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Temporal trends of C8 – C36 Chlorinated Paraffins in Swedish Coastal Sediment Cores over the Past 80 Years Bo Yuan, Volker Brüchert, Anna Sobek, and Cynthia A. de Wit Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.7b04523 • Publication Date (Web): 20 Nov 2017 Downloaded from http://pubs.acs.org on November 29, 2017
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Environmental Science & Technology
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Temporal trends of C8 – C36 Chlorinated Paraffins in Swedish
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Coastal Sediment Cores over the Past 80 Years
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Bo Yuan1*, Volker Brüchert2, Anna Sobek1, Cynthia A. de Wit1
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University, Svante Arrhenius väg 8, SE-10691 Stockholm, Sweden
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SE-10691 Stockholm, Sweden
Department of Environmental Science and Analytical Chemistry, Stockholm Department of Geological Sciences, Stockholm University, Svante Arrhenius väg 8,
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* Corresponding author address and e-mail:
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Svante Arrhenius väg 8, SE-10691 Stockholm, Sweden;
[email protected].
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TOC GRAPHIC
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(Graphic and Photo by Bo Yuan)
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Abstract
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Temporal trends of chlorinated paraffins (CPs) were analyzed in three sediment
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cores collected near different potential CP sources along the Swedish Baltic Sea
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coast. C8–C36 CPs were found in sediment dating back to the 1930s. The maximum
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CP concentrations found in proximity to a metropolitan sewage treatment plant, a
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wood-related industrial area, and a steel factory were 48, 160, and 1400 ng/g d.w.,
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respectively, in sediment sections dated from the early 1990s or the 2000s. The
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temporal trends agree with statistics on CP importation in Sweden or local industrial
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activities. MCCPs (C14–C17 CPs) and LCCPs (C≥18 CPs) predominated in most
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sediments with average percentage compositions of 47±20% and 37±20%,
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respectively. Concentrations of SCCPs in the three cores showed a decreasing trend
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in recent years. The temporal trends of MCCPs indicated that these are currently the
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predominant CPs in use. This study showed for the first time that LCCPs from C18 to
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C36, as well as C8–C17 CPs, are persistent in sediments over the last 50–80 years,
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indicating that CPs are persistent chemicals regardless of alkane-chain lengths.
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Introduction
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Chlorinated paraffins (CPs) refer to complex mixtures of polychlorinated n-alkane
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chains, from n-hexane to n-octatriacontane (i.e. C6–38 CPs).1 The use of CPs started
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during the World War I, and large-scale industrial production started around the
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1930s.2, 3 CPs have been commonly used as lubricants, plasticizers, flame retardants
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and metal cutting fluids.4 Annual global production volumes have increased rapidly,
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with 1 million tons in 2013.4 In Sweden, CPs are only imported. In 1991,
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approximately 4 800 tons of CPs were imported. Since the early 1990s, the use of
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CPs in Sweden has decreased by 80%.5 CPs are commonly divided into short chain
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(C10-13, SCCPs), medium chain (C14-17, MCCPs), and long chain (C≥18, LCCPs)
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products according to the alkane-chain-length range. These products are further
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subcategorized according to their chlorination degrees (30 – 70 %Cl by weight).6, 7
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The U.S. EPA further subcategorized LCCP products composed of C>20 CPs as very
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long chain products (vLCCPs).8 There is no certain categorization for CPs shorter
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than SCCPs (i.e. C6-9 CPs), which may occur as impurities in CP products9 or as
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by-products.
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SCCPs, MCCPs, and LCCPs are considered toxic to aquatic organisms such as
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invertebrates.7 SCCPs and MCCPs are on the EU priority list of substances for 3
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further evaluation of their potential endocrine disruptive effects.10 SCCPs are now
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included in the Stockholm Convention on persistent organic pollutants (POPs)11
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given the evidence that they are persistent in the environment12, bioaccumulative13,
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potentially carcinogenic14 and subject to long-range transport.15 Regulation of
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MCCPs and LCCPs has been under consideration in different jurisdictions around
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the world.7, 16, 17 For example, the U.S. EPA recently took action in regulating the
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production and import of CPs into the U.S., whereby they did not differentiate
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between SCCPs, MCCPs or LCCPs.18
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Concentrations of SCCP in sediment cores12, 19 and archived soils20 have shown
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decreasing trends in the past decade. However, recent studies have shown that
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MCCPs and/or LCCPs have become the predominant CPs in sewage sludge,21, 22
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soil,20 indoor environments,23,
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different continents. MCCPs and even LCCPs were also identified in human
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tissues,26 human blood,27 and mothers’ milk.28-30 Meanwhile, C9 CPs were recently
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identified in a CP product,31 lubricants32 and in environmental samples.33 Whether
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these LCCPs and CPs shorter than C10, are “new” contaminants in the environment
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is unclear.
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and marine mammals25 in many countries on
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Recent developments of analytical techniques based on atmospheric-pressure
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chemical ionization quadrupole time-of-flight mass spectrometry (APCI-QTOF-MS)
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have enabled quantification of CPs of a wide range in alkane chain lengths34 with
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different chlorination degrees32,
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historical trends of CP pollution, we implemented APCI-QTOF-MS to measure CPs
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with alkane-chain lengths ranging from C8 to C36 in dated slices of sediment cores
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collected nearby different typical emission sources from the Baltic Sea coast in
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Sweden. This study not only describes how different CPs have evolved over time,
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but also exhibits what the situation is today, thus touching upon potential risks of
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CPs for the near future.
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Materials and methods
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Sampling. Three sediment cores were collected from accumulation bottoms to
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represent different kinds of known emission sources: a sewage treatment plant, a steel
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factory and a wood-related industrial area (Figure 1). Sediment samples were collected
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from these sites given that wastewater treatment plants may serve as both sink and
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source of CPs,36 and CPs are commonly used as metal working fluids37 and in a variety
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of other industrial processes such as additives for adhesives, sealants, and paints.38, 39
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in environmental matrices.21 In order to study
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Detailed information on the three sediment cores and the sampling areas are given in
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Table S1. The sediment cores were collected in September 2016 using gravity corers.
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Core no. 1 (58 56.2379 N/17 43.1141E) was collected near Himmerfjärden wastewater
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treatment plant (SYVAB), which serves about 340 000 persons in the southern
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Stockholm metropolitan area. A sediment grab sample was collected in the same area
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for analytical method performance tests. Core no. 2 (63 32.358 N/19 27.505 E) was
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collected from the Rundvik industrial area, with a long tradition of wood-related
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industry.40 The wood-related industry manufactures fiberboard, chipboard, and other
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wood-based board materials for constructing walls, floors, and roofs of buildings. Core
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no. 3 (58 40.7739 N/17 08.4929 E) was collected near an active steel factory in
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Nyköping, that has produced steel since 1899, with increasing production capacity. The
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cores were sliced into 1.2 – 2.5 cm sections and stored in Whirl-Pak® sampling bags in
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a -20 ℃ freezer before dating and analysis.
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Sediment core dating. The sediment cores were dated primarily using 210Pb but also
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137
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applying a constant rate of supply model (Figure S1). Then, to support the
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interpretation of the 210Pb method, 137Cs and/or 226Ra methods were employed.
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Sample preparation. CPs were generally analyzed in every second section of each
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core. The extraction and cleanup process for CP analysis was adopted from previous
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studies.23, 42 Briefly, approximately 10 g of freeze-dried sediment was spiked with 10
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ng 13C10-1,5,5,6,6,10-hexachlorodecane as internal standard and extracted by
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accelerated solvent extraction (ASE 300; Dionex Europe, Leeds, UK) using a mixture
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of dichloromethane and n-hexane (50:50 v/v) as solvent. The extracts were blown to
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near dryness with nitrogen, sulfur was removed using activated copper and then the
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extract was cleaned-up on a multilayer SPE column. The eluent was reconstituted in
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100 µL isooctane and 20 ng dechlorane-603 was added as volumetric standard.
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Instrumental Analysis. Samples were directly injected into an APCI-QTOF-MS
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(QTOF Premier, Waters, UK). Instrument settings were given in previous studies.34, 35
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The eluent was n-hexane. The observed resolution was 8000 – 9000. Since there were
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no C6-7 or C37-38 CPs detected in this study, CP congener groups from C8Cl3 to C36Cl15
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were considered to form a congener group pattern. The m/z ratios corresponding to the
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congener groups are available in our previous works.23, 32, 43
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Quantification. CP congener group patterns of a set of CP technical products (n = 65)
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were initially analyzed, and a sub-set of 16 products (Table S8) were selected for
Cs and 226Ra.41 First, the 210Pb activities were measured for all sediment sections by
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quantification in this study, consisting of 5 SCCPs, 6 MCCPs, and 5 LCCPs. The CP
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congener group pattern of each sediment section was reconstructed by a deconvolution
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algorithm34 from CP patterns of the selected products. Relative contributions of the
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products were then used to calculate instrument response factors of SCCPs, MCCPs,
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and LCCPs in the sample. Here CPs shorter than C10 were considered as impurities of
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SCCPs.9 Their concentrations were included in those of SCCPs.33 A detailed
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deconvolution procedure has been given in Wong et al,23 and a brief description is
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given in Figure S6.
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Characterization of temporal trends. The temporal trends of SCCPs, MCCPs, and
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LCCPs in the sediment cores were described according to Iozza et al.12, Assefa et al.44,
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and Sobek et al.45, by determination of (1) the first year with concentrations above the
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limit of quantification (LOQ), (2) peak year, (3) peak concentration, and (4) reduction
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from peak year to current levels (%).
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QA/QC. Background levels of CPs were first screened for in silica, sulfuric acid,
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solvents, rinsing solvents of glassware, containers and ASE cells. No CPs were
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detected in these matrices. During sample preparation, each batch of samples included a
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laboratory blank to assess background contamination of CPs. The procedural LOQ was
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defined based on the mean laboratory blank value plus ten times the standard deviation
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(SD), and the procedural LOQs were 1.4 and 6.5 ng/g dry sediment for SCCPs and
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MCCPs, respectively. LCCPs were not detected in the blanks. Herein the instrumental
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LOQ of LCCPs (0.67 ng when the signal-to-noise ratio was 10:1) was used to calculate
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the procedural LOQ of LCCPs, which was 0.067 ng/g dry sediment.
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Sediment grab samples collected from Himmerfjärden were used for method
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performance tests. Aliquots of 10 g dry sediment with and without a spiked mixture of
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CPs were analyzed in triplicates, respectively, in order to validate recoveries of SCCPs,
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MCCPs and LCCPs. The recovery mixture of CPs consisted of equal concentrations of
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five CP reference standards: 1) SCCP 51.5%Cl, 2) SCCP 63.0%Cl, 3) MCCP 42.0%Cl,
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4) MCCP 57.0%Cl, and 5) LCCP 49.0%Cl (Dr. Ehrenstorfer GmbH, Augsburg,
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Germany), spiked at an environmentally realistic amount (250 ng). 10 ng of
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spiked amounts of SCCPs, MCCPs, and LCCPs were 107 ± 11%, 95 ± 21%, and 112 ±
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18% of the assigned amounts (Tables S5 – S7), and were calculated by subtracting the
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concentrations of native CPs in the sediment. The recovery of 13C-labelled CP congener
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standard in the sediment cores was 91 ± 26%. In this study, CP patterns in the sediments
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were satisfactorily reconstructed21 for quantification with the CP technical products.
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The goodness of fit R2 was 0.88 ± 0.09 (Tables S8 – S10).
C-labelled CP congener standard was used as an internal standard. The recovered
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Results
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CPs in Sediments Receiving Discharge from a Sewage Treatment Plant
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The temporal trends of total CP concentrations (∑CPs; consisting of ∑SCCPs,
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∑MCCPs, and ∑LCCPs) in the three sediment cores from the Baltic Sea are
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illustrated in Figure 2. ∑CPs in the sediment core from the site near the sewage
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treatment plant (Core no. 1) ranged from
