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Biodegradation of 2,4-dichlorophenol in the presence of volatile organic compounds in soils under different vegetation types

Angela H. Rhodes, Susan M. Owen, Kirk T. Semple
DOI: http://dx.doi.org/10.1111/j.1574-6968.2007.00657.x 323-330 First published online: 1 April 2007


It has been suggested that monoterpenes emitted within the soil profile, either by roots or by decaying biomass, may enhance the biodegradation of organic pollutants. The aim of this study was to evaluate the effect of biogenic volatile organic compounds (VOCs) on the catabolism of 2,4-dichlorophenol in soils. Soils were collected from areas surrounding monoterpene (woodland) and nonmonoterpene (grassland)-emitting vegetation types. Soils were spiked with [UL-14C] 2,4-dichlorophenol at 10 mg kg−1 and amended with α-pinene, p-cymene or a mix of monoterpenes (α-pinene, limonene and p-cymene in 1 : 1 : 1 ratio). The effects of monoterpene addition on the catabolism of [UL-14C] 2,4-dichlorophenol to 14CO2 by indigenous soil microbial communities were assessed in freshly spiked and 4-week-aged soils. It was found that aged woodland soils exhibited a higher level of [UL-14C] 2,4-dichlorophenol degradation, which was subsequently enhanced by the addition of monoterpenes (P<0.001), with the VOC mix and α-pinene amendments showing increased [UL-14C] 2,4-dichlorophenol catabolism. This study supports claims that the addition of biogenic VOCs to soils enhances the degradation of xenobiotic contaminants.

  • volatile organic compounds
  • monoterpenes
  • 2,4-dichlorophenol
  • biodegradation


Plants have the metabolic potential to produce a large variety of volatile organic compounds (VOCs), of which isoprene (C5H8) and the monoterpenes (C10H16) are most frequently studied due to their atmospheric reactivities and their large contribution to total global hydrocarbon emissions (Hewitt et al., 1995; Fall, 1999). Biogenic VOCs have a significant impact on photochemical processes that lead to the formation of O3 and other photooxidants in the planetary boundary layer (Hewitt et al., 1995). Consequently, most research relates to the source strength and control of VOC emissions from plant foliage, with only limited attention given to the study of emissions from soil components and processes.

Soil microorganisms have the ability to utilize VOCs as their sole carbon and energy source (Cleveland & Yavitt, 1998). It has been suggested that the emission and consumption of VOCs within the rhizosphere form a significant part of the carbon cycle (Misra et al., 1996; Misra & Pavlostathis, 1997). There is speculation that VOCs emitted within soil either by roots or by decaying biomass may enhance the biodegradation of persistent organic pollutants through cometabolism (Hernandez et al., 1996, 1997; Gilbert & Crowley, 1997; Tandlich et al., 2001). Monoterpenes are considered as likely analogues for the cometabolism of polychlorinated biphenyls (PCBs) due to a similarity between the conjugated double-bond structure of the cyclic 6-carbon ring and the 2,3 site at which di-oxygenation occurs with biphenyl (Hernandez et al., 1997). Several studies have demonstrated the role of monoterpene compounds in the induction or enhancement of PCB biodegradation (Gilbert & Crowley, 1997; Hernandez et al., 1997; Tandlich et al., 2001).

2,4-Dichlorophenoxyacetate, a systemic herbicide, is directly applied to various vegetation types, including cereals, maize, orchards, forests and noncropland, for post emergence control of annual and perennial broad-leaved weeds (Tomlin, 1997). 2,4-Dichlorophenol is the main catabolic metabolite of 2,4-dichlorophenoxyacetate in aerated soil and may be detected in sites of 2,4-dichlorophenoxyacetate use (Tomlin, 1997). It is also a precursor in the manufacture of antiseptics, disinfectants and wood preservatives. 2,4-Dichlorophenol is considered representative of common soil and water contaminants (Tomlin, 1997; Xing & Pignatello, 1998) and is known to undergo ‘ageing’ within soil, characterized by reduced bioavailability due to sequestration processes (Shaw et al., 2000).

2,4-Dichlorophenol is structurally analogous to phenolic plant derivatives suggesting the possibility of enhanced degradation in the presence of similar compounds, e.g. VOCs. The identification of biogenic VOCs that enhance microbial degradation of organic contaminants, such as 2,4-dichlorophenol, may expedite an advancement of plant-derived approaches for the bioremediation of contaminated soils. The aim of this study was to evaluate the effect of monoterpene amendments on the biodegradation of 2,4-dichlorophenol in freshly spiked and aged soil. It was hypothesized that α-pinene, p-cymene and limonene would enhance both the rates and total extents of 2,4-dichlorophenol degraded. Limonene, α-pinene and p-cymene were selected as they have previously been observed in emission samples from natural rhizosphere sources (Hayward et al., 2001; Boucard, 2004).

Materials and methods


Unlabelled and [UL-14C] 2,4-dichlorophenol standards were obtained from Sigma Aldrich, UK. Chemicals for the minimal basal salts solution were supplied by BDH Laboratory Supplies and Fisher chemicals. The liquid scintillation cocktails (Ultima Gold and Ulitma Gold XR) were purchased from Canbera Packard, UK. Sodium hydroxide used for the CO2 traps were obtained from Sigma Aldrich, UK. Limonene, (+)-α-pinene and p-cymene were obtained from Fisher Scientific, UK.

Soil sampling and preparation

Soil samples were collected from three sites on Lancaster University campus, Lancaster, UK. The sampling sites were located in close proximity to pine trees (Pinus sylvestris), oak trees (Quercus robur) or mixed turf grass. Each site was free from herbicide spraying. The foliage of P. sylvestris emits monoterpenes (Holzke et al., 2006), Q. robur emits mainly isoprene(Schnitzler et al., 2002) and possibly monoterpenes, whereas grasses are generally nonemitters of these compounds (Guenther et al., 1995). Soil samples were passed through a 2 mm sieve and stored at 4oC before experimental work.

Soils were then spiked with nonlabelled 2,4-dichlorophenol (10 mg kg−1) at field moisture content using acetone as the carrier solvent. Soils were also amended with or without 100 µg kg−1 VOCs, based on levels of monoterpenes found in soils within a Sitka spruce forest (Hayward et al., 2001), as an α-pinene, p-cymene and limonene mix (volumetric ratio 1 : 1 : 1) or individually. The soils, 2,4-dichlorophenol and VOCs were blended using a stainless steel spoon to give a homogenous distribution (Doick et al., 2003), stored in amber glass jars and aged for 4 weeks in darkness at room temperature.

Soil properties

Soil moisture content was measured by weighing field wet soil (3 g) into crucibles. The soil samples were then dried at 105°C for 24 h and reweighed to estimate the moisture content (%) (Table 1). Measurements of pH were made on soil suspensions prepared using air-dry soil (10 g) and de-ionized water (25 mL), with and without the addition of 2 mL 0.125 M calcium chloride (CaCl2) solution, using a Meterlab PHM220 pH meter (Table 1). An adaptation of the method described by Nieuwenhuize (1994) for the determination of organic and inorganic carbon and nitrogen was used. Soil samples were oven dried at 105°C over night. Samples were then sieved to a size range of 2 mm and 1 g mixed with 0.5 mL of 25% HCl; further 0.5 mL aliquots of HCl were added repeatedly until samples no longer effervesced. The soil samples were then oven dried at a temperature gradient of 50–120°C for c. 3 h. A further 0.5 mL of HCl was added to ensure complete removal of all inorganic constituents. The samples were oven dried again for c. 2 h at 120°C to remove all traces of excess HCl. Samples were homogenized and weighed to determine weight gain/loss during acidification. A Carlo Erba CHNS-OEA 1108 CN–Elemental Analyser was used to determine total carbon and nitrogen content in soil (4 mg). Acidified samples were used to determine the organic carbon and nitrogen content and nonacidified samples were used to measure the total carbon content, from which inorganic carbon content was obtained by difference (Nieuwenhuize et al., 1994) (Table 1). For the measurement of potassium and phosphate content, air-dried soil (1 g) was weighed into 50 mL Erlenmeyer conical flasks to which 10 mL of concentrated HNO3 was added. The flasks were gently heated on a hot plate over a period of 36 h to allow the oxidation of organic matter. The samples were cooled and then filtered through Whatman No. 54 hardened filter paper into 25 mL volumetric flasks. The filtrate volume was made up to 25 mL with deionized water and stored in plastic vials. Potassium was analysed directly using a Sherwood 410 Flame Photometer. For phosphate, aliquots of each filtered sample (2 mL) were mixed with 4 mL of a solution containing ascorbic acid (2.69 g) and phosphate-reducing agent (20 mL) in 25 mL volumetric flasks, which were then made up to volume with de-ionized water. The flasks were mixed thoroughly and allowed to stand for c. 30 min until a permanent blue colour developed. The absorbance of each solution was measured using a Cecil Ce 1011 UV spectrometer set at 882 nm (Table 1).

View this table:
Table 1

The major chemical and physical properties of each soil (mean ± SEM)

Soil typeMoisture content (%)Inorganic carbon (%)Organic carbon (%)Inorganic nitrogen (%)Organic nitrogen (%)PO4 (µgg−1)K (µgg−1)pHpH with CaCl2ΔpH
Pine68.43 ± 0.2311.71 ± 0.4812.53 ± 0.660.61 ± 0.020.64 ± 0.030.471 ± 0.0042.57 ± 2.503.94 ± 0.0192.77 ± 0.0311.16 ± 0.018
Oak54.65 ± 0.4815.16 ± 1.3711.05 ± 0.760.71 ± 0.050.49 ± 0.040.573 ± 0.0038.59 ± 3.395.36 ± 0.0094.64 ± 0.0060.72 ± 0.015
Grass43.14 ± 0.313.09 ± 0.152.75 ± 0.040.28 ± 0.010.26 ± 0.010.436 ± 0.0229.74 ± 1.084.28 ± 0.0093.26 ± 0.0101.02 ± 0.019

Catabolism of [UL-14C] 2,4-dichlorophenol in soil

To determine the catabolic degradation of [UL-14C] 2,4-dichlorophenol in freshly spiked and 4-week-aged soils, soil samples (10 g) were mixed with 30 mL minimal basal salt (MBS) solution, in 250 mL screw-cap Erlenmeyer flasks (respirometers), to form a slurry (Reid et al., 2001). A solution of 2,4-dichlorophenol and [UL-14C] 2,4-dichlorophenol (80 Bq radiolabelled 2,4-dichlorophenol per gram of soil), using acetone as a carrier solvent, was added equivalent to a concentration of 10 mg kg−1. The flasks were then amended with or without (control) VOCs, which were added as a mix of α-pinene, limonene and p-cymene in a 1 : 1 : 1 ratio, or α-pinene and p-cymene individually both to a concentration of 100 µg kg−1 soil dry weight. A 7 mL glass vial containing 1 M NaOH solution (1 mL) was suspended from the lid of each respirometer to trap the 14CO2 that was emitted from the soil slurry as a result of [UL-14C] 2,4-dichlorophenol catabolism.

The respirometers were placed in a SANYO® Gallenkamp orbital incubator set at 100 r.p.m. and 25°C, to agitate and ensure adequate mixing of the slurry over a period of 14 days. NaOH traps were replaced at regular intervals. To each spent trap, 6 mL of Ultima Gold scintillation fluid was added and the contents analysed using a Packard Canberra Tri-Carb 2250CA liquid scintillation counter. An analytical blank containing no [UL-14C] 2,4-dichlorophenol determined levels of background radioactivity and a sterile blank, achieved by autoclaving the soil three times (before spiking), allowed the estimation of 2,4-dichlorophenol loss through volatilization.

Statistical analysis

The data were analysed using sigma stat® version 2.03 and sigma plot® 2000 software packages. The significance of [UL-14C] 2,4-dichlorophenol degradation between treatments and soil types were assessed by implementing two and three way anova and Tukey's test.


Catabolism of 14C-2,4-dichlorophenol in soil

The catabolism of [UL-14C] 2,4-dichlorophenol in each of the soil types, freshly spiked and aged for 4 weeks, with and without the addition of VOCs is displayed in Fig. 1. Maximum rates, total extents and lag times of [UL-14C] 2,4-dichlorophenol catabolism are presented in Table 2.

Figure 1

Degradation (%) of 10 mg kg−1 2,4-dichlorophenol by indigenous soil microbial communities in freshly spiked pine (a), oak (c) and grassland (e) soil and in 4 week aged pine (b), oak (d) and grassland (f) soil amended with a VOC mix of α-pinene, p-cymene and limonene (ratio 1 : 1 : 1) (•); α-pinene (o); p-cymene (▪) or with no VOCs (control) (□). A sterile control is also shown (▾) for the freshly spiked soil. Error bars are the SEM of three replicates.

View this table:
Table 2

Degradation rates, total extents and lag times (mean ± SEM) for [UL-14C] 2,4-DCP degradation in freshly spiked and 4-week aged pine, oak and grassland soils amended with a VOC mix of α-pinene, p-cymene and limonene (ratio 1 : 1 : 1), α-pinene, p-cymene or no VOCs (control)

Sterile controlNo VOCVOC mixα-pinenep-cymene
Freshly-spiked soil
Pine soil
Fastest degradation rate (% h−1)0.14 ± 0.021.72 ± 0.642.47 ± 0.412.08 ± 0.391.51 ± 0.98
Total degraded (%)1.20 ± 0.0912.82 ± 1.3914.15 ± 1.0413.13 ± 0.8812.74 ± 2.16
Lag Time (days)N/A6.605.826.014.85
Oak soil
Fastest degradation rate (% h−1)0.11 ± 0.041.63 ± 0.181.31 ± 0.051.36 ± 0.131.72 ± 0.33
Total degraded (%)1.27 ± 0.3011.47 ± 1.5210.25 ± 0.819.52 ± 0.5011.57 ± 0.97
Lag Time (days)N/A5.195.895.775.40
Grassland soil
Fastest degradation rate (% h−1)0.40 ± 0.052.78 ± 0.472.36 ± 0.202.63 ± 0.363.09 ± 0.25
Total degraded (%)3.67 ± 0.4311.47 ± 1.5212.77 ± 0.8111.87 ± 0.8313.60 ± 0.78
Lag Time (days)N/A2.
Aged soil
Pine soil
Fastest degradation rate (% h−1)N/A15.03 ± 0.7717.63 ± 1.6516.51 ± 1.2114.18 ± 2.42
Total degraded (%)N/A27.21 ± 0.6334.43 ± 3.0527.25 ± 1.4326.65 ± 2.24
Lag Time (days)N/A0.3330.2840.3030.353
Oak soil
Fastest degradation rate (% h−1)N/A8.99 ± 2.0214.16 ± 1.2419.61 ± 1.418.27 ± 0.41
Total degraded (%)N/A16.87 ± 1.8626.79 ± 0.8329.34 ± 1.3519.58 ± 1.14
Lag Time (days)N/A0.5560.3530.2550.605
Grassland soil
Fastest degradation rate (% h−1)N/A8.02 ± 1.579.52 ± 0.299.72 ± 0.514.42 ± 0.93
Total degraded (%)N/A16.97 ± 1.8618.87 ± 0.3919.66 ± 1.5513.58 ± 1.17
Lag Time (days)N/A0.6230.5250.5140.368

Degradation curves for [UL-14C] 2,4-dichlorophenol in freshly spiked soils are shown in Fig. 1a, c and e. After 14 days of incubation, c. 10–15% of the added [UL-14C] 2,4-dichlorophenol had been recovered as 14CO2; significant differences were observed in total [UL-14C] 2,4-dichlorophenol degraded among soil types, but not treatments. The total extent of [UL-14C] 2,4-dichlorophenol degradation in the pine soil was significantly greater than that in oak and grassland soils (P<0.001). Less than 4% of the [UL-14C] 2,4-dichlorophenol added was degraded in the sterile control soils after 14 days (Fig. 1), suggesting that biological degradation accounted for the observed 2,4-dichlorophenol loss in nonsterile soils.

Differing maximum rates, total extents and lag times for [UL-14C] 2,4-dichlorophenol catabolism were observed in each of the freshly spiked soils (Table 2). Maximum degradation rates were significantly greater in pine (P=0.026) and grassland (P<0.001) soils, compared with that found in the oak soil. Although no significant differences were observed between treatments, maximum degradation rates were highest for the p-cymene treatment and lowest for the VOC mix treatment in both grass (p-cymene 3.09% h−1; VOC mix 2.36% h−1) and oak (p-cymene 1.72% h−1; VOC mix 1.31% h−1) soils. However, both maximum degradation rate and total extent in the pine soil were highest for the VOC mix treatment (2.47% h−1; 14.15%). The lag times before significant degradation (>5% of 14CO2 evolution) occurred, ranged between 2 and 6 days, with shortest lag times observed for grassland soil.

Degradation curves for [UL-14C] 2,4-dichlorophenol in the aged pine, oak and grassland soils are presented in Fig. 1b, d and f. A direct comparison between aged and freshly spiked soils revealed significant differences for all three soil types in both the total extent degraded and maximum degradation rates (P<0.001). Enhanced rates and total extents of [UL-14C] 2,4-dichlorophenol degradation in the aged soils coincided with significantly reduced lag times (P<0.001); lag times were less than 1 day for each of the aged soils (Table 2). The total [UL-14C] 2,4-dichlorophenol degraded in both the aged pine and oak soils was significantly more (P<0.01) than that in the grassland soil; degradation in the grassland soil was consistently less than 20% for all treatments. Maximum degradation rates were also significantly greater in pine (P<0.001) and oak (P=0.009), when compared with the grassland soil. For each of the aged soils, degradation increased rapidly during the first 24 h before reaching a maximum rate, and subsequently declined exponentially until termination of the experiment.

In the aged pine soil, maximum rates and total extents of degradation were highest for the VOC mix (17.63% h−1; 34.43%) treatment and lowest for the p-cymene (14.18% h−1; 26.65%) treatment, respectively (Table 2); however, no significant differences were observed between treatments. In the aged oak soil, the VOC mix and α-pinene treatments resulted in significantly greater degradation of [UL-14C] 2,4-dichlorophenol (Fig. 1). The total [UL-14C] 2,4-dichlorophenol degraded was significantly higher for the α-pinene treatment when compared to p-cymene (P<0.05) and control treatments (P<0.05). Significant differences were also observed between the VOC mix and both p-cymene (P<0.05) and control (P<0.05) treatments. The maximum rates of degradation were also significantly higher (P<0.01) for the α-pinene treatment (19.61% h−1) than for p-cymene (8.27% h−1) and control (16.87%) treatments. In the aged grassland soil, no significant differences were found in total [UL-14C] 2,4-dichlorophenol degraded between treatments, however, maximum rates of degradation were significantly higher for α-pinene (9.72% h−1) and VOC mix (9.52% h−1) treatments when compared with the p-cymene (4.42% h−1) treatment.


Roots of pine species contain high concentrations of monoterpenes, and high monoterpene concentrations have been found in rhizosphere soil of P. sylvestris (Hayward et al., 2001). Several studies have illustrated the effects of biogenic VOCs toward enhancing the biodegradation of organic contaminants in soils, namely PCBs. In this study, the presence of VOCs did not statistically alter 2,4-dichlorophenol degradation over 14 days in freshly spiked soils. However, significant differences between each soil type were apparent, as total extents of [UL-14C] 2,4-dichlorophenol degradation in the pine soil were statistically greater than those in the oak or grassland soils. In addition, the aged oak soil exhibited significantly higher levels of degradation when treated with a mix of VOCs, and α-pinene individually, suggesting that VOCs enhanced [UL-14C] 2,4-dichlorophenol degradation in these 4-week-aged soils. The precise mechanism for this enhancement remains unclear, but it is clear that biodegradation is stimulated by the presence of VOCs.

The indigenous catabolic activity of the soils was measured with the addition of 10 mg kg−1 2,4-dichlorophenol (80 Bq radiolabelled 2,4-dichlorophenol g−1 soil). After a lag phase of between 2 and 6 days, degradation occurred with c. 9–14%14CO2 evolved over 14 days. In a previous study, Shaw (2000) reported an increased soil catabolic potential, with 25% 2,4-dichlorophenol released as 14CO2 after 21 days (total concentration 20 mg kg−1). However, in the present study the total amount degraded was determined after only 14 days incubation using a lower concentration of 2,4-dichlorophenol added (10 mg kg−1).

Several authors have stated that increasing soil-contaminant contact time (‘ageing’) allows the adaptation of microbial communities to degrade specific contaminants (Spain et al., 1980; Spain & VanVeld, 1983; Misra et al., 1996; Carmichael & Pfaender, 1997; Hwang & Cutright, 2002; Macleod & Semple, 2002; Reid et al., 2002; Lee et al., 2003). For example, Macleod & Semple (2002) and Reid (2002) reported increased catabolic behaviour in soils towards pyrene and phenanthrene, respectively, with increased soil-PAH contact time. In this study, [UL-14C] 2,4-dichlorophenol degradation was significantly greater in 4-week aged soils; degradation began without an acclimation period and plateaued after c. 5 days, although this varied between treatments. For example, biodegradation in woodland soils amended with α-pinene appeared to reach a plateau before that of soils amended with other VOC amendments. Such results are consistent with a study conducted by Hwang & Cutright (2002) in which it was found that total biodegradable extents of pyrene and phenanthrene were greater in aged soils than in freshly spiked soils. These findings are also in general agreement with Lee (2003) who observed the evolution of catabolic potential in an uncontaminated pasture soil towards phenanthrene (with and without the addition of transformer oil), resulting in reduced lag phases to degradation and increased overall extents of degradation following <180 days soil-oil-contaminant contact time.

Acclimation of microbial communities to utilize organic contaminants is thought to occur through: (1) the induction of specific enzymes involved in biodegradation of the contaminant, (2) an increase in the number of degrading organisms with the desired metabolic capabilities, or (3) enhanced metabolic capabilities through genetic changes (Spain et al., 1980; Spain & VanVeld, 1983; Jensen, 1997; Macleod & Semple, 2002). Although it is not possible to determine the exact processes leading to enhanced 2,4-dichlorophenol degradation, it is assumed that prior exposure allowed the indigenous microbial community to adapt, and develop tolerance, to both 2,4-dichlorophenol and the monoterpenes within soils.

The lengths of lag times are often used to express the degree of adaptation to degradation of organic contaminants (Macleod & Semple, 2002; Reid et al., 2002; Lee et al., 2003). It has previously been suggested that microbial adaptation leads to a reduction in the lag phase and consequently faster rates of degradation (Gonod et al., 2003). In each of the aged soils, the lag phase before degradation was negligible (<1 day). These results comply with several other studies, where microbial adaptation has been observed in soils previously exposed to the target compound. Spain (1980) used degradation of 14C-radiolabelled substrates in pre-exposed and control cores to detect the adaptation of microbial communities. In a later study, Spain & VanVeld (1983) found that degradation of 2,4-dichlorophenoxyacetate and p-nitrophenol was much slower in control cores, with a lag period of several days. Similarly, Macleod & Semple (2002) assessed the development of pyrene catabolic activity in two different soils and observed the effects of increasing soil-contaminant contact time on the degradation of 14C-pyrene. It was concluded that adaptation not only leads to reduced lag times and faster rates of degradation but also increased the proportion degraded to 14CO2. The results of this study are in agreement with such findings where total extents of 2,4-dichlorophenol degraded significantly increased by 5–20% in each of the soils. On this basis, it is thought that microbial populations within the 4-week-aged soils adapted to the presence of 2,4-dichlorophenol, as indicated by the absence of a lag phase.

The pH values for all soil types were relatively low, possibly having profound effects on [UL-14C] 2,4-dichlorophenol degradation by the indigenous soil microbial communities. The pH of an environment may affect biodegradation indirectly through influences on the dissociation and solubility of many molecules (Jensen, 1997). According to Jensen (1997), chlorophenols, especially those with few chlorine atoms, are generally considered immobile in acidic soils with high amounts of organic matter. Furthermore, evidence suggests that strong sorption of 2,4-dichlorophenol to organic matter constituents may be linked to species dissociation (Boucard, 2004). In a study by Boucard (2004), nondissociated species were shown to account for a high percentage of the 2,4-dichlorophenol molecules within one particular soil. It is known that sorption of chlorophenols occurs predominantly through partitioning of the nondissociated species into SOM, which subsequently enhances the sequestration process. This suggests a possible explanation for the overall low level of 2,4-dichlorophenol degradation observed in both freshly spiked and aged soils. Furthermore, the woodland soils were found to contain significantly larger quantities of organic/inorganic carbon and nitrogen and other nutrients (phosphate and potassium). Organic carbon has the potential to accelerate biodegradation through a general stimulation of microbial biomass (Kogel-Knabner, 2002), or slow biodegradation by promoting sorption, which causes subsequent reductions in bioavailability (Benoit et al., 1996; Macleod & Semple, 2000, 2002; Shaw et al., 2000). In this study, the pine soil exhibited significantly greater extents of mineralization compared with grassland and oak soils, although it contained the highest quantity of both organic carbon and nitrogen. This suggests that the indigenous microbial population were perhaps stimulated by the presence of organic carbon (Kogel-Knabner, 2002).


In this study, the effects of biogenic VOCs (monoterpenes) on the catabolism of 2,4-dichlorophenol in soils were investigated. Our results show that degradation of 2,4-dichlorophenol by indigenous microorganisms is greater in those soils amended and ‘aged’ with monoterpenes, (α-pinene, limonene and p-cymene) than in freshly spiked or control soils. These data suggest that prior exposure of soils to 2,4-dichlorophenol and monoterpenes, by increased soil-contaminant contact time, further enhances indigenous microbial degradation of the chlorophenol. It is therefore possible that the remediation of contaminated soils may be promoted by stimulating indigenous microorganisms either through planting monoterpene-emitting vegetation, particularly pine species, or through direct application of natural substances with high monoterpene content, for example pine needle litter or citrus waste.


  • Editor: J.C. Murrell


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