Degui Tang

Distributions of carbohydrates, including uronic acids, in estuarine waters of Galveston Bay

Abstract The concentrations of carbohydrates, including uronic acids, in dissolved (≤0.45μm) and colloidal (1 kDa—0.45 μm) phases were measured in estuarine waters of Galveston Bay, TX, in order to study their role in heavy metal detoxification. The concentrations of dissolved monosaccharides (MCHO) in Galveston Bay ranged from 13 to 62 μM-C, and those of dissolved polysaccharides (PCHO) ranged from 10 to 42 μM-C. On average, MCHO and PCHO contributed about 11% and 7% to dissolved organic carbon (DOC), respectively. The colloidal carbohydrates (CCHO) in Galveston Bay varied from 7 to 54 μM-C, and accounted for 9% to 24% of the colloidal organic carbon (COC), with an average value of 17%, suggesting that CCHO is abundant in the high molecular weight (HMW) fraction of DOC. The concentration of CCHO is generally significantly higher than that of PCHO. This result is attributed to entrainment of low molecular weight (LMW) carbohydrates into the retentate fraction during ultrafiltration. The concentration of total dissolved uronic acids (DUA) in the same samples varied from 1.0 to 8.3 μM-C, with an average value of 6.1 μM-C, while the colloidal uronic acids (CUA) ranged from 0.8 to 6.4 μM-C, with an average value of 4.8 μM-C. The concentrations of DUA are higher than the previously reported values in coastal waters. Furthermore, CUA represent a dominant component of DUA in Galveston Bay waters. More importantly, significant correlations of PCHO and DUA to dissolved Cu concentrations (≤0.45 μm) were found, suggesting that acid polysaccharides were produced in response to trace metal stressors.

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.

Sensitive determination of dissolved sulfide in estuarine water by solid-phase extraction and high-performance liquid chromatography of methylene blue

A sensitive method involving solid-phase extraction and HPLC analysis of methylene blue has been developed to measure nanomolar levels of dissolved sulfide in oxic surface waters. The procedure included 1) a preconcentration step, in which methylene blue generated from sulfide reaction with n,n-dimethyl-p-phenylenediamine in acidic conditions in the presence of ferric ion was absorbed onto Waters tC18 cartridge; and 2) a determination step, in which methylene blue was separated by HPLC in a gradient elution to minimize natural organic matter interference and detected by absorbance. The concentrations of the dissolved sulfide, quantified by standard addition, were about 2.1-4.7 nM in oxic surface waters from Galveston Bay, Texas.

Distribution and partitioning of trace metals (Cd, Cu, Ni, Pb, Zn) in Galveston Bay waters

The distribution of several trace metals has been studied in the surface waters of Galveston Bay, Texas, in order to assess the impact of complexation with organic and reduced sulfur species on the partitioning of trace metals between particulate and aqueous species. The distribution of trace metals in the filter-passing fraction ( Cu>Cd>Zn>Pb>Mn>Fe, while an increasing trend was found in the same sequence for the acid-leachable fractions. The average values of Kd1, the particle-water partition coefficient, expressed as the ratio of weak acid-leachable particulate fractions to the filter-passing fractions, increased in the order Ni<Cu<Cd<Zn<Mn<Pb<Fe. This sequence is consistent with the relative importance of particulate transport of these trace metals from estuaries to coastal oceans. The observed decrease of Kd1 of Cu with increasing concentrations of suspended particulate matter (SPM), also called the “particle concentration effect” (PCE), can be eliminated when the free ionic, rather than the total concentration of Cu in the filter-passing fraction is used for calculating this ratio. A particle concentration effect would be expected if the binding of these trace metals by particles is mediated by solution (i.e., filter-passing) phase ligands. Complexation of Cd, Cu, Ni, Pb, and Zn with reduced sulfur species could be one of the causes for the observed linear correlations between metals and reduced sulfur species in both the filter-passing and filter-retained fractions. Significant correlations between Cu in the weak acid-leachable fraction and chlorophyll a (Chl a) concentrations suggest biological mediation of Cu uptake into the particulate fraction.

Performance optimization of a commercially available iminodiacetate resin for the determination of Mn, Ni, Cu, Cd and pb by on-line preconcentration inductively coupled plasma-mass spectrometry

The on-line preconcentration performance characteristics of a commercially available iminodiacetate resin (Toyopearl AF-Chelate 650M) were investigated. The method was optimized for several parameters, including buffer pH, rinsing of matrix salts from the resin, elution acid type and strength, and the nebulizer gas flow rate. An ammonium chloride buffer with a pH of 8.80 was mixed with the sample on-line prior to loading. This pH was found to be optimal for Mn, Cu, Cd and Pb, whereas a pH of ≥9.2 was optimal for Ni analysis. Column rinse experiments showed that both buffer and water reduce Na concentrations to <100 μM in the rinse solution within 3 min. It was also determined that using 1 M HNO3 acid for column elution yielded higher intensities for Mn, Ni, Cu and Pb, while 1 M HCl yielded higher count rates for Cd. The change from the optimization solution, with a 0.2% HNO3 acid concentration, to the 10% elution acid required a reduction in the nebulizer gas flow rate of 0.05 l min−1 in order to obtain reduced blank intensity ratios. Calibrations performed using standard solutions (1 ml) with concentrations ranging from 0 to 10 pg ml−1 (ppt) resulted in regression coefficients of 0.990–0.998. Method detection limits of 1.1, 0.08, 0.47, 0.06 and 0.16 pg ml−1 for Mn, Ni, Cu, Cd and Pb, respectively, were obtained. Accuracy was demonstrated by results from runs of the certified standard reference materials (SRMs), CASS-4, a newly available coastal seawater reference standard and NASS-4, an open ocean seawater reference material.

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.