Elsevier

Chemosphere

Volume 255, September 2020, 126958
Chemosphere

Concentrations and profiles of persistent organic pollutants unintentionally produced by secondary nonferrous metal smelters: Updated emission factors and diagnostic ratios for identifying sources

https://doi.org/10.1016/j.chemosphere.2020.126958Get rights and content

Highlights

  • PCBs, PCNs, PeCBz, and HxCBz emitted from secondary nonferrous smelters were stated.

  • Emission factors of UPOPs in stack gas from various smelting sources were derived.

  • Diagnostic ratios of specific congeners were suggested for source appointment.

  • UPOPs emissions from secondary nonferrous smelters should be emphasized.

Abstract

Secondary nonferrous metal smelters are important sources of unintentionally produced persistent organic pollutants (UPOPs) including polychlorinated biphenyls (PCBs), polychlorinated naphthalenes, pentachlorobenzene, and hexachlorobenzene. Quantifying UPOP emissions by the main sources is an important step when evaluating UPOP emissions and establishing an inventory. In this study, field investigations were performed to allow UPOP emissions and distributions in stack gases emitted by secondary nonferrous metal smelters to be compared. A total of 25 stack gas samples were collected from secondary copper smelters (SCus), secondary zinc smelters, and secondary lead smelters in China. The mean toxic equivalent concentrations (TEQs) and mass concentrations of most of the UPOPs were highest in the secondary zinc smelter stack gas samples, next highest in the SCu stack gas samples, and lowest in the secondary lead smelter stack gas samples. The mean dioxin-like PCB and polychlorinated naphthalene TEQs were ∼8.9 and ∼6.6 times higher in stack gases from a SCu equipped with an oxygen-enriched smelting furnace than in stack gases from a SCu with a converter furnace. The mean PCB-118 to PCB-123 ratios and CN-10 to CN-35 ratios varied strongly and could be used as diagnostic ratios for apportioning the sources of UPOPs in the environment. Emission factors for dioxin-like PCBs, polychlorinated naphthalenes, pentachlorobenzene, and hexachlorobenzene in stack gases from secondary nonferrous metal smelters were derived and updated. The results improve our understanding of UPOP emission and provide data for establishing UPOP emission inventories for secondary nonferrous metal smelters.

Introduction

Polychlorinated dibenzo-p-dioxins and dibenzofurans, polychlorinated biphenyls (PCBs), polychlorinated naphthalenes (PCNs), pentachlorobenzene (PeCBz), and hexachlorobenzene (HxCBz) are unintentionally produced persistent organic pollutants (UPOPs) that are included in Annex C of the Stockholm Convention on Persistent Organic Pollutants, and these compounds have been intentionally produced as pesticides or industrial chemicals and are therefore also listed in Annex A of the Convention. In the last decades it has been found that these UPOPs can be produced and emitted during many industrial processes such as municipal solid waste incineration (Takasuga, 1994; Zhang et al., 2011; Li et al., 2016; Pham et al., 2019), coke production (Liu et al., 2009, 2010), and nonferrous metal production (Grochowalski et al., 2007; Ba et al., 2010). UPOPs contribute to carcinogenic and mutagenic effects in cocktails of environmental pollutants, so their emissions during industrial thermal processes have to be decreased/eliminated and controlled (Grochowalski et al., 2007; Xu and Cai, 2015; Varjani et al., 2017; Dat et al., 2019). Quantifying UPOP emissions from major sources is an important step in evaluating and controlling UPOP emissions and therefore mitigating environmental pollution and the risks posed to humans or vulnerable wildlife through exposure to UPOPs.

Secondary non-ferrous metal production in China has continually and rapidly increased in recent decades, and has been higher than in any other country for many years (China Nonferrous Metals Industry Association, 2018). The secondary nonferrous metal smelting industry has been found to be an important source of polychlorinated dibenzo-p-dioxin and dibenzofuran (PCDD/F) emissions because of the large number of secondary nonferrous metal smelters and high PCDD/F concentrations in stack gases emitted by such smelters (Ba et al., 2009a, 2009b; Yang et al., 2020). Many studies of PCDD/F and PCNs formation mechanisms and emissions have been conducted (Falandysz, 1998; Takasuga et al., 2004; Yu et al., 2006; Wang et al., 2016; Wu et al., 2018), but few studies of emissions of other UPOPs (particularly PeCBz, and HxCBz) into the atmosphere from secondary nonferrous metal smelters have been performed. Oxygen-enriched smelting furnaces have started to be used in the recycled copper smelting industry because they have fast smelting processes, simple material preparation procedures, and high smelting efficiencies. Raw materials such as copper sludge and waste copper can be converted into crude copper with a higher copper content in an oxygen-enriched smelting furnace, and the crude copper can then be refined further in an anode furnace or using another process (Ministry of ecology and environment of the people’s Republic of China, 2017). To the best of our knowledge, little information is available on UPOP concentrations and profiles emitted from oxygen-enriched smelting furnaces. It is therefore essential for studies of UPOP emissions during secondary nonferrous metal smelting processes (particularly using oxygen-enriched smelting furnaces) to be performed to allow UPOP emissions from these important sources to be assessed and strategies to be developed to decrease UPOP emissions. It is also important to compare the profiles of UPOPs emitted from secondary nonferrous metal smelters and to identify diagnostic ratios that can be used to identify the sources of UPOPs in the environment (Liu et al., 2015; Yang et al., 2020). However, profiles of UPOPs emitted by secondary nonferrous metal smelters have rarely been studied, and UPOP diagnostic ratios have not yet been identified.

In this study, stack gas samples from secondary copper smelters (SCus), secondary zinc smelters (SZns), and secondary lead smelters (SPbs) in China were collected, and the dioxin-like (dl-) PCB, PCN, PeCBz, and HxCBz concentrations in the stack gases were determined. Updated emission factors (EFs) for dl-PCBs, PCNs, PeCBz, and HxCBz in stack gases emitted by SCus, SZns, and SPbs were derived. The UPOP profiles for the different types of smelters were compared, and diagnostic ratios for apportioning the sources of UPOPs in the environment were identified. The results provide important data to support the establishment of an UPOP emission inventory and apportioning the sources of UPOPs in the environment. The data will be useful in the development of strategies for decreasing the environmental burden of UPOPs and the risks posed by UPOPs in the environment to humans.

Section snippets

Descriptions of the secondary nonferrous metal smelting plants and the sample collection procedure

Samples were collected from seven secondary nonferrous metal smelting plants (three SCus, two SPbs, and two SZns). Detailed information on the plants is given in Table S1. A total of 25 stack gas samples were collected from the plants. Information on the raw materials, smelting furnace types, and air pollution control devices used at the smelting plants was collected to allow the factors affecting UPOP emissions from the different smelting plants to be investigated. We collected 13 flue gas

UPOP mass and toxic equivalent concentrations in stack gases from the secondary metal smelters

The UPOP mass concentrations and toxic equivalent (TEQ) concentrations in the stack gas samples are shown in Table 1. The dl-PCB TEQ concentrations were calculated using World Health Organization (WHO) toxic equivalence factors (Van den Berg et al., 2006). The PCN TEQ concentrations were calculated using previously published relative potency factors (Falandysz et al., 2014).

Obviously, the average concentrations of UPOP in the stack gas samples from the different smelting plants varied

Conclusions

The concentrations and distribution patterns of dl-PCBs, PCNs, PeCBz, and HxCBz in stack gas samples from secondary nonferrous metal smelters in China were evaluated and compared. The mean concentrations of most of the UPOPs in the stack gas samples from the smelters decreased in the order SZn > SCu > SPb. The PCN and dl-PCB TEQ concentrations were much higher in stack gases produced by a SCu with an oxygen-enriched smelting furnace than in stack gases produced by a SCu with a converter

CRediT authorship contribution statement

Yuanping Yang: Formal analysis, Investigation, Writing - original draft. Lili Yang: Data curation, Formal analysis. Minxiang Wang: Resources, Writing - review & editing, Supervision. Qiuting Yang: Investigation. Xiaoyun Liu: Investigation, Methodology. Jia Shen: Investigation. Guorui Liu: Conceptualization, Investigation, Writing - review & editing. Minghui Zheng: Investigation, Methodology.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This work was supported by the National Natural Science Foundation of China (grant nos. 21936007 and 21777172), CAS Interdisciplinary Innovation Team (grant no. JCTD-2019-03), and the Youth Innovation Promotion Association of the Chinese Academy of Sciences (grant no. 2016038).

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