Key factors controlling colloids-bulk soil distribution of polybrominated diphenyl ethers (PBDEs) at an e-waste recycling site: Implications for PBDE mobility in subsurface environment

Soil colloids can significantly enhance spreading of polybromodiphenyl ethers in groundwater by serving as an effective carrier

Polybromodiphenyl ethers (PBDEs), the widely used flame retardants, are common contaminants in surface soils at e-waste recycling sites. The association of PBDEs with soil colloids has been observed, indicating the potential risk to groundwater due to colloid-facilitated transport. However, the extent to which soil colloids may enhance the spreading of PBDEs in groundwater is largely unknown. Herein, we report the co-transport of decabromodiphenyl ester (BDE-209) and soil colloids in saturated porous media. The colloids released from a soil sample collected at an e-waste recycling site in Tianjin, China, contain high concentration of PBDEs, with BDE-209 being the most abundant conger (320 ± 30 mg/kg). The colloids exhibit relatively high mobility in saturated sand columns, under conditions commonly observed in groundwater environments. Notably, under all the tested conditions (i.e., varying flow velocity, pH, ionic species and ionic strength), the mass of eluted BDE-209 correlates linearly with that of eluted soil colloids, even though the mobility of the colloids varies markedly depending on the specific hydrodynamic and solution chemistry conditions involved. Additionally, the mass of BDE-209 retained in the columns also correlates strongly with the mass of retained colloids. Apparently, the PBDEs remain bound to soil colloids during transport in porous media. Findings in this study indicate that soil colloids may significantly promote the transport of PBDEs in groundwater by serving as an effective carrier. This might be the reason why the highly insoluble and adsorptive PBDEs are found in groundwater at some PBDE-contaminated sites.

Advanced understanding of the polybrominated diphenyl ethers (PBDEs): Insights from total environment to intoxication

Polybrominated diphenyl ethers (PBDEs) are brominated compounds connected by ester bonds between two benzene rings. There are 209 congeners of PBDEs, classified according to the number and position of the bromine atoms. Due to their low cost and superior flame retardant properties, PBDEs have been extensively used as flame retardants in electronic products, plastics, textiles, and other materials since the 1970s. PBDEs are classified as persistent organic pollutants (POPs) under the Stockholm Convention because of their environmental persistence, bioaccumulation, and toxicity to both humans and wildlife. Due to their extensive use and significant quantities, PBDEs have been detected across a range of environments and biological organisms. These compounds are known to cause damage to the metabolic system, exhibit neurotoxicity, and pose reproductive hazards. This review investigates the environmental distribution and human exposure pathways of PBDEs. Using China-a country with significant PBDE use-as an example, it highlights substantial regional and temporal variations in PBDE concentrations and notes that certain environmental levels may pose risks to human health. The article then examines the toxic effects and mechanisms of PBDEs on several major target organs, summarizing recent research and the specific mechanisms underlying these toxic effects from multiple toxicological perspectives. This review enhances our understanding of PBDEs' environmental distribution, exposure pathways, and toxic mechanisms, offering valuable insights for further research and management strategies.

Effects of transient flow conditions on colloid-facilitated release of decabromodiphenyl ether: Implications for contaminant mobility at e-waste recycling sites

Polybrominated diphenyl ethers (PBDEs) are ubiquitous contaminants, especially in the soil and groundwater of contaminated sites and landfills. Notably, 2,2',3,3',4,4',5,5',6,6'-decabromodiphenyl ether (BDE-209), one of the most frequently and abundantly detected PBDE congeners in the environment, has recently been designated as a new pollutant subject to rigorous control in China. Colloid-facilitated transport is a key mechanism for the release of PBDEs from surface soils and their migration in the aquifer, but the effects of hydrodynamic conditions, particularly transient flow, on colloid-facilitated release of PBDEs are not well understood. Herein, we examined the effects of typical transient flow conditions on the release characteristics of colloids and BDE-209 from surface soil collected from an e-waste recycling site by undisturbed soil core leaching tests involving multiple dry-wet cycles (with different drying durations) and freeze-thaw cycles. We observed significant positive correlations between BDE-209 and colloid concentrations in the leachate in both the dry-wet and freeze-thaw leaching experiments, highlighting the critical role of colloids in facilitating BDE-209 release. However, colloids mobilized during the dry-wet cycles contained higher contents of BDE-209 than those in the freeze-thaw cycle tests, and the difference was primarily due to the more intensive disintegration of soil aggregates and elution of newly formed inorganic colloidal particles (mainly primary silicate minerals such as quartz and albite) with low BDE-209 content during the freeze-thaw process. These findings underscore the necessity of considering transient flow conditions when assessing the fate and risks of PBDEs at contaminated sites.

Dynamic modeling of the occurrence, sources, and environmental behavior of polybrominated diphenyl ethers in Zhelin Bay, China

This study analyzed polybrominated diphenyl ethers (PBDEs) in Zhelin Bay, China, investigating their occurrence, sources, and environmental behavior. PBDE congeners were detected in all sampled media. The Σ13PBDE concentrations in the dissolved phase ranged from 1.04 to 41.40 ng/L, while the concentrations ranged in suspended particulate matter from 0.02 to 12.56 ng/L. In sediments, PBDE concentrations ranged from 1.41 to 8.57 ng/g. The higher proportion of PBDEs in the dissolved phase in the bay than in the estuary is attributable to the type of PBDE products used in the aquacultural process in Zhelin Bay. Moreover, correlation analysis between PBDE concentrations and environmental parameters showed that the primary factor influencing PBDE concentrations in Zhelin Bay sediments may shift from riverine inputs to aquaculture. Principal component analysis and positive matrix factorization revealed that PBDEs in the water of Zhelin Bay primarily originated from the degradation of octa-BDE, deca-BDE, and penta-BDE products employed in aquaculture. In contrast, the PBDEs in Zhelin Bay sediments mainly originated from riverine inputs. In addition, a level IV dynamic fugacity-based multimedia model was used to simulate the temporal variation of PBDE concentrations in Zhelin Bay. Modeled short-term trends showed a relatively swift transport of PBDE congeners in the water column to the atmosphere and sediments. Over the long term, sediment concentrations gradually decreased, in contrast to the less rapid declines observed in the atmosphere and water. Furthermore, this study revealed that the transport and transformation processes of PBDEs in the Zhelin Bay environment were considerably influenced by the diffusion coefficient in water, the water-side mass transfer coefficient at the water-sediment interface, the sediment resuspension rate, and the organic carbon-water partition coefficient.

Preferential association of polycyclic aromatic hydrocarbons (PAHs) with soil colloids at an e-waste recycling site: Implications for risk of PAH migration to subsurface environment

Polycyclic aromatic hydrocarbon (PAH) contamination at e-waste recycling sites poses high ecological and human-health risks. Of note, PAHs in surface soils can be mobilized through colloid-facilitated transport, and may migrate into the subsurface and pollute groundwater. Here, we show that the colloids released from the soil samples at an e-waste recycling site in Tianjin, China contain high concentrations of PAHs, with total concentrations of 16 PAHs as high as 1520 ng/g dw. Preferential association of the PAHs with the colloids is observed, with the distribution coefficients of PAHs between colloids and bulk soil often above 10. Source diagnostic ratios show that soot-like particles are the main source of PAHs at the site, due to the incomplete combustion of fossil fuels, biomass, and electronic wastes during the e-waste dismantling practices. Due to their small sizes, a large fraction of these soot-like particles can be remobilized as colloids, and this explains the preferential association of PAHs with colloids. Moreover, the colloids-soil distribution coefficients are higher for the low-molecular-weight PAHs than for the high-molecular-weight ones, possibly attributable to the different binding routes/modes of these two groups of PAHs to the particles during combustion. Notably, the preferential association of PAHs with colloids is even more pronounced for the subsurface soils, corroborating that the presence of PAHs in the deeper soils is primarily the results of downward migration of PAH-bearing colloids. The findings highlight the important role of colloids as a vector for the subsurface transport of PAHs at e-waste recycling sites, and call for further understanding of colloid-facilitated transport of PAHs at e-waste recycling sites.

Ferroptosis mediates decabromodiphenyl ether-induced liver damage and inflammation

Decabromodiphenyl ether (BDE-209) is an environmental toxin. Increasing evidence showed that BDE-209 exposure induced liver injury, but the mechanism still remains unknown. The present study explored the effect and mechanism of ferroptosis on hepatotoxicity triggered by BDE-209 in vivo and in vitro. In vivo experiment, ICR mice were exposed to BDE-209 for 50 days, and then recovered for 50 days; HepG2 and L02 cells were treated with BDE-209 or/and ferrostatin-1 (Fer-1) for establishing in vitro model. In vivo, the results showed that BDE-209 accumulated in liver and induced liver damage, increased Fe²⁺ and MDA contents, and blocked the activation of SLC7A11/GSH/GPX4 pathway in liver; BDE-209 also activated IKK/IκB/NF-κB pathway and elevated inflammatory cytokines levels in liver after exposure for 50 days. After BDE-209 stopping exposure 50 days, the severity of liver damage, ferroptosis and inflammatory response were still higher than the corresponding control group. In vitro, ferroptosis inhibitor Fer-1 rescued ferroptotic damage and attenuated cell death in BDE-209-treated HepG2 and L02 cells. In addition, Fer-1 reversed the activation of IKK/IκB/NF-κB pathway and the increase of pro-inflammatory cytokines levels in BDE-209-treated HepG2 and L02 cells. Together, the above results suggested that BDE-209 induced tissue damage and inflammatory response by activating ferroptosis through increasing iron-dependent lipid peroxidation and blocking the activation of SLC7A11/GSH/GPX4 pathway in liver, indicating that ferroptosis is a potential mechanism for BDE-209-induced hepatotoxicity.

Treatment of PBDEs from Soil-Washing Effluent by Granular-Activated Carbon: Adsorption Behavior, Influencing Factors and Density Functional Theory Calculation

Soil-washing is a potential technology for the disposal of soil contaminated by e-waste; however, the produced soil-washing effluent will contain polybrominated diphenyl ethers (PBDEs) and a large number of surfactants, which are harmful to the environment, so the treatment of PBDEs and the recycling of surfactants are the key to the application of soil-washing technology. In this study, coconut shell granular-activated carbon (GAC) was applied to remove PBDEs from Triton X-100 (TX-100) surfactant which simulates soil-washing effluent. The adsorption results show that, GAC can simultaneously achieve effective removal of 4,4′-dibromodiphenyl ether (BDE-15) and efficient recovery of TX-100. Under optimal conditions, the maximum adsorption capacity of BDE-15 could reach 623.19 μmol/g, and the recovery rate of TX-100 was always higher than 83%. The adsorption process of 4,4′-dibromodiphenyl ether (BDE-15) by GAC could best be described using the pseudo-second-order kinetic model and Freundlich isothermal adsorption model. The coexistence ions had almost no effect on the removal of BDE-15 and the recovery rate of TX-100, and the solution pH had little effect on the recovery rate of TX-100; BDE-15 had the best removal effect under the condition of weak acid to weak base, indicating that GAC has good environmental adaptability. After adsorption, GAC could be regenerated with methanol and the adsorption effect of BDE-15 could still reach more than 81%. Density functional theory (DFT) calculation and characterization results showed that, Van der Waals interaction and π–π interaction are dominant between BDE-15 and GAC, and hydrogen bond interactions also exist. The existence of oxygen-containing functional groups is conducive to the adsorption of BDE-15, and the carboxyl group (-COOH) has the strongest promoting effect. The study proved the feasibility of GAC to effectively remove PBDEs and recover surfactants from the soil-washing effluent, and revealed the interaction mechanism between PBDEs and GAC, which can provide reference for the application of soil-washing technology.