Cd In Seawater Research Articles

Determination of Cd and Pb in seawater by graphite furnace atomic absorption spectrometry with the use of hydrofluoric acid as a chemical modifier

High concentration of added hydrogen fluoride converted the seawater chloride to the corresponding fluoride matrix, and the liberated hydrochloric acid could be removed during the drying step. The atomization of cadmium and lead could be performed at a relatively low temperature (∼1300 °C) at which the vaporization of the fluoride matrix was relatively slow, and the corresponding weak background signals could be separated from the analytical signals in time. Experimental conditions for the determination of Cd and Pb in seawater in the presence of HF were optimized with the use of the a priori calculation of the limit of detection. The experimental limit of detection obtained for Cd and Pb were, respectively, 0.007 and 0.25 μg l −1 for a 15-μl seawater sample (3σ, 20 replicates). The concentrations of Cd determined in a SLEW-1 estuarine water and a CASS-2 seawater were 0.020±0.002 and 0.016±0.002 μg l −1 Cd, respectively, in good agreement with the 0.018±0.003 and 0.019±0.004 μg l −1 Cd certified values (At the 95% confident level, 10 replicates).

Design of a field flow preconcentration system for cadmium determination in seawater by flow-injection-atomic absorption spectrometry

A field flow preconcentration system (FFPS) for cadmium determination in seawater is described. Seawater samples are collected and preconcentrated in situ by passing them with a peristaltic pump through a minicolumn packed with Amberlite XAD-4 impregnated with the complexing agent 1-(2-pyridylazo)-2-naphthol. Thus, cadmium is complexed, retained, and preconcentrated without the interference of the saline matrix. Minicolumns loaded with cadmium are then returned to the laboratory where they are incorporated into a flow injection system and eluted with a small volume of an ethanolic solution of hydrochloric acid into the nebuliser–burner system of a flame atomic absorption spectrometer. The optimization of FFPS design is presented, and the stability and characteristics of the Cd-loaded minicolumns are studied in detail. The detection limit for Cd in seawater based on an enrichment factor of 1059 was 3.8 ng l −1. The precision (R.S.D.) obtained for different amounts of cadmium was in the range 4.1–6.5% at the 25–100 ng l −1 level. Analysis of certified reference materials (SLEW-3 and NASS-5) showed good agreement with the certified value. This procedure was applied to the determination of cadmium in seawater samples from Galicia (Spain).

Effect of Zn, Mn, and Fe on Cd accumulation in phytoplankton: Implications for oceanic Cd cycling

Cd and phosphate concentrations in seawater are closely related, suggesting that Cd distributions, like those of PO4, are controlled by algal uptake and regeneration. But the factors that control Cd levels in phytoplankton and their influence on oceanic Cd versus PO4 relationships are poorly known. We examined the effect of important controlling factors (free ion concentrations of Cd, Zn, and Mn and Fe limitation of growth rate) on Cd accumulation by an oceanic diatom (Thalassiosira oceanica). More limited comparative experiments were also conducted with a coastal diatom (T. weissflogii) and an oceanic coccolithophore (Emiliania huxleyi). Cellular Cd:C ratios increased with increasing Cd ion concentrations and decreasing Zn ion concentrations in all species and with decreasing ionic Mn in the diatoms. The effects of Mn and Zn apparently are related to the uptake of Cd by the cells' Mn and Cd/Co transport systems, which are under negative feedback regulation by cellular Mn and Zn. Cd:C ratios were determined in the oceanic diatom as functions of free ion concentrations of Cd, Zn, and Mn over the oceanic range of these metal ions. The data were combined with estimates of free ion concentrations of these metals in seawater to construct models of Cd:C and Cd:P ratios in oceanic phytoplankton. The modeled Cd:P ratios showed good agreement with slopes of Cd versus P relationships in different oceanic regimes. The models suggest that the high Cd versus phosphate slopes found in iron‐depleted waters of the Southern Ocean and subarctic Pacific result from unusually high levels of zinc depletion in these waters. The resulting low zinc ion concentrations induce high levels of Cd uptake by phytoplankton, yielding high algal Cd:P ratios. The heavy depletion of zinc may be linked to elevated Zn:C and Zn:P ratios in iron‐limited diatoms, as observed in experiments we conducted with T. oceanica.

Cd in planktonic and benthic foraminiferal shells determined by thermal ionisation mass spectrometry

A highly sensitive method for Cd determination in foraminiferal shells by isotope-dilution TIMS has been developed and applied to (i) a more detailed reconstruction of seawater Cd depth profiles for the North Atlantic in the Holocene and at the Last Glacial Maximum (LGM); (ii) the analysis of Cd/Ca in individual benthic foraminifera shells; and (iii) determination of Cd/Ca in Holocene and glacial planktonic foraminifera. Although Cd has a high first ionisation potential, through chemical separation of Cd from the Ca and optimisation of the loading technique, it is possible to analyse routine sized samples (10 benthics) with a reproducibility in Cd/Ca of ±0.0025 μmol/mol between replicate picks from a single sample. The blank of the method is 1.1 pg, permitting analysis of individual benthics and of planktonic foraminifera. The seawater Cd reconstruction for the LGM is consistent with previous work, but also suggests that depths >2500 m were ventilated by a northern source of nutrient depleted deep water on the western side of the Mid Atlantic Ridge. Individual benthic Cd/Ca ratios show interspecimen variability which is averaged in routine analysis of multiple specimens. Planktonic Cd/Ca from N. Atlantic cores shows interspecific differences between Globigerina bulloides and Neogloboquadrina pachyderma and Holocene-LGM contrasts which offers potential for use of planktonic Cd/Ca as a palaeochemical tracer.

Chemical fractionation of zinc versus cadmium among other metals nickel, copper and lead in the northern North Sea

Concentrations of dissolved Ni, Cu, Zn, Cd and Pb were measured in water samples collected during a cruise with R.V Pelagia (29-6/14-7-1993) in the northern North Sea and N.E. Atlantic Ocean. At least six depths (0–90 m) were sampled with modified Go-Flo samplers from a rubber zodiac . In the study area, the first 25 m were well mixed and stratification occurred below this depth. The local bloom of Emiliania huxleyi hardly affected the trace metals concentration, except for some removal of Cd as seen from its correlation with nitrate. The mean dissolved concentrations were for Ni (3.66 nM), Cu (1.61 nM), Zn (4.5 nM), Cd (48 pM) and Pb (108 pM). These concentrations are among the lowest reported for the North Sea and are of similar magnitude to those found in the eastern North Atlantic at the same latitude. Zn was the only exception with values 10 times higher compared to those in the Atlantic Ocean, suggesting external inputs, mainly atmospheric and possibly from surrounding land masses. The observed ratio Zn:Cd in the North Sea and estuaries is in between the high ratio 600–900 for continental sources and the low ratio 5–10 for oceanic waters. Latter low ratio is consistent with the 21-fold stronger inorganic complexation of Cd in seawater which, in combination with the preferential biological uptake of Zn, may lead to the observed about hundredfold fractionation of Zn versus Cd in the marine system. Other processes may play a role but would need further investigation. The dissolved Pb values tend to be lower than found before in the North Sea, indicating decreasing inventories due to reduced anthropogenic emissions.

Determination of cadmium, mercury and lead in seawater by electrothermal vaporization isotope dilution inductively coupled plasma mass spectrometry

Electrothermal vaporization isotope dilution inductively coupled plasma mass spectrometry (ETV-ID-ICP-MS) has been applied to the determination of Cd, Hg and Pb in seawater samples. The isotope ratios of the elements studied in each analytical run were calculated from the peak areas of each isotope. Various modifiers were tested for the best signal of these elements. After preliminary studies, 0.15% m/v TAC and 4% v/v HCl were added to the sample solution to work as the modifier. The ETV-ID-ICP-MS method has been applied to the determination of Cd, Hg and Pb in NASS-4 and CASS-3 reference seawater samples and seawater samples collected from Kaohsiung area. The results for reference sample NASS-4 and CASS-3 agreed satisfactorily with the reference values. Results for other samples determined by isotope dilution and method of standard additions agreed satisfactorily. Detection limits were approximately 0.002, 0.005 and 0.001 ng ml −1 for Cd, Hg and Pb in seawater, respectively, with the ETV-ICP-MS method. Precision between sample replicates was better than 20% for most of the determinations.

Determination of ultra-trace amounts of cadmium, cobalt and nickel in sea-water by electrothermal atomic absorption spectrometry with on-line preconcentration

A miniature column packed with Muromac A-1 chelating resin and a laboratory-built automatic on-line preconcentration system for electrothermal atomic absorption spectrometry were used to determine Cd, Co and Ni in sea-water. The preconcentration system was modified from a Perkin-Elmer AS-40 autosampler by mounting a Muromac A-1 microcolumn near the tip of the autosampler capillary, and we replaced the pull-and-push pump of the autosampler with a peristaltic pump. Retention of the metal ions as a complex on the microcolumn was achieved by using Muromac A-1 as the chelating resin; 20% HNO3 was then used for elution. The procedures of preconcentration were performed by using a four-way distribution valve and a programmable controller. Detection limits (and sample volumes) were 1.2 × 10–4 µg l–1 for Cd (400 µl), 0.007 µg l–1 for Co (1800 µl) and 0.033 µg l–1 for Ni (800 µl). Relative standard deviations for the determination of Cd, Co and Ni in sea-water (CASS-3) were 2.9, 5.6 and 4.1%, respectively. The accuracy of the method was confirmed by the analysis of certified reference saline waters (NASS-4, CASS-3 and SLEW-1).

Use of 4-(2-pyridylazo)resocinol or 2-(2-pyridylazo)-5-dimethylaminophenol as chelating agent for determination of cadmium in seawater by atomic absorption spectrometry with on-line flow-injection sorbent extraction

A home-made automatic on-line flow-injection sorbent extraction system for graphite furnace atomic absorption spectrometry (GFAAS) was used to determine Cd in seawater using octadecyl functional group (C 18) bonded silica gel as sorbent, 4-(2-pyridylazo)resocinol (PAR) or 2-(2-pyridylazo)-5-dimethylaminophenol (PADMAP) as chelating agent and methanol as eluent. The range of pH for the determination of Cd in seawater was 4.7–7.4 and 7.1–9.0 for using PAR and PADMAP as chelating agents, respectively. For the long-term stability studies, the complexes (PAR–Cd or PADMAP–Cd) are stable within the pH range 4.7–7.4 (for PAR) or 7.1–9.0 (for PADMAP) for 1 h at least. Sample volume of only 500–1000 μl was required to determine Cd in seawater. The simple calibration curve method was used and the detection limits of the determination of Cd in seawater were 4.0 and 1.7 ng l −1 for PAR and PADMAP as chelating agents, respectively. The sample throughput is 9–12 h −1. The accuracy and precision of the method were confirmed by the analysis of three kinds of certified reference saline water.

Control of Cd Concentrations in a Coastal Diatom by Interactions among Free Ionic Cd, Zn, and Mn in Seawater

Cadmium and phosphate concentrations in seawater are closely correlated, suggesting that Cd distributions, like those of PO4, are controlled by algal uptake and regeneration. But the factors controlling Cd levels in phytoplankton are poorly known. Experiments in metal ion buffer systems with a coastal diatom Thalassiosira pseudonana revealed that cellular Cd:C ratios within the Cd ion concentration ([Cd2+]) range (10-13 to 10-10 M) in seawater were generally proportional to [Cd2+] and inversely related to concentrations of Zn and Mn ions ([Zn2+] and [Mn2+]) and specific growth rate. The effects of Mn and Zn reflect cellular uptake of Cd by two inducible transport systems: the Mn system whose capacity (Vmax) is enhanced at low [Mn2+] and a separate system induced at low cellular zinc. At the low [Zn2+] of surface oceanic waters (≤10-11.0 M), Cd uptake is controlled by this latter system and, therefore, is inversely related to ionic zinc levels. However, at the higher [Zn2+] range of coastal waters, Cd uptake by this system is strongly suppressed and Cd instead is taken up by the Mn system; as a result it is inversely related to [Mn2+] and largely independent of variations in [Zn2+]. Because of the suppression of Cd uptake by high [Zn2+] and [Mn2+] in coastal waters, algal Cd concentrations may be lower in these waters than in the ocean despite the presence of higher coastal [Cd2+].

Trace elements in the Korean coastal environment

The present article reports on the results of trace metal analysis in the Korean coastal environment during the last decade. Trace metals of Cd, Cu, Pb and Zn in seawater, sediments and mussels were determined in coastal areas of East, South and Yellow Seas. Clean sampling, the use of ultrapure reagents, reference materials and clean-room analysis were carried out to assure quality control. The concentrations of trace metals in the Korean coastal environment were compared with the results from other parts of the world oceans.

Chelating resin preconcentration and Hg(II) assisted elution followed by differential-pulse anodic stripping voltammetry for the determination of Cd, Cu, and Pb in seawater

A new and efficient Hg(II) back-elution method for the desorption of Cd, Cu, and Pb from Chelex-100 chelating resin was developed. A smaller eluent volume and shorter elution time can be achieved using an Hg(II) containing eluent rather than pure nitric acid. Owing to the remaining Hg(II) ion in the effluent, a mercury thin-film electrode is formed in-situ during the anodic stripping voltammetric determination without any further addition of Hg(II). The results indicate that all the analytes in seawater matrix can be completely adsorbed on Chelex-100 resin from the sample at pH 6.5, and subsequently eluted from the resin with an acid solution of 5 × 10–4 mol/L Hg2+ + 1 mol/L HClO4. The detection limits obtained from the differential-pulse anodic (μg L–1 to ng L–1) stripping voltammetry are at sub-ppb to ppt (μg L–1 to ng L–1) levels permitting to determine Cd, Cu and Pb traces in seawater. The analytical reliability was confirmed by the analysis of the certified reference material CASS-II (open ocean seawater).

Determination of trace elements in sea-water by inductively coupled plasma mass spectrometry after preconcentration by formation of water-soluble complexes and their adsorption onC18-bonded silica gel

A simple and reliable preconcentration method was developed for the determination of seven trace metals (Mn, Fe, Ni, Cu, Zn, Cd and Pb) in sea-water by ICP-MS. The method is based on the formation of water-soluble complexes in an aqueous sample followed by adsorption of the complexes onto a C18-bonded silica gel column. The chelating reagent used was 2-(5-bromo-2-pyridylazo)-5-(N-propyl-N-sulfopropylamino)phenol (5-Br-PAPS). By passage of 100 ml of sea-water sample, after addition of 5-Br-PAPS and adjustment of the pH to 8.3, quantitative adsorption of the metal complexes onto the column took place while the major matrix ions in sea-water passed through the column. A similar but separate sample work-up at pH 4.5 provided acceptably low blank values for Fe. The metals were subsequently eluted with 4.0 ml of 1.0 M HNO3. All seven elements were determined with an all-argon plasma, whereas ultratrace levels of Fe were determined with a nitrogen–argon mixed-gas plasma to reduce the isobaric interference by 40Ar16O on 56Fe. The detection limits of the method, based on a 25-fold preconcentration, range from 0.08 ng l–1 for Cd to 16 ng l–1 for Fe. The precision and accuracy of the method were demonstrated by analyzing coastal and open-ocean sea-water certified reference materials.

Determination of copper, cadmium, lead, bismuth and selenium(iv) in sea-water by electrothermal vaporization inductively coupled plasma mass spectrometry after on-line separation

A procedure for the determination of Cu, Cd, Pb, Bi and SeIV in sea-water by electrothermal vaporization inductively coupled plasma mass spectrometry, after on-line separation using a flow injection system, is proposed. Matrix separation and analyte preconcentration was accomplished by retention of the analytes complexed with the ammonium salt of O,O-diethyldithiophosphoric acid on C18 immobilized on silica in a minicolumn coupled directly to the autosampler arm of the vaporizer. The methanol used as eluent was vaporized after being automatically injected into the graphite tube, prior to the vaporization of the analytes. The conditions for the on-line complexation and separation as well as the vaporizer temperature program were optimized. The recoveries from sea-water ranged from 90 to 110%. The accuracy of the method was tested by the analysis of two certified sea-waters, CASS-3 and NASS-4, from the National Research Council of Canada. The concentration of Bi in these sea-waters was below the method detection limit. The relative standard deviation was below 10% (n=6). The throughput was 22 samples h–1 and the volume of sample consumed was only 2.3 ml. Tl and AsIII were also separated but their complexation in sea-water was not efficient.

Biomonitoring with benthic macroalgae and direct assay of heavy metals in seawater of the Oporto coast (northwest Portugal)

The concentrations of dissolved Cd, Cu, Hg and Pb in seawater and algae ( Enteromorpha spp. and Porphyra spp.) were determined in parallel on three beaches located in the Oporto coast (Portugal), during 8 successive months, comprising periods of low and high biological productivity. The concentrations of dissolved metals in seawater varied markedly during the sampling period and exhibited seasonality. The concentrations of Cd were high in autumn and winter, but low in spring. The concentrations of Cu and Hg were high in autumn, low in winter and peaked in May. The concentrations of Pb were low in autumn and winter, and also peaked in May. It is likely that biological activity was, at least partially, responsible for the observed seasonal changes. The mean concentrations of dissolved metals in seawater were similar to those reported for polluted and industrialized european coastal areas. Metal concentration factors, calculated month-to-month for each alga, metal and site, varied markedly during the sampling period, indicating that concentration factors based on single or few determinations could be misleading. On the contrary, mean concentration factors (calculated by dividing the mean metal concentration in the algae by the mean metal concentration in seawater) were relatively constant at all three sites, indicating that in the Oporto coast, Enteromorpha spp. can be used to estimate the mean concentration of dissolved Cd, Cu and Hg in seawater, and Porphyra spp., the mean concentration of Cd, Cu and Pb. However, considering that future estimates of the concentrations of these metals in seawater should be based on determinations of the metal contents in Enteromorpha spp. and Porphyra spp. carried out on several occasions spanning a considerable period of time, the use of these algae as monitors of heavy metal pollution can have limited practical advantages over the direct assay of the metals in seawater.

Experimental determination of cadmium uptake in shells of the planktonic foraminifera Orbulina universa and Globigerina bulloides: Implications for surface water paleoreconstructions

Laboratory culturing is a direct means of determining Cd uptake in shells of planktonic foraminifera. We employed a new stable isotope technique using both 110Cd and 111Cd to assess uptake in the symbiont bearing species, Orbulina universa, and the nonsymbiont bearing species, Globigerina bulloides. In certain experiments with G. bulloides the three endmember isotope dilution method was combined with a recently described 48Ca labeling technique. Shells of Orbulina universa cultured under a 12 h high light:12 h dark cycle are found to incorporate very little Cd. Foraminifera can be induced to take up slightly more Cd by growth under 24 h darkness or under a 12 h high light:12 h dark cycle with exposure to the photosynthesis inhibitor, DCMU. These results demonstrate that O. universa under-represents the Cd concentration of seawater in which the shell is precipitated. Additionally, the results suggest a previously unknown influence of symbiotic dinoflagellates on foraminiferal shell chemistry. There are two different mechanisms by which symbionts might play a role in influencing Cd uptake in O. universa: (1) algal sequestration and removal of Cd from the foraminiferal calcification microenvironment or (2) photosynthetic enhancement of calcification rate, leading to Cd exclusion. If these results apply generally to bioactive trace metal uptake by dinoflagellate-bearing planktonic foraminifera, they suggest that shells of species such as O. universa only record qualitative changes in surface water metal concentrations. The response for Cd uptake in nonsymbiont bearing G. bulloides (cultured under a 12 h high light: 12 h dark cycle) appears linear within and slightly above the range of Cd concentrations found in the modern ocean, with an effective partition coefficient equal to 1.9 ± 0.2 (95% C.I.). The Cd partition coefficient determined for G. bulloides falls within the range of D Cd previously found for fossil benthic foraminifera but is twenty times higher than that for O. universa ( D cd = 0.095 ± 0.021 (95% C.I.)) grown under identical culture conditions. Because G. bulloides appears to reliably record seawater Cd concentrations, it should be suitable for accurate paleoreconstructions of surface water Cd and PO 4 3− concentrations.

Rapid and simultaneous analysis of trace metals (Cu, Pb and Cd) in seawater by potentiometric stripping analysis

A potentiometric stripping method for a simultaneous measurement of copper, lead and cadmium in oceanic waters using a TraceLab PSU22 unit has been developed. Compared to the earlier TraceLab PSU20 unit, the PSU22 has a sampling rate of the potential during the stripping step that is three times lower. This results in the decrease of the detection limit by about four times. The detection limits obtained with a pre-electrolysis time of 15 min were 44 ng l −1 (0.7 nM), 3 ng l −1 (14 pM) and 1 ng l −1 (9 pM) for Cu, Pb and Cd, respectively. The precision, accuracy and reproducibility of the method agree well with those obtained by other techniques for trace metals analysis in seawater. Vertical profiles of Cd in the Mediterranean waters obtained by AA and PSA were concordant.

Low Blank Preconcentration Technique for the Determination of Lead, Copper, and Cadmium in Small-Volume Seawater Samples by Isotope Dilution ICPMS

A simple low-blank method is described for the analysis of Pb, Cu, and Cd in seawater using Mg(OH)(2) coprecipitation and isotope dilution inductively coupled plasma mass spectrometry (ICPMS). Here, 20-40 μL of 9 M aqueous NH(3) is mixed into a 1.3 mL seawater sample spiked with enriched isotopes of Pb, Cu, and Cd. After centrifugation, the supernatant is discarded and the Mg(OH)(2) precipitate dissolved in 100 μL of 5% HNO(3) for ICPMS analysis. This method is simple, accurate, and precise, with detection limits of Pb = 1.3 pM, Cu = 39 pM, and Cd = 5.0 pM and blanks of Pb = 0.62 pM, Cu = 27 pM, and Cd = 6.0 pM. The method is demonstrated by oceanographically consistent profiles of these trace metals at an ocean station in the eastern North Atlantic.

Simultaneous determination of several trace metals in seawater using cathodic stripping voltammetry with mixed ligands

Cathodic stripping voltammetry (CSV) is normally restricted to the determination of one or two elements simultaneously due to the specificity of the ligand. By using a mixture of ligands we have attempted to enable the simultaneous determination of several elements (Cu, Pb, Cd, Ni, Co and Zn) in seawater. Scans containing six resolved peaks corresponding to these metals were obtained using a combination of DMG (dimethylglyoxime) and oxine (8-hydroxyquinoline) in seawater. These metals can be quantified at concentrations above 0.3 nM Cu, 0.2 nM Pb, 0.l nM Cd, 0.4 nM Ni, 0.6 nM Zn and 0.02 nM Co. The sensitivity for Co and Zn is not sufficient for their determination in unpolluted waters. Several procedures were developed to determine various combinations of metals at lower concentrations, and optimised by making use of different ligand combinations, resulting in higher sensitivities. Nitrite was used to improve the sensitivity for Co using a catalytic reaction. The metals were found not to interfere with each other when present at concentrations normally encountered in seawater. Suitable linear ranges of voltammetric response were identified. The limits of detection using the optimised mixed ligand solutions are similar to those for the ligands separately. The major improvement is the possibility of simultaneous determination of several metals in a sample within a few minutes and the applicability to ship-board automated determinations.

Improved dithiocarbamate/oxine solvent extraction method for the preconcentration of trace metals from seawater using metal exchange back-extraction

A rapid single extraction procedure using dithiocarbamate complexing agent, a di-isobutyl ketone (DIBK) organic phase and Hg exchange back-extraction is described for the simultaneous quantitative preconcentration of Cd, Co, Cu, Fe, Ni, Pb and Zn in seawater. An 8-hydroxyquinoline (oxine) extraction technique is also presented for the subsequent determination of Mn using the same reagents and operating system. The proposed method gave quantitative spike recoveries for all metals and was in excellent agreement with the certified results for CASS-3 marine reference seawater. Blanks and detection limits are in the low ppt range. The method gives a preconcentration factor of 72 for an 80-ml sample, facilitating the analysis of pristine seawater samples.

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A rapid single extraction procedure using dithiocarbamate complexing agent, a di-isobutyl ketone (DIBK) organic phase and Hg exchange back-extraction is described for the simultaneous quantitative preconcentration of Cd, Co, Cu, Fe, Ni, Pb and Zn in seawater. An 8-hydroxyquinoline (oxine) extraction technique is also presented for the subsequent determination of Mn using the same reagents and operating system. The proposed method gave quantitative spike recoveries for all metals and was in excellent agreement with the certified results for CASS-3 marine reference seawater. Blanks and detection limits are in the low ppt range. The method gives a preconcentration factor of 72 for an 80-ml sample, facilitating the analysis of pristine seawater samples.