Paul K.S. Lam

Relationships between tissue concentrations of polycyclic aromatic hydrocarbons and antioxidative responses of marine mussels, Perna viridis.

Local mussels, Perna viridis, were transplanted from a relatively clean site to various polluted sites in Hong Kong. After a 30-day field exposure, different antioxidant parameters including glutathione S transferase (GST), superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR), NADPH DT-diaphorase (DT-d), glutathione (GSH) and lipid peroxidation were quantified, and tissue concentrations of benzo[a]pyrene (B[a]P) as well as a total of five polycyclic aromatic hydrocarbons (PAHs) with potential carcinogenicity were determined for individual mussels. Results indicated that: (1) tissue concentrations of B[a]P and total PAHs from the same site were highly variable; (2) gill SOD, DT-d and lipid peroxidation showed no response to tissue pollutants; (3) the majority of the antioxidant parameters were induced by increasing tissue pollutant concentrations; and (4) amongst the various parameters, oxyradical scavenger GSH best correlated with tissue concentrations of pollutants.

Developmental toxicity and alteration of gene expression in zebrafish embryos exposed to PFOS

Perfluorooctanesulfonate (PFOS) is a persistent organic pollutant, the potential toxicity of which is causing great concern. In the present study, we employed zebrafish embryos to investigate the developmental toxicity of this compound. Four-hour post-fertilization (hpf) zebrafish embryos were exposed to 0.1, 0.5, 1, 3 and 5 mg/L PFOS. Hatching was delayed and hatching rates as well as larval survivorship were significantly reduced after the embryos were exposed to 1, 3 and 5 mg/L PFOS until 132 hpf. The fry displayed gross developmental malformations, including epiboly deformities, hypopigmentation, yolk sac edema, tail and heart malformations and spinal curvature upon exposure to PFOS concentrations of 1 mg/L or greater. Growth (body length) was significantly reduced in the 3 and 5 mg/L PFOS-treated groups. To test whether developmental malformation was mediated via apoptosis, flow cytometry analysis of DNA content, acridine orange staining and TUNEL assay was used. These techniques indicated that more apoptotic cells were present in the PFOS-treated embryos than in the control embryos. Certain genes related to cell apoptosis, p53 and Bax, were both significantly up-regulated upon exposure to all the concentrations tested. In addition, we investigated the effects of PFOS on marker genes related to early thyroid development (hhex and pax8) and genes regulating the balance of androgens and estrogens (cyp19a and cyp19b). For thyroid development, the expression of hhex was significantly up-regulated at all concentrations tested, whereas pax8 expression was significantly up-regulated only upon exposure to lower concentrations of PFOS (0.1, 0.5, 1 mg/L). The expression of cyp19a and of cyp19b was significantly down-regulated at all exposure concentrations. The overall results indicated that zebrafish embryos constitute a reliable model for testing the developmental toxicity of PFOS, and the gene expression patterns in the embryos were able to reveal some potential mechanisms of developmental toxicity.

The use of biomarkers in environmental monitoring programmes

The monitoring of biological effects has recently become an integral component of environmental monitoring programmes as a supplement to the commonly used contaminant monitoring. Over the years, many biomarkers have been developed that are claimed to be efficient at providing an early warning of deleterious effects on biological systems and for estimating biological effects due to contaminants. Although biomarkers are potentially useful, they have a number of important limitations. In this paper, we examine some of the key assumptions behind the theory and practice of use of biomarkers, and propose a scheme, which may facilitate decisions by environmental managers as to how and when to use biomarkers in their monitoring programmes.

Toxicology and Risk Assessment of Freshwater Cyanobacterial (Blue-Green Algal) Toxins in Water

The occurrence of cyanobacterial toxins affects aquatic organisms, terrestrial animals (both wild and domestic), and humans. Detrimental effects have been documented in the scientific literature during the past 50 years. Possible guideline values of some cyanobacterial toxins (microcystins, cylindrospermopsin, and anatoxin-a) are estimated, and they show that children and infants are more susceptible to cyanobacterial toxins than adults. Therefore, particular attention should be paid when cyanobacterial blooms occur, even at relatively low cell counts, to protect children and infants from possible risks. Based on these guideline values and the occurrence of the toxins, it can be concluded that chronic and subchronic exposure to cyanobacterial toxins does occur in some populations, particularly in developing countries where high proportions of the population consume untreated surface water directly, such as pond, ditch, river, or reservoir water. Because wildlife and domestic animals consume a large amount of untreated water daily, they are at higher risk than humans from cyanobacterial toxins. Calculated guideline values in Section X show that a relatively high risk posed by the toxins to these animals is likely to occur, even at low cell densities.

Distribution of polyfluoroalkyl compounds in water, suspended particulate matter and sediment from Tokyo Bay, Japan

This study examined the environmental behaviour and fate of polyfluoroalkyl compounds (PFCs) found in water, suspended particulate matter (SPM) and sediment. The sampling of the sediment was performed at two stations from Tokyo Bay, Japan, in 2008. In addition, a depth profile of seawater was collected at three water layers from both sampling stations. The summation operatorPFC concentrations ranged from 16.7 to 42.3ngL(-1) in the water column, from 6.4 to 15.1ngg(-1) dry weight (dw) in the SPM fraction and from 0.29 to 0.36dw in surface sediment. The distribution of PFCs was found to depend on their physicochemical characteristics. While short-chain perfluoroalkyl carboxylic acids (PFCAs) (C<7) were exclusively detected in the dissolved phase, longer-chain PFCAs (C7), perfluoroalkyl sulfonates (PFSAs), ethylperfluorooctane sulfonamidoacetic acid (EtFOSAA), and perfluorooctane sulfonamide (PFOSA) appeared to bind more strongly to particles. Results showed that the sorption of PFCs on SPM increases by 0.52-0.75 log units for each additional CF(2) moiety and that the sorption of PFSAs was 0.71-0.76 log units higher compared to the PFCA analogs. In addition, the sorption of PFCs was influenced by the organic carbon content. These data are essential for modelling the transport and environmental fate of PFCs.

Distribution, fate and risk assessment of antibiotics in sewage treatment plants in Hong Kong, South China.

Occurrence, removal, consumption and environmental risks of sixteen antibiotics were investigated in several sewage treatment plants (STPs) featuring different treatment levels in Hong Kong, China. Cefalexin, ofloxacin and erythromycin-H(2)O were predominant with concentrations of 1020-5640, 142-7900 and 243-4740 ng/L in influent, respectively; 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. The target antibiotics behaved differently depending on the treatment level employed at the STPs and relatively higher removal efficiencies (>70%) were observed for cefalexin, cefotaxime, amoxicillin, sulfamethoxazole and chloramphenicol during secondary treatment. ß-lactams were especially susceptible to removal via the activated sludge process while macrolides were recalcitrant (<20%) in the dissolved phase. Two fluoroquinolones, ofloxacin (4%) and norfloxacin (52%), differed greatly in their removal efficiencies, probably because of disparities in their pK(a) values which resulted in different sorption behaviour in sludge. Overall antibiotic consumption in Hong Kong was back-calculated based on influent mass flows and compared with available prescription and usage data. This model was verified by a good approximation of 82% and 141% to the predicted consumption of total ofloxacin, but a less accurate estimate was obtained for erythromycin usage. Risk assessment indicated that algae are susceptible to the environmental concentrations of amoxicillin as well as the mixture of the nine detected antibiotics in receiving surface waters.

Hexabromocyclododecane-induced developmental toxicity and apoptosis in zebrafish embryos

Hexabromocyclododecane (HBCD) is widely used as a brominated flame retardant, and has been detected in the aquatic environment, wild animals, and humans. However, details of the environmental health risk of HBCD are not well known. In this study, zebrafish embryos were used to assess the developmental toxicity of the chemical. Four-hour post-fertilization (hpf) zebrafish embryos were exposed to various concentrations of HBCD (0, 0.05, 0.1, 0.5, and 1.0 mg L(-1)) until 96 h. Exposure to 0.1, 0.5, and 1.0 mg L(-1) HBCD significantly increased the malformation rate and reduced survival in the 0.5 and 1.0 mg L(-1) HBCD exposure groups. Acridine orange (AO) staining showed that HBCD exposure resulted in cell apoptosis. Reactive oxygen species (ROS) was significantly induced at exposures of 0.1, 0.5, and 1.0 mg L(-1) HBCD. To test the apoptotic pathway, several genes related to cell apoptosis, such as p53, Puma, Apaf-1, caspase-9, and caspase-3, were examined using real-time PCR. The expression patterns of these genes were up-regulated to some extent. Two anti-apoptotic genes, Mdm2 (antagonist of p53) and Bcl-2 (inhibitor of Bax), were down-regulated, and the activity of capspase-9 and caspase-3 was significantly increased. The overall results demonstrate that waterborne HBCD is able to produce oxidative stress and induce apoptosis through the involvement of caspases in zebrafish embryos. The results also indicate that zebrafish embryos can serve as a reliable model for the developmental toxicity of HBCD.

Cylindrospermopsin, A cyanobacterial alkaloid: Evaluation of its toxicologic activity

This paper describes the natural occurrence of the toxin, cylindrospermopsin, in two species of cyanobacteria found in Australia. The structure and chemical properties of this compound are described along with a nontoxic analog of cylindrospermopsin. The results of both intraperitoneal (IP) and oral dosing of mice show that hepatotoxicity is the main effect of cylindrospermopsin in vivo, but that a thrombohemorrhagic phenomenon is observed in a proportion of dosed animals. It has been shown that the toxin can be metabolized in vivo and that a bound metabolite occurs in the liver. Cytotoxicity experiments using cell cultures show that cylindrospermopsin is more cytotoxic to isolated rat liver hepatocytes than to other cell types. Risk assessment calculations show that guideline values for cylindrospernopsin in drinking water should lie in the low microgram per liter range.

Antibiotics in the Hong Kong metropolitan area: Ubiquitous distribution and fate in Victoria Harbour.

We investigated the presence and fate of 16 antibiotics belonging to seven groups (beta-lactams, fluoroquinolones, macrolides, sulfonamides, tetracyclines, trimethoprim and amphenicols) in effluents of sewage plants and receiving waters in Hong Kong. Cefalexin, amoxicillin, ofloxacin and erythromycin-H(2)O were ubiquitous in sea water throughout Victoria Harbour, indicating continuous discharge to the environment. This is one of the few studies reporting the frequent occurrence of cefalexin and amoxicillin in sewage effluents and sea water (170-5070 and 64-1670 ng/L in sewage; 6.1-493 and 0.64-76 ng/L in sea water, respectively). Mass flows from seven sewage plants discharged an estimated total of 14.4 kg/day to the Harbour. Typhoon shelters also appeared to play an important role as sources of antibiotics, as evidenced by elevated concentrations within their boundaries. Mass balance estimations suggested significant quantities of antibiotics are discharged to the Harbour without passage through treatment plants.

DNA ADDUCT FORMATION AND DNA STRAND BREAKS IN GREEN LIPPED MUSSELS (PERNA VIRIDIS) EXPOSED TO BENZO[A]PYRENE: DOSE AND TIME DEPENDENT RELATIONSHIPS

Green-lipped mussels, Perna viridis, were exposed to 0, 0.3, 3 and 30 micrograms l-1 (nominal concentrations) B[a]P under laboratory conditions over a period of 24 days. Mussels were collected on day 0, 1, 3, 6, 12, 18 and 24, and the levels of DNA adducts and DNA strand breaks in their hepatopancreas tissues monitored. Mussels exposed to 0.3 and 3 micrograms l-1 B[a]P showed marked increases in strand breaks after 1 day of exposure. DNA strand break levels in these mussels remained high and significantly different from the control values until day 3 for the 0.3 microgram l-1 treatment group, and day 6 for the 3 micrograms l-1 treatment group. This was followed by a gradual reduction in strand breaks. After 12 days, the levels of both groups had returned to the same level as that of the control. No increase in DNA strand breaks was observable in mussels exposed to 30 micrograms l-1 B[a]P in the first 12 days of exposure, but a significant increase was observed from day 12 to day 24. Increasing B[a]P concentrations resulted in elevated DNA adduct levels after 3-6 days of exposure, but this pattern of dose-related increase disappeared after 12 days. These results indicate that a better understanding of the complex interactions between exposure levels and durations is crucially important before DNA adduct levels and DNA strand breaks in P. viridis can be used as effective biomarkers for monitoring genotoxicants in marine waters.