Amendment of soil by biochars and activated carbons to reduce chlordecone bioavailability in piglets

The boom era of emerging contaminants: A review of remediating agricultural soils by biochar

Emerging contaminants (ECs) are widely sourced persistent pollutants that pose a significant threat to the environment and human health. Their footprint spans global ecosystems, making their remediation highly challenging. In recent years, a significant amount of literature has focused on the use of biochar for remediation of heavy metals and organic pollutants in soil and water environments. However, the use of biochar for the remediation of ECs in agricultural soils has not received as much attention, and as a result, there are limited reviews available on this topic. Thus, this review aims to provide an overview of the primary types, sources, and hazards of ECs in farmland, as well as the structure, functions, and preparation types of biochar. Furthermore, this paper emphasizes the importance and prospects of three remediation strategies for ECs in cropland: (i) employing activated, modified, and composite biochar for remediation, which exhibit superior pollutant removal compared to pure biochar; (ii) exploring the potential synergistic efficiency between biochar and compost, enhancing their effectiveness in soil improvement and pollution remediation; (iii) utilizing biochar as a shelter and nutrient source for microorganisms in biochar-mediated microbial remediation, positively impacting soil properties and microbial community structure. Given the increasing global prevalence of ECs, the remediation strategies provided in this paper aim to serve as a valuable reference for future remediation of ECs-contaminated agricultural lands.

The Effect of Granulometry of Carbonaceous Materials and Application Rates on the Availability of Soil-Bound Dichlorodiphenyltrichloroethane (DDT) and Its Metabolites

Biochars (BCs) and activated carbons (ACs) are well-known carbon-rich materials that are being increasingly studied in environmental sciences for water treatment applications to remediate pollutant sequestration in soil. This study aimed to assess the impact of Sargasso BC particle size and amendment rate on the environmental availability of DDT and DDT metabolites in two distinct Kazakh soils. These two soils were collected in the vicinity of storehouse facilities in Kyzylkairat and Beskainar that store banned pesticides. They presented very distinct concentration levels of DDT and DDT metabolites. Three different types of carbonaceous matrices were tested: Sargasso BC and two commercial ACs (ORBOTM and DARCO©). For the granulometry effect, Sargasso BC was ground, and two particle sizes were tested (<150 µm, >150 µm) and compared to an unground material. Four distinct application rates were tested (0.25, 0.5, 1, and 2% (w/w)). After a three-month maturation period, environmental availability was assessed using an ISO/DIS 16751, part B-modified methodology. Interestingly, the best reductions in DDT environmental availability were obtained with the finest particle size (both ACs and Sargasso BC < 150 µm). More specifically, the effectiveness of the strategy seemed to depend on many factors. Firstly, a clear soil effect was demonstrated, suggesting that the more contaminated the soil, the more efficient this strategy may be. Secondly, the results showed that an increase in the amendment rate improves the immobilization of DDT and DDT metabolites. The sequestration material demonstrated different efficiency values (up to 58 ± 4% for Sargasso BC < 150 µm and 85 ± 4% for DARCO at a 2% application rate). Finally, a clear molecule effect was displayed, demonstrating the following immobilization order: p,p'-DDE > p,p'-DDD > p,p'-DDT > o,p'-DDT.

Comparison of in vitro strategies for predicting Dichlorodiphenyltrichloroethane (DDT) and its metabolites bioavailability from soils

In vitro strategies have widely been used to assess bioaccessibility of organic pollutants in soils. However, studies for comparing in vitro models with in vivo data are still limited. In this study, Dichlorodiphenyltrichloroethane (DDT) and its metabolites (called as DDTr) bioaccessibility in nine contaminated soils were measured using physiologically based extraction test (PBET), in vitro digestion model (IVD), and Deutsches Institut für Normung (DIN) with/without Tenax as an absorptive sink, and DDTr bioavailability was assessed using an in vivo mouse model. Whether or not Tenax was added, DDTr bioaccessibility significantly varied among three methods, suggesting that DDTr bioaccessibility depended on the in vitro method employed. Multiple linear regression analysis indicated that sink, intestinal incubation time and bile content are identified to be the dominant factors in controlling DDTr bioaccessibility. Comparison of in vitro and in vivo results demonstrated that DIN assay with Tenax (TI-DIN) provided the best prediction for DDTr bioavailability (r² = 0.66, slope=0.78). After extending intestinal incubation time to 6 h or increasing bile content to 4.5 g/L (same to DIN assay) of the TI-PBET and TI-IVD assays, the in vivo-in vitro correlation will improved significantly, with r² = 0.76 and slope= 1.4 for TI-PBET and r² = 0.84 and slope= 1.9 for TI-IVD under 6 h intestinal incubation, and r² = 0.59 and slope= 0.96 for TI-PBET and r² = 0.51 and slope= 1.0 for TI-IVD under 4.5 g/L of bile content. The results suggest that it is essential to understand these key factors influencing bioaccessibility for the development of standardized in vitro methods, which helps to refine the risk assessment of human exposure to contaminants via soil ingestion.

Effects of particle size and amendment rates of Sargassum biochar on chlordecone sequestration in West Indian soils

The use of biochars (BCs) and activated carbons as a way of sequestering soil-bound pollutants such as chlordecone (CLD) is increasingly being studied. This study aims at assessing the impact of Sargassum BC/AC particle size and Sargassum BC amendment rate on CLD adsorption in Nitisol and in Andosol. Four different types of carbonaceous matrices were tested: Sargasso carbon activated by phosphoric acid (SargH3PO4), Sargasso carbon activated by steam (SargH2O), biochar of Sargasso (Ch Sarg700), and a commercial activated carbon (ORBO™). In a first experiment, CLD contaminated Andosol and Nitisol were amended with 2% of each carbonaceous matrix divided into four particles size classes (< 50 µm, 50-150 µm, 150-200 µm, and > 200 µm). In a second experiment, the contaminated soils were amended with the biochar of Sargasso at five application rates (0, 0.25, 0.5, 1, and 2% (w/w)). After a 4-month aging, environmental availability tests were carried out on the soils of both experiments. The results of the first experiment showed that the best reductions of CLD environmental availability were obtained in both soils with the biochar of Sargasso and the ORBO™. More specifically, in nitisol, particle size under 50 µm of biochar of Sargasso and AC ORBO™ showed a CLD environmental availability reduction up to 72 ± 2.6% and 79 ± 2.6%. In Andosol, there was no significant difference between the three particle sizes (< 50 µm, 50-150 µm, and 150-200 µm) of the biochar of Sargasso on the reduction of environmental availability (average reduction of 43 ± 2.5%). The results of the second experiment showed that an amendment rate increase improves the immobilization of CLD. When the amendment rate was increased from 0.25 to 2%, the environmental availability was reduced by 43% in Nitisol and 50% in Andosol.

Organochlorine POPs sequestration strategy by carbonaceous amendments of contaminated soils: Toward a better understanding of the transfer reduction to laying hens

PCBs, PCDD/Fs, and Chlordecone (CLD) are POPs found in soils and transferred to animals through involuntary soil ingestion. In this frame, the amendment of contaminated soil with porous matrices, like Biochars (BCs) and Activated Carbons (ACs), is a promising technique for reducing this transfer. In this study, the efficiency of 3 biochars and 3 activated carbons was assessed by amending 2% (by weight) of these matrices on (i) CLD or (ii) PCBs and PCDD/Fs contaminated artificial soils. Porosity of the carbon-based materials and molecules physico-chemical characteristics were then linked to the obtained results. The concentrations of pollutants were then measured in the egg yolks of laying hens (n = 3), which were fed on a daily basis pellets containing 10% of soil for 20 days. Overall, no significant transfer reduction was observed with the biochar and the granular AC amendments for all the compounds. However, significant reductions were obtained with the two efficient activated carbons for PCDD/Fs and DL-PCB up to 79-82% (TEQ basis), whereas only a slight reduction of concentrations was obtained with these activated carbons for CLD and NDL-PCBs. Thus, (i) biochars were not proven efficient to reduce halogenated pollutants transfer to animals, (ii) powdered AC amendments resulted in reducing the bioavailability of soil POPs, and (iii) the effectiveness of such strategy depended on both characteristics of the matrix and of the pollutants.

Effects of biochar-based materials on the bioavailability of soil organic pollutants and their biological impacts

Motivated by the unique structure and superior properties, biochar-based materials, including pristine biochar and composites of biochar with other functional materials, are considered as new generation materials for diverse multi-functional applications, which may be intentionally or unintentionally released to soil. The influencing mechanism of biochar-based material on soil organisms is a key aspect for quantifying and predicting its benefits and trade-offs. This work focuses on the effects of biochar-based materials on soil organisms within the past ten years. 206 sources are reviewed and available knowledge on biochar-based materials' impacts on soil organisms is summarized from a diverse perspective, including the pollutant bioavailability changes in soil, and potential effects of biochar-based materials on soil organisms. Herein, effects of biochar-based materials on the bioavailability of soil organic pollutants are detailed, from the perspective of plant, microorganism, and soil fauna. Potential biological effects of pristine biochar (PBC), metal/metal compounds-biochar composites (MBC), clay minerals-biochar composites (CMBC), and carbonaceous materials-biochar composites (CBC) on soil organisms are highlighted for the first time. And possible mechanisms are presented based on the different characters of biochar-based materials as well as various environmental interactions. Finally, the bottleneck and challenges of risk assessment of biochar-based materials as well as future prospects are proposed. This work not only promotes the development of risk assessment system of biochar-based materials, but broadens the strategy for the design and optimization of environmental-friendly biochar materials.

In vitro and in vivo assessment of a CLD sequestration strategy in Nitisol using contrasted carbonaceous materials

Chlordecone (Kepone) (CLD) is a highly persistent pesticide formerly used in the French West Indies. High levels of this pesticide may be found in soils and constitute a subsequent source of contamination for outdoor-reared animals due to involuntary ingestion of consistent amounts of soil. In that context, carbonaceous materials may be used to amend soil to efficiently decrease the bioavailability of such organic pollutants. The present study aims to assess the efficiency of diverse amendments of a contaminated Guadeloupe nitisol using two physiologically based approaches. A set of 5 carbonaceous materials (ORBO, DARCO, Coco CO2, Oak P1.5, Sargasso biochar) was tested and used to amend Nitisol at 2% (mass basis). Bioaccessibility assessment was performed using the Ti-PBET assay (n = 4). The relative bioavailability part involved 24 piglets randomly distributed into 6 experimental groups (n = 4). All groups were exposed during 10 days to a contaminated soil, amended or not with carbon-based matrices. A significant decrease in relative bioaccessibility and CLD concentrations in liver were observed for all amended groups in comparison to the control group, with the exception of the biochar amended soil in the bioaccessibility assay (p < 0.05). Extent of this reduction varied from 22 to more than 82% depending on the carbonaceous matrix. This decrease was particularly important for the ORBO™ activated carbon for which bioaccessibility and relative bioavailability were found lower than 10% for both methodologies.

Assessment of an NDL-PCBs Sequestration Strategy in Soil Using Contrasted Carbonaceous Materials through In Vitro and Cucurbita pepo Assays

The present study aims to assess the respective efficiency of Biochars (BCs) and activated carbons (ACs) to limit PCB 101, 138, 153 and 180 transfer to plants. A set of 6 high carbon materials comprising 3 BCs and 3 ACs was tested and used to amend a soil at 2% rate. Then, the two most efficient carbonaceous materials were used as an amendment of an historically contaminated soil sampled in the St Cyprien vicinity (Loire, France). An environmental availability assessment was performed using the ISO/DIS 16751 Part A assay (n = 3). For the in vivo part, Cucurbita pepo were grown for 12 weeks. Significant decreases of transfer were found for both assays notably for powdered ACs (up to 98%). By contrast, significantly lower levels of transfer reduction were observed when BCs amendments were performed, ranging from 27 to 80% for environmental availability assessment and 0 to 36% for C. pepo. Reduction factors above 90% for the 2 selected materials were found from amended historically contaminated soils. Present results led to consider such a sequestering strategy as valuable to ensure plant production on non-dioxin-like polychlorobiphenyls (NDL-PCBs) contaminated soils.

Reduction of chlordecone environmental availability by soil amendment of biochars and activated carbons from lignocellulosic biomass

Chlordecone (kepone or CLD) was formerly used in French West Indies as an insecticide. Despite its formal ban in 1993, high levels of this pesticide are still found in soils. As such, sequestering matrices like biochars or activated carbons (ACs) may successfully decrease the bioavailability of halogenated compounds like CLD when added to contaminated soils. The present study intends (i) to produce contrasted sequestering matrices in order to (ii) assess their respective efficiency to reduce CLD environmental availability. Hence, the work was designed following two experimental steps. The first one consisted at producing different sequestering media (biochars and ACs) via pyrolysis and distinct activation processes, using two lignocellulosic precursors (raw biomass): oak wood (Quercus ilex) and coconut shell (Cocos nucifera). The chemical activation was carried out with phosphoric acid while physical activation was done with carbon dioxide and steam. In the second step, the CLD environmental availability was assessed either in an OECD artificial soil or in an Antillean contaminated nitisol (i.e., 2.1^-1μg CLD per g of soil dry matter, DM), both amended with 5 wt% of biochar or 5 wt% of AC. These both steps aim to determine CLD environmental availability reduction efficiency of these media when added (i) to a standard soil material or (ii) to a soil representative of the Antillean CLD contamination context. Textural characteristics of the derived coconut and oak biochars and ACs were determined by nitrogen adsorption at 77 K. Mixed microporous and mesoporous textures consisting of high pore volume (ranging from 0.38 cm³.g^-1 to 2.00 cm³.g^-1) and specific (BET) surface areas from 299.9 m².g^-1 to 1285.1 m².g^-1 were obtained. Overall, soil amendment with biochars did not limit CLD environmental availability (environmental availability assay ISO/DIS 16751 Part B). When soil was amended with ACs, a significant reduction of the environmental availability in both artificial and natural soils was observed. AC soil amendment resulted in a reduced CLD transfer by at least 65% (P < 0.001) for all lignocellulosic matrices (excepted for coconut sample activated with steam, which displayed a 47% reduction). These features confirm that both pore structure and extent of porosity are of particular importance in the retention process of CLD in aged soil. Owing to its adsorptive properties, AC amendment of CLD-contaminated soils appears as a promising approach to reduce the pollutant transfer to fauna and biota.

Control of poultry contamination in chlordecone-contaminated areas of the French West Indies

The consumption of private hold poultry foodstuffs, escaping of official maximum residue limit (MRL) controls in the commercial foodstuff, is an important exposure way for the local populations to chlordecone on the French West Indies. Therefore, chlordecone contamination of different tissues in 42 birds from 32 private holders was determined depending on the contamination of the soil of the outside plot but also surveying the rearing practices of these holders of both islands. Chlordecone contents in tissues increased rapidly with this of the topsoil of the site. The most sensitive tissues to chlordecone presence were egg yolk and liver, followed by abdominal fat and finally leg tissue. The rearing practices varied between the surveyed private holders of both islands. Nevertheless, practices for the distribution of feed and water as well as covering of soil were hardly protective, what would increase the exposure risk of these birds to this potentially present soil-bound contaminant. Although depuration of birds seems possible, the ongoing modelization of the necessary time to meet MRL thresholds indicates that such time lapse seems hardly compatible with acceptable delays for private holders. Therefore, very protective rearing practices are the main way to obtain poultry foodstuffs compliant to MRL, what seems possible if the topsoil is contaminated at less than 0.1 mg kg^-1 and perhaps up to 0.5 mg kg^-1 if protective practices vis-a-vis of soil exposure are very strict. Nevertheless, a higher contamination of the topsoil seems not compatible with compliant poultry foodstuffs.

Role of biochar and Eisenia fetida on metal bioavailability and biochar effects on earthworm fitness

Biochar has gained extensive attention due to its remediation role in soil pollution. However, its hazardous effects on the soil fauna in contaminated soil and its remediation efficiency affected by soil organisms are still obscure. The individual and combined effects of biochar and earthworms (Eisenia fetida) on soil properties, metal bioavailability, and earthworm fitness were investigated in historically heavy metal (HM)-contaminated soil. The results showed that biochar increased the soil pH by 0.31, decreased DTPA-extractable Cd, Cu, Zn and Pb contents by 11.9%, 14.3%, 5.27% and 23.8%, respectively, and immobilized the HMs from a bioavailable fraction to a residual fraction. The co-incubation of biochar and E. fetida decreased soil pH by 0.11 and increased DTPA-extractable Cu, Zn, and Pb contents by 3.75%, 20.9% and 4.43%, respectively. The results of the correlation analysis showed that soil pH was significantly negatively correlated with HM bioavailability, and it was a potential factor contributed to this opposite effect. Furthermore, biochar decreased the biomass growth of E. fetida and inhibited the activities of SOD, CAT and GSH in E. fetida by 31.1%, 51.3% and 29.6% after 28 days of incubation. Overall, biochar and E. fetida showed the opposite effects on the soil remediation, and biochar also led to a negative effect on earthworms. These findings provided insights on verifying the actual remediation effects of biochar and its ecological risk in situ soil remediation.

Effects of biochar on the earthworm (Eisenia foetida) in soil contaminated with and/or without pesticide mesotrione

The plant-derived biochars act as soil conditioners, and thus may influence biological interactions in the soil environment. However, their unintended negative and positive effects on soil organisms remain largely understudied. Therefore, we investigated the effect of 0, 1, 3, and 10% of wheat straw-derived biochar amendments on earthworm (Eisenia foetida) activity in the soil contaminated with and/or without pesticide mesotrione (10 mg/kg dry soil) after 28 days of incubation. The pesticide mesotrione did not affect earthworm growth or reproduction; however, it induced oxidative stress and DNA damage. Although biochar application significantly decreased the concentration of mesotrione in earthworms, it delayed the degradation of pesticide in the soil environment. Compared to zero amendment, the amendment of 1 and 3% of biochar significantly increased (P < 0.05) the earthworm weight and reduced the toxicity effects of mesotrione on earthworms. However, the application of 10% biochar significantly decreased (P < 0.05) earthworm growth and caused DNA damage even in the absence of mesotrione. This study suggests that it is necessary to investigate the effects of different levels of biochar amendments on earthworms and other soil organisms in agricultural fields to develop a broader understanding about the use of biochar and its consequences on soil health.