No abstract

The main objective of this study was to investigate occurrence of polycyclic aromatic hydrocarbons (PAHs) in the sources of the drinking water supply of Hong Kong. The main emphasis was on the Dongjiang River in mainland China which is the major source, supplying 80% of the total consumption in Hong Kong (the remaining 20% is obtained from rain water). Sediments were collected from four sites along the Dongjiang River and four reservoirs in Hong Kong during both the dry and wet weather seasons. The concentrations of total PAHs in the sediments ranged between 36 and 539 microg/kg dry wt. The lower levels were detected at the upstream site on the Dongjiang River and at the reservoirs in Hong Kong (44-85 microg/kg dry wt), while the mid- and downstream sites on the Dongjiang River were more polluted (588-658 microg/kg dry wt). Examination of the PAH profiles revealed that the mid- and downstream sections of the Dongjiang River contained high percentages of 4,5,6-ring PAHs, similar to the amounts of atmospheric particulate matter and road dust collected during the dry weather season from the Pearl River Delta region as reported in the literature. Seasonal changes were revealed in the reservoirs of Hong Kong, with higher PAH levels in the wet weather season than in the dry weather season. For those reservoirs in Hong Kong that store water from the Dongjiang River, a distinct seasonal pattern was also observed, namely, that under dry weather season conditions the PAHs found in the sediments were primarily from petrogenic source, while under wet weather season conditions they were from pyrolytic sources. No such pattern was detected in the reservoirs which stored only rain water.

The body concentrations of Ag in a top marine predator, the whelk Thais clavigera, varied significantly (1.10 to 4.67 µg g -1 dry wt) in individuals collected from 3 intertidal rocky shores in Hong Kong, whereas there was no significant difference in Ag concentrations in species from lower trophic levels (macroalgae Ulva sp. and rocky oyster Saccostrea cucullata). We compared the variation in Ag biodynamics in whelks collected from these 3 locations. There was no significant difference in the Ag dietary assimilation efficiency, Ag dissolved uptake rate, or estimated metallothionein concentration among the 3 locations. Significant differences were found in the Ag efflux rate constant and the subcellular distribution of Ag. Whelks from Clear Water Bay, which had the lowest body concentration of Ag, had a higher Ag efflux rate constant (0.0268 d ), as well as a correspondingly lower fraction of Ag in the metallothionein-like protein pool (which might contain both metallothioneins and other low molecular weight thiols). The Ag distribution in the other 4 subcellular fractions (metal-rich granules, cellular debris, organelles, heatsensitive proteins) was similar among the 3 sites. The biokinetic model demonstrated that biokinetic parameters can predict this 4-fold inter-site difference of body Ag concentrations in whelks. Moreover, such variation was mainly caused by variation in Ag efflux, although other parameters such as dietary assimilation and the concentration of Ag in prey were also important. Our calculations suggest that the prey composition may be specific to the site. The complexity of food webs should thus be considered when examining metal bioaccumulation in marine predators.