Bioaccumulation of hexachlorobenzene in Eisenia foetida at different aging stages

Groundwater-level fluctuation effects on petroleum hydrocarbons in vadose zones and their potential risks: Laboratory studies

Despite the role of the vadose zone protecting groundwater from contamination, the non-stationarity in this zone makes it difficult to predict the behavior of petroleum hydrocarbons (PH) therein. In laboratory soil columns with sandy and sandy loam soils, we simulated a vadose zone subjected to repeated groundwater-level fluctuation (GLF) to evaluate the behavior of PH under hydrodynamic conditions. The GLF vertically redistributed the PH, the extent of which was pronounced in the sandy soil with a high initial concentration due to the enhanced transport of the immiscible PH through the larger pores. The frequency of GLF did not show a substantial effect on the extent of PH redistribution but largely affected their attenuation. The greater GLF hindered PH volatilization by maintaining a high degree of water saturation, while the subsequent development of a local anaerobic regime inhibited biodegradation, which was more apparent in the sandy loam. Finally, a specific potential risk index was introduced to quantitatively compare the potential risk of PH contamination in different vadose zones exposed to GLF. Overall, the sandy soil contaminated with the higher total PH (TPH) concentration showed markedly higher potential risk indices (i.e., 18.4-29.0%), while the ones comprised of the sandy loam showed 0.6-4.9%, which increased under the greater number of GLF cycles.

What determines the efficacy of landfarming for petroleum-contaminated soils: Significance of contaminant characteristics

Identifying the cause of inconsistent landfarming efficacy is critical to designing optimal remedial strategies for petroleum-contaminated sites. We assessed contaminated soils collected from two former military bases in South Korea to better understand the role and influence of different factors. Landfarming remediation was simulated in the laboratory by applying comparable practices (such as tillage and bioaugmentation) and the relevant mechanism was examined. We then systematically examined potential factors affecting petroleum-removal efficacy, including the content of fine soil particles, the initial concentration and composition of petroleum contaminants, and the degree of soil-contaminant interaction. The distribution range of total petroleum hydrocarbons (TPHs) and the size of unresolved complex mixture (UCM) found in gas chromatography data showed that petroleum composed of TPHs with lower carbon numbers and having smaller size of UCM could be treated more effectively by landfarming. Incorporating the evaluation of the distribution range and UCM properties of petroleum, rather than simply considering its total concentration, is a more accurate and efficient method for determining the site-specific suitability of landfarming as a remedial option, as well as for assessing the necessity of supplementary processes.

Toxicokinetics of hydrophobic organic compounds in oligochaeta: A critical review

Toxicokinetic studies appertain to the fundamental research of soil bioavailability. However, the research outcomes of aspects influencing uptake and elimination of hydrophobic organic compounds have not been summarized so far. In our review, a recapitulation of available toxicokinetic data (i.e. experimental conditions, if the steady state was reached, uptake and elimination rate constants, and bioaccumulation factors) is presented in well-arranged tables. Further, toxicokinetic models are overviewed in the schematic form. In the review, the required information could be quickly found and/or the experimental gaps easily identified. Generally a little is known about the effects of soil properties other than soil organic matter. Limited or no data are available about soil treatment, food supply during laboratory exposure, and metabolization in oligochaeta. The impact of these factors might be important especially for arable soils with typically low organic matter content but high consequences on humans. Besides these circumstances, other uncertainties between published studies have been found. Firstly, the scientific results are provided in heterogenous units: bioaccumulation factors as well as the rate constants are reported in dry or wet weight of soil and earthworms. The steady state is another critical factor because the time to reach the equilibrium is influenced not only by soil and compound characteristics but for example also by aging. Nevertheless, toxicokinetic studies bring irreplaceable information about the real situation in soil and our review help to define missing knowledge and estimate the scientific priorities.

What are the effects of soil treatment procedures (sterilization by γ-irradiation and solvent-assisted spiking) on DDE bioaccumulation by earthworms?

Ionizing γ-irradiation and solvent-assisted spiking are frequently applied to eliminate microbial activity and to induce hydrophobic organic compounds (HOCs) into soil, respectively, when studying the accumulation of chemicals in terrestrial organisms. However, the side-effects that may arise from these treatments on soil-HOC interaction and, subsequently, the kinetics and extents of bioaccumulation are not thoroughly understood. To this end, the accumulation of 1,1-dichloro-2,2-bis(p-chlorophenyl)etylene (p,p'-DDE) by Eisenia andrei was studied in sterilized or unsterilized and freshly spiked (FS) or historically contaminated (HC) soils in parallel with an analysis of aliphatic and hydrophilic soil organic matter (SOM) moieties using mid-infrared diffuse reflectance spectroscopy (DRIFT-S). Irradiation did not impart significant changes on spectral SOM descriptors. In contrast, earthworm inhabitation increased the relative presence of aliphatic moieties to a greater extent than hydrophilic ones, reaching or exceeding pre-treatment levels. Overall, effects on SOM chemistry can be ranked as earthworms > spiking > irradiation. Corresponding changes at the bioaccumulation level were observed for the FS soil (i.e., a 27% reduction in bioaccumulation upon sterilization) but not for the HC soil. This implies that in contrast to the interactions between aged p,p'-DDE and sterilized HC soil, the interactions established between freshly added p,p'-DDE and sterilized FS soil were altered by γ-irradiation-induced secondary effects alone or in combination with earthworm inhabitation. Thus, although the soil treatment processes studied here should not drastically impact compound bioaccumulation, they should be considered in mechanistic studies where the qualitative and quantitative aspects of compound-soil (organic matter)-earthworm interactions are at the centre of attention.

Bioavailability of weathered hydrocarbons in engine oil-contaminated soil: Impact of bioaugmentation mediated by Pseudomonas spp. on bioremediation

Heavier fraction hydrocarbons (C₁₅-C₃₆) formed in soil after biotic and abiotic weatherings of engine oil are the continuing constraints in the bioremediation strategy, and their bioavailability remains a poorly quantified regulatory factor. In a microcosm study, we used two strains of Pseudomonas, P. putida TPHK-1 and P. aeruginosa TPHK-4, in strategies of bioremediation, viz., natural attenuation, biostimulation and bioaugmentation, for removal of weathered total petroleum hydrocarbons (TPHs) in soil contaminated long-term with high concentrations of engine oil (39,000-41,000 mg TPHs kg^-1 soil). Both the bacterial strains exhibited a great potential in remediating weathered hydrocarbons of engine oil. Addition of inorganic fertilizers (NPK), at recommended levels for bioremediation, resulted in significant inhibition in biostimulation/enhanced natural attenuation as well as bioaugmentation. The data on dehydrogenase activity clearly confirmed those of bioremediation strategies used, indicating that this enzyme assay could serve as an indicator of bioremediation potential of oil-contaminated soil. Extraction of TPHs from engine oil-contaminated soil with hydroxypropyl-β-cyclodextrin (HPCD), but not 1-butanol, was found reliable in predicting the bioavailability of weathered hydrocarbons. Also, 454 pyrosequencing data were in accordance with those of bioremediation strategies used in the present microcosm study, suggesting the possible use of pyrosequencing in designing approaches for bioremediation.

Bioremediation of heavy metals and petroleum hydrocarbons in diesel contaminated soil with the earthworm: Eudrilus eugeniae

A laboratory study on the bioremediation of diesel contaminated soil with the earthworm Eudrilus eugeniae (Kingberg) was conducted. 5 ml of diesel was contaminated into soils in replicates and inoculated with E. eugeniae for 90 days. Physicochemical parameters, heavy metals and total petroleum hydrocarbons were analyzed using AAS. BTEX in contaminated soil and tissues of earthworms were determined with GC-FID. The activities of earthworms resulted in a decrease in pH (3.0 %), electrical conductivity (60.66 %), total nitrogen (47.37 %), chloride (60.66 %), total organic carbon (49.22 %), sulphate (60.59 %), nitrate (60.65 %), phosphate (60.80 %), sodium (60.65 %), potassium (60.67 %), calcium (60.67 %), magnesium (60.68 %), zinc (60.59 %), manganese (60.72 %), copper (60.68 %), nickel (60.58 %), cadmium (60.44 %), vanadium (61.19 %), chromium (53.60 %), lead (60.38 %), mercury (61.11 %), arsenic (80.85 %), TPH (84.99 %). Among the BTEX constituents, only benzene (8.35 %) was detected in soil at the end of the study. Earthworm tissue analysis showed varying levels of TPH (57.35 %), benzene (38.91 %), toluene (27.76 %), ethylbenzene (42.16 %) and xylene (09.62 %) in E. eugeniae at the end of the study. The study has shown that E. eugeniae could be applied as a possible bioremediator in diesel polluted soil.

Perfluorooctane sulfonate release pattern from soils of fire training areas in Australia and its bioaccumulation potential in the earthworm Eisenia fetida

Aqueous film-forming foams (AFFF) are used to extinguish hydrocarbon fuel fires. Certain AFFF products such as 3M Lightwater contain perfluorooctane sulfonate (PFOS) as the active ingredient which is highly persistent in the environment and is thus globally prevalent. With thousands of tons of soils potentially contaminated with PFOS stockpiled at a number of sites in Australia, the lack of reliable information on bioavailability of this recalcitrant contaminant constrains the application of a risk-based strategy for managing such soils. In this study, the PFOS release pattern from soils collected from the contaminated sites of fire training areas and its bioaccumulation potential in earthworm were investigated. The study was conducted at two temperatures (25 and 37 °C) and 60 % of the maximum water-holding capacity of soils. The greatest release into water was found to occur from the soil having the highest PFOS concentration, 16.17 μg g(-1) (Tindal FTA064), thereby demonstrating the role of contaminant loading on release behaviour. The release could also be related to the soil physico-chemical properties. The maximum amount of PFOS was desorbed from the soil with the lowest clay and organic matter content. Bioaccumulation of PFOS in earthworms (Eisensia fetida) as expressed by the bioaccumulation factor (BAF) was found to be highest from soil with the lowest PFOS concentration (RBD soil). The range of BAF found in our study was 1.23 (spiked Tindal SS01 soil) to 13.9 (field contaminated RBD soil). Our study suggests that PFOS could indeed pose a potential risk to ecological safety of soil if present even at concentrations as low as 0.8 μg g(-1) since the highest bioaccumulation factor was found to be from such a soil (field contaminated RBD).

Identification of the source of PFOS and PFOA contamination at a military air base site

Although the use of perfluorooctane sulfonic acid (PFOS)/perfluorooctanoic acid (PFOA)-based aqueous fire-fighting foams (AFFF) has been banned due to their persistence, bioaccumulation and toxicity to biota, PFOS and PFOA are still present at significant levels in the environment due to their past usage. This study investigated the reasons for detection of PFOS and PFOA in an evaporation pond used to collect the wastewater arising from fire-fighting exercises at a military air base despite the replacement of PFOS/PFOA-based foam with no PFOS/PFOA-foam about 6 years ago. Concentrations in the wastewater stored in this pond ranged from 3.6 to 9.7 mg/L for PFOS and between 0.6 and 1.7 mg/L for PFOA. The hypothesis tested in a laboratory study was that PFOS and PFOA have accumulated in the sediments of the pond and can be released into the main body of the water. Concentrations detected in the sediments were 38 and 0.3 mg/g for PFOS and PFOA, respectively. These values exceed the recently reported average global values for sediments (0.2-3.8 ng/g for PFOS and from 0.1 to 0.6 ng/g for PFOA) by a factor of several thousands. PFOS and PFOA distribution coefficients were derived for the organic content of the pond sediment (1.6%). Identification of the source of contamination and knowledge of the partition between soil and aqueous phases are vital first steps in developing a sustainable remediation technology to remove the source from the site. This study clearly suggests that unless the sediment is cleaned of PFOS/PFOA, these chemicals will continue to be detected for a long period in the pond water, with potential adverse impacts on the ecosystem.

Uptake kinetics of five hydrophobic organic pollutants in the earthworm Eisenia fetida in six different soils

Hydrophobic organic contaminants in soils may pose toxicity or transfer to food chains after their uptake to soil biota. However, uptake data for earthworms are usually limited, as: (a) only fixed exposure times are studied instead of whole uptake kinetics and (b) studies including compounds with different environmental properties and more than two soils of different properties are quite rare. In our study, five persistent organic pollutants (phenanthrene, pyrene, lindane, p,p'-dichlorodiphenyltrichloroethane (p,p'-DDT), and polychlorinated biphenyl congener No. 153 (PCB 153)) were added to six soils of a wide range of soil properties. Detailed kinetics of uptake to earthworms Eisenia fetida were measured. Results indicated that an equilibrium of concentrations for p,p'-DDT and PCB 153 was reached after 11 days of exposure in all soils. Uptake of phenanthrene, pyrene, and lindane was strongly influenced by the decrease in concentrations in the soils, resulting in peak-shaped accumulation curves. Only in soils with the highest total organic carbon content (7.9 and 20.2%), the equilibrium of lindane concentrations was achieved (after 17 and 5 days of exposure, respectively). We recommend calculating bioaccumulation factors as a ratio of the uptake and elimination rate constants to precise the risk assessment.

A combined approach of physicochemical and biological methods for the characterization of petroleum hydrocarbon-contaminated soil

Main physicochemical and microbiological parameters of collected petroleum-contaminated soils with different degrees of contamination from DaGang oil field (southeast of Tianjin, northeast China) were comparatively analyzed in order to assess the influence of petroleum contaminants on the physicochemical and microbiological properties of soil. An integration of microcalorimetric technique with urease enzyme analysis was used with the aim to assess a general status of soil metabolism and the potential availability of nitrogen nutrient in soils stressed by petroleum-derived contaminants. The total petroleum hydrocarbon (TPH) content of contaminated soils varied from 752.3 to 29,114 mg kg(−1). Although the studied physicochemical and biological parameters showed variations dependent on TPH content, the correlation matrix showed also highly significant correlation coefficients among parameters, suggesting their utility in describing a complex matrix such as soil even in the presence of a high level of contaminants. The microcalorimetric measures gave evidence of microbial adaptation under highest TPH concentration; this would help in assessing the potential of a polluted soil to promote self-degradation of oil-derived hydrocarbon under natural or assisted remediation. The results highlighted the importance of the application of combined approach in the study of those parameters driving the soil amelioration and bioremediation.

The effects of aging time on the fraction distribution and bioavailability of PAH

Understanding the effects of aging time on the fraction distribution and bioavailability of PAH, such as phenanthrene (PHE) and pyrene (PYR), has considerable benefits for risk assessment, food security and remediation strategies for contaminated soil. The results of the present study show that the proportion of the desorbed PHE decreased from ca. 82% at day 0 to ca. 65% at day 150. In addition, non-desorbed PHE increased from ca. 18% at day 0 to ca. 31% at day 150, whereas the changes of desorbed and non-desorbed PYR showed no significant trend during this aging period. The proportion of desorbed PYR was lower than that of PHE, whereas the opposite occurred with the non-desorbed fraction. After 150 d of aging, the proportion of bound residues (PHE and PYR) increased significantly with the cultivating time from ca. 0.2% to ca. 4.7% and ca. 0.1% to ca. 1.2% for PHE and PYR, respectively. In addition, the bioavailability of PAH (PHE and PYR) to earthworms was also assessed over 0-150 d. The results showed that the uptake rate and bioconcentration factor (BCF) of pollutants by earthworms displayed the following biphasic character: a rapid decrease over the first 15 d followed by a slow decrease over the next 135 d. Moreover, the earthworm uptake rate of PHE was greater than that of PYR throughout the incubation period, indicating that PHE has a higher bioavailability than PYR. In addition, the positive correlation between the uptake rate of earthworms and PAH extractability suggested that a three-step extraction is a reliable approach to predict PHE bioavailability in soil. However, a limit was observed for PYR.