Assessment of Organophosphate Flame Retardants and Plasticizers in Aquatic Environment of China
Student thesis: Doctoral Thesis
Flame retardants are chemicals used for increasing the fire resistance of materials, and hence reduce the risk of fire in human society. Growing demand for a higher standard of fire safety supports the continuous expansion of the global flame retardant market. Nonetheless, some of these chemicals, such as the technical mixtures of polybrominated diethyl ethers (PBDEs), have been restricted in production and use due to their potential adverse effects on the environment. Thus, to compensate for the restrictions, the use of other non-regulated flame retardants, such as organophosphate flame retardants (OPFRs), has been increasing in a large number of applications, including plastics, textiles, electronic equipment, and other commercial products. The intensive use of OPFRs may hence lead to their frequent detection in various environmental compartments worldwide. Some of the OPFRs are suggested to have toxic effects on different organisms. The widespread occurrence of OPFRs and their suspected adverse effects in the global environment has become an emerging concern. Their distribution and fate in the environment, however, are not well studied.
To evaluate the occurrence of OPFRs in the aquatic environment, abiotic and biotic samples were examined in this study. Different methodologies were developed and validated for abiotic and biotic sample analyses to initiate the comprehensive investigation of the OPFR contamination in the aquatic environment. OPFR analytes in water samples were extracted and purified by a solid phase extraction method, and they were identified and quantified by the ultra-performance liquid chromatography-tandem mass spectrometer system (UPLC-MS/MS). In this study, 19 OPFR compounds were selected, and they were categorised into four main groups, i.e. alkyl, aryl, and halogenated phosphates, and phosphine oxide, based on their chemical structures. The analytes included trimethyl phosphate (TMP), triethyl phosphate (TEP), tri-n-propyl phosphate (TPrP), tri-iso-propyl phosphate (TIPrP), tri-iso-butyl phosphate (TIBP), tri-n-butyl phosphate (TNBP), trihexyl phosphate (THP), tris(2-butoxyethyl) phosphate (TBOEP), tris(2-ethylhexyl) phosphate (TEHP), triphenyl phosphate (TPHP), diphenyl cresyl phosphate (DCP), 2-ethylhexyl diphenyl phosphate (EHDPHP), tricresyl phosphate (TCP), tris(2-chloroethyl) phosphate (TCEP), tris(1-chloro-2-propyl) phosphate (TCPP), tris(2-chloropropyl) phosphate (T2CPP), tris(1,3-dichloro-2-propyl) phosphate (TDCIPP), tris(1,3-dichloro-2-propyl) phosphate (TDBPP), and triphenyl phosphine oxide (TPPO). The recovery rates of the target analytes in water matrices ranged from 58 to 107%. For biotic samples, a simple and efficient analytical method was developed with the use of ultrasonic-assisted extraction and sample purification by EZ-POP, a cartridge of solid phase extraction equipped with multiple sorbents, namely Z-Sep, C18, and Florisil, to remove the interferences, such as pigments and lipid molecules. The method was validated by matrix spike recovery tests in the samples of marine eel, molluscs, crustaceans, and fish. An additional analyte, tris(2-isopropylphenyl) phosphate (TIPPP), was included on top of the 19 analytes in the water analysis due to its potential neurotoxicity. The recovery rates in the matrices of molluscs, crustaceans and fish were 59-123%, 70-115%, and 70-117%, respectively.
To date, information concerning OPFR contamination in the aquatic environment of China is limited. The production volumes of OPFRs are increasing in Asia-Pacific countries, including China and Japan. Coastal pollution has become a great concern due to industrialisation and urbanisation, given that various organic pollutants, such as PBDEs and polychlorinated biphenyls (PCBs), have been identified in the coastal environment of these countries. It was suspected that other organic flame retardants, such as OPFRs, could occur in these regions. However, little information is available on the OPFR contamination status and trends in the coastal environment of China. Thus, an investigation was conducted to identify the occurrence of OPFRs in the coastal environment of China and Japan for parallel comparison. The investigated regions in China included the Pearl River Delta (PRD), the northern part of the South China Sea (SCS), and the estuary region of the Yellow River. In Japan, Tokyo Bay was studied. As a result, the coastal water study identified the ubiquitous occurrence of the target OPFRs in the coastal aquatic environment of China and Japan. The results indicate that the coast of China contains higher concentrations of OPFRs (median = 361 ng L-1) than Tokyo Bay in Japan (median = 177 ng L-1) among the studied regions, and the OPFR levels could be spatially varied in the PRD at concentrations up to 1790 ng L-1. Hence, a significant association (R2 = 0.668, p = 0.004) is suggested between the socioeconomic activity of the cities nearby and the OPFR concentrations in coastal waters, implying that such activity could be an emission source of OPFRs in the studied regions. Heavy manufacturing and construction industries account for not only the gross domestic product (GDP) of the secondary sector but also the correlation between human activities and the OPFR levels in the receiving environment. The harmfulness to the aquatic organisms is unknown by exposure to the OPFRs at the currently detectable levels. A preliminary hazard assessment was conducted, and the results suggest a potential threat arising from exposure to TCEP (HQ > 1), a halogenated OPFR that has been prohibited for certain usage in Europe due to its potential carcinogenicity to humans. The subsequent investigation proposed its risk to freshwater algae and crustaceans, implying potential threats to the aquatic ecosystems in the studied regions. The results urge further assessment of the exposure status of the recipients of the region, which are the aquatic organisms.
In view of the coastal OPFR contamination, aquatic organisms are suspected to suffer from OPFR exposure in the highly industrialised and urbanised PRD region of China. To date, OPFRs have been detected in biota from different countries, but little is known about the aquatic organisms in China. Thus, this study examined the contamination status of OPFRs for various aquatic species from different trophic levels in Hong Kong, South China, including molluscs, crustaceans, and fish. The potentials of bioaccumulation and biomagnification were also explored. As a result, the target OPFRs were detected in all samples at concentrations of 0.1-8.6 ng g-1 ww. Some OPFRs, such as TCEP and TCPP, were detected in biota samples across different trophic levels. Halogenated OPFRs were ubiquitously found in the aquatic biota, suggesting the relative persistence of these OPFRs compared to non-halogenated compounds. TCPP was detected in all mollusc samples at a median concentration of 0.57 ng g-1 ww, while it was less frequently detected in fish. Instead, TCEP was detected in all fish samples with a median concentration of 0.3 ng g-1 ww. Levels of OPFRs, particularly TBOEP, were observed to be statistically lower (p = 0.031) in the samples from the southern waters of Hong Kong, indicating the significance of degradation resistance of OPFRs for their environmental distribution. Inhabiting environment and feeding habit, in addition, were suggested to have an influence on the composition profiles of OPFRs in aquatic biota, resulting in a relatively diversified composition of detected OPFRs in mobile organisms, such as fish. Further assessments suggest the positive correlation (R = 0.6, p < 0.001) of bioaccumulation of OPFRs and their lipophilicity. Nonetheless, the potentials of bioaccumulation and trophic biomagnification were unlikely to be observed in the examined aquatic organisms as a whole, in which the median log BAFs of OPFRs are estimated to range from 0.4 to 2.2. In general, most of the OPFR compounds demonstrated an increasing level in aquatic organisms with increasing trophic levels, although no significant trend was observed. An exception could be TEHP, a relatively lipophilic OPFR, which showed a potential of trophic dilution. These observations indicate the vulnerability of OPFRs to the complex aquatic environment. As a result, the overall levels of OPFR contamination in aquatic biota of Hong Kong, South China, are fairly comparable to other studies but considerably mild compared to the other persistent organic contaminants, such as hexabromocyclododecanes (HBCDs) (maximum level = ca. 30 ng g-1 ww), which were found at higher levels than OPFRs in the same samples. This suggests a negligible risk for the Hong Kong population as estimated by dietary exposure assessment via the consumption of these organisms, from which the estimated daily intake (EDI) of OPFRs from seafood consumption (EDIworst-case = 9.2 ng kg-1 day-1) is suggested to be less significant especially when compared to that of dust ingestion in the PRD reported elsewhere (EDIworst-case = 74 ng kg-1 day-1). In addition, the EDIs of OPFRs from seafood consumption are expected to be lower than their estimated reference dose, implying that an immediate threat is unlikely presented by OPFR intake from seafood consumption.
To further explore OPFR contamination in aquatic organisms, this study also examined the blubber collected from stranded marine mammals in Hong Kong, namely Indo-Pacific humpback dolphin (Sousa chinensis) and finless porpoise (Neophocaena phocaenoides), given that various organic contaminants have been detected in these species. Considering the scarce information on OPFR distribution in marine mammals, this study contributes to the study of OPFR contamination in the aquatic environment. The results show a mild contamination of OPFRs in cetaceans, and the median OPFR levels were found to be 5.2 and 2.2 ng g-1 ww in dolphin and porpoise, respectively. Halogenated OPFRs dominate the composition profiles, in which TCEP was detected in all samples at a median concentration of 1 ng g-1 ww. The overall OPFR concentrations were similar between male and female marine mammals, although DCP levels were found to be higher in males (p = 0.047), implying the potential influence of sex-dependent factors, such as maternal transfer of OPFRs observed in avian organisms that can reduce the chemical burden in females exclusively. The similarity of the composition profiles of marine mammals and their fish prey explore the possibility of dietary intake being a potential pathway to cause the occurrence of OPFRs in the top marine predators based on the similarity of the profiles among them. Further analysis revealed the compositional difference of OPFRs in the abiotic and biotic compartments of the aquatic environment. An increasing average proportion of TCEP up to 48% was observed in the OPFR composition profiles of aquatic biota, suggesting the potential problem of OPFRs in the aquatic environment due to the increasing significance of this suspected carcinogen.
In conclusion, this study contributes to the comprehensive study of OPFRs in the aquatic environment of China, and the results show the bioavailability of OPFRs in the studied aquatic systems. The hazard assessment identified the potential threat of OPFRs, particularly TCEP, to aquatic organisms, and an increasing proportion of TCEP was observed in the composition profile of biotic compartments. Although there is insufficient evidence to support the bioaccumulative and trophic-biomagnifying potentials of OPFRs, this study revealed the certain bioavailability of OPFRs in the aquatic environment of China, and their ubiquitous occurrence in the waters and biota, i.e. molluscs, crustaceans, fish, and marine mammals. Considering the potential toxicity and the unclear effects of prolonged exposure to OPFRs, as well as the rapid growth of the OPFR market in the world, continuous monitoring and investigation of OPFRs are necessary, especially in China, to safeguard aquatic life and humans in the foreseeable future.