Polybrominated Diphenyl Ethers Brominated Chemicals Biology Essay

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The presence of brominated flame retardant chemicals and particularly polybrominated diphenyl ethers (PBDEs) has aroused increasing concern to scientists over the past decades. Meanwhile, sediment is an important sink and reservoir of anthropogenic pollutants and has large impact on their distribution in aquatic environment. PBDE released from various sources could be transported to coastal areas through riverine inputs and also atmospheric deposition. As PBDEs have lipophilic and hydrophobic characteristics, they absorb to sediments strongly.

In this review paper, I aim to summarize the local PBDE concentrations in sediments and evaluate their sources and patterns in China in past few years, and make regional comparison with other Asian countries such as Korea, Japan and Singapore. A global comparison with European countries and North America would also been made to see whether there are similarities or differences.

Statistical data demonstrated that Asian countries shared about 40% of the global PBDE consumption in 2001, with approximately 25000 tons.

^ Bromine Science and Environmental Forum. Major Brominated Flame Retardants Volume Estimates: Total Market Demand By Region in 2001. 21 January 2003.

Introduction

Polybrominated diphenyl ethers (PBDEs) are a group of brominated chemicals that serve as flame retardant that are widely used in many kinds of manufactured products such as furniture, carpets, textiles, and plastics used in electrical appliances and equipment. PBDEs work as they decompose at high temperature and release bromine radicals. These bromine radicals are effective at slowing and stopping the basic chemical reactions that drive oxygen- dependent fires, and thus reduce the rate of combustion and dispersion of fire (De Wit, 2002), which allows more time for people to extinguish or escape from the fire.

PBDES were firstly produced in 1960s and have been used widely since 1970s (Fowles et al., 1994). In 1999, PBDEs' global annual consumption reached ca. 70,000 tons, and it was estimated that PBDE concentration in biota was doubling every 5 years (De Wit, 2002). This raised a growing concern about PBDEs' persistence in the environment and their bioaccumulation in food chain. In recent years, scientists have measured PBDEs in human adipose tissues, serum and even breast milk. Also, PBDEs are everywhere including fish, birds, marine mammals, sediments, sludge, supermarket foods, indoor and outdoor air, and house dusts. A recent study which was aiming on US population found that unlike other persistent organic pollutants (POPs), the key route of human exposure of PBDEs is house dust rather than food. It was estimated house dusts accounted for 82% of the overall intakes of PBDEs (Lober M, 2008).

Studies have been conducted in laboratory animals so as to get a better understanding of the potential health risks of PBDEs. Studies of individual congeners and various commercial mixtures have suggested potential concerns about liver toxicity, thyroid toxicity, development toxicity, and development neurotoxicity. Furthermore, the presences of PBDEs in house dust and breast milk indicate that there are likely some pathways of PBDEs exposure particularly to children. Due to health risks, commercial Penta- and Octa-BDE were banned by the European Union (Cox and Ethymiou, 2003), Maine and California (National Caucus of Environmental Legislators). Though industry voluntarily stopped production (Tullo, 2003), commercial Deca-BDE were excluded in these bans, which made commercial Deca-BDE products widely used and their demands in total markets reached 56,418 tons in 2003 (Bromine Sci. and Env. Forum).

There are no known natural sources of PBDE (ATSDR 2004), and they are man-made chemicals that are structurally similar to polychlorinated biphenyls (PCB). PBDEs exist as mixtures of distinct chemicals called congeners, which are isomers of different bromine substitutions patterns. Each of them contains unique molecular structures, ranging from one to ten bromine atoms attached (Figure 1). The PBDE congeners might be different in the total numbers and positions of bromine atoms attached to the ether group.

Figure 1. Generalized Structure of Polybrominated Diphenyl Ethers where (m+n) = 1 to 10 bromines

In this review paper, the objective is to summarize the local PBDE concentrations in sediments and evaluate their sources and patterns in China, and make regional comparison with other Asian countries such as Korea, Japan and Singapore. A global comparison would also been made to see whether there are similarities or differences.

Location

na

PBDE without BDE-209

BDE-209

Reference

Pearl River Delta

Zhujiang River

10

1.1 - 49.3

26.3 - 3580

Mai et al. (2005)

Dongjiang River

10

2.2 - 94.7

21.3 - 7340

Mai et al. (2005)

Xijiang River

10

0.1 - 0.6

1.9 - 77.4

Mai et al. (2005)

Pearl River Estuary

10

0.3 - 21.8

0.7 - 111.9

Mai et al. (2005)

South China Sea

10

0.04 - 4.5

0.4 - 9.1

Mai et al. (2005)

Macau Coast

10

0.6 - 41.3

6.7 - 149

Mai et al. (2005)

Yangtze River Delta

Yangtze River Estuary

13

30.8

Chen et al. (2006)

Hangzhou Bay

13

n.d. - 0.01

80.3

Chen et al. (2006)

Qiantang River

13

0.1 - 0.55

20.5

Chen et al. (2006)

Korea

Busan Bay

20

0.38 - 5.86

14.4 - 2253

Moon et al. (2007)

Jinhae Bay

20

0.03 - 6.02

2.0 - 145

Moon et al. (2007)

Ulsan Bay

20

0.12 - 6.87

3.42 - 286

Moon et al. (2007)

Korean Coast

20

0.45 - 494

0.22 - 493

H.B. Moon et al. (2004)

Japan

Osaka Bay

6

8 - 352

Ohta et al. (2002)

Tokyo Bay

6

0.05 - 0.78

0.89 - 85

N.H.Minh et al. (2007)

Hong Kong

13

0.96 - 58.5

n.d. - 2.92

Liu et al. (2005)

Singapore

3

3.4 - 13.8

Wurl and Obbard (2005)

Europe

U.K.

1.3 - 1270.8

0.6 - 3190

Sweden

8 - 50

68 - 7100

Netherlands

5

0.6 - 17.6

4 - 510

De Boer et. al. (2003)

Spain

11

0.4 - 34.1

2.1 - 132

Eljarrat et. al. (2005)

Denmark

0.53

3.67 - 21.5

Portugal

17

0.5 - 20

Lacorte et. al. (2003)

Romania

North America

USA

< 0.5 -52.3

Great Lake

9

0.5 - 6.33

4 - 242

Song et. al (2005)

San Francisco Bay

16

n.d. - 212

Oros et. al (2005)

Niagara River

9

n.d. - 148

Samara et. al (2006)

n = number of PBDE congener analyzed in sediment samples

n.d. = not detected

Chapter 1:

Local Comparison of PBDE concentrations in between China

Pearl River Delta

Studies in China have found BDE-28, BDE-47, BDE-66, BDE-99, BDE-100, BDE-138, BDE-153, BDE-154, BDE-183 and BDE-209 in sediments of Pearl River Delta and adjacent South China Sea (Bixian et el., 2005). The concentration of PBDEs (except BDE-209) and BDE-209 were ranged from 0.04 to 94.7 ng/g, and 0.4 to 7340 ng/g respectively. In general, the concentrations of BDE-209 were 1-2 orders of magnitude higher than those of PBDEs. The PBDE patterns in South China Sea and Pearl River Estuary sediments were similar to the sediments of Dongjiang and Zhujiang Rivers, indicating that the widespread influence from local inputs, probably from the three fastest growing urban centers in Pearl River Delta, namely Shenzhen, Guangzhou and Dongguan, to river, estuarine and marine sediments of Southern China.

Samples collected from Dongjiang River and Zhuhai River had far too higher concentrations of PBDEs than those collected from other geographical territories of Pearl River Delta. It is explained that Dongguan has become the world's largest manufacture industries for electronics and electrical products addition, and moreover, as the capital of Guangdong Province, Guangzhou is an urban city with dense population, heavy industrial and commercial activities (Mai et al. 2005). And thus, it could be concluded that waste discharge from the cities of Dongguan and Guangzhou are most likely the source of PBDEs to the Pearl River Delta.

The PBDE concentrations were also high in samples collected from the Macau Coast. Due to a South China coastal current originating from the clockwise Coriolis force in the Northern Hemisphere and the prevailing westward wind, the costal region received fluvial suspended particles from the Pearl River Delta water network and effluents from Macau and Hong Kong (Mai et. al. 2005). In addition, this area is influenced by waste discharges from the Shenzhen River. It receives large amount of domestic sewage and industrial effluent from Shenzhen, which is the second largest urbanized and industrialized centre in Pearl River Delta.

On the other hand, Xijiang River showed relatively lower concentration of PBDEs than the other regions. As the watershed of Xijiang River is less urbanized and industrialized comparing to those areas drained by the Dongjiang River and Zhujiang River, and also the high flows of the Xijiang River reduces the magnitude of desposition for organic contaminants in the riverbed, therefore, the concentrations of PBDEs in Xijiang River is just nearly 1/80 of the PBDEs and 1/150 of those in Dongjiang River.

Yangtze River Delta

For the study discussing the surface sediment in Yangtze River Delta, the congeners components are a bit different from Pearl River Delta. A total of 13 PDE congers including BDE-7, BDE-11, BDE-15, BDE-17, BDE-28, BDE-47, BDE-66, BDE-99, BDE-100, BDE-153, BDE-154, BDE-183 and BDE-209 were found in the sediments (S. J. Chen et al., 2006). The concentration of PBDEs (except BDE-209) and BDE-209 varies from n.d. to 0.55 and from 0.16 to 94.6 ng/g respectively. These data are far more less than those detected in Pearl Delta River. Relative high concentrations of PBDEs were observed in Qiantang River (0.1 - 0.55 ng/g) and along the southern shore of Yangtze River, followed by those found around the upper part of Hangzhou Bay, and the lowest PBDEs concentration was in the north shore of outer Hangzhou Bay.

Compared to other researches about riverine, estuarine and coastal sediments, PBDEs in Yangtze River are in the lower range. Unlike the extremely high concentration of BDE-209 found in Pearl River Delta, the generally low to moderate PBDE levels found in Yangtze River are presumably attributed to the small quantity of PBDE flame retardants, especially the technical penta-BDE products used in the region. On the other hand, the low PBDE levels may be due to the specific hydrodynamic conditions of the Yangtze River Estuary and Hangzhou Bay. As Yangtze River is characterized by large flows of water and suspended sediments, dilution by the vast amounts of both water and sediments from upper streams plays an important role in distributing domestic and industrial discharge into the estuaries. Meanwhile the high current velocity also affects the deposition of fine suspended particles, which have the tendency to combine with organic contaminants. These contaminants adhered to fine grain particles, which are further dispersed to the continental shelf and the East China Sea, and would pose harm to marine biota.

Hong Kong

Study in Hong Kong has found a total of 15 PDE congers including BDE-3, BDE-15, BDE-28, BDE-47, BDE-60, BDE-85, BDE-99, BDE-100, BDE-138, BDE-153, BDE-154, BDE-183, BDE-197, BDE-207 and BDE-209 (Liu et al. 2005). PBDEs in sediments ranged from 1.7 to 53.6 ng/g, with the highest concentrations located around the most heavily populated areas of Sai Kung and Victoria Harbour, while the lowest concentrations of PBDEs were found at more remote locations such as Sha Tau Kok, Castle Peak Bay, Wong Chuk Bay, and Gold Coast.

Chapter 2:

Regional Comparison of sediment PBDE

Korea

Brominated flame retardants have not been produced in Korea, but they were just imported from various countries. Data showed that the consumption of flame retardants in Korea has been increasing steadily with approximately 10% per year during 1990s (Korea Environment Institute, 2001), and the total consumption of brominated flame retardants in Korea was over 49,000 tons in 2002 (Korea Institute of Science and Technology Information, 2002). Meanwhile, deca-BDE accounted for nearly 25% of the portions, but penta-BDE and octa-BDE just accounted for a minor proportion of about 0.2% of the total Korean brominated flame retardant market (Wantabe and Sankai, 2003).

Studies in Korea have found BDE-3, BDE-7, BDE-15, BDE-17, BDE-28, BDE-47, BDE-49, BDE-66, BDE-71, BDE-77, BDE-85, BDE-99, BDE-100, BDE-119, BDE-126, BDE-138, BDE-153, BDE-154, BDE-183 and BDE-209, a total of 20 PBDE congeners in sediments of Ulsan Bay, Busan Bay and Jinhae Bay, which are all heavily industrialized areas and major habours in Korea (Moon et el., 2007). The concentration of PBDEs (except BDE-209) and BDE-209 were ranged from 0.03 to 6.87 ng/g, and 2.03 to 2253 ng/g respectively. In general, the concentrations of BDE-209 were 1-3 orders of magnitude higher than those of PBDEs.

There were several characteristics showing high concentrations of PBDE in Korean bays:

First, the PBDE concentrations were higher in estuarine and inner bay locations near to industrial complexes, as there is PBDE contamination in the sediment from local discharges of industrial complexes. An example would be Gosa Stream, one of the major routes of PBDE contamination in Ulsan Bay. As there are many different kinds of industrial complexes such as petrochemical plants, automobile factories, steel manufacturing factories and stainless manufactories located nearby, these would contribute to PBDE contamination in the bays by the local waste discharge.

Second, PBDE concentration would be higher in places with slower seawater flushing rate. Due to the narrow width of Onsan Bay and the breakwater in the outer part of bay, sediments are concentrated in inland rivers or streams and at inner locations of Onsan Bay. These indicated that contamination sources of PBDEs are mainly located in inland rivers and inner regions of bays. However, the PBDE concentrations in sediments would decrease rapidly towards the open sea. The concentration of PBDEs in Busan Bay were 543380 ng/g, which was 20 times higher than the PBDEs found in outer bay 276.7 ng/g.

Third, high PBDE concentration could be found in habour zones with various shipyard activities. One example would be the sediment analyzed in Busan Bay, with the highest PBDE concentrations among other bays studied in Korea. The concentration of PBDEs (except BDE-209) and BDE-209 in Busan Bay were ranged from 0.38 to 5.86 ng/g, and 14.4 to 2253 ng/g respectively, which contained the largest amount of deca-BDE with about ten folded among the others. This strongly suggested that habour and shipyard activities are closely associated with PBDE contamination in costal marine water, and a huge marine product market and a variety of industrial complexes including shipyards and electronics manufacturing factories would contribute to PBDE contamination.

Japan

In Japan, the use of tetra-BDE, octa-BDE and deca-BDE commercial technical mixtures increased rapidly up to 1990, and gradually decreased afterwards (Watanabe and Sakai, 2003). Recent research papers showed that PBDEs were detected in 6 surface sediments of Tokyo Bay with concentrations of PBDEs (except BDE-209) ranged from 0.051 to 3.6 ng/g and concentrations of BDE-209 ranged from 0.89 to 85 ng/g (N.H. Minh et. al., 2007). Compared to former study in Osaka Bay (Ohta et. al., 2002), PBDEs (except BDE-209) in Tokyo Bay were similar to those of Osaka Bay and other industrial areas; while concentrations of BDE-209 was lower than those in Osaka Bay. The consumption of deca-BDE increased a double from 1960s to 2000, suggesting that there is an increasing input of deca-BDE mixture to the environment in Japan. In contrast, the consumption of tetra-BDE mixture and octa-BDE mixture in 2000 decreased to one-third of their contributions in 1960s.

There are two similar characteristics of PBDE distribution that we could find in Japanese bays:

First, a concentration gradient showed that the level of PBDEs and BDE-209 decreased from inner bays towards the mouth of the bays, indicating that municipal and industrial wastewaters would be the possible sources of PBDE contamination.

Second, levels of PBDE would be higher near to urbanized areas, as the research result showed the major emission source of PBDEs to Tokyo Bay would be related to populated areas such as Tokyo and Yokohama in Japan.

Singapore

Singapore is the world's third largest petroleum refining industry, which has more than 1 million barrels refining capacity per day. Study in Singapore has tested BDE-47, BDE-49 and BDE-100 in thirteen surface sediments at northeastern and southwestern costal regions of Singapore, but only BDE-47, a kind of tetra-BDE, could be detected with a concentration range from 3.4-13.8 ng/g (O. Wurl, J.P. Obbard, 2005). Though the research paper claimed that the main source of PBDEs at those sample locations are likely to be shipyard, industrial activities and intensive traffics, there are not enough data to support their views in this paper.

Regional Comparison

According to statistics, Asian countries shared about 40% of the global PBDE consumption in 2001, with approximately 25000 tons (Bromine Science and Environmental Forum, 2003). Among Asian countries, China and Korea are two of the major consumers. In China, the domestic demand of brominated flame retardants has increased at a rate of 8% per year (Mai et. al 2005). There are many brominated flame retardant manufacturing plants located in eastern China, especially in Jiangsu and Shandong Provinces (Jin et. al 2008). PBDEs were widely detected in riverine and costal sediments of the Pearl River Delta, especially high in concentrations of BDE-209 (Zheng et al. 2004; Mai et al. 2005). Also, there are a lot of electronic and electrical manufacturing plants in Guangdong Province, which provide large amount of PBDE containing waste discharge.

Compared to other Asian countries, Korea has the most variety of PBDE congerer, indicating PBDEs in Korean coastal waters are widespread contaminated. The main source of PBDEs in sediments from Korean costal environment are likely to be industrial activities and intensive ship traffics, and this is similar to what were reported from Pearl River Delta and Singapore Coast. Rapid growth of electronic market in Korea could also be one of the explanations of the increase in the demand of PBDE. Though the importance of wastewater treatment plant has been emphasized as a potential source of PBDE contamination in some studies (Anderson and MacRae, 2006; Samara et al., 2006), the sediment samples collected next to the Korean wastewater treatment plants contained relatively lower PBDE concentrations among the others. This indicated that wastewater treatment plant might not be the major source of PBDE contamination to Korean costal waters.

BDE-209 was the dominant congener in sediment samples, which accounted for over 80-90% of the total PBDE concentrations. Besides BDE-209, the most abundant congeners in sediment around Asian countries were BDE-47, BDE-99, BDE-100 and BDE-183, which could all be found in Pearl River Delta, Yangtze River Delta, Hong Kong and Korea. Furthermore, BDE-66, BDE-138, BDE-153 and BDE-154 could also be detected in the sample sediments. These similar patterns in Asian countries indicated that the sources of the PBDE congeners are more or less the same. When comparing the studies in these countries, there are several common characteristics that contribute to the PBDE contaminations. Shenzhen, Guangzhou, Ulsan and Busan have lots of industrial manufacturing complexes such as electronic and electrical product industries, while Hong Kong, Tokyo and Yokohama are urbanized cities with dense population. As there is still no banning of PBDEs in Asian countries, they continue to be used as fire retardants in a range of materials and electrical components. All these compounds would have their potential to enter the marine environment by leaching from waste deposits or other materials or through atmospheric deposition to the sea surface. As a result, these characteristics could be then emphasized as a potential source of PBDE contaminations.

On the other hand, sediments from Tokyo Bay in Japan showed different compositions with an absence of BDE-100 (N.H. Minh et. al., 2007). This suggested that there are different types of PBDE product usages in Japan from other Asian countries. Meanwhile, accurate data on the composition of tetra-BDE used in Japan are limited and not yet available for further discussion.

Chapter 3:

Global Comparison of sediment PBDE

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