Lead has been central to technological development for centuries; however, its release into the environment and subsequent human exposure pose significant public health risks. The review presented here critically assesses the contemporary environmental lead risk as global lead production and use are rapidly increasing, largely driven by the rising demand for electrification. We show that environmental lead exposure persists today due to legacy contamination, ongoing coal usage, and insufficient protection of workforces during production, use, and recycling of lead-acid batteries and other lead-containing products, particularly in low- and middle- income countries. We estimate that contemporary childhood lead exposure alone leads to an annual global economic loss exceeding $3.4 trillion (2021 US dollars adjusted for purchasing power parity), with pronounced disparities between high- and low- and middle- income countries. To prevent a large-scale resurgence in lead exposure, we identify four critical areas for urgent policy intervention.

Although the crucial role that dissolved trace metals (dTMs) play in both carbon cycling and climate have been revealed over the past three decades, much about the oceanic budgets of dTMs remains unknown. Rivers are one of the most important dTM sources to the ocean, and estuaries are a key interface between land and ocean. However, our understanding of how dTMs behave as they pass through the estuarine transition is limited, leading to uncertainties in estimating fluvial metal fluxes to the ocean and balancing oceanic dTM budgets. Alongside concentrations, metal stable isotopes offer an additional dimension to constrain estuarine processes, but data on metal isotopes in estuaries are scarce. Here we present dTM concentrations and their stable isotope ratios along a full salinity gradient in the Pearl River Estuary (PRE), southeastern China. Concentration data show a large apparent loss of dFe (86%) during estuarine mixing, moderate losses of dNi (13%) and dZn (36%), and nearly conservative behavior for dCu. However, examination of metal isotope data (δ56Fe, δ60Ni, δ65Cu, and δ66Zn) reveals more complex biogeochemistry, requiring either a two-stage scenario or a three-endmember mixing process. The two-stage process involves fractionation of dTM isotopes at low salinities, likely driven by particle adsorption and colloidal flocculation, followed by conservative mixing between intermediate-salinity estuarine waters and South China Sea waters. Alternatively, the three-endmember mixing process includes influences from riverine, oceanic endmembers, and external sources such as benthic flux and industrial activities, shaping dTM isotope distributions. Specifically, capturing δ56Fe fully proves challenging, yet it appears strongly influenced by inputs of benthic Fe within the PRE, characterized by dFe > 13 nmol kg−1 and δ56Fe < −0.80‰. δ60Ni and δ66Zn can be described by either two-stage or there-endmember mixing processes. In the former, the Rayleigh fractionation with αd-p of 1.00004 for δ60Ni and 1.0001 for δ66Zn, or the steady state fractionation with αd-p of 1.00005 for δ60Ni and 1.0002 for δ66Zn, could be derived to explain their patterns at low salinity, likely driven by colloidal flocculation. Additionally, a third source with dNi > 33 nmol kg−1 and δ60Ni > +1.26‰ and a third source with dZn > 13 nmol kg−1 and δ66Zn > +0.96‰, both influenced by human activities, could also shape the δ60Ni and δ66Zn patterns in the PRE, respectively. The description of δ65Cu is best achieved by a three-endmember mixing process, with the external source having dCu > 20 nmol kg−1 andδ65Cu < +1.3‰, indicative of processes like organic matter remineralization or discharge from wastewater treatment plant. Our study highlights the need for more extensive and detailed studies on estuarine settings to elucidate their potentially crucial role in global dTMs budgets.

Lead (Pb) isotopes are widely used in tracing processes that transport Pb within the environment due to the globally spread Pb pollution. In today &#39;s ocean, Pb is mainly sourced from anthropogenic emissions and is removed by particle scavenging. However, recent efforts involving Pb isotopes have started to indicate that sediments at ocean boundary, either suspended or benthic, are a previously underestimated source and sink of Pb to the seawater dissolved pool. To assess the contributions of Pb from seawater-sediment boundary, we measured the dissolved Pb concentrations and isotopic compositions in seawater from the outer East China Sea (ECS) and along the Kuroshio. Along the Kuroshio, depth profiles exhibit highly similar Pb concentrations across constant density planes, suggesting isopycnal transport. Pb isotope ratios in most of the samples show strong contributions of aerosol Pb, except for seawaters from the ECS and deep Okinawa Trough (& gt;800 m), which show evidences of crustal Pb contribution. The Okinawa Trough deep water has overlapping Pb isotope ratios with ECS water, where the suspended particulate matter is abundant. Our data on Pb isotopes in the ECS and the Okinawa Trough deep water, together with data from previous studies at other continental margins suggest that the seawater-sediment boundary along the continental shelves may be an important source and sink in marine Pb cycling.

Material fluxes at the land-ocean interface impact seawater composition and global cycling of elements. However, most attention has been focused on the fluvial dissolved fluxes. For elements like lead (Pb), whose fluvial particulate flux into the ocean is two orders of magnitude higher than the dissolved counterpart, the role of particulates in elemental cycling is potentially important but currently less appreciated. Using both chemical analyses on samples collected from around equatorial Southeast Asia and model simulations, we show that particulate-dissolved exchange is an important mechanism controlling the concentration and isotopic composition of dissolved Pb in the ocean. Our model indicates that Pb contributed from particulate-dissolved exchange at ocean boundaries is larger than, or at least comparable to, other major Pb sources to the seawater before the Anthropocene, when the anthropogenic Pb was absent. Our work highlights the importance of boundary exchange in understanding marine element cycling and weathering-climate feedback.

Since North America and European countries phased out leaded gasoline, Asia has become the major contemporary lead (Pb) source to the marine environment, at first from leaded gasoline, but more recently from coal burning and other high-temperature industrial activities. Pb in the Indian Ocean remains relatively under-evaluated after & sim;2000 and is further complicated by various oceanic processes (e.g., monsoons, boundary exchange with particulates). Here, we present three annually resolved coral skeletal Pb isotope and concentration records from the central and eastern Indian Ocean (Salomon Atoll, 1989-2009; Diego Garcia Atoll, 1999-2009; and Phuket Island, 1945-2010), and synthesize published coral/sedimentary records to reconstruct the spatial-temporal variability of anthropogenic Pb around the region. Pb isotopes in all corals coherently fall along the mixing line between Asian aerosols and the natural crust. However, higher contributions of natural Pb are found in corals located in the coastal region than those in the open ocean, despite the greater contributions of anthropogenic Pb expected in coastal water near human emission sources. This geographical difference suggests that exchanges between dissolved Pb and natural particles at ocean boundaries significantly contribute to the Pb isotope compositions in regional seawater and are subsequently recorded in corals. The temporal variability of Pb concentrations in corals and sedimentary records signifies decreasing trends in Southeast Asia but increasing trends in South Asia. This study contributes new and timely Pb and Pb isotope data for the Indian Ocean and illustrates the importance of boundary exchange in marine Pb cycling.

Reversible scavenging, the oceanographic process by which dissolved metals exchange onto and off sinking particles and are thereby transported to deeper depths, has been well established for the metal thorium for decades. Reversible scavenging both deepens the elemental distribution of adsorptive elements and shortens their oceanic residence times in the ocean compared to nonadsorptive metals, and scavenging ultimately removes elements from the ocean via sedimentation. Thus, it is important to understand which metals undergo reversible scavenging and under what conditions. Recently, reversible scavenging has been invoked in global biogeochemical models of a range of metals including lead, iron, copper, and zinc to fit modeled data to observations of oceanic dissolved metal distributions. Nonetheless, the effects of reversible scavenging remain difficult to visualize in ocean sections of dissolved metals and to distinguish from other processes such as biological regeneration. Here, we show that particle-rich "veils" descending from high-productivity zones in the equatorial and North Pacific provide idealized illustrations of reversible scavenging of dissolved lead (Pb). A meridional section of dissolved Pb isotope ratios across the central Pacific shows that where particle concentrations are sufficiently high, such as within particle veils, vertical transport of anthropogenic surface-dissolved Pb isotope ratios toward the deep ocean is manifested as columnar isotope anomalies. Modeling of this effect shows that reversible scavenging within particle-rich waters allows anthropogenic Pb isotope ratios from the surface to penetrate ancient deep waters on timescales sufficiently rapid to overcome horizontal mixing of deep water Pb isotope ratios along abyssal isopycnals.

Anthropogenic lead (Pb) has been the overwhelming Pb source to the global ocean, primarily contributed from Pb gasoline and industrial emissions. However, since Pb gasoline has been phased out globally, questions about whether there was a decrease in seawater Pb concentration, or if there are other sources taking over remains unclear in Southeast Asia. Here, combining Pb concentrations in seawater from Singapore Strait in 2010-2017; trap sediment in 2018-2019; and the previously published coral reconstruction covering 1975-2010; we found that the seawater Pb concentration in Singapore Strait over past decades followed the regional gasoline emissions, and no additional major source had contributed the Pb in the seawater since ~2010. The present-day Pb in Singapore Straits' water mainly follows the monsoonal current reversals, with variable degrees of scavenging that peak in inter-monsoon season. Minor Pb sources still contribute to some local-scale variabilities, despite a decadal-scale decreasing trend of Pb in seawater.

Ocean deoxygenation is one of the big impacts of climate change.Ocean oxygen levels have been decreasing for the past 50 years and ocean models suggest they will continue to decrease into the future.This decrease greatly impacts the ocean intermediate depths (200-1500m) and especially oxygen deficient zones (ODZs).In order to better understand the processes that control oxygenation of the ocean, we need to have longer records, which can only be obtained from geological archives such as sediments and cold-water corals.Chromium and Cr isotopes are sensitive to ocean oxygenation levels, particularly near ODZs.We are undertaking the first tests of the fidelity of cold-water corals as recorders of intermediate-water Cr and Cr isotope ratios to evaluate its use as a proxy of paleoredox state of seawater.Here we report preliminary results of Cr and Cr isotopes (δ 53 Cr) from specimens of Lophelia pertusa, a species that is increasingly used for paleo-environmental reconstructions.The three test samples used were collected from the Florida Strait (a modern coral) and the Iberian margin (a glacial-aged and a modern coral).The samples were chemically cleaned prior to analysis to remove contamination from ferromanganese oxides and detrital silicates.Initial analytical results revealed that smallsized samples (~0.5 g) negatively affect the quality of the analysis, requiring the re-analysis using larger samples (~2.5 g).As suspected, we found very low Cr/Ca ratios on these cleaned coral samples (compared to previous reports for unclean samples), at a sub-ppm coral Cr concentration (0.01-0.03 ppm).The LGM coral sample had a δ 53 Cr of -0.42 +/-0.11‰.Considering the L. pertusa species, the use of bigger coral samples of around 2-5 g correspond approximately to coral branches of 2-10 cm in length, depending on the skeletons' thickness.With an average linear growth ranging between 5-35 mm yr -1 , such analytical conditions would still allow reconstructions at an approximate resolution of 1 to 20-year (with higher resolution for older, thicker coral specimens).However, efforts are still underway to improve our analytical method and validate cold-water coral δ 53 Cr as paleoredox proxy.

Changes in chromium (Cr) isotope ratios due to fractionation between trivalent [Cr(III)] and hexavalent [Cr(VI)] are being utilized by geologists to infer oxygen conditions in past environments. However, there is little information available on Cr in the modern ocean to ground-truth these inferences. Transformations between the two chromium species are important processes in oceanic Cr cycling. Here we present profiles of hexavalent and trivalent Cr concentrations and stable isotope ratios from the eastern tropical North Pacific (ETNP) oxygen-deficient zone (ODZ) which support theoretical and experimental studies that predict that lighter Cr is preferentially reduced in low-oxygen environments and that residual dissolved Cr becomes heavier due to removal of particle-reactive Cr(III) on sinking particles. The Cr(III) maximum dominantly occurs in the upper portion of the ODZ, implying that microbial activity (dependent on the sinking flux of organic matter) may be the dominant mechanism for this transformation, rather than a simple inorganic chemical conversion between the species depending on the redox potential.

Ocean time‐series sites are influenced by both temporal variability, as in situ conditions change, as well as spatial variability, as water masses move across the fixed observation point. To remove the effect of spatial variability, this study made sub‐daily Lagrangian observations of trace elements and isotopes (Al, Sc, Mn, Fe, Co, Ni, Cu, Zn, Cd, Pb, Th, and Th) in surface water over a 12‐day period (July–August 2015) in the North Pacific near the Hawaii Ocean Time‐series Station ALOHA. Additionally, a vertical profile in the upper 250 m was analyzed. This dataset is intercalibrated with GEOTRACES standards and provides a consistent baseline for trace element studies in the oligotrophic North Pacific. No diel changes in trace elements could be resolved, although day‐to‐day variations were resolved for some elements (Fe, Cu, and Zn), which may be related to organic matter cycling or ligand availability. Pb concentrations remained relatively constant during 1997–2015, presenting a change from previous decreases. Nutrient to trace element stoichiometric ratios were compared to those observed in phytoplankton as an indication of the extent of biological trace element utilization in this ecosystem, providing a basis for future ecological trace element studies.

Trace element (TE) fluxes and their residence times (Fe, Mn, Cu, Pb, Cd, and V) within the surface ocean were determined along the GEOTRACES East Pacific Zonal Transect (GP16/EPZT) and found to reflect the diverse physical and geochemical conditions encountered across the track. The TE flux from atmospheric deposition, vertical mixing, and upwelling into the mixed layer and into the particle production zone (PPZ) along the GEOTRACES EPZT transect were evaluated with Be-7-based methods developed in earlier works. A horizontal input flux is driven from east to west by the South Equatorial Current (SEC), and estimated advection velocities were applied to horizontal gradients in the distributions of several TEs to approximate this term. There is a minimum in atmospheric deposition in the central gyre, with higher fluxes to the east due to large near-shore aerosol TE loadings, and higher to the west due to greater precipitation-driven deposition velocities (V-b). The Be-7-derived vertical diffusion (K-z) values range from 2.5 to 39 m(2)/d (0.29 x 10(-4) to 4.5 x 10(-4) m(2)/s) with higher values generally within the nearshore upwelling region and the lowest values within the stratified central gyre. Manganese displayed a well-defined gradient extending from the nearshore stations into the central gyre such that the advective term is a major component of the total input flux, particularly within the central gyre. Relative to other inputs the atmospheric input of soluble Mn is only of minor importance. Unlike Mn, there is no discernable horizontal gradient in the dissolved Fe data and therefore, there is no horizontal component of flux. Nearshore removal processes are more intense for dissolved Fe than for dissolved Mn and as a result, dissolved Mn remains elevated much farther offshore than does dissolved Fe. For the stratified mid-ocean gyre stations, the total input of Fe from all sources is relatively small compared to the inshore stations, and atmospheric deposition becomes the dominant mode of input. Aerosol Fe solubility determined by a 25% acetic acid leach with hydroxylamine hydrochloride was much greater than that derived from a leach using ultra-pure deionized water. This led to significant differences in the residence time of Fe calculated for the mid-ocean gyre using these different solubilities. Generally, each element displays relatively short (weeks-months) residence times within the nearshore region of robust upwelling, reflecting large input terms and rapid removal. Moving offshore, total input fluxes decrease and the residence times of the TEs increase markedly until the western edge of the transect. There, relaxation of ocean stratification permits greater upward turbulent flux and greater rainfall leads to greater atmospheric input of TEs.

Most of the lead (Pb) in today's ocean is from human activities, although natural sources contribute small amounts of Pb that are usually masked by massive anthropogenic emissions. In the U.S. GEOTRACES East Pacific Section (GP16), anthropogenic Pb is observed throughout the water column, and as seen elsewhere in the Pacific, Pb concentrations are highest in the upper hundreds of meters of the ocean and generally decrease with depth. Thermocline Pb concentrations are higher in the eastern portion of the section near the South American coast, decreasing with distance from the South American continent, as previously reported for redox sensitive trace elements (e.g., Mn). High precision Pb isotope ratios show that there has been a change over the past few decades in the source of Pb in the westernmost upper waters, shifting from an American-Australian type Pb intermixture to a Chinese-American-type Pb intermixture. Although it is known from the study of hydrothermal solutions and sediments that there is a large primary Pb flux from high temperature ridge crest hydrothermal springs, most of this Pb precipitates near the hydrothermal vents and very little escapes into the open water column. In fact, hydrothermal ferromanganese oxyhydroxides precipitated from the hot spring emissions strip anthropogenic Pb out of the water column, resulting in the lowest Pb concentrations ever observed in the ocean (a few tenths of a picomole/kg) in the high He-3-plume to the west of the East Pacific Rise. Deeper waters have similarly low Pb concentrations, probably as a result of the sinking veil of hydrothermalsource ferromanganese oxyhydroxides. Core top sediments from this section and previous work show clear evidence of less-radiogenic Mid Ocean Ridge Basalt (MORB) Pb distinct from the crustal and anthropogenic Pb seen in non-ridge crest sediments, specifically, low values of Pb-206/Pb-207 (1.189), Pb-208/Pb-207 (2.449), and Pb-206/Pb-204/ (18.42), compared to similar to 1.195, similar to 2.475, and similar to 18.75 respectively for the non- hydrothermal sediments. Near bottom dissolved ( < 0.2 mu m filter) water column Pb (with concentrations < 2 pmol kg(-1)) at the ridge crest and in the near-downstream neutrally-buoyant hydrothermal plume show Pb-206/Pb-207 - Pb-208/Pb-206 trends that are lower than observed throughout the rest of the water column and fall within the mixing endmember isotope ratios of less radiogenic MORB and more radiogenic anthropogenic Pb sources. Thus there is a very small leakage (similar to 1%) of primary high temperature hydrothermal Pb into the water column. But at the westernmost station (36), which shows a diluted continuation of the He-3, manganese (Mn), and iron (Fe) plume from 2200 to 2700 m, the > 2200 m Pb isotope ratios deeper than 2000 m return to the non-hydrothermal ratios with no remaining detectable MORB.

Cr isotope geochemistry is being explored in the context of a variety of geological problems as well as the environmental remediation of pollutant Cr(VI). There is a strong Cr isotope fractionation during reduction of oxidized Cr(VI) to reduced Cr(III). We present chromium concentration and Cr isotope data for samples from highly reducing environments ([O-2] < 2 mu mol/kg) in the Eastern Tropical North Pacific (ETNP) Oxygen Deficient Zone (ODZ) off of Mexico and the deep Santa Barbara Basin off of California. Total dissolvable Cr in the upper ETNP ODZ is slightly depleted (by up to 0.8 nmol/kg) and delta Cr-53 is up to 0.1-0.2 parts per thousand heavier compared to oxic waters of the same density seen at the SAFe station (30 degrees N, 140 degrees W), presumably both a result of reduction of Cr(VI) and removal of light Cr(III) by sinking particles. The Cr depletion and Cr isotope fractionation peak at the same depth as the highest delta N-1(5) of NO3- and decrease within the equally oxygen-deficient waters below, implying that microbial reduction dependent on the sinking organic matter flux may be the mechanism of Cr reduction. These data are consistent with a fractionation mechanism with a net isotope fractionation factor of epsilon approximate to -0.44 parts per thousand. In the deepest anoxic waters of the Santa Barbara Basin in July 2014, dissolved ( <0.2 mu m) Cr is depleted by up to 1.8 nmol/kg and delta Cr-53 is up to 0.5 parts per thousand heavier compared to SAFe station waters of the same density. This is consistent with a net isotope fractionation factor of epsilon approximate to -0.65 parts per thousand. At the Santa Barbara Basin site, it is possible that abiotic Fe(II) reduction (from Fe(II) diffusing out of reducing continental shelf sediments) also contributes to Cr reduction in addition to the microbial reduction mechanism.

Two sediment cores collected in the shelf off Rio de Janeiro (RJ13-01B: 10.8 cal kyr BP, and RJ13-02B: 4.7 cal kyr BP) were investigated in high-resolution to evaluate changes in sedimentary processes and paleoclimatic and paleoceanographic variability during the Holocene in the Southeastern Brazil. Information from inorganic proxies of continental input (Al/Ca and Fe/Ca), redox-sensitive elements (Fe/Al, V/Al and Mn/Al), paleoproductivity (Sr/Al, Cd/Al and Ba/Al), as well as data for grain size, geophysical properties (p-wave velocity, gamma-ray density, acoustic impedance, magnetic susceptibility and porosity), Si, total organic carbon and calcium carbonate were considered. The data revealed three main periods of sediment accumulation: (i) from 10.8 cal kyr BP to 7.6 cal kyr BP the sediment was coarse, Si content was high (27%), the magnetic susceptibility was low and the presence of shell fragments all suggest a period of low continental input and the deposition site was shallow (i.e, lower sea level); (ii) from 7.5 cal kyr BP to 4.6 cal kyr BP the elevated ratios of Al/Ca (0.69 +/- 0.08), Fe/Ca (0.27 +/- 0.04), Sr/Al (31.57 +/- 4.47) x 10(-4), Cd/Al (0.09 +/- 0.03) x 10(-5) and Ba/Al (0.70 +/- 0.16) x 10(-4 )are consistent with a period of maximum sea transgression and elevated influence of the nutrient-rich South Atlantic Central Water (SACW); (iii) from 4.5 cal kyr BP to the present, events of higher fluxes of TOC, Ni, Cu and Zn were observed from ca 3.2 cal kyr BP to 3.4 cal kyr BP, in both cores, related to humid climate. Overall, the multi-proxy approach shed light on the effects of climate and oceanographic variability on sediment input and accumulation in a less-studied portion of the Brazilian shelf, which are consistent with other shelf areas and with changes in regional climate systems like the Intertropical Convergence Zone (ITCZ), South American Monsoon Systems (SAMS) and South Atlantic Convergence Zone (SACZ).

The environmental impacts of the urban expansion in Rio de Janeiro was evaluated based on the historical accumulation of black carbon (BC), aliphatic (AHs) and aromatic hydrocarbons (PAHs) and sterols in a sediment core retrieved from Botafogo Cove. BC related to oil combustion sources increased significantly since the 1990s. AHs were associated with petroleum inputs and revealed a high level of contamination. Multivariate statistical methods (a Principal Component Analysis associated with a linear multiple regression - PCA/LMR) applied to PAHs suggests changes in the sources in recent years. This can be ascribed to a reduction in pyrogenic emissions over the last four decades and to an increase in petrogenic inputs since the 1990s. The sterol dinosterol registered the increased eutrophication over the last three decades, but the sewage marker coprostanol was present at relatively low concentrations (0.40 to 1.16 mu g g(-1)) probably caused by enhanced bacterial activity in the sediment.

Fluxes of lead (Pb), mercury (Hg), and several other elements into the oceans have been significantly increased by human activities. Of these, only Pb has a well documented history of this increase based on atmospheric flux estimates, ocean water column measurements, and historical archives such as corals and ocean sediments. Most of the Pb in the ocean today is from human emissions. Sedimentary and ice core archives and atmospheric measurements document the Hg increase, but accurate water column measurements are available only recently. For other elements, there are clear increases in some archives and in coastal environments, but not for the open ocean.