Linking bioavailability and toxicity changes of complex chemicals mixture to support decision making for remediation endpoint of contaminated soils

A novel bioaccessibility prediction method for complex petroleum hydrocarbon mixtures in soil

More evidence shows that bioaccessibility instead of total concentrations based on exhaustive extraction methods can better reflect the actual risk level of petroleum hydrocarbon contaminated sites, so it is essential to establish an effective assessment method for bioaccessibility. This study utilized Tenax extraction, butanol extraction, hydroxypropyl-β-cyclodextrin (HPCD) extraction, and a composite extraction method involving HPCD with LMWOAs (citric acid, CA) and surfactants (rhamnolipid, RL; Tween80, TW80; sodium dodecyl sulfate, SDS) at varying concentrations. These methods were employed to predict the bioaccessibility of earthworms to soil at different aging time of petroleum hydrocarbons. The results showed that traditional extraction methods such as Tenax 6h extraction and n-butanol extraction were ineffective in evaluating petroleum hydrocarbons' bioaccessibility. In contrast, the composite extraction of HPCD and solubilizer enhanced the extraction efficiency of HPCD greatly, and the extraction results showed a significant positive correlation with earthworm accumulation. By the comparison of the extraction results of different fractions of petroleum hydrocarbons, heavy fractions of petroleum hydrocarbons (C29-C40) are essential factors affecting chemical extraction effects. The correlation coefficients of four composite extraction methods and total petroleum hydrocarbons (TPH) of earthworm accumulation by linear regression analysis ranged from 1.1797 to 1.7990, and the slopes ranged from 0.8727 to 0.9792. Among them, the combined extraction method of 50 mmol/L HPCD and 0.5 mmol/L rhamnolipid had the best effect (r2 = 0.9792, slope = 1.1797), which could be used as an evaluation method suitable for the bioaccessibility of petroleum hydrocarbons in soil. This study could provide a new method for evaluating the bioaccessibility of organic pollutants and technically supporting risk assessment and bioremediation of complex petroleum hydrocarbons in soil.

Updating risk remediation-endpoints for petroleum-contaminated soils? A case study in the Ecuadorian Amazon region

In Ecuador, the regulatory framework for the remediation of petroleum-contaminated soils is based on predefined concentration endpoints for a selected range of petroleum hydrocarbon compounds. However, such approach may lead to over or under-estimation of the environmental risk posed by contaminated soils. In this study, the end-point remediation criteria according to Ecuadorian Environmental legislation were evaluated using different approaches. The first one was based on Total Extractable Petroleum Hydrocarbons (TEPH) and the second one on Total Bioavailable Petroleum Hydrocarbons (TBPH). Both were compared with ecotoxicological determinations using EC50 -Microtox® bioassay at 5 and 15 min of exposure. The correlation (R2) between EC50 values vs TEPH was of 0.2 and 0.25 for 5 and 15 min, respectively. Meanwhile, R2 between EC50 and TBPH was of 0.9 and 0.65 for 5 and 15 min, respectively, demonstrating a stronger correlation. Our results suggest that a contaminated site where the concentration of the TEPH is higher than the relevant regulatory concentrations may be deemed to present an acceptable risk even though their concentrations exceed the target values in soils. The results also challenge the notion that hormesis is associated with TEPH, contrary to some literature. This study is the first in Ecuador to propose incorporating bioavailability into environmental regulations, highlighting the need for further research to establish realistic and achievable remediation goals based on toxicity studies involving various trophic levels.

Environmental effects from petroleum product transportation spillage in Nigeria: a critical review

Nigeria has struggled to meet sustainable development goals (SDGs) on environmental sustainability, transportation, and petroleum product distribution for decades, endangering human and ecological health. Petroleum product spills contaminate soil, water, and air, harming humans, aquatic life, and biodiversity. The oil and gas industry contributes to environmental sustainability and scientific and technological advancement through its supply chain activities in the transport and logistics sectors. This paper reviewed the effects of petroleum product transportation at three accident hotspots on Nigeria highway, where traffic and accident records are alarming due to the road axis connecting the southern and northern regions of the country. The preliminary data was statistically analysed to optimise the review process and reduce risk factors through ongoing data monitoring. Studies on Nigeria's petroleum product transportation spills and environmental impacts between the years 2013 and 2023 were critically analysed to generate updated information. The searches include Scopus, PubMed, and Google Scholar. Five hundred and forty peer-reviewed studies were analysed, and recommendations were established through the conclusions. The findings show that petroleum product transport causes heavy metal deposition in the environment as heavy metals damage aquatic life and build up in the food chain, posing a health risk to humans. The study revealed that petroleum product spills have far-reaching environmental repercussions and, therefore, recommended that petroleum product spills must be mitigated immediately. Furthermore, the study revealed that better spill response and stricter legislation are needed to reduce spills, while remediation is necessary to lessen the effects of spills on environmental and human health.

Effects of biochar and zero valent iron on the bioavailability and potential toxicity of heavy metals in contaminated soil at the field scale

Heavy metals (HMs) such as copper, nickel and chromium are toxic, so soil contaminated with these metals is of great concern. In situ HM immobilization by adding amendments can decrease the risk of contaminants being released. A five-month field-scale study was performed to assess how different doses of biochar and zero valent iron (ZVI) affect HM bioavailability, mobility, and toxicity in contaminated soil. The bioavailabilities of HMs were determined and ecotoxicological assays were performed. Adding 5 % biochar, 10 % ZVI, 2 % biochar + 1 % ZVI, and 5 % biochar + 10 % ZVI to soil decreased Cu, Ni and Cr bioavailability. Metals were most effectively immobilized by adding 5 % biochar + 10 % ZVI, and the extractable Cu, Ni, and Cr contents were 60.9 %, 66.1 % and 38.9 % lower, respectively, for soil with 5 % biochar + 10 % ZVI added than unamended soil. The extractable Cu, Ni, and Cr contents were 64.2 %, 59.7 % and 16.7 % lower, respectively, for soil with 2 % biochar + 1 % ZVI added than unamended soil. Experiments using wheat, pak choi and beet seedlings were performed to assess the remediated soil toxicity. Growth was markedly inhibited in seedlings grown in extracts of soil with 5 % biochar, 10 % ZVI, or 5 % biochar + 10 % ZVI added. More growth occurred in wheat and beet seedlings after 2 % biochar + 1 % ZVI treatment than the control, possibly because 2 % biochar + 1 % ZVI simultaneously decreased the extractable HM content and increased the soluble nutrient (carbon and Fe) content of the soil. A comprehensive risk assessment indicated that adding 2 % biochar + 1 % ZVI gave optimal remediation at the field scale. Using ecotoxicological methods and determining the bioavailabilities of HMs can allow remediation methods to be identified to efficiently and cost-effectively decrease the risks posed by multiple metals in soil at contaminated sites.

Use of natural sorbents for accelerated bioremediation of grey forest soil contaminated with crude oil

Due to the extensive oil extraction and transportation that occurs in oil-producing countries, many lands remain contaminated because of accidental leakages. Despite its low cost and environmentally safe nature, bioremediation technology is not always successful, mainly because of the soil toxicity to the degrading microbial populations and plants. Here we report a three-year microfield experiment on the influence of natural sorbents of mineral (zeolite, kaolinite, vermiculite, diatomite), organic (peat), carbonaceous (biochar) origin, and a mixed sorbent ACD (composed of granular activated carbon and diatomite) on the bioremediation of grey forest soil contaminated with weathered crude oil (40.1 g total petroleum hydrocarbons (TPH) kg^-1). Optimal doses of the sorbents significantly accelerated bioremediation of petroleum-contaminated soil through bioaugmentation followed by phytoremediation. The main reason for the influence of the sorbent amendments relied upon the creation of optimal conditions for the activation of hydrocarbon-utilizing bacteria and plant growth due to the reduction of soil toxicity, as well as maintaining an optimal pH and water-air regime in the soil. That happened because of reducing the soil hydrophobicity, increasing porosity and water holding capacity. The content of the TPH in the best samples (2% biochar or ACD) reduced to their local permissible concentration accepted for remediated soils in the Russian Federation (≤5 g kg^-1) after two warm seasons compared to that after three warm seasons in the other samples. Although some sorbents decelerated biodegradation of highly condensed polycyclic aromatic hydrocarbons (PAHs, including benzo(a)pyrene) in the soil, the overall risk from the residual contaminants present in the remediated soil and plants was minimized. The final total content of the main PAHs in the sorbent-amended soils did not exceed the maximal permissible levels that are accepted in most EU countries (1000-40,000 μg kg^-1), and they did not accumulate in the aboveground phytomass of grasses in dangerous concentrations.

Advanced remediation of pyrene contaminated soil by double dielectric barrier discharge (DDBD) plasma and subsequent composting process

Due to increasing industrialization, soils are increasingly contaminated by polycyclic aromatics such as pyrene and need gentle treatment to keep the soil functioning. This study applied a double dielectric barrier discharge (DDBD) plasma reactor and composting reactor to remediate pyrene-contaminated soil. The effect of peak-to-peak applied voltages on the remediation efficiency of pyrene was investigated. The experimental results illustrate that pyrene remediation efficiency increased from 43% to 85% when the peak-to-peak applied voltage was increased from 28.0 to 35.8 kV. When using the combined method of DDBD and composting, 90-99% of pyrene could be removed, while a reduction of 76.5% was achieved using only composting, indicating the superiority of the combined system. Moreover, the authors could demonstrate that DDBD plasma treatment improves humification in the post-composting process as humic acid (HA) concentrations increased to 7.7 mg/g with an applied voltage of 35.8 kV; when composting was used as the sole treatment method, only 3.4 mg/g HA were produced. The microbial activity in the DDBD plasma-treated soil peaked on the 5th day and had a 2nd rise afterwards. The authors demonstrate that the combined technology of DDBD plasma and composting is a promising method for soil remediation with persistent organic pollutants. This treatment approach improves pollutant degradation efficiency and facilitates further humification, potentially restoring the function of contaminated soil. This approach could be considered a cost-effective and green strategy for soil remediation with persistent organic pollutants.

Bioengineered biochar as smart candidate for resource recovery toward circular bio-economy: a review

Biochar's ability to mediate and facilitate microbial contamination degradation, as well as its carbon-sequestration potential, has sparked interest in recent years. The scope, possible advantages (economic and environmental), and future views are all evaluated in this review. We go over the many designed processes that are taking place and show why it is critical to look into biochar production for resource recovery and the role of bioengineered biochar in waste recycling. We concentrate on current breakthroughs in the fields of engineered biochar application techniques to systematically and sustainable technology. As a result, this paper describes the use of biomass for biochar production using various methods, as well as its use as an effective inclusion material to increase performance. The impact of biochar amendments on microbial colonisation, direct interspecies electron transfer, organic load minimization, and buffering maintenance is explored in detail. The majority of organic and inorganic (heavy metals) contaminants in the environment today are caused by human activities, such as mining and the use of chemical fertilizers and pesticides, which can be treated sustainably by using engineered biochar to promote the establishment of a sustainable engineered process by inducing the circular bioeconomy.

Recent advances in biochar engineering for soil contaminated with complex chemical mixtures: Remediation strategies and future perspectives

Heavy metal/metalloids (HMs) and polycyclic aromatic hydrocarbons (PAHs) in soil have caused serious environmental problems, compromised agriculture quality, and have detrimental effects on all forms of life including humans. There is a need to develop appropriate and effective remediation methods to resolve combined contaminated problems. Although conventional technologies exist to tackle contaminated soils, application of biochar as an effective renewable adsorbent for enhanced bioremediation is considered by many scientific researchers as a promising strategy to mitigate HM/PAH co-contaminated soils. This review aims to: (i) provide an overview of biochar preparation and its application, and (ii) critically discuss and examine the prospects of (bio)engineered biochar for enhancing HMs/PAHs co-remediation efficacy by reducing their mobility and bioavailability. The adsorption effectiveness of a biochar largely depends on the type of biomass material, carbonisation method and pyrolysis conditions. Biochar induced soil immobilise and remove metal ions via various mechanisms including electrostatic attractions, ion exchange, complexation and precipitation. PAHs remediation mechanisms are achieved via pore filling, hydrophobic effect, electrostatic attraction, hydrogen bond and partitioning. During last decade, biochar engineering (modification) via biological and chemical approaches to enhance contaminant removal efficiency has garnered greater interests. Hence, the development and application of (bio)engineered biochars in risk management, contaminant management associated with HM/PAH co-contaminated soil. In terms of (bio)engineered biochar, we review the prospects of amalgamating biochar with hydrogel, digestate and bioaugmentation to produce biochar composites.

Cytogenetic toxicity from pesticide and trace element mixtures in soils used for conventional and organic crops of Allium cepa L

Pesticides and trace elements occur in complex mixtures in agroecosystems, affecting soil health and food security. Hence, it is necessary to determine their toxicity in field conditions and to develop monitoring approaches to assess conventional and organic agriculture. The aim of this research was to evaluate the associations between Allium cepa L. cytogenetic biomarkers and the realistic mixture of pesticides and trace elements found in soils of conventional, conversion, and organic crops in an intensive agricultural region in Colombia. Pesticide screening was conducted using GC-MS/MS and LC-MS/MS methods. Arsenic, cadmium, lead, and zinc were analyzed by ICP-MS; chromium, copper, nickel, and selenium by ICP-OES; and mercury by a direct analyzer. The meristematic cells in roots of Allium cepa L. were analyzed through microscopic observations to quantify cytogenetic effects. In conventional crops, 26 pesticides were detected in the soil samples, and those were below the limit of quantification in organic crops. The mean levels of As, Cd, Cr, Ni, Pb, and Se were also greater in soils of conventional crops compared to the organics. In addition, the biomarkers of cytotoxicity and genotoxicity appeared augmented in conventional samples, and those were correlated with pesticide and trace element concentrations, pollution indices, and hazard quotients. Subsequently, a discriminant function based on the mitotic index, chromosomal aberrations, and nuclear abnormalities was suitable to classify the samples by crop type. These results demonstrate the sensitivity of Allium cepa L. to the toxicity of complex mixtures in field crops and its potential as an in-situ approach for soil health monitoring in organic and conventional crop systems.

Effects of organic matter addition on chronically hydrocarbon-contaminated soil

Soil is the recipient of organic pollutants as a consequence of anthropogenic activities. Hydrocarbons are contaminants that pose a risk to human and environmental health. Bioremediation of aging contaminated soils is a challenge due to the low biodegradability of contaminants as a result of their interaction with the soil matrix. The aim of this work was to evaluate the effect of both composting and the addition of mature compost on a soil chronically contaminated with hydrocarbons, focusing mainly on the recovery of soil functions and transformations of the soil matrix as well as microbial community shifts. The initial pollution level was 214 ppm of polycyclic aromatic hydrocarbons (PAHs) and 2500 ppm of aliphatic hydrocarbons (AHs). Composting and compost addition produced changes on soil matrix that promoted the release of PAHs (5.7 and 15 % respectively) but not the net PAH elimination. Interestingly, composting stimulated AHs elimination (about 24 %). The lack of PAHs elimination could be attributed to the insufficient PAHs content to stimulate the microbial degrading capacity, and the preferential consumption of easily absorbed C sources by the bacterial community. Despite the low PAH catabolic potential of the aging soil, metabolic shift was driven by the addition of organic matter, which could be monitored by the ratio of Proteobacteria to Actinobacteria combined with E₄/E₆ ratio. Regarding the quality of the soil, the nutrients provided by the exogenous organic matter contributed to the recovery of the global functions and species diversity of the soil along with the reduction of phytotoxicity.

Recent Advances in the Study of the Remediation of Polycyclic Aromatic Compound (PAC)-Contaminated Soils: Transformation Products, Toxicity, and Bioavailability Analyses

Polycyclic aromatic compounds (PACs) encompass a diverse group of compounds, often found in historically contaminated sites. Different experimental techniques have been used to remediate PACs-contaminated soils. This brief review surveyed over 270 studies concerning remediation of PACs-contaminated soils and found that, while these studies often measured the concentration of 16 parent polycyclic aromatic hydrocarbons (PAHs) pre- and post-remediation, only a fraction of the studies included the measurement of PAC-transformation products (PAC-TPs) and other PACs (n = 33). Only a few studies also incorporated genotoxicity/toxicity/mutagenicity analysis pre- and post-remediation (n = 5). Another aspect that these studies often neglected to include was bioavailability, as none of the studies that included measurement of PAH-TPs and PACs included bioavailability investigation. Based on the literature analysis, future remediation studies need to consider chemical analysis of PAH-TPs and PACs, genotoxicity/toxicity/mutagenicity, and bioavailability analyses pre- and post-remediation. These assessments will help address numerous concerns including, among others, the presence, properties, and toxicity of PACs and PAH-TPs, risk assessment of soil post-remediation, and the bioavailability of PAH-TPs. Other supplementary techniques that help assist these analyses and recommendations for future analyses are also discussed.

Remediation of pyrene contaminated soil by double dielectric barrier discharge plasma technology: Performance optimization and evaluation

Polycyclic aromatic hydrocarbons (PAHs) in soil are not only detrimental to environment but also to human health. Double dielectric barrier discharge (DDBD) plasma reactor used for the remediation of pyrene contaminated soil was studied. The performance of DDBD reactor was optimized with influential parameters including applied voltage, type of carrier gas, air feeding rate as well as pyrene initial concentration. The analysis of variance (ANOVA) results showed that input energy had a great effect on pyrene remediation efficiency followed by pyrene initial concentration, while, the effect of air feeding rate was insignificant. More specifically, the remediation efficiency of pyrene under air, nitrogen and argon as carrier gas were approximately 79.7, 40.7 and 38.2% respectively. Pyrene remediation efficiency is favored at high level of applied voltages and low level of pyrene initial concentration (10 mgkg^-1) and air feeding rate (0.85 L/min). Moreover, computation of the energy efficiency of the DDBD system disclosed that an optimal applied voltage (35.8 kV) and higher initial pyrene concentration (200 mgkg^-1) favored the high energy efficiency. A regression model predicting pyrene remediation under DDBD plasma condition was developed using the data from a face-centered central composite design (FCCD) experiment. Finally, the residual toxicity analysis depicted that the respiratory activity increased more than 21 times (from 0.04 to 0.849 mg O₂ g^-1) with a pyrene remediation efficiency of 81.1%. The study demonstrated the DDBD plasma technology is a promising method not only for high efficiency of pyrene remediation, but also recovering biological function without changing the physical-chemical properties of soil.

Biodegradation of mixed polycyclic aromatic hydrocarbons by pure and mixed cultures of biosurfactant producing thermophilic and thermo-tolerant bacteria

Applicability of thermophilic and thermo-tolerant microorganisms for biodegradation of polycyclic aromatic hydrocarbons (PAHs) with low water solubility is an interesting strategy for improving the biodegradation efficiency. In this study, we evaluated utility of thermophilic and thermo-tolerant bacteria isolated from Unkeshwar hot spring (India) for biodegradation of four different PAHs. Water samples were enriched in mineral salt medium (MSM) containing a mixture of four PAHs compounds (anthracene: ANT, fluorene: FLU, phenanthrene: PHE and pyrene: PYR) at 37 °C and 50 °C. After growth based screening, four potent strains obtained which were identified as Aeribacillus pallidus (UCPS2), Bacillus axarquiensis (UCPD1), Bacillus siamensis (GHP76) and Bacillus subtilis subsp. inaquosorum (U277) based on the 16S rRNA gene sequence analysis. Degradation of mixed PAH compounds was evaluated by pure as well as mixed cultures under shake flask conditions using MSM supplemented with 200 mg/L concentration of PAHs (50 mg/L of each compound) for 15 days at 37 °C and 50 °C. A relatively higher degradation of ANT (92%- 96%), FLU (83% - 86%), PHE (16% - 54%) and PYR (51% - 71%) was achieved at 50 °C by Aeribacillus sp. (UCPS2) and mixed culture. Furthermore, crude oil was used as a substrate to study the degradation of same PAHs using these organisms which also revealed with similar results with the higher degradation at 50 °C. Interestingly, PAH-degrading strains were also positive for biosurfactant production. Biosurfactants were identified as the variants of surfactins (lipopeptide biosurfactants) based on analytical tools and phylogenetic analysis of the surfactin genes. Overall, this study has shown that hot spring microbes may have a potential for PAHs degradation and also biosurfactant production at a higher temperature, which could provide a novel perspective for removal of PAHs residues from oil contaminated sites.

Predicting bioavailability change of complex chemical mixtures in contaminated soils using visible and near-infrared spectroscopy and random forest regression

A number of studies have shown that visible and near infrared spectroscopy (VIS-NIRS) offers a rapid on-site measurement tool for the determination of total contaminant concentration of petroleum hydrocarbons compounds (PHC), heavy metals and metalloids (HM) in soil. However none of them have yet assessed the feasibility of using VIS-NIRS coupled to random forest (RF) regression for determining both the total and bioavailable concentrations of complex chemical mixtures. Results showed that the predictions of the total concentrations of polycyclic aromatic hydrocarbons (PAH), PHC, and alkanes (ALK) were very good, good and fair, and in contrast, the predictions of the bioavailable concentrations of the PAH and PHC were only fair, and poor for ALK. A large number of trace elements, mainly lead (Pb), aluminium (Al), nickel (Ni), chromium (Cr), cadmium (Cd), iron (Fe) and zinc (Zn) were predicted with very good or good accuracy. The prediction results of the total HMs were also better than those of the bioavailable concentrations. Overall, the results demonstrate that VIS-NIR DRS coupled to RF is a promising rapid measurement tool to inform both the distribution and bioavailability of complex chemical mixtures without the need of collecting soil samples and lengthy extraction for further analysis.