Seasonal Distributions, and Risk Assessment of Polychlorinated Biphenyls (PCBs) in the Surcial Sediments from the Turag River, Dhaka, Bangladesh

11 Polychlorinated biphenyls (PCBs) assessment in sediments of Turag River, Dhaka, Bangladesh 12 has been conducted for the first time. This River provides critical ecological services to agriculture, 13 industry, and transportation. However, the Turag River is one of the most industrially polluted 14 rivers surrounding Dhaka in Bangladesh. In this study, six PCB congeners namely PCB 10, PCB 15 28, PCB 52, PCB 138, PCB 153, and PCB 180, were analyzed in surface sediments by GC-ECD 16 at 9 sampling sites. Pre-monsoon and post-monsoon season sampling were collected in this study. The total concentrations of PCBs varied from 344.49 to 0.22 ng/g dw and 10.6 to 1.68 ng/g dw in 18 pre-monsoon and post-monsoon, respectively. The paramount contributor congener to the total 19 PCBs was PCB 180 and was found at all sites. The ecological risk assessment indicated a high 20 potential risk in pre-monsoon (  = 277.32) and low potential risk in post-monsoon ( = 25.69). Sediment quality guideline quotients (SQGQs) showed that PCBs in pre-monsoon would cause no 22 or moderate biological effects on organisms at most sampling sites except in surface sediments of site S5 (high biological effects), while no adverse ecotoxicological effect was observed in post- 24 monsoon. Considering both probable effect level (PEL) and threshold effect level (TEL), the new 25 sediment quality guideline quotient (NSQGQ) showed that in post-monsoon PCBs contamination 26 would cause moderate biological effects, while in pre-monsoon the findings remained consistent 27 with the findings of SQGQ. This study gave a quick look at the PCB contamination scenario in the 28 Turag River sediments and also allowed for a comparison between the investigated River and other 29 rivers worldwide. 30 31


Sediments serve as reservoirs for PCBs as being absorbed by them (Ranjbar Jafarabadi et al. 2019). 46
When PCBs are transported into the aquatic environment through the diverse paths, they tend to 47 deposit on the surface sediments and a small portion of PCBs adsorbed on the suspended 48 particulate matter in water (Mechlińska et al. 2010). Then, these sediments bound contaminants 49 are carried away through incorporating with trophic level e.g., consumption of benthic organisms 50 by fish (Bjermo et al. 2013). Again, sediment can resuspend with changes in environmental 51 components, and then be released back into the water and begin another cycle of environmental 52 contamination and may end up in the food chain (Cui et al. 2020). Therefore, the surface sediments The quantification of polychlorinated biphenyls (PCBs) was performed by injecting 1.0 µl aliquot 112 of final extract into a gas chromatograph (Simadzu 2010 plus) equipped with a 63 Ni electron 113 capture detector (ECD) and a moving needle-type injection system and injection mode was 114 splitless. The column consisted of SH Rtx-5, 30 m long, 0.32 mm i.d.0.25 µm film thickness. Here, 115 the column temperature was started from 120 °C (1 min hold) at a rate of 20 °C / min to 210 °C (4 116 min hold) and then at a rate of 5 °C / min to 290 °C (3 min hold). Detector and injector temperatures 117 were maintained at 300 °C and 200 °C respectively. Nitrogen gas was the carrier gas 118 Data acquisition and processing were carried out by a chromatogram, named GCsolution Postrun, 119 Version 2.41.00 with a workstation (GCsolution), and a computer. PCBs were quantified by 120 comparing the individual peak areas between the sample and the standard. 121

Quality assurance and quality control 122
For the study of linear range, a diluted PCBs standard mixture solution series of 2.5, 5, 10, 50, 100, 123 and 200 ng/mL were prepared and injected onto the GC-ECD. The results show that the relation 124 is linear up to 200 ng/mL and the coefficients of determination (R 2 ) values showed good linearity 125 ranging between 0.9844 and 0.9971. 126 All solvents were of analytical grade for PCBs analysis. Quality assurance (QA) and quality 127 control (QC) measures are baking all glassware at 400 °C and rinsing them with solvent before 128 use, running method blanks, and matrix blanks for every batch of 10 samples. An S/N (signal-to-129 noise) ratio equivalent to 10 was applied to set the limit of detection (LOD) for each analyte. The 130 limit of detection (LOD) was ranged from 0.01 ng/mL (dw) to 200 ng/mL (dw). <0.001ng/g levels 131 were taken as not detected in the PCB calculations. Moisture content was assessed to present data 132 on a dry weight basis.

Composition and occurrence of PCBs in sediments 168
In the present study, detectable levels of PCBs were noticed in all sedimentary samples. The PCB 169 congeners concentration in sediments from Turag are presented in Table 1. The PCB  170 concentrations ranged from 0.217 to 344.49 ng/g and 1.68 to 10.6 ng/g dry weight (dw) in pre-171 monsoon and post-monsoon, respectively in the surface sediments. 172 In pre-monsoon, the highest concentration (344.49 ng/g) was observed in sediments collected from 173 Site 5 with the only presence of PCB 180 (344.412 ng/g dw) and PCB 52 (0.074 ng/g dw) (Table  174 4.1). Followed by Site 5, both Site 3 and 8 were higher in PCB concentrations. For Site 8 and 3, 175 the concentrations were 124.82 ng/g and 121.18 ng/g, respectively. 176 The percentage composition of six PCB congeners is shown in Fig. 2. In pre-monsoon, PCB 180 177 was the most abundant among the analyzed congeners with an average concentration of 178 67.67 ± 115.6 ng/g in the investigated samples, followed by PCB 28 (0.786 ± 2.17ng/g) and PCB 179 138 (0.441± 0.68 ng/g). PCB 180 alone contributed more than 97% to the total PCBs in the 180 analyzed sediments. PCB 180 showed predominance at all sites. From Fig. 2(a), PCB 52 was the 181 second dominant congener at Sites 7 and 9. PCB 28 was the second dominant congener at Sites 1 182 (> 40%) and 2. Also, PCB 138 was the second dominant congener at Sites 4 and 6 (> 15%). 183 Whereas, in post-monsoon ( Fig. 2(b)), PCB 180 was the most abundant congener with an average 184 concentration of 4.38 ± 2.78 ng/g, followed by PCB 28 (.86 ± 2.48 ng/g) and PCB 52. Here, PCB 185 180 alone contributed more than 68% to the total PCBs in the analyzed sediments. From

Seasonal and spatial differences of PCBs in sediments 211
In the study area, the seasonal and spatial dissemination of PCBs in sediments are shown in Fig.  212 3. Seasonally, neither the levels of total PCBs nor the identified congeners distribution patterns 213 differ significantly (p > 0.05). Where ERI is the summation of ecological risk factors of seven heavy metals and PCBs. As this 274 study is about PCBs, so heavy metals were disregarded. So, in this calculation, ERI is equivalent 275 to (monomial potential ecological risk factor). is the toxic-response factor for PCBs. is 276 the contamination factor, and denotes reference value for ∑PCBs, and it is 0.01 ppm or 10 277 ng/g. 278 The potential ecological risk factor ( ) had been graded into following five categories 279 (Hakanson, 1980): < 40, low risk; 40-79 , moderate risk; 80-159 , considerable risk; 280 160-319 , high risk; and > 320, very high risk. 281 The ERI was calculated using Eqs. (3) and (4). The ERI value indicated high potential ecological 282 risk during pre-monsoon ( = 277.32) and low potential ecological risk during post-monsoon 283 ( = 25.69). The ecological risk factor of the Turag River is shown in Table 2. 284

Sediment Quality Guideline Quotients (SQGQs) 286
The average values of SQGQ for both seasons are shown in Fig. 4.5. Six sampling sites of pre-287 monsoon are below 0.1. Besides, the SQGQs in two sampling sites, namely, Site 3 and Site 8 288 indicate the benthic organisms might suffer from moderate adverse biological effects due to 289 sediment-bound PCBs. The SQGQ of PCBs at Site 5 is above 1, suggesting that this surface 290 sediment of the sampling site was suffering from high adverse biological effects (Table 3). 291 Whereas, the SQGQs of post-monsoon show that PCBs would not cause any effects on benthic 292 organisms (Table 3). 293

New sediment quality guideline quotient (NSQGQ) 294
Wang et al., 2019 showed in their study that there was a significant linear correlation (R 2 = 0.9869, 295 p < 0.01) between SQGQs and NSQGQs while specifying that NSQGQs perhaps a valid method 296 to evaluate the ecotoxicological risks of PCBs. They recommend NSQGQs can better estimate the 297 ecotoxicological risks for PCBs. Here, the effect levels were divided into the following categories: 298 NSQGQ < 0.2, no or low effects; 0.1 ≤ NSQGQ < 2, moderate effects; and NSQGQ ≥ 2, high 299 adverse effects. 300 In pre-monsoon, the NSQGQs reflect that the PCBs contamination would cause low to moderate 301 biological effects on the Turag River except Site 5 indicating a high adverse effect on biological 302 organisms (Table 3). Whereas, in post-monsoon, the NSQGQs denote that PCBs contamination 303 caused moderate biological effects during the post-monsoon, while according to SQGQ, this 304 season had no effects on aquatic species of the Turag River (Table 3). 305

Comparison with previous studies worldwide 306
A comparison of mean sedimentary ∑PCBs concentration of the Turag River with those recorded 307 from other rivers around the world is presented in Table 4. The total sedimentary PCBs levels reported from developed countries (China, England, France, 326 Italy, and South Africa) were generally a little comparable or higher than the total PCBs levels in 327 the present study. This suggests that eminent industrial activities, and a variety of waste discharges 328 in the environmental compartments of developed countries (Kampire et al. 2017). Whereas, the 329 levels of total PCBs on the river sediments from developing countries (Egypt, Vietnam, Romania, 330 and Mexico) were generally comparable or lower than the total PCBs levels in the present study. 331 The history of PCBs is prevalent and more extensive in developed nations than in developing 332 countries, and the contamination seems to be more profound in developed countries (Mochungong 333 and Zhu 2015). 334

Conclusion 335
The present study was the first to focus on the levels of PCB organic pollutants in the surficial 336 sediments of the Turag River, Dhaka, Bangladesh. PCB 180 was the most conspicuous one in 337 sediments during both seasons. Considering seasonal variation, the mean concentration of ∑PCBs 338 in pre-monsoon (69.33 ng/g dw) was higher than in post-monsoon (6.42 ng/g dw). Sites 3, 5, and 339 8 in pre-monsoon were subjected to moderate to high adverse biological effects on benthic 340 organisms. Ecological risk assessment reflected high potential ecological risk in pre-monsoon ( 341 = 277.32) and low potential ecological risk in post-monsoon ( = 25.69). The sedimentary PCB 342 concentrations of the investigated area were comparable with rivers around the world. 343 The possible sources of PCBs are from dyeing, chemicals, paper mills, domestic industrial and 344 wastewater discharge from factories, (e.g., paper, paint, iron, and textile factories) of industrial 345 clusters. The sources also include landfills, e-wastes, transformers, constructions and demolition 346 wastes, municipal waste open burning, etc. into the Turag River. In the lack of any data on PCBs 347 in the study area, the present study will yield baseline data for subsequent ecological studies in the future. Again, this study will put stress on the assays of Bangladesh's national implementation 349 plan (NIP) to the exclusion of PCBs as being a party of the Stockholm Convention, 2001. 350 Industrial Effluent. Int J Eng Inf Syst 2017:105-118. https://hal.archives-ouvertes.fr/hal- Figure 1 Sampling sites along the Turag River Note: The designations employed and the presentation of the material on this map do not imply the expression of any opinion whatsoever on the part of Research Square concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries. This map has been provided by the authors. Distribution of total PCBs in surface sediment along the Turag River collected in post-monsoon and premonsoon Note: The designations employed and the presentation of the material on this map do not imply the expression of any opinion whatsoever on the part of Research Square concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries. This map has been provided by the authors.