A comparison of POPs bioaccumulation in Eisenia fetida in natural and artificial soils and the effects of aging

The close relationship between soil organic matter and the bioavailability of POPs in soils suggests the possibility of using it for the extrapolation between different soils. The aim of this study was to prove that TOC content is not a single factor affecting the bioavailability of POPs and that TOC based extrapolation might be incorrect, especially when comparing natural and artificial soils. Three natural soils with increasing TOC and three artificial soils with TOC comparable to these natural soils were spiked with phenanthrene, pyrene, lindane, p,p'-DDT, and PCB 153 and studied after 0, 14, 28, and 56 days. At each sampling point, total soil concentration and bioaccumulation in earthworms Eisenia fetida were measured. The results showed different behavior and bioavailability of POPs in natural and artificial soils and apparent effects of aging on these differences. Hence, direct TOC based extrapolation between various soils seems to be limited.     

Using supercritical fluid extraction to measure the desorption and bioaccessibility of phenanthrene in soils

The aim of this paper was to measure the changing desorbable fraction and bioaccessibility of phenanthrene in two different soils with increasing soil-phenanthrene contact time using supercritical fluid extractions (SFE). Both soils were spiked with 100 mg kg⁻¹ phenanthrene and aged for 28 d. Desorption profiles were measured every 7 d using selective SFE conditions and the results were compared to ¹⁴C-phenanthrene mineralisation assays. Selective SFE showed significant differences in the rates and extents of desorption in the two soils, likely to be due to different organic matter composition. Post-extraction fitting of data yielded consistent SFE extraction times within ageing soils for bioaccessibility prediction.     

The influence of a NAPL on the loss and biodegradation of 14C-phenanthrene residues in two dissimilar soils

This study was carried out to assess the influence of diesel, applied over a log concentration range, on the loss and extractability of phenanthrene (measured as putative 14C-phenanthrene residues) in two different soils. The influence of diesel on the ability of a cyclodextrin based extraction method to predict the microbial bioavailability of 14C-residues was also assessed. An increase in loss of 14C-residues with increasing diesel concentration from 0 to 2000 mg kg-1 was generally observed with time in both soils. It is suggested that this trend is attributable to competitive sorption for soil sorption sites and to a lesser extent to displacement of 14C-residues from soil sorption sites by diesel resulting in greater compound availability and therefore greater loss by degradation via the actions of indigenous microorganisms. However, in the 20000 mg kg-1 diesel treatments of both soils, results indicated a delayed loss. It is suggested that this retarded loss was due to the formation of a discrete NAPL-phase into which 14C-phenanthrene residues partitioned, thereby decreasing their availability and as a consequence their degradation. Furthermore, it is suggested that nutrient limitation may have slowed down degradation rates as diesel concentrations increased. Comparison between cyclodextrin-extractability and microbial mineralisation supported the use of cyclodextrin to assess microbial bioavailability of 14C-residues after 50 d or more ageing up to diesel concentrations of 2000 mg kg-1. However, results suggested that at high diesel concentrations (specifically 20000 mg kg-1) co-extraction of 14C-phenanthrene residues may have occurred as a result of the combined solvation powers of both the cyclodextrin and the diesel. Furthermore, mineralisation of 14C-phenanthrene residues may have been affected by extreme nutrient limitation in this treatment.     

The adaptation of two similar soils to pyrene catabolism

The development of pyrene catabolic activity was assessed in two similar soils (pasture and woodland) amended with 100 mg pyrene kg(-1) In the pasture and woodland soils, significant mineralisation of 14C-pyrene was observed after 8 and 76 weeks soil-pyrene contact times, respectively. In both soils, there were significant decreases (P<0.05) in the lag times and significant increases (P <0.05) in the maximum rates and extents of 14C-pyrene mineralised with increasing soil-pyrene contact time. A microbial inoculum was added to the woodland soil to assess if the previously added, but undegraded 14C-pyrene was bioavailable at 16 and 24 weeks. This resulted in the immediate mineralisation of the previously added 14C-pyrene, indicating that it was bioavailable but that the microbial community in the woodland soil had not developed the ability to mineralise pyrene. The relative contributions of the indigenous microflora to 14C-pyrene mineralisation were assessed by the addition of celective inhibitors, with bacteria seeming to be responsible for the mineralisation of pyrene in both soils. It is suggested that the rate of pyrene-transfer from the soil to the microorganisms was lower in the woodland soil due to its higher organic matter content.     

Impact of carbon nanomaterials on the behaviour of 14C-phenanthrene and 14C-benzo-[a] pyrene in soil

The impact of fullerene soot (FS), single-walled (SWCNTs) and multi-walled (MWCNTs) carbon nanotubes on the behaviour of two ¹⁴C-PAHs in sterile soil was investigated. Different concentrations of carbon nanomaterials (0, 0.05, 0.1 and 0.5%) were added to soil, and ¹⁴C-phenanthrene and ¹⁴C-benzo[a]pyrene extractability assessed over 80 d through dichloromethane (DCM) and hydroxypropyl-β-cyclodextrin (HPCD) shake extractions. Total ¹⁴C-PAH activity in soils was determined by combustion, and mineralisation of ¹⁴C-phenanthrene was monitored over 14 d, using a catabolically active pseudomonad inoculum. No significant loss of ¹⁴C-PAH-associated activity from CNM-amended soils was observed over the ‘aging’ period. CNMs had a significant impact on HPCD-extractability of ¹⁴C-PAHS; extractability decreased with increasing CNM concentration. Additionally, ¹⁴C-phenanthrene mineralisation was inhibited by the presence of CNMs at concentrations of ≥0.05%. Differences in overall extents of ¹⁴C-mineralisation were also apparent between CNM types. It is suggested the addition of CNMs to soil can reduce PAH extractability and bioaccessibility, with PAH sorption to CNMs influenced by CNM type and concentration.     

The influence of single and multiple applications of pyrene on the evolution of pyrene catabolism in soil

The influence of pyrene added in a single application (0, 50, 100 and 200 mg kg(-1)) was investigated in multiple applications (1 x 50, 2 x 50 and 4 x 50 mg kg(-1)) on the evolution of catabolic activity in a pristine pasture soil. The microbial community's ability to degrade pyrene was assessed at 0, 4, 8 and 12 weeks by the mineralization of added 14C-pyrene. Significant mineralization (>5%) of added 14C-pyrene only occurred after 4 weeks soil-pyrene contact time in most of the pyrene-amended soils. Pyrene-amended soils showed statistically significantly shorter (P<0.05) lag times compared to the control soil after 8 and 12 weeks soil-pyrene contact time. Further, the rates of degradation increased in the presence of pyrene, peaking at 8 weeks. In terms of the overall extents of pyrene mineralization, there were statistically significant increases (P<0.05) between 4 and 8 weeks, with little difference between 8 and 12 weeks, with the general trend that an increase in pyrene concentration resulted in higher levels of mineralization. Increasing the concentration and number of pyrene additions can have a significant impact on the adaptation of the soil microflora to degrade pyrene over time.     

Physicochemical soil parameters affecting sequestration and mycobacterial biodegradation of polycyclic aromatic hydrocarbons in soil

Six soils, obtained from grasslands and wooded areas in Northeastern Illinois, were physicochemically characterized. Measured parameters included total organic carbon (TOC) content, contents of humic acid, fulvic acid and humin, pore volume and pore size distribution, and chemical makeup of soil organic matter (determined using solid-state ¹³C-NMR). Moistened, gamma-sterilized soils were spiked with 200 ppm of either phenanthrene or pyrene (including ¹⁴C label); following 0, 40, or 120 days of aging, the contaminant-spiked soils were then inoculated with Mycobacterium austroafricanum strain GTI-23, and evolution of ¹⁴CO₂ was assessed over a 28-day period. Results for both phenanthrene and pyrene indicated that increased contact time led to increased sequestration and reduced biodegradation, and that TOC content was the most important parameter governing these processes. One soil, although only tested with phenanthrene, showed significantly lower-than-expected sequestration (higher-than-expected mineralization) after 40 days of aging, despite a very high TOC value (>24%). Because the level of sequestration in this soil was proportional to the others after 120 days of aging, this implies some difference in the temporal progression of sequestration in this soil, although not in its final result. The primary distinguishing feature of this soil was its considerably elevated fulvic acid content. Further experiments showed that addition of exogenous fulvic acid to a soil with very low endogenous humic acids/fulvic acids content greatly enhanced pyrene mineralization by M. austroafricanum. Extractabilities of 13 three- to six-ring coal tar PAHs in n-butanol from the six soils after 120 days of sequestration were strongly TOC-dependent; however, there was no discernible correlation between n-butanol extractability and mycobacterial PAH mineralization.     

Effect of metals on the adsorption and extractability of 14C-phenanthrene in soils

The fate of polycyclic aromatic hydrocarbons (PAHs) in contaminated soils may be affected by several environmental factors including the presence of co-contaminants. This study was conducted in order to assess the effect of metals on (i) the adsorption of 14C-phenanthrene in soils and (ii) its extractability and ability to form non-extractable residues. The first objective was accomplished using batch adsorption experiments with an uncontaminated agricultural soil spiked with the metals Cd, Cu, Pb, and Zn. Adsorption of phenanthrene was significantly higher after the addition of the metals (Kf = 21.48 vs. 8.55) and the desorption less readily reversible when compared to the unspiked soil. The extractability of phenanthrene was assessed with incubation (4 months, laboratory conditions) and microlysimeter experiments (6 months, natural climatic conditions) on three soils spiked with metals. All the soils were labelled with 14C-phenanthrene. The amount of extractable phenanthrene residues was significantly higher when the metals had been added to the soils. Nevertheless, the quantity of non-extractable residues was non-significantly different between the spiked and unspiked soils. The mechanism leading to increased adsorption and extractability of phenanthrene in the presence of metals is still unknown. In perspective, it would be interesting to assess the bioavailability of PAHs in the presence of metals in further experiments.     

Can microbial mineralization be used to estimate microbial availability of organic contaminants in soil?

The aim of this study was to characterize the behaviour of a PAH-degrading bacterium to determine whether mineralization plateaus as a result of substrate removal, a decrease in microbial activity or nutrient availability in sterile soils over time. To investigate this, the mineralization of 14C-phenanthrene was measured until it plateaued; subsequently, additional 14C-phenanthrene, catabolic inocula or nutrients were introduced and mineralization was measured for a further 10 d. Cell numbers were also measured together with 14C-uptake into microbial biomass. Freshly added 14C-phenanthrene was rapidly metabolised by the microorganisms. Neither the addition of a catabolic inoculum nor nutrients affected the extent of 14C-phenanthrene mineralization. Cell numbers remained constant over time, with only a small amount of the 14C-activity incorporated into the microbial biomass. This study indicated that the termination of mineralization was due to the removal of available phenanthrene and not decreasing cellular activity or cell death. The mineralization values also correlated with 14C-phenanthrene extractability using beta-cyclodextrin.     

Biogenic volatile organic compounds as a potential stimulator for organic contaminant degradation by soil microorganisms

The effects of monoterpenes on the degradation of ¹⁴C-2,4-dichlorophenol (DCP) were investigated in soils collected from areas surrounding monoterpene and non-monoterpene-emitting vegetation. Indigenous microorganisms degraded ¹⁴C-2,4-DCP to ¹⁴CO₂, after 1 d contact time. Degradation was enhanced by prior exposure of the soils to 2,4-DCP for 32 d, increasing extents of mineralisation up to 60%. Monoterpene amendments further enhanced 2,4-DCP degradation, but only following pre-exposure to both 2,4-DCP and monoterpene, with total 2,4-DCP mineralisation extents of up to 71%. Degradation was greatest at the higher monoterpene concentrations (≥1 μg kg⁻¹). Total mineralisation extents were similar between concentrations, but higher than the control and the 0.1 μg kg⁻¹ amendment, indicating that increases in monoterpene concentration has a diminishing enhancing effect. We suggest that monoterpenes can stimulate the biodegradation of 2,4-DCP by indigenous soil microorganisms and that monoterpene amendment in soils is an effective strategy for removing organic contaminants.     

Biodegradation of PAHs in soil: Influence of chemical structure, concentration and multiple amendment

The influence of PAH chemical structure and concentration, added in either single (75 or 300 mg kg⁻¹) or multiple (2 × 75, 2 × 150 or 4 × 75 mg kg⁻¹) applications as single- or multiple-contaminant systems, on the development of PAH biodegradation in a pristine soil was investigated. Development in microbial catabolic ability was assessed at 0, 28, 56 and 84 d by monitoring ¹⁴C-naphthalene, ¹⁴C-phenanthrene and ¹⁴C-pyrene mineralisation over 14 d in respirometric assays. The presence of other contaminants influenced the ability of the indigenous microflora to mineralise structurally different contaminants over time. ¹⁴C-Naphthalene mineralisation was inhibited by the presence of other contaminants; whereas the presence of naphthalene significantly enhanced rates of mineralisation in multiple-contaminant systems containing ¹⁴C-phenanthrene and ¹⁴C-pyrene. Generally, increasing the number of contaminant applications has implications for catabolic activity of soil microbes. It is suggested the toxic nature of PAHs retarded mineralisation at increased contaminant concentrations.     

Mathematical analysis of the whole core injection method accuracy for measuring phenanthrene biodegradation rates in undisturbed marine sediments

Rates of 14C-phenanthrene mineralization in contaminated, undisturbed marine sediments were measured using the whole core injection method to assess microbial natural attenuation activity as a function of sediment depth. Submerged sediments were sampled from Eagle Harbor, a marine superfund site in Puget Sound. Experiments show significant biodegradation activities (0.0012-0.0036 day(-1)) in the sediment horizons from 0 to 10 cm. The purpose and scope of this paper is to evaluate the range of experimental conditions giving valid results; a mathematical simulation described competing contaminant 14C-phenanthrene diffusion and simultaneous biodegradation (Monod kinetics), both retarded by sorption. The effect of aging was examined with two sorption models in presumed pseudo-homogenous sediments having effective properties. The simulation predictions provide quantitative guidelines for the successful use of the whole core injection method. (1) The effective Monod constant KS' in sediment is increased by a large partition coefficient KP between sediment and water and makes the apparent 14C-phenanthrene biodegradation approach first-order kinetics. (2) When KS'>1 mg(-1) l(-1), the measured 14C-phenanthrene biodegradation extent is biased by inadequately distributed injected tracer only when less than 7% of the sediment horizon is initially probed and mixed with injected tracer. (3) A short incubation time (<20 days) is necessary when a mobile indicator, e.g., gaseous 14CO2, is used. For longer incubation times, predictions show that a 14CO2 indicator diffuses to adjacent horizons, thus smearing the depth profile of biodegradation. (4) This method employing a radiolabeled tracer provides accurate biodegradation rates for freshly contaminated sediments, and represents an upper limit to the natural phenanthrene biodegradation extents if the contaminant is aged over 50 days.     

Effect of clay and organic matter type on the ecotoxicity of zinc and cadmium to the potworm Enchytraeus albidus

Clay and organic matter are considered as important parameters influencing bioavailability and ecotoxicity of metals in soils. As there exists a large variation in the type of clay and organic matter in field soils, the quantity of these variables alone may not be good indicators of metal bioavailability. To test this hypothesis, toxicity experiments with the potworm Enchytraeus albidus were conducted in artificial soils with three types of clay and seven types of organic matter, while the soil pH was kept constant. The 14d LC₅₀ of zinc and cadmium varied from 83.0 to 1140 mg Zn/kg D.W. and from 55.2 to 704 mg Cd/kg D.W., respectively, depending on the type of clay and organic matter that were used. Simultaneous measurements of the cation exchange capacity showed that this soil parameter is a better indicator of the bioavailability as it takes into account the type of clay and organic matter as well as other adsorption phases such as metal oxyhydroxides.     

Mineralisation of target hydrocarbons in three contaminated soils from former refinery facilities

This study investigated the microbial degradation of ¹⁴C-labelled hexadecane, octacosane, phenanthrene and pyrene and considered how degradation might be optimised in three genuinely hydrocarbon-contaminated soils from former petroleum refinery sites. Hydrocarbon mineralisation by the indigenous microbial community was monitored over 23 d. Hydrocarbon mineralisation enhancement by nutrient amendment (biostimulation), hydrocarbon degrader addition (bioaugmentation) and combined nutrient and degrader amendment, was also explored. The ability of indigenous soil microflora to mineralise ¹⁴C-target hydrocarbons was appreciable; ≥16% mineralised in all soils. Generally, addition of nutrients or degraders increased the rates and extents of mineralisation of ¹⁴C-hydrocarbons. However, the addition of nutrients and degraders in combination had a negative effect upon ¹⁴C-octacosane mineralisation and resulted in lower extents of mineralisation in the three soils. In general, the rates and extents of mineralisation will be dependent upon treatment type, nature of the contamination and adaptation of the ingenious microbial community.     

The ratio of clay content to total organic carbon content is a useful parameter to predict adsorption of the herbicide butachlor in soils

Thirteen soils collected from 11 provinces in eastern China were used to investigate the butachlor adsorption. The results indicated that the total organic carbon (TOC) content, clay content, amorphous Fe2O3 content, silt content, CEC, and pH had a combined effect on the butachlor sorption on soil. Combination of the data obtained from the 13 soils in the present study with other 23 soil samples reported by other researchers in the literature showed that Koc would be a poor predictive parameter for butachlor adsorption on soils with TOC content higher than 4.0% and lower than 0.2%. The soils with the ratio of clay content to TOC content (RCO) values less than 60 adsorbed butachlor mainly by the partition into soil organic matter matrix. The soils with RCO values higher than 60 apparently adsorbed butachlor by the combination of the partition into soil organic matter matrix and adsorption on clay surface.     

Enhanced degradation of carbofuran in pacific northwest soils

Abstract

Persistence of ¹⁴C‐carbonyl carbofuran was measured in Pacific Northwest soils that had received 1–14 applications of the insecticide for root weevil control on perennial crops. Insecticide decay curves were obtained in nonautoclaved soil and several autoclaved soil samples from previously‐treated fields and in nonautoclaved soils from paired control sites not previously treated with carbofuran. The insecticide usually degraded faster in soil from previously‐treated fields than in soil from corresponding control fields. Among 26 previously‐treated fields, the pseudo half‐life (time for 50% loss) of carbofuran was < one wk in 11 soils, 1–3 wks in 8 soils and > 4 wks in the remaining soils. Among the nontreated control fields the pseudo half‐life was > than 2 wks in all cases and > than 15 wks in 5 of the soils. The carbofuran decay curve always possessed an initial lag phase where soil mixing enhanced insecticide decline. Carbofuran degraded very slowly in autoclaved soil samples. The half‐life of carbofuran exceeded 16 wk in all autoclaved soils tested and in most instances 85–90% of the original dosage remained when the tests were terminated 112 days after treatment. These results provided evidence that many of the soils which received applications of carbofuran over the past several years have developed a capacity to degrade carbofuran very rapidly.     

Induction of PAH-catabolism in mushroom compost and its use in the biodegradation of soil-associated phenanthrene

This paper describes the induction of phenanthrene-catabolism within Phase II mushroom compost resulting from its incubation with (1) phenanthrene, and (2) PAH-contaminated soil. Respirometers measuring mineralization of freshly added 14C-9-phenanthere were used to evaluate induction of phenanthrene-catabolism. Where pure phenanthrene (spiked at a concentration of 400 mg kg(-1) wet wt.) was used to induce phenanthrene-catabolism in compost, induction was measurable, with maximal mineralization observed after 7 weeks phenanthrene-compost contact time. Where PAH-contaminated soil was used to induce phenanthrene-catabolism in un-induced compost, induction was observed after 5 weeks soil-compost contact time. Microcosm-scale amelioration of soil contaminated with 14C-phenanthrene (aged in soil for 516 days prior to incubation with compost) indicated that both induced (using pure phenanthrene) and uninduced Phase II mushroom composts were equally able to promote degradation of this soil-associated contaminant. After 111 days incubation time, 42.7 +/- 6.3% loss of soil-associated phenanthrene was observed in the induced-compost soil mixture, while 36.7 +/- 2.9% loss of soil-associated phenanthrene was observed in the uninduced-compost soil mixture. These results are notable as they indicate that while pre-induction of phenanthrene-catabolism within compost is possible, it does not significantly increase the extent of degradation when the compost is used to ameliorate phenanthrene-contaminated soil. Thus, compost could be used directly in the amelioration of contaminated land i.e. without pre-induction of catabolism.     

2,4-Dichlorophenoxyacetic acid (2,4-D) sorption and degradation dynamics in three agricultural soils

The fate and transport of 2,4-dichlorophenoxyacetic acid (2,4-D) in the subsurface is affected by a complex, time-dependent interplay between sorption and mineralization processes. 2,4-D is biodegradable in soils, while adsorption/desorption is influenced by both soil organic matter content and soil pH. In order to assess the dynamic interactions between sorption and mineralization, 2,4-D mineralization experiments were carried using three different soils (clay, loam and sand) assuming different contact times. Mineralization appeared to be the main process limiting 2,4-D availability, with each soil containing its own 2,4-D decomposers. For the clay and the loamy soils, 45 and 48% of the applied dose were mineralized after 10 days. By comparison, mineralization in the sandy soil proceeded initially much slower because of longer lag times. While 2,4-D residues immediately after application were readily available (>93% was extractable), the herbicide was present in a mostly unavailable state (<2% extractable) in all three soils after incubation for 60 days. We found that the total amount of bound residue decreased between 30 and 60 incubation days. Bioaccumulation may have led to reversible immobilization, with some residues later becoming more readily available again to extraction and/or mineralization.     

Ammonia volatilization loss from surface applied livestock manure

Ammonia (NH₃) emission from livestock manures used in agriculture reduces N uptake by crops and negatively impacts air quality. This laboratory study was conducted to evaluate NH₃emission from different livestock manures applied to two soils: Candler fins sand (CFS; light-textured soil, pH 6.8 and field capacity soil water content of 70 g kg^{? 1}) from Lake Alfred, Florida and Ogeechee loamy sand (OLS; medium-textured soil, pH 5.2 and field capacity soil water content of 140 g kg^{? 1}) from Savannah, Georgia. Poultry litter (PL) collected from a poultry farm near Douglas, Georgia, and fresh solid separate of swine manure (SM) collected from a farm near Clinton, North Carolina were used. Each of the soil was weighed in 100 g sub samples and amended with either PL or SM at rates equivalent to either 0, 2.24, 5.60, 11.20, or 22.40 Mg ha^{? 1} in 1L Mason jars and incubated in the laboratory at field capacity soil water content for 19 days to monitor NH₃ volatilization. Results indicated a greater NH₃ loss from soils amended with SM compared to that with PL. The cumulative NH₃volatilization loss over 19 days ranged from 4 to 27% and 14 to 32% of total N applied as PL and SM, respectively. Volatilization of NH₃ was greater from light-textured CFS than that from medium-textured OLS. Volatilization loss increased with increasing rates of manure application. Ammonia volatilization was lower at night time than that during the day time. Differences in major factors such as soil water content, temperature, soil type and live stock manure type influenced the diurnal variation in volatilization loss of NH₃ from soils. A significant portion (> 50%) of cumulative NH₃ emission over 19 d occurred during the first 5–7 d following the application of livestock manures. Results of this study demonstrate that application of low rates of livestock manure (≤ 5.60 Mg ha^{? 1}) is recommended to minimize NH₃ emissions.     

Study of sorption kinetics of some ionic liquids on different soil types

In the present contribution sorption kinetics experiments under static conditions were utilized in three selected ionic liquids cations (1-ethyl-3-methylimidazolium, 1-butyl-3-methylimidazolium, 1-hexyl-3-methylimidazolium chlorides) study with five type of soil, differing in total organic carbon (TOC) content. The experimental results indicate the sorption capacity growth with increase in TOC content and hydrophobicity of ionic liquid cation. The obtained kinetic sorption parameters as well as distribution coefficients (K_d) were used to estimate the sorption properties of the soil types towards the ionic liquids in question. The Gibbs free energy values indicate that ionic liquid cations sorption on soils could be generally considered as a physical adsorption with exothermic effect. But the values of −dG for studied cations sorption on soil with very high of TOC content in soil (45%) may testify to nature of chemical adsorption. Sorption of the analyzed compounds occurs probably by means of hydrogen bonds, electrostatic and π  π interaction with the organic matter and the clay minerals of the soils.