Effects of heavy metals on oxygen consumption and ammonia excretion in green-lipped mussels (Perna viridis)

Physiological responses (oxygen consumption and ammonia excretion) of the green-lipped mussel (Perna viridis) exposed to four concentrations of Cd (0.15, 0.32, 0.70 and 1.50 ppm) and four concentrations of Zn (0.60, 1.29, 2.79 and 6.00 ppm) were monitored for 21 days. Changes occurred in the ammonia excretion rates and O:N ratios with individual mussels experiencing different metal concentrations over time. Oxygen consumption rate decreased significantly with time for Cd-exposed individuals and also decreased significantly with the interaction between the concentration of Zn and time for Zn-exposed individuals. Although low O:N ratios (<30) were obtained in most of the treatments, no predictable correlation was found between concentrations of metals and values of O:N obtained. The value of using O:N ratio as a stress index is questioned.     

Characterization of sewage sludge and toxicity evaluation with microalgae

Heavy metal contents (Cd, Cr, Cu, Pb, Ni and Zn) of digested sludge, collected from sewage treatment works (Shatin (ST), Shek Wu Hui (SWH), Tai Po (TP) and Yuen Long (YL)) in 1992, 1993 and 1994, were analysed by atomic absorption spectrophotometry after sequential extraction by 1 KNO₃, 0.5 KF, 0.1 Na₄P₂O₇, 0.1 EDTA and 6 HNO₃. It was found that the major forms of Cu, Pb, Ni and Zn were in the sulphide phase, organically-bound phase, adsorbed phase and carbonate phase, respectively. A dinoflagellate (Dunaliella tertiolecta) and a diatom (Thalassiosira sp.) were used as bioindicators to test the toxicity of digested sludge samples collected in 1994. Each of the algae were inoculated to elutriates of digested sludge at different concentrations. The toxicities of the four types of sludge, according to 96 h-IC₅₀s, were ranked as follows: TP > ST > SWH > YL for D. tertiolecta and ST > SWH > TP > YL for Thalassiosira sp. For D. tertiolecta, a significant correlation was found between algal inhibition and ammonium-N, both in sludge (p<0.05) and elutriates (p<0.01).     

Effects of copper on survival, development and growth of Metapenaeus ensis larvae and postlarvae (decapoda: Penaeidae)

Effects of copper on survival, development and growth of the early developmental stages of the penaeid shrimp, Metapenaeus ensis, were studied in the laboratory. High variability in survival rates were observed among animals from different spawners. Larvae exposed to 0.06 and 0.10 mg Cu l⁻¹ over a 10-day period had lower survival rates and exhibited slower development than control animals. No significant treatment effects were found at 0.04 and 0.08 mg Cu l⁻¹. Effects of copper on survival and growth of postlarvae were studied over an 8-day period. Copper concentrations lower than 0.10 mg l⁻¹ did not affect survival rates. Slower growth rates were observed in postlarvae exposed to 0.08 and 0.10 mg Cu l⁻¹.     

Reduction roasting of limonite ores: effect of dehydroxylation

The effect of pre-calcination in the reducibility of tropical limonite ore, obtained from New Caledonia, was investigated in this study. A series of reduction tests were carried out with pre-calcined and raw limonite ores. The extent of metallisation was determined from nickel and iron which dissolved in ammoniacal solution. Mineralogical transformations that occurred during reduction were analysed using thermal gravimetric, differential thermal analysis (TGA/DTA) and in situ high temperature synchrotron based X-ray diffraction. Bulk mineral analysis of the raw ore was also obtained using neutron diffraction. This study suggests that there is benefit in the pre-calcination of limonite ores. Pre-calcination of the ores which opens the main gangue mineral structure, goethite, allows a rapid interaction between the reductant gases and the nickel species during reduction. The greater nickel metallisation achieved in reduction of pre-calcined ores resulted in higher dissolved nickel whilst reduced raw limonite showed poorer nickel recovery. Reduction of metal minerals was also accompanied by diffusion of nickel into the reduced iron matrix that resulted in the formation of ferro-nickel alloy (Ni₃Fe). The formation of this solid solution was monitored by in situ synchrotron based X-ray diffraction and was also reflected by the lower nickel leachability in ammoniacal solution. It was found that incorporation of nickel into the reduced iron oxide resulting from pre-calcination is significantly less in comparison to the diffusion occurring in reduced raw or uncalcined limonite ores. This effect is prevalent in prolonged reduction periods (greater than 20 min), at higher temperatures (>500 °C) and highly reducing conditions (H₂/CO₂=1:1). This study showed that optimal nickel recovery can be achieved by controlling the incorporation of nickel into the reduced iron structure by pre-calcination of the limonite ore.     

Ciliate communities in a constructed mangrove wetland for wastewater treatment

In wetlands constructed for treating municipal and industrial wastewater, including mangroves, the effect of wastewater discharged on the substrate has often been neglected. Ciliates, an important group of protozoa, are sensitive to pollutants and any changes in ciliate diversity and community structure reflects the habitat quality. The ciliate communities at six sections along a constructed mangrove belt (33 m in length) planted with Aegicerascorniculatum were investigated in Shenzhen, South China. In all samples collected in both rainy and dry seasons, 183 ciliate species were observed. Most species (56%) were free-swimming forms, while only 10.8% were sessile ciliates. The abundance and species number of ciliates were both found to decrease from the anterior (the wastewater inlet) to the posterior (the outlet) parts of the wetland belt, indicating that organic matter and bacteria in wastewater, which served as food for most ciliates, were gradually removed by the constructed wetland. The r/K (number of r- and K-selected species) ratios at the six sections were relatively small, between 0.2 and 0.4, whereas the C/P (abundance of colpodids and polyhymenophorans) quotient at some sections was higher than 1. These results indicate that although most of the environments along the constructed wetland belt were not stressful for ciliate communities, there were habitats that favored colpodids in high abundances.     

Use of ciliates (Protozoa: Ciliophora) as bioindicator to assess sediment quality of two constructed mangrove sewage treatment belts in Southern China

To complement physical and chemical data, information of biological communities is important to assess the qualities of mangrove sediments receiving wastewater. Ciliate communities have cosmopolitan distribution, short life cycle and high sensitivity to pollutants, which make them useful as biological indicators of the sediment environment. In most literature, ciliates are widely used as bioindicators for the state of water quality. In this study, the physico-chemical parameters and ciliate community structure of surface sediment collected at different sampling points from two constructed mangrove (Aegiceras and Sonneratia) belts for treatment of municipal sewage in southern China were investigated. Results showed that most (> 80%) of the 216 species ciliates identified at the two constructed mangrove belts were either omnivorous or bacterivorous. Sediment redox potential (Eh) was considered an important factor to govern the distribution of ciliate species within the mangrove sediment. The saprobic system originally derived from freshwater ecosystem was used to evaluate the saprobic degrees of these constructed mangrove belts. Saprobic index (SI) values declined from the sewage inlet to the outlet points of the constructed belts, suggesting better sediment quality at the outlet point caused by treatment processes within the mangrove belt system. Sediment quality of the sewage outlet area of the constructed Aegiceras belt was determined as class II-III (SI = 2.48), while that of the Sonneratia belt was as class III (SI = 2.71) according to the saprobic classification, indicating that a better sewage treatment efficiency was apparent in the Aegiceras than Sonneratia belt. The present data suggested that ciliates could serve as a good bioindicator in assessing organically polluted sediment qualities.     

Seasonal changes in imposex and tissue burden of butyltin compounds in Thais clavigera populations along the coastal area of Mirs Bay, China

We assessed the current status of tributyltin (TBT) contamination of Thais clavigera (Gastropoda) along the coastal area of Mirs Bay, China for the first time. The snail samples were collected from 10 different sites in the summer (June) and winter (December) of 2006, respectively. They were analyzed for imposex status, i.e. relative penis size index (RPSI) and vas deferens sequence index (VDSI), followed by quantification of butyltins in their tissues. Most of the collected females suffered from imposex, but the level of butyltin contamination varied with the distance from Yantian Port, which is currently the fourth busiest container port in the world. The tissue concentration of TBT varied with season. For a particular site, the winter samples in general contained much higher concentration of TBT than the summer samples. RPSI, VDSI and organotin concentrations were higher in T. clavigera collected from sites closer to the Port, such as the Seafood Street and Kat O. Both RPSI and VDSI were positively correlated with the tissue burden of tributyltin. VDSI exhibited little seasonal variability, whereas RPSI showed marked seasonal variability, with lower values in the summer samples. The current results will serve as an important reference for long-term monitoring of butyltin contamination in this area.