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Published in final edited form as: Sci Total Environ. 2019 Nov 21;704:135455. doi: 10.1016/j.scitotenv.2019.135455

Transformation of 1,1,1,3,8,10,10,10-octachlorodecane in air phase increased by phytogenic volatile organic compounds of pumpkin seedlings

Yanlin Li a,b,c, Weifang Chen a,d, Wenqian Kong a,d, Jiyan Liu a,d,*, Jerald L Schnoor b, Guibin Jiang a,d
PMCID: PMC7029796  NIHMSID: NIHMS1558488  PMID: 31791777

Abstract

Short chain chlorinated paraffins (SCCPs) are widely distributed persistent organic pollutants (POPs). Airborne chlorodecanes were hypothesized to be transformed by reactive phytogenic volatile organic compounds (PVOCs) in our previous work. To test this hypothesis, PVOCs of pumpkin (Cucurbita maxima × C. moschata) were collected and reacted with 1,1,1,3,8,10,10,10-octachlorodecane in the air phase of a sealed glass bottle under illumination for 10 days (reaction system I, simulating atmospheric reaction conditions with PVOCs). The reaction control group (reaction system II) was set at the same conditions but only had chlorodecane (without PVOCs) inside the bottle. Transformation of SCCPs in the air phase of reaction control group was unexpectedly found. Results showed that 1,1,1,3,8,10,10,10-octachlorode cane was transformed to a great extent to C10Cl5–8, C9Cl6–8, and C8Cl7–8 in the air phase after 10-d illumination in both with and without the presence of PVOCs, which is explained by carbon chain decomposition, dechlorination and chlorine rearrangement products of the parent SCCP. Those transformation processes were increased to some extent by the PVOCs from pumpkin seedlings. This study provides the first experimental data on atmospheric transformation of SCCPs and also the first evidence that plant emissions (PVOCs) can increase the transformation of SCCPs in air under light and experimental conditions. It provides new insight into the potential transformation and fate of CPs in the environment.

Keywords: SCCPs, PVOCs, Transformation, Air phase, Pumpkin seedlings

GRAPHICAL ABSTRACT

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1. Introduction

Chlorinated paraffins (CPs), also known as polychlorinated nalkanes, are a class of industrial chemicals with thousands of congeners and isomers (Wei et al., 2016). CPs came into use during Word War I, and were produced on an industrial scale since the 1930s (Zeng et al., 2017). According to carbon chain length, CPs are subdivided into short-chain CPs (SCCPs, C10–13), medium-chain CPs (MCCPs, C14–17) and long-chain CPs (LCCPs, C18–30) (Gluge et al., 2018). CPs have been used in a wide variety of applications (van Mourik et al., 2016). For example, they are used as both plasticizers and flame retardants in PVC plastic and sealants, and as additives in metal-working fluids, paints and lubricants (van Mourik et al., 2015). In 2017, SCCPs have been listed into Annex A as a group of persistent organic pollutants (POPs) by the Stockholm Convention due to their high environmental persistence (Marvin et al., 2003; Yuan et al., 2017b), bioaccumulation potential (Houde et al., 2008; Ma et al., 2014; Zhou et al., 2018), long-range transport ability (Chaemfa et al., 2014), and high toxicity to aquatic organisms (Madeley and Birtley, 1980; Ren et al., 2018). Moreover, they have been subjected to regulation in Canada, U.S., Norway and the Europe Union (Fiedler, 2010).

Recent studies on SCCPs have focused mainly on environmental distribution and human exposure. It was reported that worldwide production of SCCPs is at least 165,000 t/year (Glüge et al., 2016), and emissions range from 1690 to 41,400 t, 1660–105,000 t, and 9460–81,000 t of SCCPs to air, surface water and soil, respectively, from 1935 to 2012 (Glüge et al., 2016). Thus, extensive contamination of SCCPs in various environmental media has occurred in air (Barber et al., 2005; Diefenbacher et al., 2015; Li et al., 2012; Wang et al., 2012; Wang et al., 2013; Wu et al., 2017), water (Houde et al., 2008; Iino et al., 2005; van Mourik et al., 2016), soil (Wang et al., 2013; Yuan et al., 2017c; Zeng et al., 2011), sediment cores (Iozza et al., 2008; Yuan et al., 2017b), sludge (Zeng et al., 2013), wildlife (Yuan et al., 2019; Zeng et al., 2017; Zeng et al., 2015), breast milk (Xia et al., 2017), and human blood and placenta (Li et al., 2017a; Wang et al., 2018). Relatively high SCCP levels, up to 1700 ng/L in water, 8700 ng/g dw in sediment, and 24,000 ng/g lw in biota, were also measured (van Mourik et al., 2016). SCCPs in air samples have been reported in China, Japan, South Korea, India, Pakistan, UK, Canada, Norway and Sweden (van Mourik et al., 2016; Wei et al., 2016). The highest concentrations of ƩSCCPs (517 ng/m3) were observed in outdoor air in China (Li et al., 2012; Wei et al., 2016).

Several publications show that SCCPs undergo biotic and abiotic transformations in the environment. Dechlorination of CPs by a series of soil-bacteria strains has been reported by Omori et al (1987). SCCPs with a degree of chlorination less than 60% could be readily oxidized by microorganisms (Madeley and Birtley, 1980). Biotic dechlorination, chlorine rearrangement and carbon chain decomposition of SCCPs mediated by pumpkin and soybean seedlings were found in our previous work (Li et al., 2019; Li et al., 2017b). Zhang et al. reported the chemical dechlorination of SCCPs by nanoscale zero-valent iron (Zhang et al., 2012). Cl-polyenes/chlorinated olefins and chlorinated aromatic hydrocarbons were identified as transformation products of CPs during thermal decomposition (Bergman et al., 1984; Schinkel et al., 2018; Xin et al., 2018; Xin et al., 2017). Photochemical dechlorination of CPs in water was found in the presence of hydrogen peroxide under UV radiation by Koh and Thiemann (Koh et al., 2001). SCCPs could also be degraded in the atmosphere to some extent, especially in the presence of .OH radical. The atmospheric transformation of SCCPs initiated by the .OH radical has been theoretically predicted through DFT, QSAR, and Atkinson’s .O H-radical-reaction models (Atkinson, 1986; Li et al., 2014; Liu et al., 2015). However, no experimental data on the transformation of CPs in the role of radicals in the air phase have been reported.

Plants can emit substantial amounts of reactive phytogenic volatile organic compounds (PVOCs) into the atmosphere, which include alkanes, alkenes, alcohols, aldehydes, esters and carboxylic acids – ranging up to 10% of their photosynthetically fixed carbon (Widhalm et al., 2015). The PVOCs from plants reacting with hydroxyl radicals, nitrate radicals and ozone, would play an important role in the atmospheric transformation of organic pollutants in the lower troposphere. Our previous work (Li et al., 2017b) led to the hypothesis that possible transformation of chlorodecanes was induced by the reactive PVOCs or radicals. Therefore, the transformation of chlorodecanes in the presence of PVOCs in illuminated air (reaction system I) was specially focused in this work. However, the transformation of chlorodecanes in the air phase was unexpectedly found in the reaction control group (reaction system II) which was set at the same conditions but only had chlorodecane (without PVOCs) inside the sealed reaction system and PVOCs increased the atmospheric transformation process to some extent. These are the first experimental data on transformation of SCCPs in the air. It improved our understanding on the fate and cycle of SCCPs in the environment.

2. Materials and methods

2.1. Chemicals and regents

Purchased from Chiron, Norway, were 1,1,1,3,8,10,10,10-octachlor odecane (1,1,1,3,8,10,10,10-OctaCD, 96.4%), 1,1,1,3,8,9- hexachlorononane (1,1,1,3,8,9-HexCN, 98.7%), and 1,1,1,3,6,8,8,8-octa chlorooctane (1,1,1,3,6,8,8,8-OctaCO, 99.5%). Purchased from Ehrenstorfer GmbH (Augsburg, Germany) were 1,2,5,6,9-pentachlorodecane (1,2,5,6,9-PentaCD), 1,2,5,6,9,10-hexachlorodecane (1,2,5,6,9,10-HexCD), 1,2,4,5,9,10-hexachlorodecane (1,2,4,5,9,10-HexCD), 1,2,4,5,6,9,10-heptachlorode cane (1,2,4,5,6,9,10-HepCD), 1,2,5,5,6,9,10-heptachlorodecane (1,2,5,5,6,9,10-HepCD), SCCPs mixtures (C10, 44.82, 60.09 and 65.02% chlorine content, and C10–13, 51.5%, 55.5% and 63.0% chlorine content), and ε-hexachlorocyclohexane (ε-HCH, 10 mg·L−1 in cyclohexane, 99.9%, internal standard). The purity of decane standards from GmbH has been published in elsewhere (Li et al., 2019; Li et al., 2017b). 13C10-trans-chlordane (100 mg·L−1 in n-nonane, 99.9%, surrogate standard) was obtained from Cambridge Isotope Laboratories (Andover, USA). Other chemicals and regents are shown in Text S1.

2.2. Experimental setup and procedures

Details of the plant cultivation procedures are given in Text S2. Four healthy and uniform pumpkin seedlings (shoot height of 5–6 cm) were transplanted in a 50 mL brown glass bottle after roots were rinsed by autoclaved deionized water. Each brown glass bottle was filled with 40 mL of deionized water. The bottles and the deionized water were autoclaved at 120 °C for 20 min before use. The brown bottles were wrapped with aluminum foil. These procedures were conducted in a laminar flow hood. Then each brown glass bottle with seedlings was placed into a 1.5 L colorless transparent glass bottle sealed with a silicone septum and a screw lid to obtain the PVOCs (Fig. 1A). For convenient PVOCs sampling, the screw lid and silicone septum were pre-drilled with two holes to allow two glass pipes to be easily inserted into the 1.5 L transparent glass bottle. The diameter of the holes on silicone septum was smaller than that of glass pipes to ensure a tight seal of the system. Ends of the glass pipes outside the 1.5 L transparent glass bottles were sealed with small silicone plugs. Then, the 1.5 L transparent glass bottles were placed into a growth chamber for 10 days and the PVOCs emitted from pumpkin seedlings filled the headspace of the 1.5 L bottle (PVOCs container). Conditions in the growth chamber were 25 °C with 16 h light/8h dark. The light intensity during the photoperiod was maintained at 250 μmol m−2 s−1.

Fig. 1.

Fig. 1.

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Schematic representation of the experimental reaction set-ups. (A) Shows the set-up for concentrating and accumulating the PVOCs. (B) Shows the set-up for transferring PVOCs into reaction system I containing SCCPs. (C) Is the atmospheric reaction system I (with PVOCs) and II (without PVOCs) and the reactions carried out for 10 days. (D) shows the set-up for sampling after 10 days reaction for both systems. Green dots represent PVOCs. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

After 10 days collection of PVOCs, atmospheric PVOCs reaction system (system I, including both PVOCs and the SCCP congener) and reaction control system (system II, only including SCCP congener but without PVOCs) were set simultaneously to study the reactions of individual SCCP congener in the atmosphere and evaluate the contribution of PVOCs in the atmospheric reaction of SCCPs. An amount of 7712 ng of 1,1,1,3,8,10,10,10-OctaCD dissolved in 80 μL isooctane was injected by syringe into a clean 1.5 L transparent glass bottle. After 30 s to allow for volatilization of isooctane, the 1.5 L transparent glass bottle was also sealed with the pre-perforated silicone septum and screw lid. One of the holes was inserted with an outflow glass pipe which was connected with two series connected glass columns (to avoid breakthrough) and filled with XAD resin (Amberlite XAD-2, supelco, USA) to sample the CPs inside the 1.5 L bottle. The XAD resin was cleaned by methanol, acetone, and DCM sequentially, and then further cleaned by Soxhlet extraction using dichloromethane (DCM) for 24 h before use. For reaction system I, another hole on the septum was immediately inserted by the outflow pipe of PVOCs container after unplugging the small silica plug as shown in Fig. 1B. Then, compressed air (60 mL/min) was blown into the PVOCs container through its inflow pipe to make the PVOCs enter into reaction system I containing 1,1,1,3,8,10,10,10-OctaCD standard. After 25 min, the reaction system I which had contained both PVOCs and OctaCD inside was disconnected from the PVOCs container and sealed with silicone plug (Fig. 1C). For reaction system II, the inflow pipe was inserted and immediately sealed by a small silicone plug and to determine the air phase transformation of OctaCD without the effects of PVOCs (Fig. 1C, only OctaCD inside, without PVOCs). Then, three replicates of the reaction system I and II, respectively, were all placed in the exposure chamber for another 10 days of reaction. The same temperature and illuminance conditions were set at 25 °C and 16 h light/8h dark.

2.3. Sampling and sample pretreatment

After 10 days reaction, compressed air (60 mL/min) was blown into reaction system I and II through their inflow glass pipes for 25 min, respectively (Fig. 1D). OctaCD and its daughter compounds in the headspace were adsorbed by the XAD columns. The inner walls of glass pipes and 1.5 L bottle, and outside walls of pipes inside the 1.5 L bottle were rinsed five times by DCM and hexane (1:1, v/v). The combined regent was collected as the glass wall sample then determined. Screw lid and silicone septum of the 1.5 L bottle were also rinsed by hexane and determined as the silicone septum sample. XAD resin in two series connected glass columns was sampled as XAD-A and XAD-B. The details of the pretreatment procedures are provided in Text S3.

2.4. Instrumental qualitative and quantitative analysis

Instrumental conditions of 7890A gas chromatograph (GC) coupled with a 7000B triple quadrupole mass spectrometer (MS) in the electron capture negative ionization (ECNI) mode (Agilent, Palo Alto, CA) used for qualitative and quantitative analysis are shown in the Text S4 in the SI that was similar to our previous work (Li et al., 2019; Li et al., 2017b). The mass resolution and mass accuracy of the instrument are 1000 and ±0.3 Da, respectively. The target CPs and SIM ions are shown in Table S1. The qualitative and quantitative analysis of CPs was based on former work and our previous work (Beaume et al., 2006; Li et al., 2017b; Zeng et al., 2011). The most and the second most abundant isotope ions of [M–Cl]− for CPs were selected for quantitative and qualitative measurements in selected ion monitoring (SIM) mode for congeners with different numbers of chlorine atoms and carbon atoms. Comparison of the retention time, signal shape and isotope ratio with those of standards was used to identify the CPs. The parent and daughter SCCPs were further confirmed by gas chromatography quadrupole time-of-flight mass spectrometry (GC-QTOFHRMS) (Agilent technologies, Santa Clara, USA). Its detail instrumental information is also shown in Text S4.

Individual standards were used for semiquantitative analysis based on the published work (Beaume et al., 2006; Li et al., 2019). Namely, 1,2,5,6,9-PentaCD, 1,2,5,6,9,10-HexCD, 1,2,5,5,6,9,10-HepCD, and 1,1,1,3,8,10,10,10-OctaCD were used to quantify homologues with 5, 6, 7, and 8 chlorine atoms, respectively. Concentration of daughter congeners without CCl3-goups would be biased when using individual standard with CCl3-groups (e.g., 1,1,1,3,8,10,10,10-OctaCD) as quantification standards and vice versa due to the low response factor of SCCPs with CCl3-groups in ECNI-MS as discussed in elsewhere (Beaume et al., 2006; Li et al., 2019; Rusina et al., 2011).

2.5. Quality assurance and quality control (QA/QC)

All the glassware was steeped in deionized water with Decon 90 overnight, and then rinsed with deionized water three times. Before use, all glassware was combusted at 450 °C for 6 h and rinsed with dichloromethane three times to avoid potential contamination. The silicone septum was rinsed by hexane five times before usage. Background controls (without 1,1,1,3,8,10,10,10-OctaCD and PVOCs) were set up in our preliminary experiment. No CPs was detected in background controls. Thus, no CPs existed in used compressed air. The ASE cells were ultrasonicated in dichloromethane and n-hexane (1:1, v:v) for 15 min (three times). Before usage, the empty cell was further cleaned using dichloromethane and n-hexane (1:1, v:v) by ASE extraction in the same conditions as those for sample extraction (shown in Text S3). The method detection limits (MDLs), estimated on the basis of a signal-to-noise ratio of 3, for individual SCCPs were 0.19–0.41 ng/g in XAD resin (Table S2). Spiking recoveries of 1,2,5,6,9-PentaCD, 1,2,5,6,9,10-HexCD, 1,2,5,5,6,9,10-HepCD, and 1,1,1,3,8,10,10,10-OctaCD were in the ranges of 80–100%, 85–115%, 90–105% and 75–110%, respectively. The recovery of 13C10-trans-chlordane for all samples was in the range of 79%-115%. All the results reported were corrected by the surrogate recoveries.

3. Results and discussion

3.1. Parent 1,1,1,3,8,10,10,10-Octachlorodecane in the reaction systems

The distribution of 1,1,1,3,8,10,10,10-OctaCD in different compartments of two reaction systems was investigated (Fig. 2 and Table S3). XAD resin possesses a high capacity for accumulating persistent organic pollutants (POPs) (Wania et al., 2003). However, 1,1,1,3,8,10,10,10-OctaCD was not found in XAD-A and XAD-B samples, indicating that no parent OctaCD was detected in the headspace of these two reaction systems. The largest portions of 1,1,1,3,8,10,10,10-OctaCD (over 33% of the initial amount) adsorbed on the glass wall in both reaction systems. The mass percentage of 1,1,1,3,8,10,10,10-OctaCD adsorbed on glass wall of reaction system II was 1.4 times as much as that of reaction system I, although there was no significant difference (p > 0.05). Only small amounts of 1,1,1,3,8,10,10,10-OctaCD (<2% of the initial amount) were detected on silicone septum. The mass adsorbed on silicone septum of reaction system II was also slightly higher than that of reaction system I. The total recovery of 1,1,1,3,8,10,10,10-OctaCD was only 34.8 ± 17.7% of its initial mass for reaction system I and 49.1 ± 12.9% for reaction system II (Table S3). The huge amounts of unrecovered of 1,1,1,3,8,10,10,10-OctaCD in reaction system I and II indicated that transformation of 1,1,1,3,8,10,10,10-OctaCD occurred not only in reaction system I (with PVOCs) but also in reaction system II (without PVOCs).

Fig. 2.

Fig. 2.

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The mass of 1,1,1,3,8,10,10,10-OctaCD in different compartments of reaction system I and II after 10 days illumination. No 1,1,1,3,8,10,10,10-OctaCD was detected in XAD-A and XAD-B. The initial mass added to both reaction systems was 7712 ng of 1,1,1,3,8,10,10,10-OctaCD.

These results showed that target OctaCD could be transformed in the air phase both with and without the interaction of PVOCs. In comparison, although there was no significant difference (p > 0.05) between reaction system I and II, the total recovery of 1,1,1,3,8,10,10,10-OctaCD in reaction system I was lower than that of reaction system II. In consideration that the biotransformation ratios of many organic compounds are very low, the minor transformation may not affect the variations of parent compound between the exposure and control groups. For example, after pumpkin seedlings hydroponically exposed to BDE-47 for several days, the recovered total parent BDE-47 was 93.4% ± 12.6% for exposure reactors and 95.6% ± 12.2% for unplanted controls. There was very minor difference (not calculated the significance) on the recovered parent BED-47. However, the transformation products were definitely identified in the exposure systems rather than the unplanted controls, and the concentration ratios between hydroxylated metabolites and initial exposure levels of parent BDE-47 were from 0.006% to 0.023%. (Sun et al., 2013) The difference between two reaction systems in this work, namely the transformation ratio mediated by PVOCs of pumpkin for parent 1,1,1,3,8,10,10,10-OctaCD was 14%, far higher than those of most of the organic compounds (Yu et al., 2013; Zhai et al., 2010). So transformation of parent OctaCD in the air phase was increased by PVOCs to some extent. Plants emit a large number of PVOCs, which can cross cell membranes, cell wall, cuticle, and then move into the atmosphere (Widhalm et al., 2015). Those PVOCs likely contribute to the transformation of SCCPs in the atmospheric environment.

3.2. Phytogenic volatile organic compounds (PVOCs) of pumpkin seedlings increased the transformation of 1,1,1,3,8,10,10,10-OctaCD in air phase

The potential transformation products of 1,1,1,3,8,10,10,10-OctaCD, not only the dechlorination and chlorine rearrangement products C10Cl5–8 but also the carbon chain decomposition products C8–9Cl5–8, were investigated and quantified by low resolution mass spectrometry. C10Cl5–8, C9Cl6–8 and C8Cl7–8 were detected in both reaction systems (Fig. 3 and Table S4), further confirming the transformation mechanisms of 1,1,1,3,8,10,10,10-OctaCD, including dechlorination, chlorine rearrangement and carbon chain decomposition, all which were observed in reaction system I and II. Typical samples were also qualitatively analyzed by high resolution mass spectrometry and further confirmed the existence of those transformation products in the reaction systems (Figure S1). The proposed transformation pathways from 1,1,1,3,8,10,10,10-OctaCD to transformation products is shown in Fig. 4.

Fig. 3.

Fig. 3.

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The mass of transformation products in reaction systems and impurities in 1,1,1,3,8,10,10,10-OctaCD standard. Reaction system I (with PVOCs) and Reaction system II (without PVOCs) were both illuminated for 10 days. Transformation products were detected in the air phase. No C9Cl5 and C8Cl5–6 were detected in either reaction system.

Fig. 4.

Fig. 4.

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Proposed transformation pathways of 1,1,1,3,8,10,10,10-OctaCD in reaction systems.

For reaction system II, although PVOCs from pumpkin seedlings were not present, transformation of OctaCD still occurred. CPs are generally considered to be persistent, and do not undergo direct photolysis under environmental conditions (Feo et al., 2009). However, indirect photolysis by oxidizing radicals was suggested for CPs (Feo et al., 2009). The 1.5 L transparent glass bottle of reaction system II was full of lab air during 10 days reactions. There are free radicals present in the troposphere (Monks, 2005), and transformation of POPs in the presence of radicals (e.g. hydroxyl radicals) is an important process in atmosphere. CPs, in particular, may be subject to react with OH radicals in atmosphere, which has been predicted through DFT, QSAR, and Atkinson’s OH-radical-reaction models (Atkinson, 1986; Li et al., 2014; Liu et al., 2015). Transformation of polychlorinated biphenyls (PCBs) in the gas-phase by hydroxyl radicals (OH.) was also reported experimentally (Anderson and Hites, 1996; Brubaker and Hites, 1998).

In both reaction systems, C10Cl6–8 and C10Cl6–7 were detected on the glass wall and in the XAD-A, respectively. C10Cl5–8, C9Cl6–8 and C8Cl7–8 were detected on the silicone septum. No target CPs were found in XAD-B. Therefore, CPs did not break-through the columns, and all CPs in the headspace were sampled by XAD columns. The total mass of transformation products in reaction system I and II were 288 ± 37.0 ng and 141 ± 12.7 ng for glass wall, 4835 ± 4264 ng and 4344 ± 2767 ng for silicone septum, 47.7 ± 6. 5 ng and 39.5 ± 4.3 ng for XAD-A, respectively. Thus, the largest portion of the total mass of transformation products in the two reaction systems were adsorbed by the silicone septum; less was adsorbed by the glass wall, and the least to the XAD-A. The total mass of transformation products on the glass wall (p < 0.01), silicone septum (p > 0.05) and XAD-A (p > 0.05) of reaction system I were larger than those of reaction system II, respectively, demonstrating that the PVOCs from pumpkin seedlings have a tendency to promote the transformation of CPs.

The transformation ratio (TR) and the percentage of transformed parent SCCP compared to its initial mass were calculated based on the equimolar reaction between parent OctaCD and its transformation products (details described in Text S5). In the sealed reaction systems, all the transformation processes were quantified. Therefore, the fate of the CPs in reaction systems was numerically reported (Table S5). Total TRs of 72.6% and 64.6% were detected for parent OctaCD in reaction system I and reaction system II, respectively. The TRs of parent OctaCD to form congeners with different carbon chain length in reaction system I and II were 28.8 ± 3.9% and 44.8 ± 21.2% for C10-CPs, 31.3 ± 46.0% and 8.92 ± 6.27% for C9-CPs, 12.5 ± 15.1% and 11.0 ± 10.6% for C8-CPs, respectively.

According to the mass balance results calculated from the TRs and the percentage of remaining parent OctaCD in the reaction systems, the total recovered OctaCD was 107% and 114% for system I and II, all higher than 100%. In fact, there are some limitations for the analysis of CPs by using low resolution mass spectrometry in the electron capture negative ionization mode (LRMS-ECNI) (Reth and Oehme, 2004). Detection interferences exist between some of SCCPs congeners and even between SCCPs and MCCPs (Reth and Oehme, 2004; Yuan et al., 2016). Considering that no CPs with carbon atoms larger than 10 were detected, the determination of C10H15Cl7 and C10H14Cl8 can be interfered by C10H17Cl5 and C10H16Cl6, respectively; C9H12Cl8 can be interfered by C9H14Cl6; C8H11Cl7 and C8H10Cl8 can be interfered by C10H16Cl6 and C10H15Cl7, respectively; C9H13Cl7 can be interfered by C9H15Cl5; C8H10Cl8 and C8H11Cl7 can be also interfered by C8H12Cl6 and C8H13Cl5, respectively. No C9H15Cl5, C8H12Cl6 and C8H13Cl5 congeners were detected. Currently, accurate quantification of SCCPs is impossible because of the limitation of commercially available individual congeners and the exorbitant price of some commercially available individual congeners (Yuan et al., 2017a). Although individual standards were used to quantify the CPs in this work, there are still some limitations as we discussed in “Instrumental Qualitative and Quantitative Analysis.” Thus, mass overlap and limitation of the quantification should be the main cause resulting in the biases of the results, and the high mass balances (>100%). However, the clear contributions of atmospheric transformation reactions and the promotion of the transformations by PVOCs are important findings.

To ensure further the authenticity of the experimental results, the impurities of 1,1,1,3,8,10,10,10-OctaCD standard were examined. SCCP congeners, C10Cl6, C10Cl7 and C10Cl8, were found with the mass amounts of 118 ng, 59.5 ng and 89.8 ng as impurities in 7712 ng (initial mass) of 1,1,1,3,8,10,10,10-OctaCD standard, respectively (Fig. 3). However, the amounts of ΣC10Cl6 and ΣC10-Cl8 in reaction system I were significantly higher than those of the impurities, respectively (p < 0.01). In reaction system II, the amounts of ΣC10Cl6 and ΣC10Cl8 were also higher than those of impurities, in which the difference of ΣC10Cl6 was significant (p < 0.05). Therefore, the transformation of 1,1,1,3,8,10,10,10-OctaCD in the reaction systems was certain and statistically significant. The amounts of ΣC10Cl7 in the reaction systems were lower than that of the impurities. Transformation products C10Cl7 can be further transformed, which may result in the low mass amounts of ΣC10Cl7 in the reaction systems. Impurities in 1,1,1,3,8,10,10,10-OctaCD standard might also be involved in the reactions; however, their contribution could be negligible due to their extremely low initial mass.

4. Environmental implication

This study provides the first experimental evidence for dechlorination, chlorine arrangement and carbon chain decomposition of CPs in the air phase. Results in this research also indicate that transformation of CPs in the air phase was increased by plant-derived VOCs for the first time. Though 1,1,1,3,8,10,10,10-OctaCD is less common in SCCP technical mixtures, it has higher degrees of chlorination on the terminal carbon atoms (1,1,1- and 10,10,10-chlorinated positions) making oxidative transformation more difficult. Thus, this transformation of 1,1,1,3,8,10,10,10-OctaCD in the air phase, and increased by PVOCs of pumpkin seedlings, was significant and confirmed by commercially available individual standards. PVOCs produced by plants are extremely diverse (30,000 compounds) and play an important role in the chemistry of the lower troposphere (Penuelas and Llusia, 2004; Tholl et al., 2006).

The results of this study provide new insight into the fate of SCCPs in the air phase. Although less toxic than SCCPs, transformation of MCCPs probably also occurs in the air phase through similar pathways like carbon chain decomposition, thus, increasing the risk to humans from SCCPs. This work shows that inhalation of airborne SCCPs and their transformation products via atmospheric processes in the presence of plant-derived VOCs is a viable exposure pathway that must be considered.

5. Conclusion

Transformation of 1,1,1,3,8,10,10,10-octachlorodecane in air phase was explored. Carbon chain decomposition, dechlorination and chlorine rearrangement products of 1,1,1,3,8,10,10,10-octa chlorodecane, C10Cl5–8, C9Cl6–8, and C8Cl7–8, in the air phase after 10-d illumination were observed. PVOCs of pumpkin seedlings would increase the transformation of SCCPs in the air phase. For the first time, this work experimentally demonstrates the transformation of SCCPs in the air phase, which increased by the PVOCs of pumpkin seedlings.

Capsule:

Transformation of 1,1,1,3,8,10,10,10-octachlorodecane was firstly experimentally observed in air phase and this process was increased by phytogenic volatile organic compounds of pumpkin seedlings.

Supplementary Material

SI

HIGHLIGHTS.

  • Transformation of SCCPs in air phase was shown experimentally for the first time.

  • First evidence of increased transformation of SCCPs by PVOCs is provided.

  • Carbon chain decomposition, dechlorination and chlorine rearrangement occurred.

Acknowledgments

This work was jointly supported by the National Key Research and Development Project (2018YFC1800702), the National Natural Science Foundation of China (21677158, 21621064). Jerald L. Schnoor was supported by the Iowa Superfund Research Program (ISRP), National Institute of Environmental Health Science (NIEHS), Grant Number P42ES013661, and by the 1000-Talents Program of the Chinese Academy of Sciences.

Footnotes

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.

Appendix A. Supplementary data

Supplementary data to this article can be found online at https://doi.org/10.1016/j.scitotenv.2019.135455.

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