K.C. Cheung

Assessment of metal and nutrient concentrations in river water and sediment collected from the cities in the Pearl River Delta, South China

The effects of anthropogenic activities, industrialization and urbanization on the accumulation of heavy metals and nutrients in sediments and water of rivers in the Pearl River Delta region were examined. Most sediments were seriously contaminated with Cd, Pb, and Zn in accordance with the classification by Hong Kong Environmental Protection Department. Total phosphorus (P) and nitrogen (N) concentrations in sediments ranged from 0.02% to 0.12% and 0.06% to 0.64%, respectively. High carbon (C), N, P and sulphur (S) levels at Yuen Long Creek were related to the discharge of industrial effluents along the river. The enrichment of P and ammoniacal-nitrogen (NH4+-N) in water were obvious. For most sites, the P concentration exceeded 0.1 mg/l, which is the recommended concentration in flowing water to encourage excessive growth of aquatic plants. Nine out of the 16 sites studied had NH4+-N concentration over 2 mg/l. The rivers in the south of Deep Bay (Hong Kong) had high nutrient exports compared with the rivers in the east region and western oceanic water. The concentrations of nitrate-nitrogen NO3--N in surface water were under the maximum contaminant level in public drinking water supplies (10 mg/l) except for one site. Although the concentrations of heavy metals in overlying water were low, their accumulations were significant. High contents of nickel (Ni) and zinc (Zn) in water were found at certain locations, suggesting the occurrence of some local contamination. These preliminary results indicated that river and sediment transported pollutants is likely one of the factors for the water quality degradation of Deep Bay water.

Improving phosphate removal of sand infiltration system using alkaline fly ash

Septic tank effluent is customarily disposed of by soil infiltration. Coarse, sandy soil such as those found in Perth, Western Australia, exhibit low attenuation capabilities for phosphate (PO4(3-)) during effluent infiltration. Amendment of such soil with different amounts of alkaline precipitator and lagoon fly ashes was investigated as a means of reducing phosphorus (P) leakage to ground water. Alkaline precipitator fly ash possessed the highest P sorption capacity in terms of its Langmuir and Freundlich isotherm parameters during initial batch tests. The test materials were repeatedly contacted with fresh PO4(3-) solutions over 90 contacting cycles to gain a better indication of long-term P sorption capability. Again, precipitator fly ash exhibited higher P sorption capacity than lagoon fly ash and Spearwood sand. Column studies assessed the influence of various application rates of alkaline precipitator and lagoon fly ashes on the P removal of septic tank effluent. Septic tank effluent was applied at the rate of 4 cm/day to the column for 12 weeks. Concentrations of P were monitored in the column effluent. All the fly ash columns were more efficient in reducing P migration compared to the sand column. Increased levels of fly ash in the soil columns resulted in increased P attenuation. Lagoon fly ash was inferior to precipitator fly ash for P removal; high application rates of fly ash caused clogging of the infiltration bed apparently due to their lower permeability. It is reasoned that 5-15% precipitator fly ash, and less than 30% lagoon fly ash could be added to coarse sands to produce an infiltration bed, which would result in a better quality effluent than can be obtained with untreated sand alone.

Assessment of heavy metals/metalloid (As, Pb, Cd, Ni, Zn, Cr, Cu, Mn) concentrations in edible fish species tissue in the Pearl River Delta (PRD), China

The major aim of this study was to investigate heavy metal content of edible fish in the PRD. Eleven species of fish (consisting of 711 individuals) [catfish (Clarias fuscus), tilapia (Oreochromis mossambicus), grass carp (Ctenopharyngodon idellus), bighead carp (Aristichthys nobilis), mandarin fish (Siniperca kneri), snakehead (Channa asiatiea), black bass (Micropterus salmoides), mangrove snapper (Lutjanus griseus), star snapper (Lutjanu stellatus), snubnose pompano (Trachinotus blochii) and orange-spotted grouper (Epinephelus coioides)] were collected for the analyses of heavy metals. Overall concentrations (mg/kg, ww) in the fish muscles were: As (0.03-1.53), Pb (0.03-8.62), Cd (0.02-0.06), Ni (0.44-9.75), Zn (15.7-29.5), Cr (0.22-0.65), Cu (0.79-2.26), Mn (0.82-6.91). Significant level of Pb were found in tilapia at all locations. It is recommended that heavy metal concentrations in different fish species must be determined on a regular basis in the future so as to reduce human health risks from acute and chronic food intoxication.

Risk assessment of human exposure to bioaccessible phthalate esters via indoor dust around the Pearl River Delta.

There is limited information on the bioaccessible fractions of phthalate esters in indoor dust in order to estimate human exposure. In the present study, workplace dust and settled house dust samples from Hong Kong, Shenzhen, and Guangzhou, the three major cities scattered around the Pearl River Delta (PRD) were collected. Chemical analyses showed that the phthalates in workplace dust ranged from 144 to 1810 μg/g, with dust from shopping malls containing the highest level, and in home dust ranged from 181 to 9240 μg/g. The most abundant phthalate ester found was bis(2-ethylhexyl) phthalate (DEHP) in both workplace dust and home dust, followed by di-n-butyl phthalate (DBP) and di-iso-butyl phthalate (DIBP). Principal Components Analysis (PCA) indicated that indoor dust around PRD showed similar phthalate esters patterns of composition. A significant correlation was observed between total phthalate esters concentrations in home dust and the number of year of house construction (p < 0.05). The oral bioaccessibility of phthalate esters in indoor dust ranged from 10.2% (DEHP) to 32% (DMP). Risk assessment indicated that the dominant exposure routes varied in different phthalate esters exposure profiles and the dermal contact exposure pathway was identified as an important route for indoor DEHP exposure.

Contamination and risk assessment (based on bioaccessibility via ingestion and inhalation) of metal(loid)s in outdoor and indoor particles from urban centers of Guangzhou, China.

Road dust, household air-conditioning (AC) filter dust and PM2.5 were collected to investigate the contamination of metal(loid)s (Cr, Mn, Ni, Cu, Zn, As, Cd, Sn, Sb, Hg and Pb) in outdoor and indoor urban environments of Guangzhou. Zinc was found to be the most abundant element in road dust and household PM2.5, while the concentration of Pb was the highest in AC filter dust. Enrichment factor (EF) was used to assess the influence of human activity on the contamination of these metal(loid)s. Ingestion and inhalation were the two exposure pathways applied for risk assessment. Physiologically based extraction test (PBET) was used to estimate the oral bioaccessibilities of metal(loid)s in road dust and AC filter dust. Respiratory bioaccessible fraction of metal(loid)s via household PM2.5 was extracted with lung simulating solution. Household AC filter dust was more hazardous to human health than road dust, especially to children. Arsenic was found to be the most risky element based on the risk assessment.

Size fraction effect on phthalate esters accumulation, bioaccessibility and in vitro cytotoxicity of indoor/outdoor dust, and risk assessment of human exposure

Indoor and outdoor dusts from two urban centers in the Pearl River Delta, China, were analyzed and phthalate esters varied from 4.95 to 2,220 μg g(-1) in indoor dust, significantly higher than outdoor dust (1.70-869 μg g(-1)). Di-2-ethylhexyl phthalate (DEHP) was the dominant phthalate found and the highest distribution factor (DF) (1.56 ± 0.41) was noted in the <63 μm fraction (p<0.05). In vitro cytotoxicity of dust extract on human T cell lymphoblast leukemic cell line (CCRF-CEM) indicated by Lethal Concentration 50 (LC50) decreased with particle size. The power model was found as a better fit for explaining the relationship between LC50 and phthalates (R(2)=0.46, p<0.01). Bioaccessibility of phthalates in dust varied with different particle sizes, with the greatest bioaccessible fraction (2.49-38.6%) obtained in <63 μm. Risk assessment indicated that indoor dust ingestion accounted for the major source for DEHP exposure (81.4-96.4% of non-dietary exposure and 36.5% of total exposure), especially for toddlers. The cancer risks associated with DEHP via home dust were high (10(-6)-10(-4)), with 10% of houses estimated with unacceptable risks (>10(-4)). After corrected with the bioaccessibility of phthalates, the cancer risks of dust exposure were moderate (10(-7)-10(-5)).

Exposure assessment and distribution of polychlorinated biphenyls (PCBs) contained in indoor and outdoor dusts and the impacts of particle size and bioaccessibility

The size fraction, bioaccessibility and associated human daily intake of PCBs via indoor and outdoor dust collected from two most populated urban centers of Pearl River Delta (PRD), China, were studied. The ΣPCBs levels (ng g(-1)) in indoor (51.9-264) and outdoor (4.02-228) dust in Guangzhou (GZ) were found higher than those in indoor (17.4-137) and outdoor (7.75-114) dust of Hong Kong (HK). Hexa-PCB was the largest contributor in dust samples (29-64%), followed by tri-PCB. The size fraction of PCBs indicated a high accumulation effect of particles less than 63 μm, while the lowest was found in 280-2000 μm. Toxic equivalency (TEQ) of dioxin-like PCBs in indoor dust of GZ and HK was 2 to 13 times higher than that in outdoor dust. The bioaccessibility of PCBs was determined as 5-61% depending on individual PCB congeners under study and bioaccessible PCB exposure was significantly lower than the estimate for total PCB. The daily intake of bioaccessible PCBs via dust ranged in 0.02-8.95 and 0.37-17.8 ng day(-1) in GZ while 0.01-4.95 and 0.16-9.83 ng day(-1) in HK for adults and children, respectively. Dust ingestion contributed to 0.49-10.6% of overall non-dietary PCB exposure (dust ingestion and inhalation) for adults while 12.9-35% for children, indicating the dominant contribution from inhalation.

Adsorption kinetics of Pb and Cd by two plant growth promoting rhizobacteria

A bench study was carried out to characterize the kinetics of two plant growth promoting rhizobacteria (PGPR) Azotobacter chroococcum and Bacillus megaterium to adsorb heavy metals from solution. Adsorption of Pb(2+) and Cd(2+) by bacterial cells was processed quickly with an equilibration achieved within 5 min. The adsorptions were fitted well with Freundlich and Langmuir isotherm models. The comparison of isotherm parameters indicated that A. chroococcum had a stronger capacity to bind metal ions than B. megaterium, with an average increase of 59.8% for Pb(2+) and 75.6% for Cd(2+), respectively. Both bacteria had a stronger affinity to Pb(2+) than Cd(2+) since Pb(2+) was more easily bound with the phosphoryl groups on the cell surface than Cd(2+). This demonstrated that the presence of bacteria in the rhizosphere may result in the reduction of mobile ions in soil solution.

Synergistic effects of arbuscular mycorrhizal fungi and phosphate rock on heavy metal uptake and accumulation by an arsenic hyperaccumulator.

The effects of arbuscular mycorrhizal (AM) fungi and phosphate rock on the phytorextraction efficiency of a hyperaccumulator (Pteris vittata) and a non-hyperaccumulator (Cynodon dactylon) plant were studied. Both seedlings were planted in As contaminated soil under different treatments [(1) control (contaminated soil only), (2) indigenous mycorrhizas (IM), (3) mixed AM inoculum [indigenous mycorrhiza + Glomus mosseae (IM/Gm)] and (4) IM/Gm + phosphate rock (P rock)] with varying intensities (40%, 70% and 100%) of water moisture content (WMC). Significant As reduction in soil (23.8% of soil As reduction), increase in plant biomass (17.8 g/pot) and As accumulation (2054 mg/kg DW) were observed for P. vittata treated with IM/Gm + PR at 100% WMC level. The overall results indicated that the synergistic effect of mycorrhiza and P rock affected As subcellular distribution of the hyperaccumulator and thereby altered its As removal efficiency under well-watered conditions.

Physiological and Biochemical Responses of Rice (Oryza Sativa L.) to Phenanthrene and Pyrene

Phenanthrene (Phe) and pyrene (Pyr) are two typical polycyclic aromatic hydrocarbons (PAHs) found in contaminated soil. This study investigated physiological and biochemical responses of rice (Oryza sativa L.) to PAH stress after they were planted in soils contaminated with Phe and Pyr, in the presence or absence of a PAH-degrading bacteria (Acinetobacteria sp.). A number of parameters including biomass and water, chlorophyll and chlorophyll a/b ratio, electrolyte leakage, activities of superoxide dismutase (SOD) and peroxidase, and soluble carbohydrate and soluble protein contents were monitored. Results show that rice plants have good resistance and tolerance to lower levels of PAHs stress, while adding high levels of PAHs to soils resulted in adverse effects on rice plants such as a reduction in biomass and damage to photosynthetic function. Water content and SOD activities were the most sensitive indicators of PAH stress among the observed parameters. Inoculation with PAH-degrading bacteria promoted growth and photosynthesis of rice.