Atmospheric Deposition Impact of Polychlorinated Dibenzo-p-dioxin and Dibenzofuran on an Aquatic System in Central Taiwan

1 Institute of Ocean Technology and Marine Affairs, National Cheng Kung University, Tainan 70101, Taiwan 2 School of Resources and Environmental Engineering, Hefei University of Technology, Hefei 246011, China 3 Department of Civil Engineering and Geomatics, Cheng Shiu University, Kaohsiung 83347, Taiwan 4 Center for Environmental Toxin and Emerging-Contaminant Research, Cheng Shiu University, Kaohsiung 83347, Taiwan 5 Super Micro Mass Research and Technology Center, Cheng Shiu University, Kaohsiung 83347, Taiwan


INTRODUCTION
Polychlorinated dibenzo-p-dioxin and dibenzofuran (PCDD/Fs) are persistent organic pollutants (POPs) that can remain for long periods and transport long distances in the environment due to their persistence and lipophilic properties (Welsch-Pausch et al., 1995).Generally, PCDD/Fs are the by-products of thermal industrial-chemical processes (Bumb et al., 1980), and can be produced by natural like forest fires (Prange et al., 2003).PCDD/Fs include 75 PCDD and 135 PCDF according to the different number and position of the chlorines.However, only the chlorine substitution in 2,3,7,8 has been shown to be much more harmful than the others.The health risk of PCDD/Fs include immunotoxicity, carcinogenicity, chloracne and endocrine disruptor (Bertazzi et al., 2001;Schecter et al., 2006;Yang et al., 2015).Among the 17 toxic congeners of PCDD/Fs, the 2,3,7,8tetrachlorodibenzo-p-dioxin (2,3,7, is the most toxic (Mitrou et al., 2001), and it will take at least 7 years to remove the half-life of 2,3,7,8-TCDD in humans (Cole et al., 2003).
Ambient air is the most important pathway for the transfer of PCDD/Fs (Lohmann and Jones, 1998;Kao et al., 2006;Lee et al., 2009).Since they are released into the atmosphere, they can disperse long distances and eventually reach water systems, soil and plants via dry and wet deposition, and can eventually bioaccumulate in the food chain, particularly in the case of fat (Wild et al., 1994;Welsch-Pausch et al., 1995;McLachlan et al., 1996;Halsall et al., 1997;Lohmann and Jones, 1998;Ren et al., 2007).There are two types of atmospheric deposition, dry and wet, that serve as the major removal mechanism for PCDD/Fs (Koester and Hites, 1992).Gas-particle partitioning plays an important role on the deposition process of PCDD/Fs, while meteorological conditions such as the ambient temperature, wind direction and velocity, humidity and total suspended particle concentration can affect gas-particle partitioning (Pankow, 1994;Lohmann et al., 1999;Chang et al., 2004;Zhu et al., 2017a).Ingestion, inhalation and dermal contact are the PCDD/Fs exposure pathway, but previous studies have suggested that more than 90% of human exposure occurs through the food-chain (Charnley and Doull, 2005;Correa et al., 2006).Because of the high risk to human health, tolerable daily intake (TDI) values for PCDD/Fs were set by the World Health Organization (WHO) as 1-4 pg WHO 2005 -TEQ kg -1 bw day -1 (WHO, 1998).Many studies have evaluated the potential health risks associated with daily intake of PCDD/Fs (Eduljee and Jackson, 1994;Liem et al., 2000;Fernandez et al., 2004;Kiviranta et al., 2004).
Since the daily intake of PCDD/Fs were studied for the first time in Taiwan (Hsu et al., 2002), the potential adverse effect on the ambient environment and human health due to the emission of PCDD/Fs has been a public concern in Taiwan.Taiwan's government chose incineration as the main waste disposal method due to the high population density.Generally, the PCDD/Fs are produced by the human activities, including industrial and heat-treatment processes (Addink and Altwicker, 2001;Lin et al., 2014;Cheruiyot et al., 2016).Previous studies have indicated that the highest PCDD/Fs TEQ levels occurred in fish and shellfish (Hsu et al., 2002;Sasamoto et al., 2006).In this context, it is important to measure the POPs in aquatic systems, and to evaluate the content of POPs accumulated in animals and sediments.
The objectives of this study were to investigate the potential effect of atmospheric dry and wet deposition of PCDD/Fs on the animals in Taiwan.Two biotas and four aquatic animals were chosen as the study objects: Ostrea gigas Thunberg on the coast, and Meretrix meretrix Linnaeus, Oreochromis mossambica and Lates calcarifer in fishponds.We analyzed 17 PCDD/Fs in the sediment and aquatic animal samples in the two biotas, and modeled the total deposition over a 30 to 60 year period to test the effect of PCDD/F deposition (dry and wet deposition) on the sediment and aquatic animals in the two biotas.The results of this study can provide further understanding of human exposure to PCDD/Fs.

Biota and Sample Collection
Two biotas and four aquatic animal samples were used to evaluate PCDD/F contents in Taiwan: O. gigas on the coast, and M. meretrix, O. mossambica and L. calcarifer in fishponds, and the corresponding sediment samples in the two biotas were also analyzed.O. gigas is a large oyster native to Japan that was introduced along the Pacific coast of the United States.The marine clam M. meretrix is a species of mollusk that lives on the loose bottom of water bodies.O. mossambica is a kind of freshwater teleost and native to southern Africa.L. calcarifer is native to coastal areas in the Indian and Western Pacific Oceans.It is a species of freshwater fish that migrates to salt water to breed.These aquatic animals are a favorite food not only in Taiwan, but also in other countries.For example, 40000 lbs L. calcarifer were shipped per week in Australia in 2006 (Pierce, 2006) 1.

Sample Pretreatment
Fresh tissues from the aquatic animal samples were cut into small pieces with stainless steel scissors after brushing any dirt and soil particles from their surfaces.All samples After extraction, the samples were concentrated through rotary evaporation and the lipid content was determined gravimetrically.The extracted lipids redissolved in hexane, were treated with concentrated sulfuric acid, followed by a series of sample cleanup and fractionation procedures, including multilayered silica, alumina, and activated carbon columns.The soil samples were passed through a 2 mm (16 mesh) sieve to remove large rocks and other matters.Then the samples were freeze-dried, ground in a mill and homogenized.Finally, the samples were Soxhlet-extracted using toluene for 24 h.Subsequently, the sample solutions were treated with the above cleanup and fractionation procedures.

Analysis of PCDD/Fs
All chemical analyses were conducted in the Super Micro Mass Research and Technology Centre at Cheng Shiu Institute of Technology, which has passed the international intercalibration standards test on PCDD/Fs in fly ash, sediment, mother's milk, human blood, and cod liver.Each sample was cleaned up with the use of an activated carbon column, and elution with 25 mL of DCM: hexane (1:24, v/v); the activated carbon column was sequentially eluted with 5 mL of toluene: methanol: ethyl acetate: hexane (1:1:2:16, v/v/v/v), followed by 40 mL of toluene.Finally, the eluate was concentrated to approximately 1 mL and transferred to a vial and then further concentrated to near dryness using a stream of nitrogen.Immediately before injection, 10 mL of the standard solution for evaluating recovery was added to the sample extract to minimize the possibility of loss.
High-resolution gas chromatographs/high-resolution mass spectrometers (HRGC/HRMS) were used for the PCDD/F analysis.The HRGC (Hewlett-Packard 6970 Series gas, CA) was equipped with a DB-5 fused silica capillary column (L = 60 m, ID = 0.25 mm, film thickness = 0.25 µm) (J&W Scientific, CA) with splitless injection, and the HRMS (Micromass Autospec Ultima, Manchester, UK) had a positive electron impact (EI+) source.The selected ion monitoring (SIM) analyzer mode was used with the resolution power set at 10,000.The electron energy and source temperature were set at 35 eV and 250°C, respectively.Helium was used as the carrier gas.The protocol for quality analysis/quality control was strictly followed.

PCDD/F Content in Aquatic Animals
Considering the difference in the fishpond and coastal areas, aquatic fauna in the two different habitants were chosen for analysis.For all samples in the fishponds, the PCDD/F content differed between sample sites and species.There were six sample sites for M. meretrix, four sample sites for O. mossambica, and only one sample site for L. calcarifer.The mass content of 17 PCDD/Fs in the animals in the fishponds are present in Table 2.In November 2013, the mass content of the PCDD/Fs in the three animals was in the following order: M. meretrix (0.687 pg g -1 ), O. mossambica (0.321 pg g -1 ) and L. calcarifer (0.168 pg g -1 ); the total WHO 2005 -TEQ PCDD/Fs was in the following order: O. mossambica (0.068 pg WHO 2005 -TEQ g -1 ), L. calcarifer (0.024 pg WHO 2005 -TEQ g -1 ) and M. meretrix (0.013 pg WHO 2005 -TEQ g -1 ).In May 2014, the total PCDD/Fs in the three animals was in the following order: M. meretrix (0.655 pg g -1 ), O. mossambica (0.541 pg g -1 ) and L. calcarifer (0.320 pg g -1 ); the total WHO 2005 -TEQ was in the following  3.The total mass and WHO 2005 -TEQ content of PCDD/Fs fluctuated significantly over a year.The total mass content of PCDD/Fs are in the following order in February 2014 (1.162 pg g -1 ), November 2013 (0.781 pg g -1 ), August 2014 (0.633 pg g -1 ) and May 2014 (0.331 pg g -1 ).The results for the WHO 2005 -TEQ content were slightly different from that for mass content, for which the values were in the following order: August 2014 (0.024 pg WHO 2005 -TEQ g -1 ), February 2014 (0.022 pg WHO 2005 -TEQ g -1 ), May 2014 (0.016 pg WHO 2005 -TEQ g -1 ) and November 2013 (0.008 pg WHO 2005 -TEQ g -1 ).Generally, concentrations in the ambient air fluctuate with environmental temperature.The results indicated that the PCDD/F concentrations were higher in the cold season than in the warm season (Chen et al., 2017;Zhu et al., 2017a, b).The averaged mass content of PCDD/Fs was 0.727 pg g -1 , and the corresponding WHO 2005 -TEQ content was 0.018 pg WHO 2005 -TEQ g -1 .However, the PCDD/F content in the aquatic animals in the fishponds and coastal areas did not exhibit the similar trends in ambient air, which may have been due to the fact that the PCDD/F content in animals is not only affected by the atmospheric deposition from air, but also by feed (Isosaari et al., 2002;Hoogenboom et al., 2010Hoogenboom et al., , 2015)).

PCDD/Fs Congener Profile in Aquatic Animals
The PCDD/F congener profiles in the animals in the fishponds based on WHO 2005 -TEQ fraction are shown in Fig. 1.The results show that the congener profiles in O. mossambica were dominated by the 1,2,3,7,8  such as OCDD and OCDF, for which the similar results have been detected in krill and fish (Corsolini et al., 2002;Bengtson Nash et al., 2008), but for which different results have been obtained for penguin and eggs of the Adélie penguin (Kumar et al., 2002;Mwangi et al., 2016).The WHO 2005 -TEQ PCDD/F congener profiles of the animal samples in the fishponds and coastal area were dominated by less chlorinated PCDD/F congeners such as 1,2,3,7,8-PeCDD and 2,3,4,7,8-PeCDF.

PCDD/F Content in Sediment
The mass content of 17 PCDD/Fs in the sediment in the fishponds are presented in Table 4.The mass content of total PCDD/Fs in the sediment was 56.09, 22.10, 17.The content of 17 PCDD/Fs in the sediment in the coastal areas is presented in Table 5.The mass content of total PCDD/Fs in the sediment was 63.73, 74.10 and 80.05 ng kg -1 in November 2013, February 2014 and May 2014, respectively, with an average of 72.63 ng kg -1 .The corresponding WHO 2005 -TEQ content of PCDD/Fs was 0.623, 0.446 and 0.565 ng WHO 2005 -TEQ kg -1 in November 2013, February 2014 and May 2014, respectively, with an average of 0.545 ng WHO 2005 -TEQ kg -1 .For most sites along the coast line, the mass concentrations of total PCDD/Fs increased with time, which may have been due to the accumulation of PCDD/F deposition.
On the whole, the mass PCDD/F congener profiles of the sediment samples in the fishponds and coastal areas were dominated by more highly chlorinated PCDD/F congeners such as OCDD and OCDF, and similar results were found in the soil samples in the vicinity of an industrial complex and the Antarctic coastal environment (Kuo et al., 2015;Mwangi et al., 2016).The WHO2005-TEQ PCDD/F congener profiles were dominated by the less chlorinated PCDD/F congeners such as 1,2,3,7,8-PeCDD and 2,3,4,7,8-PeCDF.

The Effects of Atmospheric Deposition on Sediment
As we know, the atmosphere is important for transferring PCDD/Fs via deposition from air to the soil and water system (Welsch-Pausch et al., 1995).Previous studies have suggested the annual dry, wet and total deposition in Yunlin County to be 4955, 254 and 5209 pg WHO 2005 -TEQ m -2 year -1 in 2014, 4524, 348 and 4872 and 4742 pg WHO 2005 -TEQ m -2 year -1 in 2015, and 4224, 518 and 4742 pg WHO 2005 -TEQ m -2 year -1 in 2016 (Chen et al., 2017).According to the results of Chen et al. (2017), we obtained the annual average total deposition which was 4941 pg WHO 2005 -TEQ m -2 year -1 .We used the annual average deposition value to model the content of PCDD/Fs in a time range from 30 to 60 years.In a context with a sediment density of 1.6 g cm -3 , scenario A was constructed        with a soil depth of 10 cm, and scenario B was constructed with a soil depth of 15 cm.The results of the modeled PCDD/F content are listed in Table 6.At a depth of 10 cm, the modeled PCDD/F content in the sediment was 9. 27, 12.36, 15.44 and 18.53 ng WHO 2005 -TEQ kg -1 for 30, 40, 50 and 60 years.When the depth was 15 cm, the modeled PCDD/F content in the sediment was 6.18, 8.24, 10.30 and 12.36 ng WHO 2005 -TEQ kg -1 for 30, 40, 50 and 60 years.
The PCDD/F content increased with the accumulation of PCDD/Fs through atmospheric deposition from the atmosphere.Compared with the observed average values of sediment in this study, the ratios of the modeled and observed values ranged from 9.4-34.0.For the sediment in the fishponds, the ratios of the modeled and observed values ranged between 14.2 and 28.3 for scenario A, and between 9.4 and 18.9 for scenario B. For the sediment in coastal area, the ratios of modeled and observed values ranged between 17.0 and 34.0 for scenario A, and between 11. 3 and 22.7 for scenario B. With economic and industrial development, the POPs pollution will get worse.Therefore, the content of PCDD/Fs in soil and animals will increase and it will eventually accumulate in the human body and affect human health.The results of this study provide useful information for prevention and control strategies for POPs.

Fig. 2 .
Fig. 2. The congener profile of mass PCDD/Fs in aquatic animals from the fishpond.

Fig. 3 .
Fig. 3.The congener profile of WHO 2005 -TEQ PCDD/Fs in aquatic animals from the coastal area.

Fig. 4 .
Fig. 4. The congener profile of mass PCDD/Fs in aquatic animals from the coastal area.

Fig. 6 .
Fig. 6.The congener profile of mass PCDD/Fs in the fishpond sediment.

Fig. 7 .
Fig. 7.The congener profile of WHO 2005 -TEQ PCDD/Fs in the coastal area sediment.

Fig. 8 .
Fig. 8.The congener profile of mass PCDD/Fs in the coastal area sediment.
. The O. gigas were collected from the shallow sea in Taisi, Sihhu and Kouhu from November 2013 to August 2014.The M. meretrix, O. mossambica and L. calcarifer were collected from fishponds in Mailiao, Taisi, Sihhu, Kouhu, Dongshih and Shueilin from November 2013 to May 2014.The detailed collection data is provided in Table

Table 1 .
The sample locations in Taiwan.

Table 2 .
Observed PCDD/Fs content in aquatic animal from the fishpond.O.mossambica (0.071 pg WHO 2005 -TEQ g -1 ), L. calcarifer (0.024 pg WHO 2005 -TEQ g -1 ) and M. meretrix (0.017 pg WHO 2005 -TEQ g -1 ).The averaged mass content of PCDD/Fs was 0.432, 0.671 and 0.244 pg g -1 in O. mossambica, M. meretrix and L. calcarifer, and the corresponding WHO 2005 -TEQ total PCDD/Fs was 0.070, 0.015 and 0.024 pg WHO 2005 -TEQ g -1 in O. mossambica, M. meretrix and L. calcarifer.On the whole, both the mass and WHO 2005 -TEQ content of total PCDD/Fs are higher in the warm season (May 2014) than in the cold season (November 2013).Unlike the other two animals, the mass content of the PCDD/Fs in M. meretrix showed a minor decrease from November 2013 to May 2014, which may have been due to its low fat content.The WHO 2005 -TEQ content showed a small increase.The mass content of 17 PCDD/Fs in animals in the coastal areas are present in Table

Table 4 .
Observed PCDD/Fs content in sediment from the fishpond.

Table 5 .
Observed PCDD/Fs content in sediment in the coastal areas.

Table 6 .
The modeled total content in the sediment and the ratio of the modeled and observed values over a 30-60 year period.