Poly‐ and Perfluorinated Alkyl Substances in Air and Water from Dhaka, Bangladesh

Bangladesh hosts extensive textile manufacturing, for some of which per‐ and polyfluorinated alkyl substances (PFAS) have been used to impart water and dirt repellency, among other things. Textile waste emissions to the atmosphere and discharge into rivers and other bodies of water could present a significant concern for human and ecosystem health, but there is little information on PFAS in Bangladesh. To assess the presence of ionic PFAS and their precursors in air and water from Dhaka, Bangladesh, polyethylene sheets were deployed for 28 days as passive samplers for neutral PFAS in outdoor air and water, while ionic PFAS were measured from discrete water grabs. Fluorotelomer alcohols (FTOHs) were detected at almost all sites in air and water; the most frequently detected compound was 6:2 FTOH, ranging from below instrumental detection limits (


INTRODUCTION
Per-and polyfluorinated alkyl substances (PFAS) are a family of over 4000 anthropogenic chemicals (Buck et al., 2011;Sunderland et al., 2019). All PFAS contain the strongly electronegative perfluoro alkyl moiety (C n F 2n + 1 -) and a hydrophilic functional group that makes PFAS useful in a wide variety of industrial and commercial applications (Arvaniti & Stasinakis, 2015;Wang et al., 2017). The PFAS are chemically and thermally stable, highly hydrophobic, lipophobic, and resistant to oxidation (Arvaniti & Stasinakis, 2015;Buck et al., 2011), which makes them highly persistent, at times bioaccumulative, and toxic in the environment (Wang et al., 2017). The most studied PFAS, perfluoroalkyl acids (PFAAs), include perfluoroalkyl carboxylic acids (PFCAs) and perfluoroalkane sulfonic acids (PFSAs; Buck et al., 2011). They may be directly released into the environment during production, usage, and disposal; or they can be abiotically or biologically formed from their precursors (Hamid et al., 2017).
Perfluoroalkyl acids such as perfluorooctanoic acid (PFOA) and perflurooctanesulfonic acid (PFOS) are known to be ubiquitous in surface waters, sediments and soils, fish, birds, humans, and other mammals (Houtz et al., 2016;Venkatesan & Halden, 2013). In an effort to regulate their emissions, PFOS and their salts were included in Annex B of the Stockholm Convention in 2008 (Stockholm Convention, 2009). Since then, long-chain PFAAs and their precursors (such as perfluorooctane sulfonamide [FOSA]) have been gradually phased out of production in the United States and Europe (US Environmental Protection Agency, 2009;Wang et al., 2014). Instead, companies have replaced these compounds with shorter PFAAs and their precursors, including 6:2 fluorotelomer alcohol (6:2 FTOH) (Jahnke et al., 2007;Winkens et al., 2017).
According to the Köppen climate classification, Bangladesh has a tropical wet and dry climate, with a wet season that happens during the monsoon months of June to mid-October and a dry season from November to May (Ahmed & Kim, 2003). Bangladesh has been a predominantly agricultural country that has undergone rapid industrialization, urbanization, and economic development (Habibullah-Al-Mamun et al., 2016). Environmental regulations have not been able to keep pace with the growth of the country, and discharges of untreated and semitreated domestic and municipal sewage enter most, if not all, rivers that eventually discharge into the Bay of Bengal (Dey & Islam, 2015;Habibullah-Al-Mamun et al., 2016). Along with sewage, heavy loads of organic and inorganic pollutants enter the water systems from large and small industries (Dey & Islam, 2015;Nargis et al., 2018Nargis et al., , 2019Nargis et al., , 2021. In addition, Bangladesh is one of the most threatened countries by climate change; and floodwater, caused by the retardation of river outflows by the rise of denser brackish or seawater at the mouth of the river, has continued to accumulate (Ali, 1999;Islam & van Amstel, 2018). Thus, Bangladesh's inland aquatic environments are recognized as some of the most polluted ecosystems in the world (Habibullah-Al-Mamun et al., 2016).
As awareness of the effects of PFAS has increased worldwide, consumer habits have become more sophisticated, and regulations in first-world countries have become stricter. However, the enormous production of poorly managed waste and the ongoing delocalization of fluorochemical industries from developed regions like the United States, Canada, and the European Union into developing countries make them important contamination hot spots (Li et al., 2015;Sharma et al., 2016). Despite becoming a party to the Stockholm Convention in 2007, Bangladesh does not regulate PFAS and has not accepted the amendment listing; PFOA, PFOS, along with other PFAS remain unregulated (International Pollutants Elimination Network, 2019). Data on PFAS environmental concentrations and emissions as well as on human exposure in developing countries are scarce, though desperately needed (Sharma et al., 2016). Only two other studies have reported PFAS in Bangladesh, focusing on PFAA in fish, surface water, and sediments from around the Bay of Bengal (Habibullah-Al-Mamun et al., 2016. Both studies reported the likelihood of the reported PFAS to come from the more industrialized region in Dhaka. Passive sampling, which can measure the concentration of freely dissolved contaminants through time, has widely been accepted as an effective detection tool for trace organic compounds in the atmosphere and water (Lohmann, 2011;Lohmann et al., 2012). Single-phase polymers, such as polyethylene (PE) sheets, have been able to accumulate a wide range of nonpolar and moderately polar contaminants that are in the gas phase or dissolved in water (Dixon-Anderson & Lohmann, 2018;Morales-McDevitt et al., 2021). In addition, PE sheets are low-cost, easy to handle, and easily transported and deployed (Lohmann et al., 2012). Recently, neutral PFAS were successfully measured in air and water using these devices (Dixon-Anderson & Lohmann, 2018).
To better understand the importance of industries manufacturing PFAS-containing textiles and clothing as sources of ionic and neutral PFAS and their precursors, outdoor air and water samples were taken in the vicinity of textile manufacturing sites in Dhaka, Bangladesh. Sheets of PE were used as passive samplers in air and water, measuring the concentration of freely dissolved neutral PFAS; ionic PFAS in water were measured using traditional active sampling. The overall goals of the present study were to (1) detect neutral PFAS in air and water, (2) measure ionic PFAS in water, and (3) assess whether legacy, long-chain PFAS, or rather their short-chain replacements dominate in Bangladesh.

MATERIALS AND METHODS
Precleaned PE sheets (for details see Supporting Information, Section 1.0) used as passive samplers (50 μm thickness, dimensions 4 × 15.5 inches) were deployed for 28-day measurements in outdoor air and water of Dhaka, Bangladesh, at nine sites during January-March 2020. Eight water grab samples were collected in precleaned 500-ml highdensity PE bottles. All samples were kept in a freezer at −20°C until their extraction. Further information on deployment locations, coordinates, collection times, and site characterization is available in Supporting Information, Table S11.

PE sheet extraction
Sheets of PE were wiped with paper fiber optic wipes to remove dust, mud, or biofouling. They were then individually inserted into 80-ml glass vials, spiked with surrogate standards, and extracted overnight in ethyl acetate. In the case of the water PE sheets, approximately 0.5 g of sodium sulfate was added to each vial to absorb any residual water. Extracts were concentrated to an approximate final volume of 50 μl by heating the sample to 35°C under a gentle stream of nitrogen. Prior to gas chromatographic analysis, all samples were spiked with injection standard. After the extraction, all PE sheets were weighed for final concentration calculations.

Water extraction
Water samples were mixed and weighed before being spiked with a mass-labeled surrogate standard. Extractions were done in accordance with a method previously developed in the Lohmann lab based on US Environmental Protection Agency Method 533 for solid-phase extraction (SPE) for select PFAS . Approximately 500 ml of sample water was run through a weak-anion exchange SPE cartridges. Elution of the cartridges was completed with 0.5% ammonium hydroxide in methanol. Extracts were concentrated down to 0.5 ml by heating the sample to 35°C under a gentle stream of nitrogen.

Instrumental analysis
The PE extracts were analyzed for nine neutral PFAS on an Agilent 7890B gas chromatograph coupled to an Agilent 5977A mass selective detector operating in positive chemical ionization mode using selected ion monitoring. Additional details on the method can be found in Supporting Information, Section 1.2 and Table S2.
Water extracts were analyzed for 34 PFAS on a Shimadzu Prominence liquid chromatograph coupled to a SCIEX Triple-Quad 5500 MS/MS operating in a negative mode. Additional details on the method and operating parameters can be found in Supporting Information, Section 2.1 and Tables S3-S5.

Data interpretation
Results from a previous indoor kinetic study (Morales-McDevitt et al., 2021) showed that amounts of 6:2 FTOH and 8:2 FTOH reached equilibrium after 14 days. Given the higher flow rates outdoors, deployment times were hence prescribed as 28 days, with results representing the final 2 weeks of sampling.
The time-averaged concentrations of neutral PFAS in air were derived using partitioning constants reported by Morales-McDevitt et al. (2021) and Dixon-Anderson and Lohmann (2018) and the concentration in the PE sheets, where C air is the time-averaged gas-phase concentration (picograms per cubic meter), C PE is the concentration in PE sheets (picograms per cubic meter), and K PEair is the partitioning coefficient between the PE sheets and air. Concentrations of neutral PFAS in water were derived similarly, and details are given in Supporting Information, Section 4.0 and Quality assurance/quality control PE sheet quality assurance/quality control. Passive sampling field blanks of air, matrix spikes, and field duplicate samples of air were included with each sample batch (for details, see Supporting Information, Section 3.0). Matrix spikes were prepared by spiking a known amount of the native and the mass-labeled standard onto a new, precleaned sampler. Method detection limits (MDLs) were calculated as the blank average plus 3 times the standard deviation; however, when a compound was not detected in the blanks, instrumental detection limits (IDLs) were used (Supporting Information, Table S6). Recoveries of the matrix spikes ranged between 74 and 130% for all compounds (Supporting Information, Table S7).
Water extraction. Deuterated surrogate or 13 C-labeled standards were added before sample extraction to both process blanks and water samples to correct the reported results for recoveries. A full list of analytes and native and mass-labeled standards can be found in the Supporting Information (Table S1). The MDLs were calculated from IDLs and measurements of laboratory blanks consisting of 50 ml of liquid chromatography-grade water (Supporting Information, Table S6). The MDLs were calculated as the greater value of the instrument detection limits or the sum of the median and 3 times the standard deviation of the analyzed laboratory blank concentrations. Only compounds with mass-labeled recoveries from 60 to 140% are reported in this publication (Supporting Information, Table S8). Recoveries of surrogate standards, MDLs, and matrix spikes are all available in the Supporting Information (Tables S6, S8, and S9).

Neutral PFAS
Neutral PFAS were analyzed in air and water at nine locations in Dhaka, Bangladesh. Sampling locations are shown in Figure 1. The most frequently detected compound in air was 6:2 FTOH, ranging from below limits of detection (<IDL) to −70 ng m −3 in air; 8:2 FTOH was detected only in Demra1 and Demra2 (17 and 14 ng m −3 , respectively) and Gazipur air (30 ng m −3 ). At 7 out of 10 sites, 10:2 FTOH was detected ( Figure 2; Supporting Information, Table S11), with concentrations ranging from <IDL to 18 ng m −3 . Of the fluorotelomer acrylates (FTAcrs), only 8:2 FTAcr was detected at four sites in air by the PE sheets, with concentrations ranging from <IDL to 8 ng m −3 .
As shown in Figure 2 and Supporting Information, Table S11, in Bangladesh, neutral PFAS were detected at every location with the exception of Turag River site 1; concentrations in air and water were of the same order of magnitude as those reported in a Chinese wastewater-treatment plant (H. Chen et al., 2017) and higher than those reported in Chinese (Lai et al., 2016), Japanese, western US (Arkadiusz et al., 2007), and European (Paragot et al., 2020) air masses. The elevated concentration of FTOHs in select locations, while other sites had concentrations below detection limits, indicates that atmospheric concentrations are not homogenous in Dhaka and suggests the likelihood of point emissions, likely representing production sites. The latter is reinforced by the detection of neutral PFAS in water at some sites. In addition, the presence of 8:2 FTAcr in multiple sites in Dhaka (Figure 2) implies that FTAcrs were being used in (textile) manufactured products (Wang et al., 2014). As stated previously, with stricter PFAS regulations being implemented in developed countries, the production of many fluorochemicals has been shifted to developing countries where environmental regulations are lax (Li et al., 2015;Sharma et al., 2016). However, some of the most popular properties of PFAS such as water/oil/dust resistance and wrinkle-proofing (Buck et al., 2011) are considered commodities. As such, the price of PFAS-treated products is higher and thus restrictive for communities living in extreme poverty or lack of disposable income (Holmquist et al., 2018).
Therefore, outside of these suggested production sites, it is highly unlikely that fluorinated products are used; thus, concentrations below detection are unsurprising.
The low concentrations of the FOSAs in both air and water ( Figure 2) could reflect their production phaseout in North America, Europe, and Japan (Shoeib et al., 2011). However, given that Bangladesh is one of the most important garment manufacturers in the world (Yunus & Yamagata, 2012), it more Savar at Denitex textile factory; S04 = Demra Site 1; S05 = Demra Site 2; S06 = Dhanmondi Lake in Dhaka; S07 = Gulshan Lake in Dhaka; S08 = Gazipur Metropolitan City; S09 = Hatirjheel Lake in Dhaka; S10 = Turag River Site 1; S11 = Turag River Site 2. Polyethylene (PE) air samples were retrieved from all sites except S03; PEwater samples were retrieved from S02, S06, S08, S09; water grabs were collected from S02, S03, S06, S07, S07, S08, S09, S10, S11. likely reflects the use of FTOHs in durable-water-resistant (DWR) clothing and not FOSAs and FOSEs (Gremmel et al., 2016). Although previously reported concentrations of ∑PFAS in surface water do not include any of the PFAA precursors, precursor concentrations were of the same order of magnitude as the ∑PFAAs detected around the Bay of Bengal previously (Habibullah-Al-Mamun et al., 2017).
Given that our samples were deployed and collected in February (i.e., dry season; Ahmed & Kim, 2003), rain did not interfere with our samples. Fugacity ratios, shown in Supporting Information, Table S12, indicated that, for the most part, 6:2 FTOH, 8:2 FTOH, and 10:2 FTOH, with values close to 1 or 2, were close to equilibrium between the air and water phases.

Ionic PFAS in surface water
Of the 34 PFAS compounds targeted by this method, 16 were detected regularly and reported above the MDL in the surface waters around Dhaka, Bangladesh. Perfluorobutanoic acid (PFBA), perfluorohexanoic acid, PFOA, perfluorohexane sulfonic acid (PFHxS), and PFOS dominated in frequency of detection and magnitude, with concentrations ranging from 1.4 to 19 ng L −1 in surface waters (Supporting Information, Table S13). The sum of 16 PFAS ranged from 13 (Dhanmondi Lake) to 42 ng L −1 (Cannel Savar Denitex) in surface water samples, as shown in Table 1 and Supporting Information,  Table S13. Individual concentrations were generally low, ranging from 1 to 5 ng L −1 , for most compounds measured in Dhaka's surface waters.
As shown in Figure 3, the Cannel Savar site had the highest ∑ 16 PFAS concentration, suggesting that a nearby textile mill could be responsible. Despite a lack of thorough regulation of PFAS in Bangladesh (Dey & Islam, 2015), the local prevalence of the four-and five-chain PFBA and perfluoropentanoic acid compounds at similar or higher concentrations than the longerchain PFAA (>C6) could indicate that local textile industries have been either importing shorter-chain PFAS treatments or pretreated textiles that contain these alternatives (Ateia et al., 2019). This abundance of shorter-chain acids was evident at many sites, including the Gulshan and Hatirjheel lakes, where PFBA was an order of magnitude higher than at other sites. Both Turag River sites (TR1, TR2) also exhibited an increase in perfluorobutanesulfonic acid (PFBS), the four-chain sulfonate acid, in relation to the other sites investigated in the present study.
Of the longer-chain PFAS, PFOS and PFOA were found at relatively high concentrations of 19 and 7.5 ng L −1 , respectively, in the same Cannel Savar canal near the Denitrex Mean measurements are reported when given, and reported ranges (minimum and maximum) were used when mean or median were not available in the cited literature or Supporting Information. PFAS = per-and polyfluorinated alkyl substances; PFBA = perfluorobutanoic acid; PFHxA = perfluorohexanoic acid; PFOA = perfluorooctanoic acid; PFBS = perfluorobutanesulfonic acid; MQL = method quantification limit.
mill; PFOS was also elevated in both the Gulshan and Hatirjheel lake sites. Sites TR1 and TR2, the Balshi River, and Dhanmondi Lake all had similar concentrations of ∑ 16 PFAS, suggesting a consistent baseline of PFAS contamination, though follow-up studies would need to evaluate these concentrations over diurnal and seasonal cycles. In addition to the Cannel Savar site, the next highest ∑ 16 PFAS were found at a site heavily influenced by a nearby wastewater outlet (Gazipur Metropolitan City) and the two aforementioned lakes with heavy influence from household wastewater and some nearby industry (Gulshan, Hatirjheel). Previous research has reported the dominance of shortchain PFAAs such as PFBA and PFBS in surface waters in the proximity of a fluorochemical manufacturing plant and textile manufacturing sites (H. Chen et al., 2018;Kim et al., 2021). In addition, the absence or low concentrations of long-chain PFAAs such as perfluorononanoic acid, perfluorodecanoic acid, perfluoroundecanoic acid, and perfluorododecanoic acid was noted in the effluent water of two textile industries (Clara et al., 2008). Similar to our results, Yu et al. (2022) reported the predominance of certain short-chain PFAAs in surface water and suggests that this is an indication of short-chain PFAAs gradually replacing long-chain PFAS.

Environmental implications
A recent study from 2016 on the occurrence of PFAAs in the Bay of Bengal, along the southern coast of Bangladesh, did not observe high concentrations of the shortest-chain PFBA or PFBS compounds (Habibullah-Al-Mamun et al., 2016). The ∑ 16 PFAS investigated in prior studies and in the present study were generally similar across seasonal measurements in the Bay of Bengal (Table 1). The relatively low concentrations of ionic PFAS in surface waters when compared to the high neutral PFAS measurements in air suggest that an atmospheric pathway may be the primary source to surface waters. The prevalence of shorter-chain carboxylic acids compared to PFOA (C6 or <) has been proposed as an indicator for atmospheric sources of ionic PFAS in surface waters as part of the FTOH degradation process (Simcik & Dorweiler, 2005). The high FTOH measurements in the immediate Dhaka area could be a source of the four-, five-, and six-chain carboxylic acids reported both locally in the present study and farther away in the region. Future studies of the area should include broader sampling of surface waters farther away from Dhaka's industrial centers, where surface water PFCA measurements may be higher because of the increased impact of atmospheric transport away from the point sources.
Overall, the results of the present study show increased concentrations of individual compounds and ∑PFAS compared to tropical latitude studies in the Caribbean portion of the Atlantic Ocean (Munoz et al., 2017), as should be expected based on the differences in the general population sizes, industrial footprint, and source dynamics. Compared to geographically closer tropical studies in a Singapore urban waterway, the samples analyzed from the Dhaka area display slightly lower PFAS concentrations but a similar shift toward shorter-chain chemistry as reflected by the abundance of 6:2 FTOH and PFBA in relation to longer-chain acids (C. E. Chen et al., 2013). The dominance of 6:2 FTOH in both air and water is a clear indication of the textile industry shifting toward shorter-chain compounds. Comparable ∑PFAS measurements and abundance of shorter-chain PFAS relative to the typical longer (>C6) were seen in the surface waters of two urban northern Chinese cities and several sites along the Ganges River, India, as well (Sharma et al., 2016;Yao et al., 2014), though the mean measurements reported for all sites in these studies are lower than the mean reported in the present study (Table 1).
The water concentrations measured in the Dhaka area appear to be lower than expected for such an active textile active textile manufacturing region, where PFAS are likely part of DWR textiles. Further research is needed to understand the full scope of PFAS contamination. The present study did not sample sediments, which have been identified as an important sink for PFAS in the environment (Codling et al., 2018;Habibullah-Al-Mamun et al., 2016;Mussabek et al., 2019). Suspect screening and other nontarget analyses are suggested to investigate if and how novel chemistry and replacement compounds, specifically shorter-chain PFAS, could be contaminating Bangladesh's surface waters.
As stated, Bangladesh became a member of the Stockholm Convention in 2007; however, it has not accepted the amendment list and has refrained from reporting legacy and emerging PFAS (Government of Bangladesh, 2007). The source of these contaminants remains unclear because there are no documented PFAS manufacturers in the country (Environmental and Social Development Organization, 2019). However, it is possible that PFAS could enter Bangladesh as part of polytetrafluoroethylene formulations that were applied to textiles in local textile factories or through the import of PFAS-treated fabrics. The low ionic concentrations and high neutral concentrations are also supported by the results of the Environmental and Social Development Organization's 2019 report, which states that textiles sold to Argentina from Bangladesh contained only 30 μg/kg ionic PFAS compared to approximately 7000 µg/kg volatile PFAS. In any case, the presence of long-chain PFAS such as PFOA, PFOS, and PFHxS and their precursors, which have already been phased out of North America and Europe, suggests that their country of origin does not thoroughly comply with global standards.

CONCLUSION
The results presented here support suggestions that Dhaka could be a source of PFAAs to the surface waters of the Bay of Bengal (Habibullah-Al-Mamun et al., 2016). The most likely source of this PFAA contamination is the use of neutral FTOH compounds that degrade into shorter-chain carboxylate PFAA (Simcik & Dorweiler, 2005) because of the relatively high ratios of shorter-chain (C6 or shorter) PFCAs to PFOA. Overall, the surface water measurements displayed low concentrations, similar to most PFAAs measured in other urban rivers on the Asian continent as well as previously measured tropical latitudes (H. Chen et al., 2017;Habibullah-Al-Mamun et al., 2016;Munoz et al., 2017;Sharma et al., 2016;Yao et al., 2014), though a more thorough study of sediments and nontarget screening is needed. Generally, shorter-chain (C6 or less) ionic compounds dominated in water, with the shortest of the neutral compounds, 6:2 FTOH, dominating in water and air as well. Measured concentrations of neutral PFAS in air were higher in comparison to established literature on Asian and US air masses (Arkadiusz et al., 2007), which points to the likely heavy use of FTOHs in Dhaka's bustling textile industry. The discrepancy between high concentrations of neutral PFAS and low concentrations of ionic PFAS could be indicative of local point sources emitting volatile PFAA precursors in large abundance. Previous studies and polymer degradation models have suggested that neutral PFAS can degrade in the atmosphere into ionic compounds such as the more commonly observed PFCA and PFSA (Ellis et al., 2004;Li et al., 2017;Shoemaker et al., 2009;Simcik & Dorweiler, 2005). The high concentrations of FTOH and FTAcr compounds measured in the Dhaka area directly contrasts with the expected theory that fluvial transport of high-concentration ionic, legacy compounds is the primary pathway for PFAS contamination in Dhaka and Bangladesh. Data Availability Statement-Data pertaining to this manuscript are deposited in the Open Science Framework at https:// osf.io/32x9p/. All relevant data will also be available in the Supporting Information. Data, associated metadata, and calculation tools are also available from the corresponding author (rlohmann@uri.edu).