Liang-Saw Wen

An ultraclean cross-flow ultrafiltration technique for the study of trace metal phase speciation in seawater

A series of laboratory and field studies were conducted to test suitability and optimal sampling conditions of an Amicon ultrafiltration system for the collection of colloidal material for trace metal phase speciation studies in marine environments. A cleaning procedure is required between each sample processed to eliminate carry-over artifacts and achieve a low system blank. Mass-balance recovery of 88–109% was achieved for ultrafiltration of trace metals (e.g., Cd, Cu, Ni, Pb, Mn, Fe, Zn, Hg) from estuarine samples. Results of sample storage experiments indicate that ultrafiltration should ideally be performed within 4 h of sample collection to prevent phase speciation shifts. The concentration of a number of trace metals in the permeate fraction, when plotted as a function of concentration factor, was found to fit the steady-state macromolecular permeation model of Kilduff and Weber (1992). A retentate concentration factor between 5 and 10 was optimal for most metals based on modeling the permeate metal concentration. For Galveston Bay, the colloidal fraction (1 kDa-0.45 μm) accounted for 65–85% of the Cu, 35–40% of the Ni, and 30–95% of the Pb in the filtered (< 0.45 μm) fraction. Colloidal Cu, Cuc (1 kDa-0.2 μm) was 64%, Nic was 6%, Pbc was 9% of the filtered (< 0.2 μm) fraction in deep Pacific water samples from the colloid intercomparison exercise.

Interactions between radioactively labeled colloids and natural particles: Evidence for colloidal pumping

It has been hypothesized that colloidal forms of trace metals can be reactive intermediaries in the scavenging processes leading to the removal of their particulate forms. A series of radiotracer experiments using natural colloidal organic matter from Galveston Bay, USA were carried out in order to test this hypothesis. Suspended particle uptake of originally colloidally bound trace metals occurred in a matter of hours to days in estuarine waters. After ten days, the majority (>50%) of the colloidal trace metals had been transferred into the particulate phase (≥0.45 μm), except for 65Zn. Two distinctively different temporal regions of removal of colloidal trace metals were identified: a faster reaction during the first four hours, followed by a slower reaction after approximately one day. In a separate river water-seawater mixing experiment, the solid/solution partitioning of the radiotracers was investigated in the absence of suspended matter. About 30% of most of the elements, except Ag and Fe (∼60%), were associated with a newly formed particulate phase after eight days. There were two major trends: (1) the particulate fraction of 59Fe and 110Ag increased while the colloidal fraction decreased, suggesting a colloidal pumping mechanism. (2) The particulate fraction of 54Mn, 133Ba, 65Zn, 109Cd, 113Sn, and 60CO increased while the LMW (≤ 1 kDa) fraction decreased, suggesting a direct uptake into the particulate fraction with less involvement of a transitory colloidal phase. The values of the particle-water (Kd) and colloid-water partitioning (Kc) coefficients for most trace metals were similar to those observed in Galveston Bay waters, suggesting complementary results to field studies. The results from these experiments suggested two different pathways for colloidal tracer uptake by particles: (1) colloidal pumping of a major component (e.g., biopolymer) of the colloidal pool and (2) coagulation of trace components (e.g., phytochelatins) with varying affinities for different trace metals. In support of these two different pathways, a number of correlations of particle-water (Kd) or colloid-water (Kc) partition coefficients with rate constants or reactive fractions were observed. In general, the higher the Kd values, the higher the reactive fractions, and the faster the trace colloid uptake by particles. Trace metals (e.g., Ag, Sn, Zn, Fe) which were found strongly organically complexed and associated mainly with colloidal matter in estuarine waters had a higher ion-colloid association rate constant. These experimental results suggest that interactions between surface-reactive fractions of the colloidal material and particles can play a crucial role in the solid-solution partitioning of many trace elements.

Analysis of biogenic thiols in natural water samples by high-performance liquid chromatographic separation and fluorescence detection with ammonium 7-fluorobenzo-2-oxa-1,3-diazole-4-sulfonate (SBD-F)

Abstract A sensitive and reliable reversed-phase high-performance liquid chromatography (HPLC) method has been developed to analyze naturally occurring low-molecular weight thiols using pre-column derivatization with ammonium 7-fluorobenzo-2-oxa-1,3-diazole-4-sulfonate (SBD-F) and fluorescence detection in a gradient elution. The derivatization procedure and separation conditions were optimized by careful control of the reaction conditions in terms of time, temperature, pH and reducing agent. A linear calibration in the nM range was obtained for all the standard compounds, allowing measurement of thiols in natural water samples. Results show that the reducing agent tri-n-butylphosphine (TBP) not only acts as an anti-oxidant/disulfide cleaving agent, but also enables the SBD-F to react with thiols complexed by soft metals. This is the first study reported using the SBD-F labeling technique to measure phytochelatin concentrations. The methodology has been successfully applied to estuarine water samples from Galveston Bay.

Trace metal analysis of natural waters by ICP-MS with on-line preconcentration and ultrasonic nebulization

Concentrations of Mn, Ni, Cu, Zn and Pb in natural waters were measured by inductively coupled plasma mass spectrometry (ICP-MS) with on-line preconcentration using Toyopearl TSK-immobilized 8-hydroxyquinoline resin columns and ultrasonic nebulization. Trace metal concentrations, quantified after analyzing calibration standards, were measured in 3 mL samples in under 15 min with better than 5% precision. Method detection limits were 0.26, 0.86, 1.5, 10 and 0.44 ng L –1 for Mn, Ni, Cu, Zn and Pb, respectively. The accuracy of the method was demonstrated by results from runs of certified reference materials SLRS-3 and CASS-3, which have very different ionic strengths. This on-line system was successfully applied to measure water column trace metal concentrations in Galveston Bay, Texas, and the results compared favorably with those obtained using state-of-the-art off-line preconcentration techniques.

Accumulation rates and sources of sediments and organic carbon on the Palos Verdes shelf based on radioisotopic tracers (137Cs, 239,240Pu, 210Pb, 234Th, 238U and 14C)

We report here bioturbation and sediment accumulation rates determined from replicate sediment cores at four different

Transport and diagenesis of trace metals and organic matter in Palos Verdes shelf sediments affected by a wastewater outfall

Abstract Particles from the Whites Point/JWPCP outfalls operated by the Los Angeles County Sanitation District (LACSD) have been discharged onto the Palos Verdes (PV) shelf, Southern California, since the late 1930s. Since the early 1950s, they have made a significant contribution to the sedimentary deposits on the shelf. In order to study the transport and diagenesis of organic carbon (OC) and associated trace metals, replicate sediment cores were collected during 1996 and 1997 at four different sites at the ∼60 m isobath on the PV shelf, and analyzed for OC, Ag, Al, Cd, Cr, Cu, Mn, Ni, Pb, and Zn. We conclude from these results that a significant fraction of OC and associated heavy metals were transported laterally on silt particles from shallower environments. Cross-shelf transport of sediments caused multiple peaks in measured profiles of OC and trace metals at site 6C, 2 km away from the outfall. The same mechanism is likely to contribute to a concentration decrease that is smaller than that expected from decreases from the Whites Point outfall emissions. Based on Pb/OC ratios in sediments, deposited in 1971, and comparisons to the outfall from the same year, we estimate that 50±10% of the OC deposited in the early 1970s, now buried at 30–50 cm depth, had oxidized since that time, implying a half-life of about 26 years for the outfall-OC, as an upper limit. The average OC oxidation rate at peak depth (about 2 mg C cm −2 year −1 ) is, however, only about 10% of the present-day OC accumulation rate (20 mg C cm −2 year −1 ), which itself is adding not much more than 1% per year to the post-1950s OC inventory (∼1500 mg cm −2 ). We furthermore estimate that the OC inventory in PV shelf sediments in 1971 was equivalent to about 35% of that emitted by the outfall. OC and trace metal inventories did not decrease in the period 1981 to 1997, contrary to those of other contaminants such as DDTs and PCBs.

Prokaryotic assemblages and metagenomes in pelagic zones of the South China Sea

BackgroundProkaryotic microbes, the most abundant organisms in the ocean, are remarkably diverse. Despite numerous studies of marine prokaryotes, the zonation of their communities in pelagic zones has been poorly delineated. By exploiting the persistent stratification of the South China Sea (SCS), we performed a 2-year, large spatial scale (10, 100, 1000, and 3000 m) survey, which included a pilot study in 2006 and comprehensive sampling in 2007, to investigate the biological zonation of bacteria and archaea using 16S rRNA tag and shotgun metagenome sequencing.ResultsAlphaproteobacteria dominated the bacterial community in the surface SCS, where the abundance of Betaproteobacteria was seemingly associated with climatic activity. Gammaproteobacteria thrived in the deep SCS, where a noticeable amount of Cyanobacteria were also detected. Marine Groups II and III Euryarchaeota were predominant in the archaeal communities in the surface and deep SCS, respectively. Bacterial diversity was higher than archaeal diversity at all sampling depths in the SCS, and peaked at mid-depths, agreeing with the diversity pattern found in global water columns. Metagenomic analysis not only showed differential %GC values and genome sizes between the surface and deep SCS, but also demonstrated depth-dependent metabolic potentials, such as cobalamin biosynthesis at 10 m, osmoregulation at 100 m, signal transduction at 1000 m, and plasmid and phage replication at 3000 m. When compared with other oceans, urease at 10 m and both exonuclease and permease at 3000 m were more abundant in the SCS. Finally, enriched genes associated with nutrient assimilation in the sea surface and transposase in the deep-sea metagenomes exemplified the functional zonation in global oceans.ConclusionsProkaryotic communities in the SCS stratified with depth, with maximal bacterial diversity at mid-depth, in accordance with global water columns. The SCS had functional zonation among depths and endemically enriched metabolic potentials at the study site, in contrast to other oceans.

Geochemical behavior of 210Pb and 210Po in the nearshore waters off western Taiwan.

Dissolved and particulate (210)Pb and (210)Po were determined at 15 stations along the coastline off western Taiwan in April 2007. The (210)Pb activities in dissolved and particulate phases fell within a relatively small range of 2.4-5.2 dpm 100 L(-1) and 1.0-3.2 dpm 100 L(-1), respectively. The dissolved and particulate (210)Po activities also fell within a small range of 0.8-3.4 dpm 100 L(-1) and 1.1-2.9 dpm 100 L(-1), respectively. The correlation of the distribution coefficients (K(d)) of (210)Pb and (210)Po with particle concentration in turbid waters are not as evident as in the open ocean. The mass balance calculation shows that the residence times of (210)Pb and (210)Po with respect to particle removal from the nearshore waters ranges from 3 to 15 days and from 14 to 125 days, respectively. The flux of particulate organic carbon was estimated by (210)Po proxy and ranged from 4.8 to 33.7 mmol-C m(-2) d(-1).

Box coring artifacts in sediments affected by a waste water outfall

Variations in porosity of surface sediments are often the major cause of sediment loss during gravity and box coring. Sediments with a high content of organic matter usually have higher porosity, and thus, lower resistance (strain) towards mechanical disturbance. Here, we demonstrate that box coring artifacts (i.e. sediment loss and core shortening) can be produced in sediments from the Palos Verdes (PV) shelf, which in the past had received relatively high loads of organic carbon (OC) enriched particulate matter originating from the Whites Point outfall that had created a high porosity layer at depth. This has been overlooked as a possibility for obtaining low estimates of sediment and pollutant accumulation rates. Since any such sediment loss during coring can lead to serious underestimates of sedimentation rates, our results here may have important implications for any attempts at reconstructing pollutant fluxes and histories in these coastal marine sediments.

The isotopic composition of dissolved cadmium in the water column of the West Philippine Sea

The dissolved concentration and isotopic compositions of cadmium (Cd) in the seawater of the West Philippine Sea were determined. In general, Cd isotopic composition in the water column decreased with depth, with e114/110Cd (e114/110Cd = [(114Cd/110Cd)sample / (114Cd/110Cd)NIST 3108 - 1]×10000) ranging from +7.2 to +10.1 in the top 60 m, from +4.8 to +5.1 between 100 and 150 m, peaking at +8.2 at 200 m, decreasing from +4.5 to +3.3 from 400 to 1000 m, and remaining constant at +3.0 from 1000 m and deeper. Different to a Rayleigh fractionation model, the isotopic composition and log scale concentrations of Cd do not exhibit a linear relationship. However, from the deep water to thermocline, the variations in Cd concentration and e114/110Cd are relevant to the variations of temperature and salinity, indicating that water mixing is the dominant processes determining the concentration and isotopic composition in the interval. At 200 m where North Pacific Tropic Water dominates the water mass, the elevated e114/110Cd could be linked to the composition in the upper portions of the water mass. In the top 150 m, the e114/110Cd varies similarly to the phytoplankton community structures, implying that Cd uptake by various phytoplankton species may be associated with the isotopic variation. However, the effects of atmospheric inputs to the e114/110Cd in the surface water cannot be excluded. A box model calculation is used to constrain the contributions of various processes to the Cd isotopes of surface water, and the results indicate that the Cd concentration and isotopic composition in most of the water body of the region are controlled by physical mixing, while the effects of biological fractionation and atmospheric inputs are limited in the euphotic zone.