Determination of Trace Metal (Mn, Fe, Ni, Cu, Zn, Co, Cd and Pb) Concentrations in Seawater Using Single Quadrupole ICP-MS: A Comparison between Offline and Online Preconcentration Setups

Biogenic-to-lithogenic handoff of particulate Zn affects the Zn cycle in the Southern Ocean

Zinc (Zn) is vital to marine organisms. Its active uptake by phytoplankton results in a substantial depletion of dissolved Zn, and Zn bound to particulate organic matter replenishes dissolved Zn in the ocean through remineralization. However, we found that particulate Zn changes from Zn bound to phosphoryls in cells to recalcitrant inorganic pools that include biogenic silica, clays, and iron, manganese, and aluminum oxides in the Southern Ocean water column. The abundances of inorganic pools increase with depth and are the only phases preserved in sediments. Changes in the particulate-Zn speciation influence Zn bioavailability and explain the decoupling of Zn and phosphorus and the correlation of Zn and silicon in the water column. These findings reveal a new dimension to the ocean Zn cycle, implicating an underappreciated role of inorganic Zn particles and their impact on biological productivity.

A new approach for the determination of As, Cu, and Pb in seawater samples using manganese oxide octahedral molecular sieve as a sorbent for dispersive solid-phase microextraction

This study introduces a novel method for preconcentrating As, Cu, and Pb from seawater samples using manganese oxide octahedral molecular sieve (OMS-2), as a sorbent, and the analysis by Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES). The OMS-2 nanomaterial was synthesized and characterized using X-ray diffraction and scanning electron microscopy, revealing a crystallite size of 20.9 nm and a typical needle-like morphology of cryptomelane structure. To optimize the ICP-OES operating conditions and the preconcentration process, a central composite design was used. The optimal conditions for ICP-OES analyses were 1200 W and 0.7 L min-1 for the levels of the radio frequency potential (RF) and nebulization gas flow rate, respectively. The optimal conditions for the adsorption process were achieved at a pH of 6.5, 30 mg of OMS-2, and 35 min of stirring time, in the presence of the sample matrix. The enrichment factors obtained were 66, 45, and 21, and a limit of detection of 0.3, 0.1, and 2.1 μg L-1 for As, Cu, and Pb, respectively. The recovery tests ranged from 80 % to 120 %. The method was successfully applied to determine As, Cu, and Pb in seawater samples.

Nanoplankton: The dominant vector for carbon export across the Atlantic Southern Ocean in spring

Across the Southern Ocean, large (≥20 μm) diatoms are generally assumed to be the primary vector for carbon export, although this assumption derives mainly from summertime observations. Here, we investigated carbon production and export potential during the Atlantic Southern Ocean's spring bloom from size-fractionated measurements of net primary production (NPP), nitrogen (nitrate, ammonium, urea) and iron (labile inorganic iron, organically complexed iron) uptake, and a high-resolution characterization of phytoplankton community composition. The nanoplankton-sized (2.7 to 20 μm) diatom, Chaetoceros spp., dominated the biomass, NPP, and nitrate uptake across the basin (40°S to 56°S), which we attribute to their low iron requirement, rapid response to increased light, and ability to escape grazing when aggregated into chains. We estimate that the spring Chaetoceros bloom accounted for >25% of annual export production across the Atlantic Southern Ocean, a finding consistent with recent observations from other regions highlighting the central role of the phytoplankton "middle class" in carbon export.

Impact of storage temperature and filtration method on dissolved trace metal concentrations in coastal water samples

Trace elements play a major role in biogeochemical cycles and oceanographic processes. To determine trace element concentrations, the dissolved and particulate phase are usually separated by filtration. However, the frequently used membrane filtration as well as sample storage can bias the dissolved elemental concentrations by adsorption or desorption/contamination. We present a comparison of two filtration methods for coastal and estuarine water samples (pressure filtration with Nuclepore™ polycarbonate filters, vacuum filtration with DigiFILTER™s) applied to aliquots of a large-volume coastal water sample that were stored at -18°C or 4°C for up to nine weeks. The filtrates were analyzed by seaFAST-ICP-MS for dissolved Cd, Ce, Co, Cu, Dy, Er, Eu, Fe, Ho, La, Mn, Mo, Nd, Pb, Pr, Sm, Tb, U, V, W, Y, and Zn. The filtration blanks of DigiFILTER™s (0.0006 ± 0.0010 ng L-1 for Ho to 110 ± 180 ng L-1 for Zn) were sufficiently low for quantification of all analyzed elements with good repeatability, enabling a fast and reliable filtration of large sample sets of coastal water. However, the findings also highlight the need to measure procedural blanks including the filtration instead of only the instrument blanks to validate results. Measured concentrations of both filtration methods did not differ significantly for Cd, Cu, Mo, U, V, W, Zn but for other investigated elements, the ratio between both methods was up to 1.8 for Ce and 4.1 for Fe. Within nine weeks of storage, the elemental concentrations decreased significantly, resulting in losses of 20% Mn in frozen samples and 63% Pb, 64% Co and 93% Mn in cooled samples. PRACTITIONER POINTS: Two fast and cheap filtration methods for coastal water samples were compared. Dissolved concentrations of 22 elements were measured by seaFAST-ICP-MS. The filtration method is important in addition to filter pore size. Filtration blanks need to be reported to maintain comparability between methods. Cool and frozen storage of water samples biases the dissolved metal concentration.

Exchange of Pb from Indian to Atlantic Ocean is driven by Agulhas current and atmospheric Pb input from South Africa

Using a spatiotemporal dataset of dissolved lead (dPb) from the subtropical oceans surrounding South Africa, this study quantifies the exchange of dPb between the Indian and Atlantic Oceans. Despite the absence of a major Pb source within the South Atlantic sector and the complete phase-out of leaded petroleum in Southern Africa, the ecologically important southeast Cape Basin shows an elevated surface dPb concentration (21-30 pmol kg^-1). We estimated up to 90% of the measured dPb in surface waters of the Cape Basin was delivered from the Indian Ocean via the Agulhas Current (AC). Eddy dynamics and leakage at Agulhas retroflection result in an increased Pb flux from winter to summer, while a long-term (2008-2019) temporal change in dPb in the AC-derived water of Cape Basin was contemporaneous to a change in atmospheric Pb emissions from South Africa. The South African-origin atmospheric Pb, however, contributes first to the Agulhas waters in the West Indian Ocean, which is then transported to the South Atlantic, thereby regulating the dPb inventory of the Cape Basin. This indirect mechanism of Pb transfer emphasizes the importance of regulating Pb emissions from Southern Africa to protect rich fishing grounds associated with the Benguela marine ecosystem.

A Green Method for the Determination of Cadmium in Natural Waters Based on Multi-Fibre Supported Liquid Membranes

Supported liquid membranes have been used to implement a hollow fibre liquid-phase microextraction (HF-LPME) method for the preconcentration of Cd(II) in natural waters as a sample preparation step for its determination by high-resolution continuum source graphite furnace atomic absorption spectrometry (HR-CS-GFAAS). This system was designed to use four hollow fibres simultaneously with the same sample, thus improving the simplicity, speed and reproducibility of the results. The organic liquid membrane bis-(2,4,4-trimethylpentyl) phosphinic acid (Cyanex^® 272) dissolved in dihexylether (DHE) was immobilised into the pores of the walls of polypropylene hollow fibres. After extraction, the cadmium-enriched acidic phases were recovered and analysed by triplicate. To optimise the extraction process, the effect of both physical and chemical variables was studied, and optimum results with an enrichment factor (EF) of 292 were obtained for a fibre length of 6 cm, 1.06 M Cyanex 272, 0.04 M HNO₃, stirring rate of 600 rpm and an extraction time of 4.26 h. For practical applications, extraction time was reduced to 2 h, keeping the EF as high as 130. Under these conditions, a detection limit of 0.13 ng L^-1 Cd(II) was obtained, with a reproducibility of 3.3 % and a linear range up to 3 µg L^-1 being achieved. The proposed method was successfully applied to the determination of cadmium in mineral, tap and seawater samples.

Wind-driven upwelling of iron sustains dense blooms and food webs in the eastern Weddell Gyre

The Southern Ocean is a major sink of anthropogenic CO₂ and an important foraging area for top trophic level consumers. However, iron limitation sets an upper limit to primary productivity. Here we report on a considerably dense late summer phytoplankton bloom spanning 9000 km² in the open ocean of the eastern Weddell Gyre. Over its 2.5 months duration, the bloom accumulated up to 20 g C m^-2 of organic matter, which is unusually high for Southern Ocean open waters. We show that, over 1997-2019, this open ocean bloom was likely driven by anomalies in easterly winds that push sea ice southwards and favor the upwelling of Warm Deep Water enriched in hydrothermal iron and, possibly, other iron sources. This recurring open ocean bloom likely facilitates enhanced carbon export and sustains high standing stocks of Antarctic krill, supporting feeding hot spots for marine birds and baleen whales.

Sustainable Downscaled Catalytic Colorimetric Determination of Manganese in Freshwater Using Smartphone-Based Monitoring Oxidation of 3,3′,5,5′-Tetramethylbenzidine by Periodate

A sustainable downscaled procedure using smartphone-based colorimetric determination of manganese (Mn(II)) was developed. This novel Mn(II) determination procedure is proposed using a simple, available microwell-plate platform and a smartphone as a detector. This approach is based on the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) by periodate using Mn(II) as a catalyst. The catalytic kinetics of Mn(II) under different conditions was investigated to determine the optimum condition where the different catalytic activities of various concentrations of Mn(II) evince. Under the optimum condition, the bluish-green product of oxidized TMB, proportioned to the concentration of Mn(II), was monitored using a smartphone camera, and the color signals were processed using ImageJ Software. The developed procedure showed great selectivity and sensitivity as linearity ranged from 1.8 × 10⁻⁶ to 4.6 × 10⁻⁵ M (0.1 to 2.5 μg/mL). The limits of detection and quantitation were 3.6 × 10⁻⁶ and 1.1 × 10⁻⁵ M (0.2 and 0.6 μg/mL), respectively. The determination of Mn(II) in freshwater samples was demonstrated to assess environmental water quality as an initial model to more easily promote water management according to the United Nations Sustainable Development Goals (UN-SDGs). The intensity of the red could be successfully applied to evaluate Mn(II) in canals and river water with no significant differences compared with the reference method of Inductively Coupled Plasma Optical Emission Spectrometry at a confidence level of 95%.