Qihang Wu

Heavy metal contamination of soil and water in the vicinity of an abandoned e-waste recycling site: Implications for dissemination of heavy metals

Illegal e-waste recycling activity has caused heavy metal pollution in many developing countries, including China. In recent years, the Chinese government has strengthened enforcement to impede such activity; however, the heavy metals remaining in the abandoned e-waste recycling site can still pose ecological risk. The present study aimed to investigate the concentrations of heavy metals in soil and water in the vicinity of an abandoned e-waste recycling site in Longtang, South China. Results showed that the surface soil of the former burning and acid-leaching sites was still heavily contaminated with Cd (>0.39 mg kg(-1)) and Cu (>1981 mg kg(-1)), which exceeded their respective guideline levels. The concentration of heavy metals generally decreased with depth in both burning site and paddy field, which is related to the elevated pH and reduced TOM along the depth gradient. The pond water was seriously acidified and contaminated with heavy metals, while the well water was slightly contaminated since heavy metals were mostly retained in the surface soil. The use of pond water for irrigation resulted in considerable heavy metal contamination in the paddy soil. Compared with previous studies, the reduced heavy metal concentrations in the surface soil imply that heavy metals were transported to the other areas, such as pond. Therefore, immediate remediation of the contaminated soil and water is necessary to prevent dissemination of heavy metals and potential ecological disaster.

Contamination, toxicity and speciation of heavy metals in an industrialized urban river: Implications for the dispersal of heavy metals

Urban rivers are often utilized by the local residents as water source, but they can be polluted by heavy metals due to industrialization. Here, the concentrations, toxicity, speciation and vertical profiles of heavy metals in sediment were examined to evaluate their impact, dispersal and temporal variation in Dongbao River. Results showed that the sediment in the industrialized areas was seriously contaminated with Cr, Cu and Ni which posed acute toxicity. Heavy metals, except Cr and Pb, were mainly associated with non-residual fractions, indicating their high mobility and bioavailability. The non-industrialized areas were also seriously contaminated, suggesting the dispersal of heavy metals along the river. The surface sediment could be more contaminated than the deep sediment, indicating the recent pollution events. Overall, when the point sources are not properly regulated, intense industrialization can cause both serious contamination and dispersal of heavy metals, which have far-reaching consequences in public health and environment.

Ecological risk and pollution history of heavy metals in Nansha mangrove, South China

Owing to the Industrial Revolution in the late 1970s, heavy metal pollution has been regarded as a serious threat to mangrove ecosystems in the region of the Pearl River Estuary, potentially affecting human health. The present study attempted to characterize the ecological risk of heavy metals (Cd, Cr, Cu, Mn, Ni, Pb and Zn) in Nansha mangrove, South China, by estimating their concentrations in the surface sediment. In addition, the pollution history of heavy metals was examined by determining the concentrations of heavy metals along the depth gradient. The phytoremediation potential of heavy metals by the dominant plants in Nansha mangrove, namely Sonneratia apetala and Cyperus malaccensis, was also studied. Results found that the surface sediment was severely contaminated with heavy metals, probably due to the discharge of industrial sewage into the Pearl River Estuary. Spatial variation of heavy metals was generally unobvious. The ecological risk of heavy metals was very high, largely due to Cd contamination. All heavy metals, except Mn, decreased with depth, indicating that heavy metal pollution has been deteriorating since 1979. Worse still, the dominant plants in Nansha mangrove had limited capability to remove the heavy metals from sediment. Therefore, we propose that immediate actions, such as regulation of discharge standards of industrial sewage, should be taken by the authorities concerned to mitigate the ecological risk posed by heavy metals.

Biological risk, source and pollution history of organochlorine pesticides (OCPs) in the sediment in Nansha mangrove, South China.

In the last century, organochlorine pesticides (OCPs) have been extensively used, especially in South China, to promote crop yield. In view of their toxicity, persistence and bioavailability, however, the Chinese government has attempted to regulate their production and use. We aimed to examine the biological risk, source and pollution history of OCPs in the sediment in Nansha mangrove which is located in the industrial region in South China. Results showed that HCHs and DDTs, mainly originating from lindane and technical DDT respectively, were the dominant OCPs, but their concentrations were too low to cause adverse effects on biota. In the last decade, the total concentration of HCHs showed a decreasing trend, whereas DDTs remained stable, despite their limited input. This suggests that management of HCHs was effective, while more management efforts should be put on DDTs, especially the use of dicofol and technical DDT, in future.

Simultaneous removal of thallium and chloride from a highly saline industrial wastewater using modified anion exchange resins

Simultaneous removal of thallium (Tl) and chloride from a highly saline industrial wastewater was investigated using modified anion ion exchange resins. The removal of thallium was mainly driven by the exchange of Tl-chlorocomplex (TlCl4-) formed in the oxidation of thallous (Tl (I)) to thallic ion (Tl (III)) by hydrogen peroxide (H2O2) under saline conditions. Over 97% of thallium and chloride removal was achieved using the modified resins, with a wide optimal conditions found to be H2O2 dosage 1.0-25.0mL/L, pH 1.6-4.3, and flow rate 0.5-4.7mL/L. The modified resins had an exchange capacity of 4.771mg Tl/g dry resins for thallium and 1800mg Cl/g dry resins for chloride. Stable regeneration could be achieved with the modified resins: over 97% of thallium and 90% of chloride can be eluted using Na2SO3 solution and alternating hot (60°C) H2SO4 and cold (25°C) water, and over 98% removal of thallium and chloride was achieved after five consecutive regeneration cycles.

Occurrence of PBDEs and alternative halogenated flame retardants in sewage sludge from the industrial city of Guangzhou, China☆

This study investigated the prevalence and abundance of halogenated flame retardants (HFRs) in sludge samples from 5 sewage treatment plants in Guangzhou, China. Detection of 18 polybrominated diphenyl ethers (PBDEs), 9 alternative HFRs including Dechlorane Plus (DP), brominated alkylbenzenes, and polybrominated biphenyls, and 2 related degradation products was conducted. Decabromodiphenyl ether (BDE 209) and decabromodiphenyl ethane (DBDPE) were the dominant HFRs, with concentrations ranging from 200 to 2150xa0ng/g and 680-27,400xa0ng/g, respectively. The DBDPE detected was the highest level reported so far, exceeding those previously reported by 10-100 times. PBDEs were surpassed as the dominant HFRs in sewage sludge, with mean DBDPE/BDE 209 ratio exceeding 2 in all samples. The review of earlier surveys reveals that DBDPE level was surging while BDE 209 was declining. Annual emissions of BDE 209, DP, and DBDPE were estimated to be 227.9, 10.5, and 979.3xa0kg/yr, respectively. Although ecological risks assessment suggested low risks for the examined sludge, the key environmental properties and transformation pathways of alternative HFRs remain largely unknown. These findings prompt for further investigations on alternative HFR and sustainable management practices for HFR-laden biosolids. The HFR emission pattern revealed in this study is likely representative of other similarly industrialized regions in the post-PBDE era.

Biological risk and pollution history of polycyclic aromatic hydrocarbons (PAHs) in Nansha mangrove, South China.

n Abstractn n Chinese government has taken various measures to alleviate pollution caused by polycyclic aromatic hydrocarbons (PAHs) in the region of Pearl River Delta since the economic reform in 1978, but the effectiveness of these measures remains largely unknown. This study aimed to elucidate the biological risk and pollution history of PAHs by measuring the concentrations of 28 PAHs in the surface and core sediments, respectively, in Nansha mangrove. Results found that the biological risk of PAHs was low without obvious spatial variation. The PAH concentration along the depth gradient indicated that PAH pollution was stabilized since the early 1990s while the source of PAHs has gradually changed from combustion of coal to petroleum products. This implied that the mitigation measures taken by the Chinese government were effective. Compared to marine bottom sediment, we propose that using mangrove sediment can provide a more accurate and precise estimate of pollution history of PAHs.n n

Contamination and distribution of heavy metals, polybrominated diphenyl ethers and alternative halogenated flame retardants in a pristine mangrove.

Owing to the expanding metal and electronics industries, pollution in the Pearl River Estuary needs special concern. Given the hydrodynamic effect, the pristine mangrove in Qiao Island would be contaminated by tidal flushing. Thus, we examined (1) the contamination of pollutants in this mangrove, including heavy metals, polybrominated diphenyl ethers (PBDEs) and alternative halogenated flame retardants (AHFRs), and (2) how habitat characteristics and sediment properties affect their distribution. Results showed that the sediment in Qiao mangrove had higher concentrations of heavy metals, PBDEs and AHFRs than that in other pristine mangroves, and similar concentrations to those mangroves impacted by point sources. Heavy metal concentrations were lower in the vegetated areas than mudflat, while the opposite was found for PBDEs and AHFRs. The findings imply that tidal flushing was an important pollution source, while mangrove plants have the capacity to minimize the impact of heavy metals, but not PBDEs and AHFRs.

Removal Efficiency and Risk Assessment of Polycyclic Aromatic Hydrocarbons in a Typical Municipal Wastewater Treatment Facility in Guangzhou, China

The loading and removal efficiency of 16 US EPA polycyclic aromatic hydrocarbons (PAHs) were examined in an inverted A2/O wastewater treatment plant (WWTP) located in an urban area in China. The total PAH concentrations were 554.3 to 723.2 ng/L in the influent and 189.6 to 262.7 ng/L in the effluent. The removal efficiencies of ∑PAHs in the dissolved phase ranged from 63 to 69%, with the highest observed in naphthalene (80% removal). Concentration and distribution of PAHs revealed that the higher molecular weight PAHs became more concentrated with treatment in both the dissolved phase and the dewatered sludge. The sharpest reduction was observed during the pretreatment and the biological phase. Noncarcinogenic risk, carcinogenic risk, and total health risk of PAHs found in the effluent and sewage sludge were also assessed. The effluent BaP toxic equivalent quantities (TEQBaP) were above, or far above, standards in countries. The potential toxicities of PAHs in sewage effluent were approximately 10 to 15 times higher than the acceptable risk level in China. The health risk associated with the sewage sludge also exceeded international recommended levels and was mainly contributed from seven carcinogenic PAHs. Given that WWTP effluent is a major PAH contributor to surface water bodies in China and better reduction efficiencies are achievable, the present study highlights the possibility of utilizing WWTPs for restoring water quality in riverine and coastal regions heavily impacted by PAHs contamination.

Evaluation of the ability of black nightshade Solanum nigrum L. for phytoremediation of thallium-contaminated soil

Thallium (Tl) pollution in agricultural areas can pose hidden danger to humans, as food consumption is the key exposure pathway of Tl. Owing to the extreme toxicity of Tl, removal of Tl from soil becomes necessary to minimize the Tl-related health effects. Phytoremediation is a cost-effective method to remove heavy metals from soil, but not all plants are appropriate for this purpose. Here, the ability of Solanum nigrum L., commonly known as black nightshade, to remediate Tl-contaminated soil was evaluated. The accumulation of Tl in different organs of S. nigrum was measured under both field and greenhouse conditions. Additionally, the growth and maximal quantum efficiency of photosystem II (Fv/Fm) under different Tl concentrations (1, 5, 10, 15, and 20xa0mgxa0kg−1) were examined after 4-month pot culture. Under both field and greenhouse conditions, Tl accumulated in S. nigrum was positively correlated with Tl concentration in the soil. Thallium mostly accumulated in the root, and bioconcentration factor was greater than 1, indicating the good capability of S. nigrum to extract Tl. Nonetheless, the growth and Fv/Fm of S. nigrum were reduced at high Tl concentration (>10xa0mgxa0kg−1). Given the good tolerance, fast growth, high accumulation, and global distribution, we propose that S. nigrum is a competent candidate to remediate moderately Tl-contaminated soil (<10xa0mgxa0kg−1) without causing far-reaching ecological consequences.