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This study evaluated the effects of the soil amendments biochar, activated carbon (AC), and attapulgite (APG) on the assessment of pentachlorobenzene (PeCB) bioavailability to earthworms ( Eisenia foetida) using the hydroxypropyl-β-cyclodextrin (HPCD) extraction method. The results showed that the amendment of soil with biochar and AC, rather than APG, significantly reduced the bioavailability of PeCB in soil being uptaken by earthworms ( p < 0.05). After 1 week aging, the HPCD extraction efficiency of PeCB in biochar - or AC - amended soils decreased relative to that in unamended soils. This reduction was greater compared with the declining extent of PeCB uptaken by earthworms in biochar - or AC - amended soils relative to unamended soils. This could underestimate the bioavailability of PeCB in the amended soils using HPCD extraction method. However, when aging period exceeded 24 weeks, there were diminished differences between earthworm uptake and chemical method results. This suggests a better assessment of the bioavailability of PeCB in the amended soil using HPCD extraction method. Therefore, HPCD extraction method could result in an underestimation of the bioavailability of PeCB in soils amended with biochar - or AC - during a short-term aging period. However, during a long term aging period with these soil amendments, HPCD extraction method was still a suitable tool to assess the bioavailability of PeCB in soil to the uptake by earthworms. [ABSTRACT FROM AUTHOR]

Abstract: The total concentration of organic contaminants in soil often overestimates their environmental risk, it is thus important to establish time- and cost-efficient chemical techniques for predicting their bioavailability. In the present study, three chemical extractions, namely: Tenax extraction, butanol extraction and HPCD extraction, were conducted to predict PAHs bioavailability in soil for earthworms. The results showed that earthworm accumulations had less correlation with total concentrations except for PAHs of low molecular weight (R2–3 PAHs). Fractions extracted by butanol/HPCD correlated to earthworm accumulated PAHs of low molecular weight (R2–3 PAHs), but not to earthworm accumulated PAHs of high molecular weight (R5–6 PAHs). Tenax 6h-extracted PAHs had significantly linear correlations with earthworm accumulated R2–3 PAHs, R4 PAHs as well as R5–6 PAHs (associated R 2 were 0.96, 0.98 and 0.97, respectively). Furthermore, Tenax 6h-extracted concentrations were comparable to earthworm accumulations for R2–3, R4 as well as R5–6 PAHs. These observations verified that Tenax 6h extraction is better than butanol and HPCD extractions to predict earthworm accumulation of PAHs in soil. Tenax 6h extraction can serve as a good technique to assess PAHs bioavailability for earthworms. [Copyright &y& Elsevier]

Abstract: The rapid-desorbing fraction plays an important role in the bioavailability of organic pollutants in soil. In the present study, DDT''s desorption from the cotton field soils was investigated by Tenax extraction. The results of the Tenax consecutive extraction (400h) indicated that the rate constants were in the order of 10−1, 10−2, and 10−4 h−1 for the rapid, slow and very-slow desorption, respectively. The rapid-desorbing fraction was about 0.3 times the total soil DDTs, and about 2 times the Tenax 6h-extracted fraction (single-point extraction). The rapid-desorbing fraction correlated well with the 6h-extracted fraction (p <0.05), implying the feasibility of measuring the rapid-desorbing fraction with Tenax 6h-extration. The strong correlation with the carrot accumulation suggested that Tenax 6h-extrated fraction could serve as a good predictor of DDT''s bioavailability to carrot roots. Risk assessment demonstrated that when based on the rapid-desorbing concentration and 6h-extracted concentration, about 60.7% and 17.9% of the soil samples were moderately polluted, however, up to 78.5% were moderately polluted when based on the total soil DDTs concentration. The risk assessment might be more representative when based on Tenax extraction because of the strong correlation with the carrot accumulation. Our results provided implications for site risk assessment and cleanup strategies. [Copyright &y& Elsevier]

Abstract Application of crop residues is a conventional practice that contributes to crop production through nutrient returns and other benefits to soil health: driving soil physicochemical and biological functions. However, little is known about the impacts of straw residue incorporation on the bioavailability of organic pollutants and associated changes in microbial community structure in contaminated soils. In this study, maize straw was added to a soil contaminated with a model polybrominated diphenyl ether (BDE-47). A pot experiment was conducted and planted with carrot (Daucus carota L.). We found that straw addition greatly reduced the bioavailability of BDE-47, changed the bacterial community structure and affected a range of soil physiochemical properties. Moreover, the amount of BDE-47 that had accumulated in carrot roots and aboveground tissues was significantly reduced. This study may therefore describe an effective agronomic strategy to reduce the bioavailability of polybrominated diphenyl ethers (PBDEs) in a soil used to grow high value vegetable crops. This strategy draws on traditional wisdom and shows promise as a practical method to support horticultural production systems, remediate soils, and help to ensure food safety. Graphical abstract Unlabelled Image Highlights • Maize straw incorporation decreased BDE-47 bioaccumulation in carrot. • Maize straw incorporation reduced the bioavailability of BDE-47 in soil. • Maize straw incorporation enhanced the dissipation of BDE-47 in soil. • Soil bacterial community was mainly affected by available P, TOC, and bioavailable concentration of BDE-47. [ABSTRACT FROM AUTHOR]

This study aimed to elucidate the mechanisms by which biochar reduces the bioaccumulation of polycyclic aromatic hydrocarbons (PAHs) in rice under anaerobic conditions. Corn straw- or bamboo-derived biochar pyrolyzed at 300 °C and 700 °C (CB300 or BB700), respectively, was amended into flooded PAH-contaminated soil. After harvest, 2% CB300, 0.5% BB700 or 2% BB700 amendments reduced the bioaccumulation of PAHs in rice root, especially that of high-molecular-weight PAHs ( p  < .05). Total PAH concentrations were higher, and their bioavailable concentrations were lower in BB700-amended soils than the control. The stimulation of PAH desorption from BB by low-molecular-weight organic acids (LMWOAs) was gentle and did not significantly retard the adsorption of PAHs on BB700, indicating that BB700 reduced PAH bioavailability primarily via immobilization. The total and bioavailable concentrations of PAHs were both lower in the 2% CB300-treated soils than the control. LMWOAs facilitated PAH release from CB300-amended soils, thus increasing the bioavailability of immobilized PAHs. The relative abundances of the bacteria, functional genes, and methanogens involved in PAH anaerobic degradation were significantly higher in the 2% CB300 treatment than other treatments. Fast PAH dissipation in soil amended with 2% CB300 may be attributed to the increased bioavailability of immobilized PAHs and enhanced biodegradation, both of which were induced by LMWOAs and CB. In summary, biochar types and root presence jointly affected the mechanisms by which biochar reduced the bioaccumulation of PAHs in rice under anaerobic conditions. [ABSTRACT FROM AUTHOR]

The aim of this study was to reveal the mechanisms on how biochar reduces bioaccumulation of polycyclic aromatic hydrocarbons (PAHs) in tuberous vegetables. Corn straw-derived biochar pyrolyzed at 300 °C (CB300) or bamboo-derived biochar pyrolyzed at 700 °C (BB700) was amended into PAH-contaminated soil planted with carrot ( Daucus carota L.). After 150 days, 2% CB300 or 2% BB700 amendments significantly reduced the bioaccumulation of PAHs in carrot root ( p < 0.05), especially for high-molecular-weight PAHs. In the non-rhizosphere, either CB300 or BB700 suppressed PAH dissipation and decreased the bioavailability via adsorption processes. Compared to the control, the total concentration of PAHs in the rhizosphere was higher in the 2% BB700 treatment but the bioavailable concentration was lower. This indicates that BB700 decreased the bioavailability of PAHs primarily via immobilization (adsorption processes). By contrast, the total and bioavailable PAH concentrations were both lower in the 2% CB300 treatment than those in the control. The abundance of bacteria such as Arthrobacter and Flavobacterium and the total number of genes playing important roles in microbial PAH degradation processes increased significantly ( p < 0.05), which were likely responsible for the rapid dissipation of PAHs in the 2% CB300 treatment in the rhizosphere. These results indicate that CB300 decreased the PAH bioavailability primarily via increasing degradation of PAHs by indigenous microorganisms. The two biochars both showed better effectiveness at reducing the bioavailability of high-molecular-weight PAHs than the low-molecular-weight PAHs in the rhizosphere. Therefore, the mechanisms on how biochar reduces the PAH uptake into carrot are dependent on the type of biochar (e.g., pyrolysis temperature and feedstock) and root presence. [ABSTRACT FROM AUTHOR]

DDT had been widely used around the world before 1980s and is still under production and use for non-agricultural purposes in China. Because of their special physicochemical properties, p,p′-DDT and its main metabolites, p,p′-DDD and p,p′-DDE, accumulated and persisted in the environment, presenting potential menace on biota. A green-house study was conducted to determine the bioavailability of p,p′-DDD and p,p′-DDE to grains of rice and the influences of traditional Chinese farming practices on their bioaccumulation. Paddy rice and dry rice were grown in submerged paddy soils and non-submerged upland soils, respectively. Two types of soil, Hydragric Anthrosols (An) and Hydragric Acrisols (Ac), were employed. Bioaccumulation factors (BAFs) of DDE ranged from 0. 67 for rice grown in non-submerged An to 0. 84 in submerged An in the control group, whilst BAFs were all below 0. 04 in experimental groups. BAFs of DDD varied from 1. 39 for submerged An to 2. 26 for submerged Ac in original soils. In contrast, BAFs were between 0. 05 for non-submerged Ac and 0. 08 for submerged An in DDD-contaminated soils. Flooding seemed to have two contradictory effects on the DDE/DDD accumulation by rice: on one hand, it made the pollutants more mobile and bioavailable; while on the other hand, it enhanced the degradation and binding of POPs. Adding rice straw to the soils protected DDE from being taken up yet promoted DDD accumulation by rice. Furthermore, the distinct inorganic component of the soils might also play an important role in the environmental activities of POPs. [Copyright &y& Elsevier]