Paul K.S. Shin

Toxicity of bisphenol A and its bioaccumulation and removal by a marine microalga Stephanodiscus hantzschii

The toxicity of bisphenol A (BPA) to Stephanodiscus hantzschii, a diatom isolated from tidal water of Futian Mangrove Nature Reserve, China, and the bioaccumulation and removal capability of the marine microalga to BPA were investigated in the present study. Toxicity experiments showed that the 96-h EC50 of BPA was 8.65+/-0.26 mg/L, and the cell number and chlorophyll a content of S. hantzschii decreased significantly with increases in BPA at concentrations higher than 3.00 mg/L. S. hantzschii had high removal capability at low BPA concentrations as BPA was bioaccumulated and biodegraded by cells. After 16-day treatment, 88%, 99%, 92%, 61%, 48%, 28% and 26% of BPA were removed by the diatom in the media supplemented with 0.01, 0.10, 1.00, 3.00, 5.00, 7.00 and 9.00 mg/L BPA, respectively. The present study demonstrated that S. hantzschii was a tolerant isolate that could be used to remove BPA from contaminated waters.

Potential use of mangroves as constructed wetland for municipal sewage treatment in Futian, Shenzhen, China.

A pilot-scale mangrove wetland was constructed in Futian, Shenzhen for municipal sewage treatment. Three identical belts (length: 33m, width: 3m, depth: 0.5m) were filled with stone (bottom), gravel and mangrove sand (surface). Seedlings of two native mangrove species (Kandelia candel, Aegiceras corniculatum) and one exotic species (Sonneratia caseolaris) were transplanted to the belts with one species for each belt. The hydraulic loading was 5m(3)d(-1) and hydraulic retention time 3d. High levels of removal of COD, BOD(5), TN, TP and NH(3)-N were obtained. The treatment efficiency of S. caseolaris and A. corniculatum was higher than that of K. candel. Faster plant growth was obtained for S. caseolaris. The substrate in the S. caseolaris belt also showed higher enzyme activities including dehydrogenase, cellulase, phosphatase, urease and beta-glucosidase. The removal rates of organic matter and nutrients were positively correlated with plant growth. The results indicated that mangroves could be used in a constructed wetland for municipal sewage treatment, providing post-treatment to remove coliforms was also included.

The spatial and temporal distribution of heavy metals in sediments of Victoria Harbour, Hong Kong

Victoria Harbour has received substantial loadings of pollutants from industrial and municipal wastewater discharged since the 1950s. Inputs of contaminants have declined dramatically during the last two decades as a result of better controls at the source and improved wastewater treatment facilities. To assess the spatial and temporal changes of metal contaminants in sediments in Victoria Harbour, core and grab sediments were collected. The central harbour areas were generally contaminated with heavy metals. The spatial distribution of trace metals can probably be attributed to the proximity of major urban and industrial discharge points, and to the effect of tidal flushing in the harbour. In the sediment cores, the highest concentrations of trace metals were observed to have accumulated during the 1950s-1980s, corresponding with the period of rapid urban and industrial development in Hong Kong. From the late 1980s, there has been a major decline in the concentrations of trace metals, due to a reduction in industrial activities and to the enactment of wastewater pollution controls in the territory. The Pb isotopic compositions of the sediments revealed the anthropogenic inputs of Pb to the harbour. The (206)Pb/(207)Pb ratios varied from 1.154 to 1.190, which were lower than those of background geological materials in Hong Kong ((206)Pb/(207)Pb: 1.201-1.279). The data also indicated that the Pb in the harbour sediments most likely originated from mixed sources, including the leaded gasoline used in the past and other anthropogenic sources.

Estrogenic potential of benzotriazole on marine medaka (Oryzias melastigma)

This study, for the first time, assessed the reproductive effects of benzotriazoles, widely used industrial chemicals, on marine fish. Marine medakas (Oryzias melastigma) were exposed to 0.01, 0.1, and 1mg/L benzotriazole for periods of four and 35 days. The results that are obtained showed that the expression levels of CYP1A1 were down-regulated in the liver, gills and intestines of both males and females. Vitellogenin (VTG) was highly induced in the liver, gills and intestine of both male and female marine medaka, and CYP19a was up-regulated in the ovaries especially after being exposed for 35 days. Most importantly, the results of the present study suggest that even at environmentally relevant concentrations detected in the aquatic environment, 0.01 mg/L, benzotriazole also caused notable changes in expression levels of VTG, CYP1A1 and CYP19a. More concerns about the toxicity of benzotriazoles on marine animals should be raised.

The combined effects of oxygen availability and salinity on physiological responses and scope for growth in the green-lipped mussel Perna viridis.

Mussels were maintained for 4 weeks under different combinations of dissolved oxygen concentration (1.5, 3.0 and 6.0 mg O2 l(-1)) and salinity (15, 20, 25 and 30) in a 3×4 factorial design experiment. Clearance rate (CR), absorption efficiency (AE), respiration rate (RR) and scope for growth (SFG) decreased with decreasing salinity and dissolved oxygen concentration (DO), while excretion rate (ER) increased with decreasing salinity and increasing DO. The O:N ratio was <10 at salinities of 15 and 20, irrespective of DO levels. SFG was negative in most of the treatments, except for those under 6.0 mg O2 l(-1) or at a salinity of 30 when DO was lower. The results may help explain the distribution pattern of Perna viridis in Hong Kong waters and provide guidelines for mussel culture site selection.

Deriving site‐specific sediment quality guidelines for Hong Kong marine environments using field‐based species sensitivity distributions

Field data of benthic communities and contaminant loadings in marine sediments measured in parallel can be used to derive sediment quality guidelines (SQGs) using a field-based species sensitivity distribution (f-SSD) approach. Recently, SQGs have been successfully derived from f-SSDs for the Norwegian continental shelf with an extensive survey (>1 million km(2)) and a large data set (1,902 sampling stations with 1,944 species). The present study examined the practicality of this approach in deriving SQGs for a much smaller geographical area, namely, the marine environment of Hong Kong (sea area: 1,651 km(2)), making use of databases of the government of Hong Kong special administrative region. As the construction of f-SSDs requires the use of a collection of responses from individual species to a chemical gradient in sediment, data screening criteria on the minimum abundance of the species were evaluated and optimized to ensure sufficient statistical power for estimating these responses. Sediment quality guidelines were derived for nine trace metals, total polycyclic aromatic hydrocarbons, and total polychlorinated biphenyls and compared with current SQGs in developed countries. The community-adjusted hazardous concentrations of 5% and 10% of the f-SSDs were adopted to represent the threshold effects level (TEL) and predicted effects level (PEL), respectively. The TELs derived from this f-SSD approach compares favorably with current SQGs, while the derived PELs were generally lower than the current SQGs, indicating that they are more protective. The f-SSDs can be directly utilized for probabilistic risk assessment, while the field-based SQGs can be used as site-specific guidelines or integrated into current SQGs. Our results suggest that the f-SSD approach can also be applicable to small areas such as Hong Kong.

Horseshoe Crabs in Hong Kong: Current Population Status and Human Exploitation

An updated survey, using both random transect and walk-through search methods, at 17 shores in Hong Kong in summer and winter showed that juvenile horseshoe crabs (Tachypleus tridentatus and Carcinoscorpius rotundicauda) were significantly reduced by over 90% in density since 2002. Of the shores where juveniles were found, the highest density of T. tridenatus was 0.31 and lowest 0.08 ind 100 m–2. Juvenile C. rotundicauda was only found using the walk-through search method, with the highest record of 1.17 and lowest 0.17 ind hr–1 person–1. The mean prosomal width of juvenile T. tridentatus obtained from the walk-through survey varied from 2.6 to 5.5 cm, which corresponded to an age of 4–8 years old. A larger size range for C. rotundicauda was, however, noted, from 2.5 to 9.0 cm.

Immune responses to combined effect of hypoxia and high temperature in the green-lipped mussel Perna viridis.

Flow cytometry was used to examine immune responses in haemocytes of the green-lipped mussel Perna viridis under six combinations of oxygen level (1.5 mg O2 l(-1), 6.0 mg O2 l(-1)) and temperature (20 °C, 25 °C and 30 °C) at 24 h, 48 h, 96 h and 168 h. The mussels were then transferred to normoxic condition (6.0 mg O2 l(-1)) at 20 °C for further 24 h to study their recovery from the combined hypoxic and temperature stress. Esterase (Est), reactive oxygen species (ROS), lysosome content (Lyso) and phagocytosis (Pha) were reduced at high temperatures, whereas hypoxia resulted in higher haemocyte mortality (HM) and reduced phagocytosis. For HM and Pha, changes were observed after being exposed to the stresses for 96 h, whereas only a 24 h period was required for ROS and Lyso, and a 48 h one for Est. Recovery from the stresses was observed for HM and Pha but not other immune responses.

The use of muscle burden in rabbitfish Siganus oramin for monitoring polycyclic aromatic hydrocarbons and polychlorinated biphenyls in Victoria Harbour, Hong Kong and potential human health risk

Muscle concentrations of polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) were determined in rabbitfish Siganus oramin collected from Victoria Harbour and its vicinity, Hong Kong from 2004 to 2007. Spatially, relatively higher levels of [summation operator]PAH (1.05-4.26 microg g(-1)) and [summation operator]PCB (45.1-76.9 ng g(-1)) were determined in the central and western sites inside the harbour. Temporally, upward trend of [summation operator]PAH, accompanied with a proportion shift from high molecular weight to low molecular weight PAHs, was detected during the three-year study period, suggesting a heavier marine traffic in Victoria Harbour and its western region. However, human health risk assessment based on five individual PAHs indicated that PAHs in fish muscles posed minimal health risk through consumption. In contrast, a downward trend of [summation operator]PCB was registered as the open use of PCBs has been banned. Despite this, the level of [summation operator]PCB in fish muscles still posed a health risk on the local people who have a high fish consumption rate. While seasonal influences on [summation operator]PAH/[summation operator]PCB accumulation in S. oramin seemed to be negligible, our findings in S. oramin were in line with the established PAH and PCB levels in sediments and/or mussels from the harbour, suggesting S. oramin can be used as a model fish species for monitoring PAHs and PCBs in the region.

Effects of the timing of initial feeding on growth and survival of spotted mandarin fish Siniperca scherzeri larvae

The effects of delayed first feeding on growth and survival of spotted mandarin fish Siniperca scherzeri larvae were examined under controlled conditions. Morphometric characters [yolk-sac volume, oil globule volume, head depth (H(D)), body depth (B(D)), eye diameter (E(D)), musculature height (M(H)), mouth diameter (M(D)) and total length (L(T))], body mass (M), specific growth rate (S(GR)) and survival were evaluated under different first-feeding time (2, 3, 4 and 5 days after hatching). Larvae began to feed exogenously at 2 days after hatching (DAH) and the point of no return (P(NR)) occurred between 5 and 6 DAH at 23 degrees C, range +/-1.0 degrees C. The yolk volume of larvae first-fed at 2 days had a significant difference compared with that of larvae first-fed at 3, 4 and 5 days on 3 and 4 DAH. The larvae first-fed at 2 days achieved comparatively better growth performance than that of 3, 4 and 5 days. On 5 DAH, all morphometric characters had significant differences between 2 and 5 days and 2 and 4 days initial feeding, respectively. Total mortality was recorded on 9 DAH for the larvae first-fed at 5 days. On 12 DAH, significant differences were observed between 2 and 4 days and 3 and 4 days initial feeding for all morphometric characters. From 16 DAH to the end of experiment, all growth variables of the larvae first-fed at 2 days were significantly higher than those in other treatments. The S(GR) (2-9 DAH) first-fed at 2 and 3 days were significantly higher than 4 and 5 day treatments, and the S(GR) (9-16 DAH) first-fed at 2 days was significantly higher than 3 and 4 day treatments. There was no significant difference, however, of S(GR) (16-28 DAH) among treatments. Survival rate was significantly higher at 2 days initial feeding (27.42%) when compared with 3 (15.96%) and 4 days (7.92%) initial feeding at the end of experiment. The present study suggests that the first feeding of S. scherzeri larvae should be initiated at 2 days after hatching for achieving good growth and survival.