Persistent organic pollutants (POPs) such as organochlorine (OCl) insecticides and polychlorinated biphenyls (PCB), together with the new generation of organophosphorus (OP) insecticides, are of global concern, due to their widespread occurrence, persistence, bioaccumulation and hormone disruption potential. This paper represents an attempt to study the source and transportation of such pollutants in estuarine and coastal environments as an integrated ecosystem, by determining the levels of 18 OCl insecticides, 21 PCB congeners, and 17 OP insecticides in the Pearl River Estuary and South China Sea. The total concentrations varied from 126-1198 ng l21 for OCl insecticides, 33.38-1064 ng l21 for PCB congeners, and 4.44-6356 ng l21 for OP insecticides in the Pearl River Estuary. In comparison, their levels in the South China Sea were significantly lower, varying from 57.09-202 ng l21 for OCl insecticides, 21.72-144 ng l21 for PCBs, and 1.27-122ng l21 for OP insecticides, respectively. The predominance of b-HCH in HCHs, and DDE in DDTs in all water samples was clearly observed, suggesting b-HCH and DDE's resistance to further degradation. The PCBs were dominated by those with 3-6 chlorines. The distribution characteristic of OP insecticides shows that five compounds (methamidophos, dimethoate, malathion, dichlorvos and omethoate) accounted for 56% and 72% of the total OP insecticide concentration. The relationship between pollutant concentrations and salinity in the estuary showed that they were all removed during the mixing process, therefore behaving non-conservatively.

The isotopic composition, size distribution, and redox speciation of plutonium (Pu) in the roundwater in the vicinity of the F-area seepage basins at the U.S. Department of Energy Savannah River Site (SRS) were examined. A low 240Pu/239Pu ratio in the upstream control well signifies a Pu source other than global fallout and indicates reactorproduced Pu. Elevated 240Pu/239Pu atom ratios downstream from the seepage basins are due to the decay of transplutonium isotopes, mainly 244Cm to 240Pu, which were generated at the SRS. Evidence suggests that the migration of basin-released Pu isotopes is minor. Rather, it is the transplutonium isotopes that migrate preferentially downstream and in the process decay to yield progeny Pu isotopes. Size fractionation studies with crossflow ultrafiltration show that <4% of the 239Pu or 240Pu is found in the colloidal fraction, a finding that is consistent with the higher Pu oxidation states observed in the SRS groundwater. The observation of a low abundance of colloidassociated Pu in SRS groundwater cannot be extrapolated to all sites, but is in contrast to the conclusions of prior groundwater Pu studies at the SRS and elsewhere. This work is unique in its application of a novel combination of sampling and processing protocols as well as its use of thermal ionization mass spectrometry for the detection of Pu isotopes. This allows uantification of the Pu source terms and better determination of the ambient Pu size and redox speciation representative of in situ conditions.

Chromophoric dissolved organic matter (CDOM) fluorescence and dissolved organic carbon (DOC) were measured in the Lingdingyang Estuary, a major component of the Pearl River Delta, China, in May 2001 and November 2002. Measurements of CDOM and DOC suggest multiple sources of dissolved organic matter (DOM) in the low-salinity region of the estuary, due to the mixing of four freshwater outlets, Humen, Jiaomen, Honqimen and Hengmen, all with different freshwater endmembers and all flowing into the head of the Lingdingyang. Our 2002 cruise expanded efforts to characterize these four major outlets, allowing for the quantification of CDOM inputs within this complex watershed. DOC and CDOM appear conservative in mid-salinity (5-20) waters, suggesting that mixing dominates production and removal processes over time scales on the order of 3 days, the residence time of water in this region of the estuary. DOC and fluorescence are linearly correlated in the mid-salinity region of the estuary north of Shenzhen, suggesting that in this region, terrestrial inputs dominate both signals. However, this relationship does not continue out onto the shelf, where water masses of differing optical properties mix. The CDOM/DOC ratio decreases with increasing salinity as would be expected through phototrasformation of CDOM into non-fluorescent DOC. Additionally, this ratio at low salinity appears to vary seasonally, with a higher value in Spring (high flow) compared to Fall (low flow).

The Zhu-jiang (Pearl River) estuary and its adjacent continental shelf in the Northern South China Sea (SCS) is unique in that its drainage basin is located entirely in a subtropical zone with heavy population development, and therefore represents an important regime for biogeochemical studies on how large rivers influence continental shelves. The near-zero salinity end member has high nutrient concentrations (silicate 130-140μM, nitrate 75-100μM and phosphate 0.2-1.2μM) and relatively high total dissolved inorganic carbon (DIC) (1500μM) and alkalinity (B1650μM) values. Water column DIC, alkalinity, and nutrient in the estuary are largely controlled by mixing of waters from different tributaries with different drainage basin chemistry, anthropogenic influence, and degree of estuarine recycling. Biological uptake of nutrients and inorganic carbon occur in the outer estuary and inner shelf areas supported by riverine nutrients. The N/Pand Si/P ratios are generally very high within the estuary. The summertime area-integrated biological production rate of 0.8 gCm-2 d-1 is estimated based on the depletion of DIC and alkalinity relative to the conservative mixing line and a plume travel time. This estimate agrees reasonably well with 14C based primary production rates (PP) and with that from effective river phosphate flux. Biological production decreases about 10-fold in the open continental shelf and slope and is largely supported by mixing with subsurface water. A comparison of DIC, phosphate, and nitrate concentrations in the surface mixing layer and at the bottom of the euphotic zone with the 14C-based PP (0.13 gCm-2 d-1) suggests that the surface water residence time in the Northern SCS is B1.3 years. The N/P, Si/P, and Si/C ratios are 15, 25, and 0.15, respectively. The subtropical Pearl River study is also compared to other large rivers with regard to differences in both natural processes (i.e., weathering rates) and anthropogenic influences (i.e., nutrient input) between these different river-estuary systems.