Rojas, S., Gomez, P., Kogan, M., 2008. Dissipation and movement offlumioxazin in soil at four field sites in Chile. Pest Manag. Sci. 64, 579–583.

Asai, H., Samson, B.K., Stephan, H.M., Songyikhangsuthor, K., Homma, K., Kiyono, Y.,Inoue, Y., Shiraiwa, T., Horie, T., 2009. Biochar amendment techniques forupland rice production in Northern Laos 1. Soil physical properties, leaf SPADand grain yield. Field Crops Res. 111, 81–84.

Bollag, J.-M., Helling, C.S., Alexander, M., 1967. Metabolism of 4-chloro-2-methylphenoxyacetic acid by soil bacteria. Appl. Microbiol. 15, 1393–1398.

Cabrera, A., Cox, L., Spokas, K.A., Celis, R., Hermosın, M.C., Cornejo, J., Koskinen, W.C.,2011. Comparative sorption and leaching study of the herbicides fluometuronand 4-chloro-2-methylphenoxyacetic acid (MCPA) in a soil amended withbiochars and other sorbents. J. Agric. Food Chem. 59, 12550–12560.

Castillo, M.D.P., Andersson, A., Ander, P., Stenstrom, J., Torstensson, L., 2001.Establishment of the white rot fungus Phanerochaete chrysosporium on

unsterile straw in solid substrate fermentation systems intended for degrada-tion of pesticides. World J. Microbiol. Biotechnol. 17, 627–633.

Chun, Y., Sheng, G., Chiou, C.T., Xing, B., 2004. Compositions and sorptive proper-ties of crop residue-derived chars. Environ. Sci. Technol. 38, 4649–4655.

Cox, L., Koskinen, W.C., Yen, P.Y., 1997. Sorption–desorption of imidacloprid andits metabolites in soils. J. Agric. Food Chem. 45, 1468–1472.

Dubus, I.G., Barriuso, E., Calvet, R., 2001. Sorption of weak organic acids in soils:clofencet, 2,4-D and salicylic acid. Chemosphere 45, 767–774.

Dyson, J.S., Beulke, S., Brown, C.D., Lane, M.C.G., 2002. Adsorption and degradationof the weak acid mesotrione in soil and environmental fate implications.J. Environ. Qual. 31, 613–618.

FOOTPRINT PPDB, 2006. Pesticide Properties Database. Available from: http://sitem.herts.ac.uk/aeru/footprint/en/index.htm (accessed 25.11.12).

Graber, E.R., Tsechansky, L., Khanukov, J., Oka, Y., 2011. Sorption, volatilization,and efficacy of the fumigant 1,3-dichloropropene in a biochar-amended soil.Soil Sci. Soc. Am. J. 75, 1365–1373.

Graber, E.R., Tsechansky, L., Gerstl, Z., Lew, B., 2012. High surface area biocharnegatively impacts herbicide efficacy. Plant Soil 353, 95–106.

Greenshields, J.E.R., Putt, E.D., 1958. The effects of 2,4-D spray drift on sunflowers.Can. J. Plant Sci. 38, 234–240.

Haberhauer, G., Temmel, B., Gerzabek, M.H., 2002. Influence of dissolved humicsubstances on the leaching of MCPA in a soil column experiment. Chemo-sphere 46, 495–499.

Hiller, E., Bartal’, M., Milicka, J., Cernansky, S., 2009. Environmental fate of theherbicide MCPA in two soils as affected by the presence of wheat ash. WaterAir Soil Pollut. 197, 395–402.

Hiller, E., Cernansky, S., Zemanova, L., 2010. Sorption, degradation and leaching ofthe phenoxyacid herbicide MCPA in two agricultural soils. Polish J. Environ.Stud. 19, 315–321.

Jackson, M.L., 1958. Soil Chemical Analysis, N.J. Prentice Hall, Inc., Englewood Cliffs.Jeffery, S., Verheijen, F.G.A., van der Velde, M., Bastos, A.C., 2011. A quantitative

review of the effects of biochar application to soils on crop productivity usingmeta-analysis. Agric. Ecosyst. Environ. 144, 175–187.

Jensen, P.H., Hansen, H.C.H.B., Rasmussen, J., Jacobsen, O.S., 2004. Sorption-controlled degradation kinetics of MCPA in soil. Environ. Sci. Technol. 38,6662–6668.

Jones, D.L., Edwards-Jones, G., Murphy, D.V., 2011. Biochar mediated alterations inherbicide breakdown and leaching in soil. Soil Biol. Biochem. 43, 804–813.

Kah, M., Brown, C.D., 2006. Adsorption of ionizable pesticides in soils. Rev. Environ.Contam. Toxicol. 188, 149–217.

Kuhlbusch, T.A.J., 1995. Method for determining black carbon in residues ofvegetation fires. Environ. Sci. Technol. 29, 2695–2702.

Laird, D.A., Fleming, P., Davis, D.D., Horton, R., Wang, B., Karlen, D.L., 2010. Impactof biochar amendments on the quality of a typical Midwestern agriculturalsoil. Geoderma 158, 443–449.

Lichtenthaler, H.K., Wellburn, A.R., 1983. Determinations of total carotenoids andchlorophylls a and b of leaf extracts in different solvents. Biochem. Soc. Trans.11, 591–592.

Martin, S.M., Kookana, R.S., Van Zwieten, L., Krull, E., 2012. Marked changes inherbicide sorption–desorption upon ageing of biochars in soil. J. Hazard.Mater. 231–232, 70–78.

McGhee, I., Burns, R.G., 1995. Biodegradation of 2,4-dichlorophenoxyacetic acid(2,4-D) and 2-methyl-4-chlorophenoxyacetic acid (MCPA) in contaminatedsoil. Appl. Soil Ecol. 2, 143–154.

Nag, S.K., Kookana, R., Smith, L., Krull, E., Macdonald, L.M., Gill, G., 2011. Poorefficacy of herbicides in biochar-amended soils as affected by their chemistryand mode of action. Chemosphere 84, 1572–1577.

Nelson, D.W., Sommers, L.E., 1996. Total carbon, organic carbon and organic matter.In: Sparks, D.L., Bartels, J.M. (Eds.), Methods of Soil Analysis: Part 3 ChemicalMethods, 3rd edition SSSA, Madison, pp. 961–1010. (SSSA book series number 5).

Paszko, T., 2009. Degradation of MCPA in soil horizons of Polish agricultural soils.Polish J. Environ. Stud. 18, 1083–1091.

Qiu, Y., Pang, H., Zhou, Z., Zhang, P., Feng, Y., Sheng, D.G., 2009. Competitivebiodegradation of dichlobenil and atrazine coexisting in soil amended with achar and citrate. Environ. Pollut. 157, 2964–2969.

Reddy, G.V.B., Joshi, D.K., Gold, M.H., 1997. Degradation of chlorophenoxyaceticacids by the lignin-degrading fungus Dichomitus squalens. Microbiology 143,2353–2360.

Schulz, H., Glaser, B., 2012. Effects of biochar compared to organic and inorganicfertilizers on soil quality and plant growth in a greenhouse experiment. J. PlantNutr. Soil Sci. 175, 410–422.

Socıas-Viciana, M.M., Fernandez-Perez, M., Villafranca-Sanchez, M., Gonzales-Pradas, E., Flores-Cespedes, F., 1999. Sorption and leaching of atrazine andMCPA in natural and peat-amended calcareous soils from Spain. J. Agric. FoodChem. 47, 1236–1241.

Sohi, S.P., Krull, E., Lopez-Capel, E., Bol, R., 2010. A review of biochar and its useand function in soil. Adv. Agron. 105, 47–82.

Sopena, F., Semple, K., Sohi, S., Bending, G., 2012. Assessing the chemical andbiological accessibility of the herbicide isoproturon in soil amended withbiochar. Chemosphere 88, 77–83.

Spokas, K.A., Koskinen, W.C., Baker, J.M., Reicosky, D.C., 2009. Impacts of woodchipbiochar additions on greenhouse gas production and sorption/degradation oftwo herbicides in a Minnesota soil. Chemosphere 77, 574–581.

Thorstensen, C.W., Lode, O., 2001. Laboratory degradation studies of bentazone,dichlorprop, MCPA, and propiconazole in Norwegian soils. J. Environ. Qual. 30,947–953.

T. Veronika et al. / Ecotoxicology and Environmental Safety 92 (2013) 215–221 221

Thorstensen, C.W., Lode, O., Eklo, O.M., Christiansen, A., 2001. Sorption ofbentazone, dichlorprop, MCPA, and propiconazole in reference soils fromNorway. J. Environ. Qual. 30, 2046–2052.

Wall, D.A., 1996. Effect of sublethal dosages of 2,4-D on annual broadleaf crops.Can. J. Plant Sci. 76, 179–185.

Wang, T.-T., Cheng, J., Liu, X.-J., Jiang, W., Zhang, C.-L., Yu, X.-Y., 2012. Effect ofbiochar amendment on the bioavailability of pesticide chlorantraniliprole insoil to earthworm. Ecotoxicol. Environ. Saf. 83, 96–101.

Wauchope, R.D., Yeh, S., Linders, J.B.H.J., Kloskowski, R., Tanaka, K., Rubin, B.,Katayama, A., Kordel, W., Gerstl, Z., Lane, M., Unsworth, J.B., 2002. Pesticidesoil sorption parameters: theory, measurement, uses, limitations and relia-bility. Pest. Manag. Sci. 58, 419–445.

Werner, D., Garratt, J.A., Pigott, G., 2013. Sorption of 2,4-D and other phenoxyherbicides to soil, organic matter, and minerals. J. Soils Sediments 13, 129–139.

Woolf, D., Amonette, J.E., Street-Perrott, F.A., Lehmann, J., Joseph, S., 2010.Sustainable biochar to mitigate global climate change. Nat. Commun. 1, 56–65,http://dx.doi.org/10.1038/ncomms1053.

Xu, T., Lou, L., Luo, L., Cao, R., Duan, D., Chen, Y., 2012. Effect of bamboo biochar onpentachlorophenol leachability and bioavailability in agricultural soil. Sci.Total Environ. 414, 727–731.

Yang, Y., Sheng, G., Huang, M., 2006. Bioavailability of diuron in soil containingwheat-straw-derived char. Sci. Total Environ. 354, 170–178.

Yu, X.-Y., Mu, C.-L., Gu, C., Liu, C., Liu, X.-J., 2011. Impact of woodchip biocharamendment on the sorption and dissipation of pesticide acetamiprid in

agricultural soils. Chemosphere 85, 1284–1289.Yu, X.-Y., Pan, L.-G., Ying, G.-G., Kookana, R.S., 2010. Enhanced and irreversible

sorption of pesticide pyrimethanil by soil amended with biochars. J. Environ.

Sci. 22, 615–620.Yu, X.-Y., Ying, G.-G., Kookana, R.S., 2009. Reduced plant uptake of pesticides with

biochar additions to soil. Chemosphere 76, 665–671.