Treatability of hexabromocyclododecane using Pd/Fe nanoparticles in the soil-plant system: Effects of humic acids
Graphical abstract
Introduction
Thousands of xenobiotic pollutants from various human activities are being introduced into the environment. Over the last two decades, the generation of persistent organic pollutants (POPs) has emerged as a big environmental concern due to their strong potential for bioaccumulation, biomagnification, persistence, long-range transport and toxicity to the ecosystem (Santillo and Johnston, 2003). In particular, 1,2,5,6,9,10-hexabromocyclododecane (HBCD, C12H18Br6), the most widely used cycloaliphatic brominated flame retardant (BFR), has been detected in various environmental matrices, especially in soil and sediment (Gao et al., 2011). Due to its physicochemical properties, HBCD was listed as a new POP under the Stockholm Convention treaty in 2014. As HBCD is an emerging contaminant, research on HBCD remediation is in its infancy (Davis et al., 2005). To date, several studies on the HBCD remediation have been reported; for example, it was proposed that HBCD could be photodegraded (Zhou et al., 2014). However, HBCD that is heterogeneously distributed in soils, sediments, and water is not readily exposed to light. Thermal degradation, electrochemical reduction, and mechanochemical technologies have been studied for HBCD degradation (Barontini et al., 2001; Wagoner et al., 2014; Zhang et al., 2014), but these technologies had low energy efficiencies and also could be costly for facilities.
Nanotechnology has been identified as a promising remediation strategy for organic pollutant degradation. In this category, nanoscale zerovalent iron (nZVI) and nZVI-based nanoparticles (NPs) are known to degrade various POPs with fast kinetics and high efficiency. To date, there have been several reports concerning the HBCD degradation using nanomaterials, particularly with bare nZVI (Tso and Shih, 2014), FeS (Li et al., 2016a) and sulfidated nZVI (S-nZVI) (Li et al., 2017). The usual strategy for increasing the reactivity of nZVI is the addition of transition metals such as Pd, Pt, Cu, and Ni on the nZVI surface for reducing their passivation (Stefaniuk et al., 2016). In particular, palladized nZVI (Pd/nFe) has been studied extensively with its hydrodehalogenation reactivity (Alonso et al., 2002). However, the application of bimetallic nZVI to promote the degradation of HBCD has not previously been investigated. In addition, most of the references were studied on the removal of POPs in aqueous solutions, and only a few reports dealt with soils and sediments. In most cases, the effectiveness achieved in soil remediation was not as good as that in water because of the high octanol-water partition coefficient (Kow), the high tendency to adsorb onto the solid surfaces of environmental compartments and the formation of intermediates that may be more toxic than the parent contaminants. Nevertheless, it should be emphasized that the soil is a much more difficult and demanding matrix than water in the remediation field (Stefaniuk et al., 2016).
Employing appropriate technologies to remediate contaminated soils is crucial due to certain site-specifications such as public acceptability and environmental sustainability of technologies. These requirements increase the need to employ eco-friendly techniques, especially for the soil remediation (Abhilash et al., 2012). In case of HBCD, it has various stereoisomers with dissimilar physical properties, resulting in varying accumulation behaviors and interactions with plant and microbes in soils (Davis et al., 2005; Zhu et al., 2016). Our previous study determined that the microbes in an HBCD-contaminated rhizosphere were a promising candidate for the bioremediation of HBCD (Le et al., 2017). Therefore, applying the combined treatment of nanomaterials with plant could also be a meaningful research trial for the remediation of soils contaminated with POPs. Another aspect of the soil remediation is that natural environmental matrices commonly contain high amounts of natural organic matters (NOM), especially humic acids (HAs), which interact strongly with organic chemicals. It has been well demonstrated that the POPs sequestration capacity of the soil is strongly related to the proportion of NOM. On the other hand, the addition of dissolved organic matter (DOM) is currently considered to be a valid strategy to accelerate bioremediation in contaminated sites (Cai et al., 2017; Plaza et al., 2009). For example, HAs can accelerate the degradation of organic pollutants by increasing their solubility and enhance their diffusive mass transfer, promoting their bioavailability to microorganisms (Tejeda-Agredano et al., 2014). HAs can also act as an electron transfer mediator in the chemical reduction of organic pollutants (Li et al., 2016b), resulting in enhancement of the degradation rate of halogenated compounds. Therefore, HAs would be a good supplement for bioremediation of contaminated soils and it is important to understand the role of HAs before it is applied to the remediation field.
Here, we investigated the degradation of HBCD in a soil system using bimetallic nZVI (Pd/nFe) under the influences of plant and HAs. Since HBCD has not been tested by bimetallic nZVI yet, a pre-test was conducted in an aqueous solution to understand its HBCD degradation mechanism and pathway. Further, we expected to observe the HBCD remediation with nanomaterials in soils under the influences of HAs and plant. In short, our observations might be the beginning for the remediation strategy using integration of the nanotechnology and bioremediation, involving plant-assisted treatment can be provide promising advantages for the remediation of recalcitrant emerging contaminants in the soil environment.
Section snippets
Materials
A technical HBCD was purchased from Accustandard (New Haven, USA), which is a mixture of different isomers with α-, β- and γ-HBCDs (in ranges of 10%–13%, 1%–12% and 75%–89%, respectively) as the predominant diastereoisomers (Tomy et al., 2004). The palladium (II) acetate, iron (II) sulfate (FeSO4∙7H2O), sodium borohydride (NaBH4), HAs, sodium chloride (NaCl), calcium chloride (CaCl2) and magnesium sulfate (MgSO4∙7H2O) were purchased from Sigma Aldrich. Deionized (DI) water (resistivity,
Debromination of HBCD by Pd/nFe
The aqueous solution is generally used for collecting basic reaction information before applying to the soil. In this study, we obtained information about HBCD degradation by NPs, such as the degradation efficiency, pathway, mechanism, and effects of HAs in the aqueous system. In the Pd/nFe treatment, over 90% of HBCD was quickly degraded after 9 h, and the remaining was completely removed within 24 h (Fig. 1A). To confirm the debromination of HBCD, the amount of released Br− was quantified;
Conclusions
We have demonstrated the application of Pd/nFe for the HBCD degradation in both aqueous solution and soil. In aqueous solution, Pd/nFe was proven a better reducing agent than other nZVIs for reductive dechlorination of HBCD due to the hydrodebromination reaction occurred by Pd. Especially, the environmental risk of α-HBCD which is the most stable HBCD stereoisomer could be reduced by the NPs treatment. Although the HBCD removal in soils treated by the NPs was relatively effective, the activity
Acknowledgments
This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) (No. NRF-2017R1A2B3012681).
References (44)
- et al.
Plant-microbe interactions: novel applications for exploitation in multipurpose remediation technologies
Trends Biotechnol.
(2012) - et al.
Degradation of triclosan by an integrated nano-bio redox process
Bioresour. Technol.
(2010) - et al.
Effects of dissolved organic matter derived from forest leaf litter on biodegradation of phenanthrene in aqueous phase
J. Hazard. Mater.
(2017) - et al.
Effect of natural organic matter on toxicity and reactivity of nano-scale zero-valent iron
Water Res.
(2011) - et al.
The transformation of hexabromocyclododecane in aerobic and anaerobic soils and aquatic sediments
Water Res.
(2005) - et al.
Binding of organic pollutants to humic and fulvic acids: influence of pH and the structure of humic material
Chemopshere
(1997) - et al.
Influence of humic acid on the colloidal stability of surface-modified nano zero-valent iron
Water Res.
(2013) - et al.
Regio- and stereoselective isomerization of hexabromocyclododecanes (HBCDs): Kinetics and mechanism of γ- to α-HBCD isomerization
Chemosphere
(2008) - et al.
Matrix-specific distribution and diastereomeric profiles of hexabromocyclododecane (HBCD) in a multimedia environment: Air, soil, sludge, sediment, and fish
Environ. Pollut.
(2017) - et al.
Transformation of hexabromocyclododecane in contaminated soil in association with microbial diversity
J. Hazard. Mater.
(2017)
Reductive transformation of hexabromocyclododecane (HBCD) by FeS
Water Res.
Abiotic transformation of hexabromocyclododecane by sulfidated nanoscale zerovalent iron: Kinetics, mechanism and influencing factors
Water Res.
Binding of polycyclic aromatic hydrocarbons by humic acids formed during composting
Environ. Pollut.
Playing with fire: The global threat presented by brominated flame retardants justifies urgent substitution
Environ. Int.
Photosensitized diastereoisomer-specific degradation of hexabromocyclododecane (HBCD) in the presence of humic acid in aquatic systems
J. Hazard. Mater.
Review on nano zerovalent iron (nZVI): from synthesis to environmental applications
Chem. Eng. J.
The transformation of hexabromocyclododecane using zerovalent iron nanoparticle aggregates
J. Hazard. Mater.
Complete catalytic debromination of hexabromocyclododecane using a silica-supported palladium catalyst in alkaline 2-propanol
Chemosphere
Electrochemical reduction of 1, 2, 5, 6, 9, 10-hexabromocyclododecane at carbon and silver cathodes in dimethylformamide
J. Electroanal. Chem.
Accumulation and phytotoxicity of technical hexabromocyclododecane in maize
J. Envrion. Sci.
Degradation of soil-sorbed trichloroethylene by stabilized zero valent iron nanoparticles: effects of sorption, surfactants, and natural organic matter
Water Res.
Mechanochemical degradation of hexabromocyclododecane and approaches for the remediation of its contaminated soil
Chemosphere
Cited by (20)
Mechanochemical destruction and mineralization of solid-phase hexabromocyclododecane assisted by microscale zero-valent aluminum
2022, Science of the Total EnvironmentCitation Excerpt :Despite remarkable research efforts, treating HBCD remains a challenging environmental issue owing to its recalcitrancy. A number of methods for degrading HBCD have been investigated, including zero-valent metals (Le et al., 2019; Li et al., 2017; Zhang et al., 2020), reduced sulfur species (Zhang et al., 2019), microbial degradation (Huang et al., 2019; Yang et al., 2020), and photocatalytic degradation (Li et al., 2019). While these methods have shown various degrees of degradation of water-soluble HBCD (Le et al., 2019), cost-effective technologies for treating solid-phase HBCD have been lacking.
Plant accumulation and transformation of brominated and organophosphate flame retardants: A review
2021, Environmental PollutionCitation Excerpt :Biochar was found to reduce the accumulation of hexa-BDE in plants due to its high adsorption capacity, while increase its root-to-shoot translocation due to phytotoxicity (Jia et al., 2019b). Other exogenous additives such as arbuscular mycorrhizal (Wang et al., 2011a), aquaculture effluent (Farzana et al., 2019), Cu (Lu et al., 2013; Wang et al., 2016a), nanomaterials (Wu et al., 2018b), humic acids (HAs) + Pd/nFe (Thao Thanh et al., 2019), dissolved humic acids (DHA), and tourmaline (a hydrous siliceous material with multiple minerals) (Wang et al., 2017) can also have different effects on plant uptake and translocation of BFRs and OPFRs. However, the compound effects with other chemicals or materials are beyond the scope of this review and these relevant studies will not be further discussed.
Biota Debromination in Aqueous Media
2021, Wastewater Treatment: Cutting-Edge Molecular Tools, Techniques and Applied AspectsAn analysis of the versatility and effectiveness of composts for sequestering heavy metal ions, dyes and xenobiotics from soils and aqueous milieus
2020, Ecotoxicology and Environmental SafetyMolecular mechanisms in phytoremediation of environmental contaminants and prospects of engineered transgenic plants/microbes
2020, Science of the Total EnvironmentCitation Excerpt :Recent researches on the sustainable remediation of recalcitrant organics (e.g., hexabromocyclododecane) with Pd/Fe NPs under soil-plant (tobacco) interactions explicitly indicated the prospects of phytoremediation (Le et al. 2019). This NP induced phytoremediation was further accelerated in the presence of humic acid (Le et al. 2019). Further, a combination of phytoremediation and nano-remediation can remove the hazardous metallic contaminants like Pb from contaminated soil to prevent its transfer to other trophic levels/food chain (Lago-Vila et al. 2019).
- 1
These two authors contributed equally to this work.