Pharmaceuticals, together with other personal care products, are collectively known as PPCPs and are regarded as a class of emerging environmental contaminants. In light of their global distribution in various matrices such as sediments and aqueous samples, and the potential threat they pose to non-target organisms, public and scientific awareness of the impacts of post-therapeutic pharmaceuticals has increased over recent decades in western countries. However, information gaps about pharmaceutical contamination and its possible consequences still exist in developing countries where less attention has been given to regulating the release of emerging chemicals. The principal objective of the present study is to investigate the occurrences and fate of pharmaceutical residues in sources (sewage treatment plants - STPs), surface waters, fish in Hong Kong and tap water in mainland China, and to carry out risk assessments on different aquatic organisms as well as human beings exposed to these contaminants.
The first stage of this study involved a preliminary assessment of the occurrence, removal, consumption and environmental risks of 16 antibiotics by sampling several STPs in Hong Kong featuring different treatment levels, as well as surface waters in Victoria Harbour, the receiving water body for STP effluents. Antibiotic concentrations were quantified using solid phase extraction (SPE) coupled with high performance liquid chromatography-electrospray ionization-tandem mass spectrometry (HPLC-ESI-MS/MS). Among the 16 target compounds, twelve were found in sewage samples, of which cefalexin, ofloxacin and erythromycin-H2O were predominant, with concentrations of 1020-5640, 142-7900 and 243-4740 ng/L in influent, respectively, and their mass loads were comparable to levels reported in urban regions in China and were at the high end of the range reported for western countries. Antibiotic consumption in Hong Kong was estimated by back-calculation based on influent mass flows and consumption rates of almost all detected compounds were higher than those of other countries by 1 to 3 orders of magnitude. The target antibiotics behaved differently depending on the treatment level employed at the STPs and relatively higher removal efficiencies (>70%) were observed only during secondary treatment. As a result, the total daily mass loading of the detected antibiotics into Victoria Harbour was 14.4 kg/day, resulting in concentrations ranged from 0.6 to 1900 ng/L in surface water. Preliminary risk assessment indicated that algae may be susceptible to the environmental concentrations of amoxicillin and erythromycin-H2O as well as the mixture of detected antibiotics in receiving surface waters.
In recognition of the need for further research on pharmaceuticals in Hong Kong based on the results from the first stage of this project, 43 pharmaceuticals comprising 17 therapeutic classes were comprehensively studied in both source STPs and in surface water, and the removal efficiencies of other advanced treatments including ultraviolet disinfection, chlorination and reverse osmosis in STPs were evaluated. Forty one of all encountered pharmaceuticals were detected in three STPs. Measured concentrations ranged from less than detection limits (<DL) to 100944 ng/L in influent samples and <DL to 66733 in effluent samples. Particularly high concentrations of caffeine (8190-100944 ng/L) and salicylic acid (15700-84765 ng/L) were observed in sewage influents. Slaughterhouse effluents were found to be one pathway for veterinary pharmaceuticals, especially sulfamethazine and chlortetracycline, to enter the environment in Hong Kong. Removal efficiencies of pharmaceuticals in different sewage treatments were examined and effective removals (≥70%) of 15 of the detected pharmaceuticals were observed after conventional activated sludge treatment, while around 80% of the detected pharmaceuticals were persistent in sewage after primary sedimentation. Notably, microfiltration coupled with reverse osmosis was found to be the most effective wastewater treatment for pharmaceutical removal, with 100% removal of all detected pharmaceuticals. Nevertheless, the total pharmaceutical load entering Victoria Harbour was estimated to be 191 kg/day. Considering the surface waters, 31 pharmaceutical compounds were detected in at least one sample and measured concentrations ranged from 0.29 to 15855 ng/L, and caffeine (max: 15855 ng/L), erythromycin-H2O (max: 353 ng/L), cefalexin (max: 1795 ng/L), norfloxacin (max: 1066 ng/L) and atenolol (max: 834 ng/L) were present in over 90% of the water samples.Compared with developed and developing countries, concentrations of some of the pharmaceuticals including cefalexin, caffeine, ofloxacin, erythromycin-H2O and gemfibrozil were found to be the highest reported globally to date. Concentrations of certain frequently-detected pharmaceuticals were significantly higher in a typhoon shelter than in the open harbour area, indicating that low flushing rates could result in accumulation of pharmaceutical residues to potentially toxic levels. A risk assessment of the detected pharmaceuticals including both individual and mixture toxicity at four trophic levels-algae, bacteria, crustaceans and fishes-was conducted. Eight pharmaceuticals, erythromycin-H2O, clarithromycin, amoxicillin, ofloxacin, propranolol, metoprolol, carbamazepine and diclofenac, posed potential risk to non-target organisms at different trophic levels.
The first two parts of this study indicated that pharmaceuticals are ubiquitous in the Hong Kong environment, raising the possibility that they may enter the food chain and ultimately affect human consumers by possible mixed biological effects. Therefore, a simultaneous extraction and quantification method for pharmaceuticals in edible tissues of a marine fish (Pampus argenteus, commonly known as orbfish or white pomfret) was developed by using pressurized liquid extraction (PLE), followed by solid phase extraction (SPE) and high-performance liquid chromatography-electrospray ionization- tandem mass spectrometry (HPLC-ESI-MS/MS). Various parameters and treatments including temperature, static time, pH, microfiltration and packing materials were optimized. The optimized ASE extraction method required pre-homogenization of the fish muscle with washed diatomaceous earth and subsequent one cycle extraction for 10 min with 40 mL of water at 1500psi and 80°C. The accuracy, precision and sensitivity were validated and presented good quality assurance with recoveries ranging from nearly 60% to 130% and with analytical variation lower than 20% except for those of some of the β-lactam antibiotics. The method detection limits are much lower than maximum residue levels (MRLs) established by Hong Kong as well as other international authorities. As regards fish samples collected from Hong Kong supermarkets and fish farms, all edible tissues did not contain detectable levels of any target analytes. Though pharmaceuticals were unlikely to threaten human health in current study preliminarily based on one species, the unintentional uptake of these bioactive substances through other foods and tap water should be further focused on.
Surface waters impacted by effluents may serve as sources of drinking water, and thus the occurrence and human health risk assessment of 32 pharmaceuticals in tap water collected from 13 major cities in China (Hong Kong, Shenzhen, Macau, Zhuhai, Guangzhou, Xiamen, Wuhan, Changsha, Nanjing, Shanghai, Hangzhou, Yancheng and Beijing) were investigated. Seventeen compounds were detected in Chinese tap water at concentrations generally lower than 100 ng/L, with the exception of caffeine, which occurred at a maximum concentration of 562 ng/L. Seasonal variations of pharmaceuticals in tap water were observed and both concentrations and the number of compounds detected were found to be greater during the dry season. Caffeine and sulfamethoxazole levels were at the top end of the concentration range reported globally to date, and the veterinary antibiotic sulfamethazine was detected only in Chinese tap water when compared to other countries. The most detected compounds at the highest levels were found in cities around the Yangtze River Delta region (Hangzhou, Shanghai and Yancheng), regarding as hot spots of pharmaceutical contamination in tap water in China. Caffeine, carbamazepine and sulfamethoxazole, derived from human use, and sulfamethazine, dimetridazole and tylosin, originating from veterinary application, are suggested to be suitable chemical indicators in tap water for municipal and agricultural wastewater contamination, respectively; however, their application as contamination markers needs to be further validated. Human health risk assessments were performed and all risk quotients were < 1 except for that of dimetridazole, for which potential risk may occur during early life exposure. Future research on more effective removal techniques during drinking water treatment and long-term monitoring are suggested in order to safeguard human health.
| Date of Award | 16 Jul 2012 |
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| Original language | English |
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| Awarding Institution | - City University of Hong Kong
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| Supervisor | Kwan Sing Paul LAM (Supervisor) |
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