J Soils Sediments (2010) 10:283–289 DOI 10.1007/s11368-009-0111-z
SOILS, SEC 3 • REMEDIATION AND MANAGEMENT OF CONTAMINATED OR DEGRADED LANDS • RESEARCH ARTICLE
Sorption of the herbicide terbuthylazine in two New Zealand forest soils amended with biosolids and biochars Hailong Wang & Kunde Lin & Zhenan Hou & Brian Richardson & Jay Gan
Received: 12 May 2009 / Accepted: 12 June 2009 / Published online: 7 July 2009 # Springer-Verlag 2009
Abstract Background, aim, and scope Terbuthylazine is one of the most commonly used herbicides for vegetation management in forest plantations in New Zealand. Knowledge about the sorption of terbuthylazine on forest soils, especially the influence of coexisting organic amendments, remains obscure. In this study, we evaluated the effects of biosolids and biochars on the sorption of terbuthylazine to forest soils. Materials and methods Two pumice soils, including a forest landing site soil with low soil organic matter content and an organic carbon rich topsoil under standard forest management, were sampled from a 2-year-old replanted pine plantation. The soils were mixed with four organic amendments, including two thermally dried biosolids with one digested and the other undigested, a biochar produced from high temperature pyrolysis (700°C), and a biochar from pyrolysis with a lower temperature (approximately 350°C). A batch equilibration method was used to determine terbuthylazine adsorption-desorption in organic amendment-treated and untreated soils. Adsorption and desorption isotherms were described with the Freundlich equation. Responsible editor: Jianming Xu H. Wang : K. Lin : Z. Hou : J. Gan Department of Environmental Sciences, University of California, Riverside, CA 92521, USA H. Wang (*) : B. Richardson Scion, Private Bag 3020, Rotorua 3046, New Zealand e-mail:
[email protected] Z. Hou College of Agriculture, Shihezi University, Shihezi City 832000 Xinjiang, China
Results and discussion Adsorption and desorption isotherms in the soils with or without organic amendments were well described by the Freundlich model. The undigested or digested biosolids added to the topsoil had a negligible or limited effect on the adsorption to terbuthylazine. The addition of the other amendments to the two soils all enhanced the adsorption. The biochars displayed higher efficiency in improving soils’ adsorption capacity to terbuthylazine than the biosolids. Among the organic amendments evaluated, the biochar obtained from high temperature pyrolysis demonstrated the most significant enhancement on adsorption with an enhancing factor of 63; whereas, the digested biosolids showed the weakest enhancement. Furthermore, terbuthylazine adsorbed by the digested biosolids appeared to be more easily desorbed than that by biochar treatments. Conclusions This work indicates that the addition of organic amendments to forest soils, particularly biochar to a soil with low native organic matter, may enhance soil sorption of terbuthylazine and thus reduce the possibility of the hydrophobic herbicide leaching to groundwater. Keywords Adsorption . Black carbon . Charcoal . Desorption . Organic amendment . Pesticides . Sewage sludge
1 Background, aim, and scope Terbuthylazine is a chloro-s-triazine herbicide that is widely used as a selective herbicide for vegetation management in agricultural and forest production (Gous 2005; Dolaptsoglou et al. 2007). It is one of the most common herbicides used to control weeds in Pinus radiata plantations in New Zealand
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(Gous 2005). Terbuthylazine can be metabolized by soil microorganisms (Abdelhafid et al. 2000; Caracciolo et al. 2005). However, monitoring data in New Zealand have shown the presence of terbuthylazine in groundwater in some regions with intensive agricultural management practice, although the concentrations were very low and drinking of the sampled groundwater would impose little health risk (Close and Flintoft 2004). It is well known that soil organic matter plays an important role in retention and movement of pesticides in soil (Chiou et al. 1979). Addition of organic amendments often changes the pathways of pesticide movement and degradation in soils, depending on the reactivity of the organic amendments and their effect on microbial activity (Alvey and Crowley 1995; Pan et al. 2008). Organic soil amendments, such as manure, biosolids, and other organic residues, are commonly applied as soil amendments to improve soil productivity (Power and Dick 2000; Laturnus et al. 2007; Wang et al. 2008; Domene et al. 2009; Natalda-Luz et al. 2009). For example, application of biosolids in low fertility forest soils has been considered as a preferred option in New Zealand due to the perceived low risk of contaminants entering the human food chain (Magesan and Wang 2003; Su et al. 2007). The addition of organic amendments in soil may result in an increase in pesticide adsorption (Celis et al. 1998; Dolaptsoglou et al. 2007; González et al. 2008), thus decreasing the leaching likelihood of pesticides (Barriuso et al. 1997; Cabrera et al. 2008). Application of biochar (i.e., black carbon derived from pyrolysis of biomass) to soil has recently been considered as to having great potential to sequester carbon and reduce greenhouse gas emission, because biochar is very recalcitrant in the environment (Lehmann 2007). A number of studies have demonstrated that biochar has a high capacity to adsorb pollutants in soils and sediments, especially for organic contaminants (Cornelissen et al. 2005; Hua et al. 2009), and is known as a ‘supersorbent’ (Lohmann 2003; Koelmans et al. 2006; Bornemann et al. 2007). Sorption of organic pollutants onto charcoals has been considered as strong and nonlinear, where adsorption or pore-filling instead of partitioning is the dominant process (Yang and Sheng 2003; Cornelissen and Gustafsson 2005). In some countries (e.g., New Zealand), woody harvesting residues left on the forest floor is one of the most abundant sources of biomass available for bioenergy and biochar production (Hall and Gifford 2008). It is expected that forest soils will receive biochar application in the future. The effect of organic amendments on the retention of terbuthylazine in forest soils is largely unknown. The objective of this study was therefore to investigate the effect of biosolids and biochar on the adsorption and desorption of terbuthylazine in two New Zealand forest soils.
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2 Materials and methods 2.1 Soil, organic amendments, and laboratory chemicals Soil samples were collected in August 2008 from a 2-year-old replanted P. radiata (D. Don) plantation in the Kaingaroa Forest in the Central North Island, New Zealand. The sandy volcanic ash soil belongs to the Pumice group and is classified as Typic Udivitrand in the US soil taxonomy. Allophane is the dominant clay mineral in the pumice soils. The surface layer (0–0.1 m) of soil was taken from a site with standard forest management (topsoil) and a nearby landing site (or skid site) created for log preparation and transporting during harvesting (landing site soil). Generally, at a landing site, the soil is highly compacted, and the topsoil is removed, so that a typical landing site soil has a high bulk density and low organic matter. Selected physicochemical properties of soils used in the current study are shown in Table 1. Soils were air-dried and sieved (2 mm) prior to their use in the following experiments. Four organic amendments were used in this study. They included thermally dried anaerobically digested granule biosolids (DBS), thermally dried undigested granule biosolids (UBS), a biochar (700BC) from high temperature (700°C) pyrolysis of sawdust, and a biochar (350BC) from commercially available charcoal. The temperature of the kiln used to produce the commercial charcoal was estimated at approximately 350°C. P. radiata wood was the feedstock for both biochar samples. To achieve a uniform soil-amendment mixture, all amendments were ground and passed through a 1-mm sieve. For biosolids treatments, soil samples were mixed with appropriate amounts of biosolids to obtain the typical field application rates equivalent to 400 kg N ha−1. The biosolids application rate represents the maximum level of biosolids allowed to be applied to a forest site in every 2 years (NZWWA 2003). Biochar applications were based on 10 t ha−1 biochar or 10 g kg−1. Selected properties of the organic amendments are shown in Table 1. Analytical standard terbuthylazine (N2–tert-butyl-6-chloro4 N –ethyl-1,3,5-triazine-2,4-diamine) with a purity of 98.6% was purchased from Sigma-Aldrich (St. Louis, MO, USA). Stock solution of 1,000 mg L−1 terbuthylazine was prepared in methanol and used for analytical purposes. Calcium chloride (CaCl2) and sodium azide (NaN3) of analytic grade and solvents (acetonitrile and methanol) of high-performance liquid chromatography (HPLC) grade were purchased from Fisher Scientific (Fair Lawn, NJ, USA). 2.2 Adsorption-desorption experiments A batch equilibration method was used to determine terbuthylazine adsorption-desorption (Weber et al. 2000) in organic amendment-treated and untreated soils.
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Table 1 Selected properties of soils (0–0.1 m) and organic amendments Properties
LS
TS
DBS
UBS
700BC
350BC
Organic carbon (%) Total N (%) pH
1.20 0.06 5.8
5.08 0.30 5.1
37.3 6.42 ND
48.2 5.13 ND
89.4 0.17 ND
83.4 0.21 ND
LS landing site soil, TS normal forest topsoil, DBS anaerobically digested biosolids, UBS undigested biosolids, 700BC biochar produced at 700°C, 350BC biochar produced at 350°C, ND not determined
An initial bulk sample of 120 g soil (dry weight) was separately mixed with the appropriate amounts of organic amendments to obtain the recommended field rates. Subsequently, 5-g aliquots of the amended soils were weighed into Teflon centrifuge tubes (40 mL) and mixed with 20 mL of 0.01 M CaCl2 solution nominally containing 0.5, 1, 2, 3, 4, and 5 mg L−1 of terbuthylazine. Approximately 5 mg of NaN3 was added to each centrifuge tube to prevent microbial degradation of terbuthylazine during sample equilibration. Several soilless blanks were prepared in the same way and used as the control. Analysis of terbuthylazine in the soilless control showed no herbicide adsorption on Teflon tubes. Triplicate samples were prepared for each concentration. The samples were shaken for 24 h (Dolaptsoglou et al. 2007) at room temperature (21±1°C) and centrifuged at 10,000 rpm for 10 min, after which, the aqueous supernatant was collected by pipetting to determine terbuthylazine concentrations in the aqueous phase Cw (mg L−1). The remaining soils were subjected to desorption experiments. The adsorbed concentration Cs (mg kg−1) was calculated from the difference of herbicide quantity in the aqueous phase between the soilless controls and the soil samples. The desorption of terbuthylazine from soils was measured following the adsorption experiment by replacing the supernatant with the same amount of terbuthylazine-free 0.01 M CaCl2 solution. The suspensions were shaken for 24 h, centrifuged, and the supernatants were collected to analyze terbuthylazine concentrations in the aqueous phase as described above. All treatments had three replicates. Adsorption and desorption isotherms of terbuthylazine were fitted to the Freundlich model (Cs =Kf Cw1/n), where Kf (L kg−1) and 1/n are the Freundlich coefficient and linearity parameter, respectively. The data were further fitted to a linear relationship to obtain an overall Kd (L kg−1), from which, organic carbon (OC) normalized sorption constant KOC was estimated. Student’s t test was used to test the significance of difference in Kd and KOC values between different treatments. 2.3 Chemical analysis To determine terbuthylazine concentrations in the collected supernatant, aliquot of 1.0 mL was passed through a 0.45-μm
Whatman glass microfiber syringe filter (Whatman, Florham Park, NJ, USA), and the filtrate was used for analysis on HPLC. Terbuthylazine concentration in the final samples was determined using a reverse-phase HPLC (Dionex, Sunnyvale, CA, USA) coupled with a PDA-100 photodiode array detector (Dionex) with absorbance detection at 220 nm. A Dionex Acclaim® 120 C18 column (4.6×250 mm, 5 μm) was employed for the separation. The isocratic mobile phase consisted of 70% acetonitrile and 30% water at a flow rate of 1.0 mL min−1. The injection volume was fixed at 25 μL. Under these conditions, the typical retention time for terbuthylazine in the HPLC system was 6.05 min. The quantification linear range for terbuthylazine was 0.01 to 2.0 mg L−1.
3 Results and discussion 3.1 Effect of organic amendments on adsorption Adsorption isotherms of terbuthylazine in the soils with or without amendments were evaluated via the Freundlich model and a linear model. Overall, adsorption of terbuthylazine in the soils with or without amendments was consistently well described by the Freundlich model, with R2 ≥0.99 (Fig. 1). Except for the adsorption in the landing site soil amended with the 350BC (1/n=0.68), adsorption isotherms for the other treatments were apparently linear within the tested concentrations (Table 2), suggesting that the adsorption isotherms of terbuthylazine in this study were close to C-type (1/n values close to 1), according to Gilles et al. (1960). Similarly, adsorption isotherms of terbuthylazine in soils with or without other organic amendments such as corn straw, poultry compost, urban sewage sludge (Dolaptsoglou et al. 2007), and olive cake (Delgado-Moreno et al. 2007) were all well described by the linear model. Therefore, Kd was selected as a more desirable index to compare the adsorption of terbuthylazine in the different treatments. The addition of organic amendments in the landing site soil consistently enhanced the adsorption of terbuthylazine. The Kd values were increased from 1.80 L kg−1 for the non-amended soil to 2.56, 3.22, 115.6, and 6.69 L kg−1 for the DBS, UBS, 700BC, and 350BC treatments, respectively (see Table 2), suggesting that the organic amendment treatments improved the soil’s ability to adsorb terbuthylazine. Although the Kd values increased with OC content in the treated soils, the increments were apparently not proportional to total OC content, likely due to the different properties of the amended OC. Generally, the biochar treatments (700BC and 350BC) displayed a stronger enhancement on terbuthylazine adsorption than the biosolids treatments. While both biosolids treatments
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J Soils Sediments (2010) 10:283–289 18
Adsorption Desorption
12
AA
BB
12
6 0
18
6
0 0.5 1.0 1.5 2.0 2.5 3.0
18
0
0
0.5
Terbuthylazine concentration in soil, mg kg-1
CC
DD
12
12
6
6
0
0
18
0.5
1.0 1.5 2.0 2.5 3.0 EE
0
12
6
6
0
18
0.5 1.0 1.5 2.0 2.5 3.0 GG
0
12
6
6
0
0.5 1.0 1.5 2.0 2.5 3.0
18 I
I
0
12
6
6
1.0 1.5 2.0 2.5 3.0 FF
0
0.5 1.0 1.5 2.0 2.5 3.0 HH
Kd;amendedsoil ¼ famendment Kd;amendment þ ð1 famendment Þ Kd;soil 0
JJ
0 0
0.5 1.0 1.5 2.0 2.5 3.0
0
ð1Þ
0.5 1.0 1.5 2.0 2.5 3.0
18
12
0
0.5
18
12
0
0
18
12
0
1.0 1.5 2.0 2.5 3.0
18
the adsorption of terbuthylazine in the topsoil (see Table 2) that contained much higher OC content (see Table 1). The biochar treatments had significantly (P350BC>DBS≈ UBS. Compared with the low Kd value (1.8 L kg−1) of the control treatment, the high Kd value (115.6 L kg−1) of terbuthylazine in the landing site soil treated with the 700BC had an exceedingly high capacity to adsorb terbuthylazine. Without considering interactions with soil, 1% of the biochar in this soil would have contributed to 113.8 L kg−1 of the adsorption. Interestingly, the Kd value for the topsoil treated with the same biochar had Kd only about half of the value in the same treatment of the landing site soil, indicating a strong interference from the topsoil. This may have been caused by the attenuation of terbuthylazine adsorption to biochar by soil-derived dissolved organic matter that blocks the pores (Cornelissen and Gustafsson 2004) or by surface competition
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effects by co-adsorbing dissolved organic matter molecules to the biochar (Koelmans et al. 2006).
5 Conclusions The addition of biosolids and biochar to the soils increased soil OC content, resulting in higher adsorption and reduced potential for leaching loss of terbuthylazine commonly applied to forest soils during vegetation management. The effectiveness of the amendments to increase soil adsorption of terbuthylazine was in the following order: biochar from high temperature pyrolysis (700BC)>biochar from low temperature pyrolysis (350BC)>UBS≈DBS. Effect of the 700BC and DBS on the soils’ sorption capacity was significantly influenced by the endogenous soil OC; whereas, that of the 350BC and UBS was not affected by the native soil OC. Terbuthylazine adsorbed by undigested biosolids appeared to be more readily desorbed than that adsorbed by other organic amendment treatments, particularly the biochar treatments. Organic amendments had greater effect on improving the ability to adsorb terbuthylazine in the landing site soil with relatively low OC content than that in the topsoil with high OC content. The presence of higher concentration of dissolved OC in the topsoil may have reduced the available sorption sites of biochar for terbuthylazine adsorption. In conclusion, application of organic amendments, especially biochar, to soil can increase herbicide terbuthylazine sorption thus may reduce the potential for leaching loss. Acknowledgements The senior author wishes to thank Dr. J. Gan for hosting his sabbatical leave at the University of California, Riverside, which was supported by the Scion Sabbatical Fellowship, the America/New Zealand Soil Science Professional Exchange Award, and New Zealand Foundation for Research, Science, and Technology.
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