Environ. Sci. Technol. 2008, 42, 1892–1897
Occurrence, Phase Distribution, and Mass Loadings of Benzothiazoles in Riverine Runoff of the Pearl River Delta, China H O N G - G A N G N I , †,| F E N G - H U I L U , †,| XIAN-LIN LUO,‡ HUI-YU TIAN,§ AND E D D Y Y . Z E N G * ,† State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China, School of Geography and Planning, Sun Yat-sen University, Guangzhou 510275, China, Department of Navigation, Guangzhou Maritime College, Guangzhou 510725, China, and Graduate School, Chinese Academy of Sciences, Beijing 100049, China
Received July 27, 2007. Revised manuscript received January 1, 2008. Accepted January 2, 2008.
A set of six benzothiazoles was determined in riverine runoff samples of the Pearl River Delta (PRD) collected monthly from March 2005 to February 2006. The concentrations of total benzothiazoles ranged from 220 to 611 ng/L, with benzothiazole (BT) being the most prominent (82%), followed by 2-methylthiobenzothiazole (MBT), thianaphthene (TN), and triphenylene (TP). The annual fluxes of TN, BT, MBT, dibenzothiophene (DBT), 2-(4morpholinyl)benzothiazole (24MoBT), and TP from the PRD to the coastal ocean were 1.94, 65.1, 10.1, 0.63, 0.18, and 0.89 tons/ yr, summing to yield an annual flux of 79 tons/yr for total benzothiazoles. In the PRD, approximately 1.1 × 105 tons of rubber are estimated to be released into the environment each year. This corresponds to the annual fluxes of 13 tons/yr for BT and 0.4 tons/yr for 24MoBT from tire particles. The annual fluxes of BT from scrap tires from Japan, Korea, Brazil, the European Union, the United States, and China were 99, 21, 36, 270, 328, and 120 tons/yr, respectively. The fluxes of 24MoBT from the same countries were 3.0, 0.5, 1.1, 8.4, 10.3, and 3.8 tons/ yr, respectively. These results indicated that tire-wear particles and scrap tires are the dominant sources of benzothiazoles in the environment. By comparison, Asia may be the major contributor to the global input of benzothiazoles from auto tires in the coming years. Overall, the six benzothiazoles under investigation appeared to be suitable tracers of pollutant inputs to surface runoff within the PRD aquatic system. In addition, 24MoBT seemed more appropriate than BT to trace tire rubber residues and therefore can be a good indicator of economic development and urbanization in a specific region.
Introduction Benzothiazoles are an important class of chemicals with various applications in industry (1). The largest amount of * Corresponding author phone: 86-20-85291421; fax: 86-2085290706; e-mail:
[email protected]. † Guangzhou Institute of Geochemistry. ‡ Sun Yat-sen University. § Guangzhou Maritime College. | Graduate School, Chinese Academy of Sciences. 1892
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ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 42, NO. 6, 2008
benzothiazoles has been used as vulcanization accelerator (e.g., 2- morpholinothiobenzothiazole) in rubber production, where they are added in the amounts of over 1% (2). Among the benzothiazoles, benzothiazole (BT) and 2-(4-morpholinyl)benzothiazole (24MoBT) are the major components that can leach from rubber and asphalt (3). Benzothiazoles are added to antifreezes and cooling liquids because of their corrosion-inhibiting properties (2). Moreover, a variety of 2-substituted benzothiazoles are utilized as slimicides in the paper and pulp industry (4), as part of various antitumor agents (3), or as photosesotizers in photography (5). Benzothiazole was also detected in wine (1). In addition, dibenzothiophene (DBT) and thianaphthene (TN) can be released from diesel fuel and motor oil (6–8), and triphenylene (TP), though not a benzothiazole-type compound, was found in tire wear and brake lining particles (9). Many applications of benzothiazoles mentioned above indicate the biological and chemical activities of benzothiazoles. Additionally, BT has been found to cause eye, skin, and respiratory irritation and skin sensitization (10). A previous study of in vivo and in vitro effects of BT on sheepshead minnow indicated that BT was a gill toxicant and not a neurotoxicant (11). Another study (12) also suggested that BT and 2-methylthiobenzothiazole (MBT) show acute aquatic toxicity in various test systems. The toxicity of 24MoBT, TN, and DBT has not been evaluated so far. Due to their widespread applications, persistence, and toxicity, benzothiazole derivatives have remained a environmental concern (13). Several benzothiazoles (such as BT, MBT, and 24MoBT etc.) have been detected in street dust (14), atmospheric aerosols (15), surface water (2, 15–19), street dust (16), street runoff (14, 16), sediment (14), starry flounder liver (14), and an industrial effluent from a tire manufacturer (20). The occurrence of benzothiazoles was ascribed mainly to the automobile tires and rubber manufacturing industries (21). Tire-wear materials are incorporated into street dust and transported to rivers and estuaries via street runoff during heavy rainfall in urban areas (22). A large amount of scrap tires are also disposed of in landfills or dump piles, creating potential environmental problems because benzothiazoles can leach from crumb rubber materials via water (3). Moreover, several benzothiazoles have been found in tire debris as well as various environmental matrices and therefore have been proposed as potential molecular markers of tire-wear materials and/or urban street runoff (14, 16, 18). It is therefore environmentally important to understand the contributions of benzothiazoles from tire-wear materials and scrap tires to the environment. No riverine inputs of benzothiazoles have been measured around the world, and only two studies determined the fluxes of benzothiazoles from tire plants and wastewater treatment plants (3, 5). The present study aimed to examine the occurrence, phase distribution, and mass loadings of six benzothiazoles in riverine runoff of the Pear River Delta (PRD), South China. The PRD is one of the most developed and populated regions in China, connected to the South China Sea via eight major runoff outlets (Figure S1 of the Supporting Information; “S” designates tables and figures in the Supporting Information thereafter), and had approximately eight million registered motored vehicles by the end of 2005 (23). Tire-wear materials, therefore, are likely an important source of benzothiazoles in the PRD. In addition to field measurements, the inputs of benzothiazoles from scrap tires in Japan, Korea, Brazil, the European Union, the 10.1021/es071871c CCC: $40.75
2008 American Chemical Society
Published on Web 02/16/2008
United States, and China, representing various degrees of economic development and urbanization, were also estimated.
Material and Methods Field Sampling. The sampling locations and adjacent areas are depicted in Figure S1. The PRD aquatic system contains three main tributaries, i.e. the Beijiang, Xijiang, and Dongjiang Rivers. The Beijiang and Dongjiang Rivers flow into the South China Sea mainly via the eastern outlets including Humen (HM), Jiaomen (JM), Hongqimen (HQ), and Hengmen (HE), whereas the Xijiang River mostly drains through the western outlets including Modaomen (MD), Jitimen (JT), Hutiao (HT), and Yamen (YM). Water samples were collected monthly from March 2005 to February 2006 during monthly neap tides to avoid tidal influences, and detailed sampling procedures are provided in the Supporting Information. Sample Extraction. BT (96%), TN (95%), MBT (97%), TP (96%), and DBT (99+%) were purchased from Sigma-Aldrich (St. Louis, MO). Because no authentic standard of 24MoBT was commercially available, the 24MoBT stock solution was prepared from a vulcanization accelerator used in the rubber industry and identified by GC/MS analysis. DBT was used as a primary standard for determining the concentration of 24MoBT in the stock solution. All water samples were filtered immediately upon delivery to the laboratory, and suspended particulate matter (SPM) was collected with GF/F glass fiber filters (142 mm diameter and 0.7 µm nominal pore size; Whatman International, Maidstone, England) precombusted at 450 °C for at least 5 h. About 20 L of each filtrate sample were passed immediately upon collection through a glass column (25 mm i.d. and 400 mm length) packed with a mixture of XAD-2 and XAD-4 resins at a 1:1 weight ratio. The resin column was then eluted three times with 50 mL of methanol each (each 50 mL portion as a whole was poured onto the column) at a flow rate of 3 mL/min, followed by three consecutive extractions with 50 mL of a methylene chloride:methanol mixture (1:1 in volume) in an ultrasonic bath. The extracts were combined and concentrated to about 1 mL with a Zymark TurboVap500 (Zymark Corporation, Hopkinton, MA), solvent-exchanged to hexane, and reduced to a final volume of approximately 1 mL. The filter papers loaded with SPM were freeze-dried and crumbed, and Soxhlet extracted with a mixture of dichloromethane and acetone with 1:1 volume ratio for 48 h. Each extract was further processed with the same procedure as used for the filtrate samples. Fractionation for benzothiazoles was conducted according to the procedures described in detail elsewhere (18) with minor modifications. Briefly, 1 mL of the extract was introduced onto a 180 mm glass column (i.d., 1 cm.) packed with alumina:silica gel (1:2 in volume). The sample was eluted into three fractions. The first fraction was eluted with 10 mL hexane and discarded. The second fraction containing most target analytes was eluted with 30 mL of a hexane and dichloromethane mixture at a 7:3 volume ratio, and then with 30 mL dichloromethane. Residual benzothiazoles remaining in the column were eluted using 25 mL of methanol. Twenty-five millimeters of distilled water were added to the third fraction and back extracted three times using 25 mL of dichloromethane each. The second and third fractions were combined and the volume was reduced to 0.5 mL under a gentle N2 stream. Internal standards were added to the extract prior to instrumental analysis. Instrumental Analysis. Concentrations of target analytes were determined using a Hewlett-Packard (HP) 5890 II gas chromatograph equipped with a 5971 mass selective detector with a splitless injection. Chromatographic separation was obtained with a 30 m × 0.25 mm i.d. (0.25 µm film thickness) DB-5 column. The mass selective detector was operated in the selected ion monitoring mode for quantitation, and
TABLE 1. Quantitation Ions and Measured (Koc′) and Predicted (Koc) Organic Carbon-Normalized Suspended Particulate Matter (SPM)-Water Partition Coefficients of Benzothiazoles analyte
CAS no.
TN 95–15–8 BT 95–16–9 TP 217–59–4 DBT 132–65–0 MBT 615–22–5 24MoBT 4225–26–7
QIa
n
log Koc′b
log Kocc
log Kowd
134 135 228 184 181 220
6 95 95 96 96 10
2.24 ( 0.88 2.46 ( 0.94 3.50 ( 0.77 2.96 ( 0.60 2.12 ( 0.67 3.72 ( 0.73
2.27-2.95 1.16-1.74 4.62-5.51 3.58-4.38 2.30-2.99 1.78-2.42
3.12e 1.99f 5.49e 4.44g 3.15e 2.62f
a Quantitation ion (m/z). b Measured organic carbonnormalized SPM-water partition coefficient. c Predicted organic carbon-normalized suspended particulate matter (SPM)water partition coefficient (28). d Octanol–water partition coefficient. e Obtained from ref 27. f Obtained from ref 3. g Obtained from refs 25and 26. TN: thianaphthene; BT: benzothiazole; TP: triphenylene; DBT: dibenzothiophene; MBT: 2-[methylthio]benzothiazole; and 24MoBT: 2-[4-morpholinyl]benzothiazole.
selected samples containing high levels of the analytes were analyzed in the full-scan mode for peak confirmation. The oven temperature was initially set at 70 °C and held for 4 min, and then ramped to 280 °C at 10 °C/min where it was held for 15 min. High purity helium was used as the carrier gas with a flow rate of 1 mL/min. The injector and detector were maintained at 250 °C. Concentrations were determined using the internal calibration technique. 2-Fluoro-11-biphenyl and p-terphenyl-d14 were used as internal standards at 1 µg/ mL. Molecular ions used for quantitation are listed in Table 1. Quality Assurance/Quality Control. Field blanks, laboratory blanks, spiked blanks, and matrix spiked samples were processed with each batch of field samples (
