Effects of phenanthrene and its nitrogen-heterocyclic analogues aged in soil on the earthworm Eisenia fetida

Major sources of homocyclic polycyclic aromatic hydrocarbons (PAHs) and N-containing analogues (N-PAHs) are found in the environment after being discharged through petrogenic, pyrogenic and biogenic activities. Using a health index tool and the OECD guideline 207, the ecotoxicity of phenanthrene and its nitrogen-containing analogues to the earthworm Eisenia fetida were assessed in agricultural soil at different times after spiking. The effects were measured over a 21 d exposure period (over time), during which earthworms’ general health condition, mortality and biomass were assessed. The LC50 and EC50 (based on weight loss) ranged from 400–500 mg kg−1 dry soil and 1.2–500 mg kg−1 dry soil, respectively. The N-PAHs were more toxic to E. fetida and over time more available in soil than the homocyclic-phenanthrene analogue. Benzo[h]quinoline (B[h]Q) was the most toxic and persistent of the chemicals. Furthermore, the observed physical damages to the earthworms showed that N-PAHs, especially B[h]Q, may have cellular autolytic impact on E. fetida. These findings offer new insight on the toxicity of aromatics in soil which might be useful in risk assessment of contaminated sites

Assessment of the effects of phenanthrene and its nitrogen heterocyclic analogues on microbial activity in soil

Microbes are susceptible to contaminant effects, and high concentrations of chemical in soil can impact on microbial growth, density, viability and development. As a result of relative sensitivity of microbes to contaminants, toxicity data are important in determining critical loads or safe levels for contaminants in soil. Therefore the aim of this study was to assess the impact of phenanthrene and the 3-ring nitrogen-containing polycyclic aromatic hydrocarbons (N-PAHs) on soil microbial respiration. Soil samples were amended with phenanthrene and its 3-ring nitrogen-containing analogues and respiration rates (using substrate induced respiration), CO2 production inhibition and/or stress and total culturable microbial numbers were measured over a 90 days soil-contact time. The study showed that inhibition of phenanthrene amended soils occurred in the first 60 days, while the nitrogen-containing analogues impacted on respiration with increased concentration and contact time. Time dependent inhibitions were more than 25 % portraying N-PAHs toxic and inhibitory effects on microbial synthesis of the added carbon substrate. Further, statistical analysis of data revealed statistically significant differences in the respiration rates over time (p < 0.05). This suggests that soil microorganisms may be more sensitive to N-PAHs in soil than the homocyclic PAH analogues. This current study provides baseline toxicity data to the understanding of the environmental impact of N-PAHs, and assists science-based decision makers for improved management of N-PAH contaminated site

The impact of carbon nanomaterials on the development of phenanthrene catabolism in soil

This study investigates the impact of different types of carbon nanomaterials (CNMs) namely C60, multi-walled carbon nanotubes (MWCNTs) and fullerene soot on the catabolism of (14)C-phenanthrene in soil by indigenous microorganisms. Different concentrations (0%, 0.01%, 0.1% and 1%) of the different CNMs were blended with soil spiked with 50 mg kg(-1) of (12)C-phenanthrene, and aged for 1, 25, 50 and 100 days. An increase in the concentration of MWCNT- and FS-amended soils showed a significant difference (P = 0.014) in the lag phase, maximum rates and overall extent of (14)C-phenanthrene mineralisation. Microbial cell numbers did not show an obvious trend, but it was observed that control soils had the highest population of heterotrophic and phenanthrene degrading bacteria at all time points

Soil contamination in China : studies on the status, priorities, policies, management and risk assessment

As China is trying to balance economic development, environmental safety and human health, the Government has released strategic plans and legislation for soil contamination management. Aspects of the quality of China’s soils and management of soil contamination in China are addressed in this thesis. Soil environmental quality standards and science-based risk assessment of contaminants in soils are evaluated. China and the UK use different risk-based approaches to derive soil screening or guideline values (SSVs; SGVs) for contaminants. The approaches are compared and values derived for 6 illustrative contaminants. China’s SSVs are derived using an approach developed in the US as follows: for carcinogens, acceptable level of risk (ACR) is set at 10-6 and the SSVs calculated as 10-6 divided by the soil exposure and toxicity data; for non-carcinogens, the hazard quotient is 1 and the SSV is calculated as 1 divided by the soil exposure and toxicity data. The UK’s SGVs are calculated by the CLEA model, for which the Average Daily Exposure (ADE) from soil sources by a specific exposure route equals the health criteria values (HCVs) for that route, whether for carcinogens or a non-carcinogens. The UK’s CLEA model is also used here to derive SSVs with Chinese input parameters. China’s SSVs, the UK’s SGVs and values for Chinese conditions derived using the UK approach were as follows (mg/kg): As, <1, 35, 20; Cd, 20, 18, 11; Cr (VI), <1, 14, 29; benzene, 1, 1, 2; toluene, 1200, 3005, 3800; ethyl-benzene, 7, 930, 1200. The difference in toxicity assessment and risk characterization for carcinogens results in the biggest difference in SSVs between the 2 countries. However, for non-carcinogenic substances, the difference of SSVs calculation method and SSVs is small. In the future, China can use the UK method to strengthen its toxicity assessment and risk characterization for carcinogenic substances. Data was made available for this thesis from an extensive field and analytical campaign of human exposure to heavy metals in China. This was used to calculate the relative contributions of exposure to As, Cd, Cr, Hg and Pb from environmental media (air, water, soils) via the inhalation, drinking and the diet for different regions of China. Dietary exposure dominated, contributing ~90-97% of the total exposure for these elements. Exposure differences were observed with gender, age and region. This survey information can be used to derive exposures from soil-borne sources. Soil organic matter (SOM) and pH are critical soil properties strongly linked to carbon storage, nutrient cycling and crop productivity, but there is a lack of information on changes in these soil properties over time for China. This study used data from Chinese soil surveys to examine changes in soil pH and SOM across different land uses (dry farmland, paddy fields, grassland, woodland, unused land), with surface soil (0-20 cm) collected in the periods 1985-90 (Survey 1; 890 samples) and 2006-10 (Survey 2; 5005 samples) from two contrasting areas. In the southern part of China, the mean pH of paddy soils fell over the two decades between surveys - from pH 5.81 to 5.19 (p<0.001), while dry farmlands in the northern sampling area fell slightly (from pH 8.15 to 7.82; p<0.001). The mean SOM content of dry farmland soil rose in both areas and the mean SOM of paddy fields in the southern area also rose (all p<0.001). Woodland soil pH in the south increased from 4.71 to 5.29 (p<0.001) but no significant difference was measured in the woodlands of the northern area, although the trend increased. The SOM content of woodland top soils rose in the northern (p=0.003) and southern (p<0.001) study areas. The implications and potential causes of these changes are discussed and suggestions made as to how large-scale soil sampling campaigns can be designed to monitor for changes and potential controlling factors. Because of rapid urbanization in China, the demand for land for urban development is increasing. To upgrade and modernize, China has also moved many major industries and factories from urban centres to less populated areas. With the high economic value of urban land, the transformation and utilization of the brownfield areas left behind has become important economically and socially. Strong scientific, regulatory and decision-making frameworks are needed, to ensure practical, careful and wise use of central and local Government resources, to manage the re-use and regeneration of these brownfield sites. The final chapter provides a thorough review of the background, context, regulations, policies and management procedures to develop and utilize brownfields in developed countries such as the US and UK, and identifies some of the priorities for brownfield governance and redevelopment in China. It is proposed: to establish a monitoring body, to identify shared responsibilities and inputs of various stakeholders, to establish brownfield databases, and to set up a remediation advisory system with technology support as future priorities of brownfield management. Recommendations are made for future research, to support China’s strategic management of soil resources

Impact of activated carbon on the catabolism of (14)C-phenanthrene in soil

Activated carbon amendment to contaminated soil has been proposed as an alternative remediation strategy to the management of persistent organic pollutant in soils and sediments. The impact of varying concentrations (0%, 0.01%, 0.1% and 1.0%) of different types of AC on the development of phenanthrene catabolism in soil was investigated. Mineralisation of (14)C-phenanthrene was measured using respirometric assays. The increase in concentration of CB4, AQ5000 or CP1 in soil led to an increase in the length of the lag phases. Statistical analyses showed that the addition of increasing concentrations of AC to the soil significantly reduced (P < 0.05) the extent of (14)C-phenanthrene mineralisation. For example, for CB4-, AQ5000- and CP1-amended soils, the overall extent of (14)C-phenanthrene mineralisation reduced from 43.1% to 3.28%, 36.9% to 0.81% and 39.6% to 0.96%, respectively, after 120 days incubation. This study shows that the properties of AC, such as surface area, pore volume and particle size, are important factors in controlling the kinetics of (14)C-phenanthrene mineralisation in soil

Extremely small amounts of B[a]P residues remobilised in long-term contaminated soils : A strong case for greater focus on readily available and not total-extractable fractions in risk assessment

There is a lack of understanding about the potential for remobilisation of polycyclic aromatic hydrocarbons (PAHs) residues in soils, specifically after the removal of readily available fractions, and the likelihood to cause harm to human and environmental health. Sequential solvent extractions, using butanol (BuOH), dichloromethane/acetone, and methanolic saponification were used to investigate the time-dependent remobilisation of B[a]P residues in aged soils, after removal of readily available or total-extractable fractions. After 120 d of aging, BuOH-remobilised B[a]P were small or extremely small ranging from 2.3 ± 0.1 mg/kg to 4.5 ± 0.5 mg/kg and from 0.9 ± 0.0 mg/kg to 1.0 ± 0.1 mg/kg, after removal of readily available and total-extractable fractions, respectively. After removal of readily available fractions, the remobilisation rates of B[a]P residues were constant over 5 re-equilibration times, as shown by first-order kinetics. The amounts of B[a]P remobilised significantly (p < 0.05) decreased with aging, particularly in hard organic carbon-rich soils. After 4 years of aging, BuOH- and total-remobilised B[a]P were generally < 5% of the initially spiked 50 mg/kg. Based on the findings of this study, the potential or significant potential for B[a]P NERs in soils to cause significant harm to human and environmental health are minimal

Infrared Spectroscopy Coupled with a Dispersion Model for Quantifying the Real-Time Dynamics of Kanamycin Resistance in Artificial Microbiota

Overusage of antibiotics leads to the widespread induction of antibiotic-resistance genes (ARGs). Developing an approach to allow real-time monitoring and fast prediction of ARGs dynamics in clinical or environmental samples has become an urgent matter. Vibrational spectroscopy is potentially an ideal technique toward the characterization of the microbial composition of microbiota as it is nondestructive, high-throughput, and label-free. Herein, we employed attenuated total reflection Fourier transform infrared (ATR-FT-IR) spectroscopy and developed a spectrochemical tool to quantify the static and dynamic composition of kanamycin resistance in artificial microbiota to evaluate microbial antibiotic resistance. Second-order differentiation was introduced in identifying the spectral biomarkers, and principal component analysis followed by linear discriminant analysis (PCA-LDA) was used for the multivariate analysis of the entire spectral features employed. The calculated results of the mathematical dispersion model coupled with PCA-LDA showed high similarity to the designed microbiota structure, with no significant difference (P > 0.05) in the static treatments. Moreover, our model successfully predicted the dynamics of kanamycin resistance within artificial microbiota under kanamycin pressures. This work lends new insights into the potential role of spectrochemical analyses in investigating the existence and trends of antibiotic resistance in microbiota

Effects of soil amendment with anaerobic digestate and wood-ash (bioenergy residues) on biodegradation of polycyclic aromatic hydrocarbons in soil.

Many organic contaminants found in the soil are associated with industrial emissions and/or spills; these include petroleum hydrocarbons and polycyclic aromatic hydrocarbons (PAHs), in particular. PAHs accumulate in soil due to their low aqueous solubility, volatility, hydrophobicity and recalcitrant chemical structures. The environmental persistence and risks associated with human and environmental health emphasize the importance of the treatment of PAH-contaminated soil. Various physical and chemical technologies known to have been employed in remediating PAH-contaminated soils are expensive and have further environmental challenges compared to microbial degradation which is less costly and environmentally sustainable. However, the stimulation of microbial activity with recurrent addition of mineral nutrients is known to damage the soil quality, while soil amendment with the residues of renewable energy production becomes a suitable option due to their nutrient contents, environmental sustainability and economic feasibility. This thesis evaluates the environmental fate and impact of PAHs in the soil and the biodegradation of PAHs in contaminated soils. It further investigates the effects of soil amendment with organic residues, particularly anaerobic digestate (AD) (a semi-solid biogas residue), wood-ash (WA) (a timber combustion residue) and their mixtures on indigenous microbial activity, and how the effects influence the indigenous biodegradation of PAHs. The findings provide insights into the implications of microbial degradation of PAHs in soils lacking in nutrients, the effects of soil amendment with AD and/or WA on biodegradation of PAHs, and the correct amounts of AD and WA that could be used as a combined soil amendment to stimulate indigenous biodegradation of PAHs

The Effect of Flavonoids on the Microbial Mineralisation of Polycyclic Aromatic Hydrocarbons in Soil,”

Abstract The effect of flavonoids (flavone, morin hydrate and 3-hydroxyflavone)on the microbial mineralisation of polycyclic aromatic hydrocarbons (PAHs) in soil slurry by the indigenous microbial communities has been investigated. The rates and extents o

Impact of single and binary mixtures of phenanthrene and N-PAHs on microbial utilization of 14C-glucose in soil

Microbes are susceptible to contaminant effects, and high concentration of chemicals in soil can impact on microbial growth, density, viability and development. The impact of single and binary mixtures of phenanthrene and its nitrogen-containing polycyclic aromatic hydrocarbon analogues (N-PAHs) on microbial metabolism of 14C-glucose in soil was measured over a 90 d soil-contact time. Impacts were assessed by measuring the rates and mean overall extents of mineralisation (%), as well as the incorporation of 14C-glucose into the microbial biomass. The result revealed that the extents of 14C-glucose mineralisation were consistently greater in N-PAH amended soils than the control and phenanthrene soils with increased incubations. This indicates a trend of increasing diversion of C from biosynthesis to maintenance requirement by soil microorganisms. Furthermore, biomass uptake in the amended soils showed reduced substrate utilization (fixed-kEC), suggesting that N-PAHs decreased the amount of substrate-C that was incorporated into the microbial biomass. This however, signifies that N-PAHs imposes oxidative stress on soil microbial community