Impact of drinking water hardness on carotid atherosclerosis and arterial stiffness: Insights from the "Corinthia" study.

BACKGROUND: Several investigations have highlighted the role of water quality in cardiovascular health. In the present study, we have investigated the effects of drinking water hardness on atherosclerotic burden in carotid arteries and arterial stiffness. METHODS: "Corinthia" study was conducted in the homonym region in Greece from 2015 to 2017. Carotid atherosclerosis was assessed by intima-media thickness (IMT). Pulse wave velocity (PWV) was used to evaluate arterial stiffness. Tap-water samples were collected from the study area and analyzed for a variety of elements, as well as pH and total hardness. RESULTS: Individuals living in lower drinking water hardness areas (Area 1) versus individuals living in higher water hardness areas (Area 2) had lower max IMT (p = 0.004) and were less susceptible to carotid plaque formation (p = 0.004). Interestingly, individuals over 65 years from Area 1 had lower mean IMT, max IMT, and less plaque formation (p < 0.001 for all). The mean value of PWV in the overall study population was below the 10 m/s cutoff, which defines arterial stiffness (9.15 ± 2.79 m/s). Nevertheless, a marginally higher rate of vascular stiffening was noted in Area 2 vs. Area 1 (16.2% and 12.8%, respectively, p = 0.048). CONCLUSIONS: According to this cross-sectional study's findings, a positive association between extra hard water and carotid atherosclerotic burden was found. However, the association with arterial stiffness is unclear and should be investigated further.

Do humans take good care of their offspring as animals do ! The Lavreotiki and Lavrion 'sagas', Hellenic Republic-Part 1: Historical outline and mapping of lead contamination.

The Lavreotiki-Lavrion area, situated in the south-eastern tip of mainland Hellas, has one of the longest mining, ore beneficiation and smelting legacies worldwide. With a history of over 5000 years of argentiferous Pb-Zn ore exploitation, Lavrion is a place that shaped human civilisation by being a major wealth producing centre of the ancient world but also represents one of the few significant industrial developments of the modern Hellenic Republic, since the second part of the 19th century. The long history of mining, ore beneficiation and smelting activities produced a vast amount of potentially toxic wastes. In the post-mining era of Lavrion, during the 1980's, cross-sectional epidemiological studies diagnosed a severe problem of blood-Pb poisoning in primary school-age children and highlighted the seriousness of environmental contamination on the health of the local population. The first part of this review deals with the contamination problem in the area with respect to Pb, and discusses the results of detailed geochemical and epidemiological studies, based on the source-pathway-receptor model. The second part of the review presents the holistic evaluation of the contamination hazard, the assessment of health-related risk to residents, and the socio-economical impact of the proposed remediation plan to the local community. The case of Lavrion-Lavreotiki area is a worldwide reference example of the environmental, economical, societal and health-related implications that the thousand-years long legacy of mineral resources exploitation has left behind.

Do humans take good care of their offspring as animals do ! the Lavreotiki and Lavrion 'sagas', Hellenic Republic-Part 2: hazard and risk assessment and remediation.

A number of geochemical and epidemiological studies verified that the Lavrion urban and suburban area is highly contaminated and has affected to a variable degree the health of the inhabitants, presented in the first part of review on the Lavrion 'sagas'. In the second part of this review, emphasis is given to the challenge environmental scientists faced in communicating the scientific results to environmental managers and the public and state officials in order for them to understand the benefits of prioritising public health over wealth. Imminent remediation actions have been developed and proposed in order to secure a healthier life for the local population. The proposed integrated environmental management scheme was based on the findings of hazard and health risk assessment. The aim was not only to remediate the contaminated land, but also to inform the local population and authorities regarding the environmental hazards that they were facing, and the necessary safety measures that should be taken. However, the proposed lifestyle changes were viewed with scepticism from all stakeholders. This paper seeks to provide some answers to questions related to the obstacles that have prevented the implementation of the proposed remediation plan on a large scale by reporting on risk perception and response to scientific evidence by the affected community in Lavrion. It also underlines the significant role of SEGH in linking applied environmental research with the public.

Estimating remobilization of potentially toxic elements in soil and road dust of an industrialized urban environment.

The mobility of potentially toxic elements (PTEs) is of paramount concern in urban settings, particularly those affected by industrial activities. Here, contaminated soils and road dusts of the medium-size, industrialized city of Volos, Central Greece, were subjected to single-step extractions (0.43 M HNO3 and 0.5 M HCl) and the modified BCR sequential extraction procedure. This approach will allow for a better understanding of the geochemical phase partitioning of PTEs and associated risks in urban environmental matrices. Based on single extraction procedures, Pb and Zn exhibited the highest remobilization potential. Of the non-residual phases, the reducible was the most important for Pb, and the oxidizable for Cu and Zn in both media. On the other hand, mobility of Ni, Cr, and Fe was low, as inferred by their dominance into the residual fraction. Interestingly, we found a significant increase of the residual fraction in the road dust samples compared to soils. Carbonate content and organic matter controlled the extractabilities of PTEs in the soil samples. By contrast, for the road dust, magnetic susceptibility exerted the main control on the geochemical partitioning of PTEs. We suggest that anthropogenic particles emitted by heavy industries reside in the residual fraction of the SEP, raising concerns about the assessment of this fraction in terms of origin of PTEs and potential environmental risks. Conclusively, the application of sequential extraction procedures should be complemented with source identification of PTEs with the aim to better estimate the remobilization of PHEs in soil and road dust influenced by industrial emissions.

Identification of sources and transformations of nitrate in Cr(VI)-impacted alluvial aquifers by a hydrogeochemical and δ15N-NO3- and δ18O-NO3 - isotopes approach.

A coupled methodology of nitrogen isotopes, hydrogeochemical characterization, multivariate statistical analysis, and SIAR Bayesian modeling has been employed to identify the sources of NO3- and N transformation processes in three alluvial aquifers (Schinos, Thiva, and Central Evia) located in central Greece where geogenic Cr(VI) co-occurs with agricultural activity and rural development. Hexavalent chromium concentrations exceed 50 µg/L in many sampling stations of the studied groundwater bodies, while nitrate contamination is evident in all three study areas with concentrations well over 50 mg/L. The mean δ15N-NO3- and δ18Ο-NO3- values are 6.67 ± 1.77‰ and 2.68 ± 1.77‰ in C. Evia, 8.72 ± 4.74‰ and 3.96 ± 4.57‰ in Schinos and 4.44 ± 1.71‰ and 2.91 ± 1.02‰ in Thiva, respectively. Domestic sewage and N-bearing fertilizers are contributing in various degrees to the observed nitrification which is the dominant transformation process of N in the studied aquifers. Multivariate statistics indicated that the main processes identified in the study areas are salinization, silicate dissolution, and groundwater contamination due to fertilizer use. It is suggested that ultramafic rock-related alluvial aquifers must be closely monitored in terms of nutrient inputs as an effective measure for controlling Cr(VI) release in groundwater.

Assessing the contamination level, sources and risk of potentially toxic elements in urban soil and dust of Iranian cities using secondary data of published literature.

Research in urban geochemistry has been expanding globally in recent years, following the trend of the ever-increasing human population living in cities. Environmental problems caused by non-degradable pollutants such as metals and metalloids are of particular interest considering the potential to affect the health of current and future urban residents. In comparison with the extensive global research on urban geochemistry, Iranian cities have not received sufficient study. However, rapid and often uncontrolled urban expansion in Iran over recent years has contributed to an increasing number of studies concerning contamination of urban soil and dust. The present work is based on a comprehensive nationwide evaluation and intercomparison of published quantitative datasets to determine the contamination levels of Iranian cities with respect to potentially toxic elements (PTEs) and assess health risks for urban population. Calculation of geoaccumulation, pollution, and integrated pollution indices facilitated the identification of the elements of most concern in the cities, while both carcinogenic and non-carcinogenic risks have been assessed using a widely accepted health-risk model. The analysis of secondary, literature data revealed a trend of contamination, particularly in old and industrial cities with some alarming levels of health risks. Among the elements of concern, As, Cd, Cu, and Pb were found to be most enriched in soils and dusts of the studied cities based on the calculated geochemical indices. The necessity of designing strategic plans to mitigate possible adverse effects of elevated PTE concentrations in urban environments is emphasized considering the role of long-term exposure in the occurrence of chronic carcinogenic and non-carcinogenic health problems.

International Analysis of Sources and Human Health Risk Associated with Trace Metal Contaminants in Residential Indoor Dust.

People spend increasing amounts of time at home, yet the indoor home environment remains understudied in terms of potential exposure to toxic trace metals. We evaluated trace metal (and metalloid) concentrations (As, Cu, Cr, Mn, Ni, Pb, and Zn) and health risks in indoor dust from homes from 35 countries, along with a suite of potentially contributory residential characteristics. The objective was to determine trace metal source inputs and home environment conditions associated with increasing exposure risk across a range of international communities. For all countries, enrichments compared to global crustal values were Zn > Pb > Cu > As > Cr > Ni; with the greatest health risk from Cr, followed by As > Pb > Mn > Cu > Ni > Zn. Three main indoor dust sources were identified, with a Pb-Zn-As factor related to legacy Pb sources, a Zn-Cu factor reflecting building materials, and a Mn factor indicative of natural soil sources. Increasing home age was associated with greater Pb and As concentrations (5.0 and 0.48 mg/kg per year of home age, respectively), as were peeling paint and garden access. Therefore, these factors form important considerations for the development of evidence-based management strategies to reduce potential risks posed by indoor house dust. Recent findings indicate neurocognitive effects from low concentrations of metal exposures; hence, an understanding of the home exposome is vital.

Tracing the sources of bioaccessible metal(loid)s in urban environments: A multidisciplinary approach.

Understanding the links between sources of magnetic particles and bioaccessibility of metal(loids) in environmental sampling media is crucial for better evaluating human health risks, although relevant information in the scientific literature is scarce. Here, soil, road and house dust samples from a heavy industrial area in Greece were characterized in a multidisciplinary study combining magnetic measurements, SEM/EDS analyses, bioaccessibility measurements and Pb isotopic analyses of bioaccessible Pb. The oral and inhalable bioaccessible fractions of As, Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn were assessed by applying simulated gastric and lung solutions. SEM/EDS analysis revealed the abundant presence of anthropogenic Fe-containing spherules of industrial origin in all sampling media, often containing minor contents of Cr, Cu, Mn, Pb and Zn. The inhalation bioaccessibility (%) in all environmental compartments was higher than the oral one for most elements analyzed in the present study. Clear associations between magnetic susceptibility and bioaccessible amounts of most of analyzed elements were encountered for the soil and road dust. The isotopic analyses of bioaccessible Pb showed that there are significant differences in the isotopic ratios between total and bioaccessible Pb. We conclude that Pb solubilized by the simulated gastric and lung extractions is principally anthropogenic, representing a mixture of industrial Pb and Pb related to the past usage of leaded petrol. Low values of 206Pb/207Pb were accompanied by high bioaccessible contents of Cd, Pb and Zn indicating that anthropogenic (mostly industrial) sources exert influence on the bioaccessible forms of these metals. Coupling magnetic and bioaccessibility measurements with stable isotopic technique of bioaccessible Pb is more reliable for determining Pb and other metal sources with high oral and inhalation bioaccessibility.

A DPSIR Approach to Selected Cr(VI) Impacted Groundwater Bodies of Central Greece.

The holistic approach of Driver-Pressure-State-Impact-Response (DPSIR) methodology was applied to selected Cr(VI) impacted groundwater bodies of Central Greece. The main driving forces in the study areas are agricultural activities, urban and industrial development as well as tourism. The main pressures induced by the anthropogenic activities are fertilizer use, uncontrolled urban sewage disposal and industrial effluents discharges. Groundwater stress is caused by the qualitative degradation due to Cr(VI), NO3-, Cl- and SO42- contamination. Hexavalent chromium occurrence is attributed to both geogenic and anthropogenic sources. The maximum Cr(VI) concentration (11.7 mg/L) was measured in Oinofyta area. Important impacts are the deterioration of groundwater body chemical status as well as the decline of groundwater use efficiency. Based on the applied DPSIR, a management framework is proposed in order to address the complex environmental issue of Cr(VI) in the study areas.

Geochemical interactions in the trace element-soil-clay system of treated contaminated soils by Fe-rich clays.

Clays have been widely applied in contaminated soils in order to reduce the mobility of potentially toxic elements (PTEs), such as Pb, Zn and Cu. In the present study, three Fe-rich clays from Greece were selected as amendments of three contaminated soils with distinct physicochemical and mineralogical characteristics. The amendments consisted of palygorskite-rich (PCM), Fe-smectite-rich (SCM) and natural palygorskite/Fe-smectite-rich (MCM) clays. The changes induced in the environment of the soil-PTE-clay system were assessed by examining the water-labile fraction of Pb, Zn and Cu, as well as the bioaccessibility of Pb, in the contaminated soils. The initial water-leachable concentrations of PTEs in soil were within the range 1826-6160 µg/kg Pb, 152-645 µg/kg Cu and 370-4052 µg/kg Zn. All three Fe-rich clays exhibited high retention efficiency toward PTEs, following the order Pb (55-70%) > Zn (45-55%) > Cu (0-45%). The high reactive surface area of the clay particles acted as a substrate for the deposition of Fe-Al oxides with a concomitant removal of PTEs that were transported through the colloidal fraction. Furthermore, the decrease in relative bioaccessibility of Pb (5-10% compared to the control) suggests dissolution of primary clays followed by entrapment of the element in secondary Fe-rich precipitates. In conclusion, the use of Fe-rich clays as soil amendments may have a positive effect in reducing the environmentally significant PTE fraction in soils, especially when different clay phases coexist.

Hexavalent chromium leads to differential hormetic or damaging effects in alfalfa (Medicago sativa L.) plants in a concentration-dependent manner by regulating nitro-oxidative and proline metabolism.

Chromium has been proven to be extremely phytotoxic. This study explored the impacts of increasing Cr(VI) exposure (up to 10 mg L-1 K2Cr2O7) on the growth and development of alfalfa plants and adaptation responses employed, in an environmentally relevant context. The threshold concentration of K2Cr2O7 in irrigation water beyond which stress responses are initiated is 1 mg L-1. Lower Cr(VI) exposure (0.5 mg L-1 K2Cr2O7) induced hormesis, evident through increased biomass and larger leaves, likely mediated by increased NO content (supported by elevated NR enzymatic activity and overexpression of NR and ndh genes). Elevated Cr(VI) exposure (5 and 10 mg L-1 K2Cr2O7) resulted in reduced biomass and smaller leaves, and lower levels of photosynthetic pigment (10 mg L-1 K2Cr2O7). Higher levels of lipid peroxidation, H2O2 and NO contents in these plants suggested nitro-oxidative stress. Stress responses included increased SOD and CAT enzymatic activities, further supported to some extent by MnSOD, FeSOD, Cu/ZnSOD and CAT transcripts levels. GST7 and GST17 gene expression patterns, as well as proline content, P5CS enzymatic activity and corresponding P5CS and P5CR gene expression levels emphasized the role of proline and GSTs in the adaptation responses. Results highlight the importance of managing Cr(VI) levels in irrigation water.

Metal(loid) and isotopic tracing of Pb in soils, road and house dusts from the industrial area of Volos (central Greece).

This study examines the metal(loid) contents (As, Cd, Cr, Cu, Mn, Ni, Pb, Sb, Tl and Zn) and Pb isotopes in different environmental compartments (soil, road dust, house dust) from the industrial vicinity of Volos, central Greece. The area surrounding two steel factories, a cement plant, an industrial area and the city core were considered as potential hot spots of metal(loid) contamination. Significant anthropogenic enrichments of Cd, Pb and Zn in relation to local baseline were identified for the soil (median Enrichment Factors of 7, 15 and 8, respectively) and road dusts around the steel factory located at Velestino area. The high contents of As, Sb and Tl in the soil and road dust around the cement plant are attributed to natural sources of contamination associated with adjacent mineralization. The soil samples in the city core exhibited moderate enrichments with respect to typical tracers (Pb, Zn) of anthropogenic contamination in urban areas. Anthropogenic influences in terms of metal(loid) concentrations were more pronounced for the road and house dust material. The Pb isotopic ratios of soil (206Pb/207Pb = 1.154 to 1.194), road dust (206Pb/207Pb = 1.144 to 1.174) and house dust (206Pb/207Pb = 1.129 to 1.171) were between those of the local bedrock and anthropogenic Pb sources. Industrial Pb from the steel plant was the predominant anthropogenic Pb source with relative contributions of ~49% for the soil, ~42% for the road dust and ~44% for the house dust samples. For the road and house dust material, the geochemical signature obtained from Pb isotopic compositions and elemental ratios suggests additional contributors from vehicular emissions. The results of this study demonstrate the suitability of soil to trace natural and anthropogenic impacts in industrial areas and the sensitivity of the road and house dust material to record anthropogenic (industrial and vehicular-derived) contamination in such environments.

Tracking the occurrence of anthropogenic magnetic particles and potentially toxic elements (PTEs) in house dust using magnetic and geochemical analyses.

The influence of anthropogenic outdoor sources on the geochemical composition of house dust material in large cities is poorly understood. In this study, we investigate the magnetic signature and the concentrations of potentially toxic elements (PTEs) in randomly selected house dust samples from the metropolitan area of Athens, the most populated city in Greece. Environmental magnetic measurements, including isothermal remanent magnetization and thermomagnetism, indicated that the main magnetic mineral is coarse-grained low-coercivity magnetite. Detailed microscopic observations of the magnetically extracted material revealed the presence of three different kinds of Fe-rich particles deriving from both combustion-related and non-exhaust vehicular sources: irregularly-shaped grains and spherules of Fe-oxides, and particles consisting of metallic Fe. Further study of the morphology of single anthropogenic magnetic spherules (size > 30 µm) identified the presence of magnetite spherical particles, typically formed by industrial combustion processes. Enrichment factors (EFs) for the PTEs calculated against the Athens urban soil showed that the house dusts were very highly enriched in Cd, Cu, Zn and significantly enriched in Pb (median EF values of 34.1, 26.2, 25.4 and 10.3, respectively). The oral bioaccessibility of PTEs in the house dust, evaluated using a simulated gastric solution (0.4 M glycine), was in the order Pb > Zn > Mn > Cd > Ni > Cu > Cr > Fe. Concentrations of Pb increased with the house age. Principal component and cluster analysis demonstrated the close association of anthropogenic Cu, Pb and Zn with the magnetic susceptibility of the house dusts. We conclude that both traffic-related and industrial sources trigger the occurrence of magnetic Fe/PTEs- rich particles in house dust. These results reinforce the use of environmental magnetism determinations for assessing anthropogenic contamination of PTEs in the indoor environment in large cities.

Arsenic and high affinity phosphate uptake gene distribution in shallow submarine hydrothermal sediments.

The toxicity of arsenic (As) towards life on Earth is apparent in the dense distribution of genes associated with As detoxification across the tree of life. The ability to defend against As is particularly vital for survival in As-rich shallow submarine hydrothermal ecosystems along the Hellenic Volcanic Arc (HVA), where life is exposed to hydrothermal fluids containing up to 3000 times more As than present in seawater. We propose that the removal of dissolved As and phosphorus (P) by sulfide and Fe(III)(oxyhydr)oxide minerals during sediment-seawater interaction, produces nutrient-deficient porewaters containing < 2.0 ppb P. The porewater arsenite-As(III) to arsenate-As(V) ratios, combined with sulfide concentration in the sediment and/or porewater, suggest a hydrothermally-induced seafloor redox gradient. This gradient overlaps with changing high affinity phosphate uptake gene abundance. High affinity phosphate uptake and As cycling genes are depleted in the sulfide-rich settings, relative to the more oxidizing habitats where mainly Fe(III)(oxyhydr)oxides are precipitated. In addition, a habitat-wide low As-respiring and As-oxidizing gene content relative to As resistance gene richness, suggests that As detoxification is prioritized over metabolic As cycling in the sediments. Collectively, the data point to redox control on Fe and S mineralization as a decisive factor in the regulation of high affinity phosphate uptake and As cycling gene content in shallow submarine hydrothermal ecosystems along the HVA.

Modes of carbon fixation in an arsenic and CO2-rich shallow hydrothermal ecosystem.

The seafloor sediments of Spathi Bay, Milos Island, Greece, are part of the largest arsenic-CO2-rich shallow submarine hydrothermal ecosystem on Earth. Here, white and brown deposits cap chemically distinct sediments with varying hydrothermal influence. All sediments contain abundant genes for autotrophic carbon fixation used in the Calvin-Benson-Bassham (CBB) and reverse tricaboxylic acid (rTCA) cycles. Both forms of RuBisCO, together with ATP citrate lyase genes in the rTCA cycle, increase with distance from the active hydrothermal centres and decrease with sediment depth. Clustering of RuBisCO Form II with a highly prevalent Zetaproteobacteria 16S rRNA gene density infers that iron-oxidizing bacteria contribute significantly to the sediment CBB cycle gene content. Three clusters form from different microbial guilds, each one encompassing one gene involved in CO2 fixation, aside from sulfate reduction. Our study suggests that the microbially mediated CBB cycle drives carbon fixation in the Spathi Bay sediments that are characterized by diffuse hydrothermal activity, high CO2, As emissions and chemically reduced fluids. This study highlights the breadth of conditions influencing the biogeochemistry in shallow CO2-rich hydrothermal systems and the importance of coupling highly specific process indicators to elucidate the complexity of carbon cycling in these ecosystems.

Assessing Lead, Nickel, and Zinc Pollution in Topsoil from a Historic Shooting Range Rehabilitated into a Public Urban Park.

Soil contamination is a persistent problem in the world. The redevelopment of a site with a historical deposition of metals might conceal the threat of remaining pollution, especially when the site has become a public place. In this study, human health risk assessment is performed after defining the concentrations of Pb, Ni, and Zn in the topsoil of a former shooting range rehabilitated into a public park in the Municipality of Kesariani (Athens, Greece). A methodology that uses inductively coupled plasma mass spectrometry (ICP-MS, 13 samples), another that uses portable X-ray fluorescence (XRF) following a dense sample design (91 samples), and a hybrid approach that combines both, were used to obtain the concentrations of the trace elements. The enrichment factor and geoacummulation index were calculated to define the degree of pollution of the site. The hazard quotient and cancer risk indicators were also computed to find the risk to which the population is exposed. The present study reveals high non-carcinogenic health risk due to Pb pollution with ingestion as the main exposure pathway. The carcinogenic risk for Pb is within tolerable limits, but the definition of land use might alter such a statement. Lastly, regarding Ni and Zn, the site is unpolluted and there is insignificant carcinogenic and non-carcinogenic risks.

Metal(loid) distribution and Pb isotopic signatures in the urban environment of Athens, Greece.

Lead concentrations and isotopic compositions of contaminated urban soils and house dusts from Athens, Greece, have been determined to identify possible sources of Pb contamination and examine relationships between these two environmental media. Different soil particle sizes (<2000 µm, <200 µm, <100 µm, <70 µm, <32 µm) and chemical fractions (total, EDTA-extractable and acetic acid-extractable (HAc)) were analyzed for their Pb content and isotopic composition. Metal(loid)s (Pb, Zn, Cu, As, Ni, Cr, Mn, Fe) are significantly enriched in the finest fraction. The Pb isotopic compositions were similar for the different soil particle size fractions and different chemical extractions. The HAc extraction proved to be a useful procedure for tracing anthropogenic Pb in urban soil. The range of (206)Pb/(207)Pb ratios (1.140-1.180) in Athens soil suggests that the Pb content represents an accumulated mixture of Pb deposited from past vehicular emissions and local natural sources. The contribution of anthropogenic Pb to total soil Pb ranged from 36% to 95%. The Pb isotopic composition of vacuum house dusts ((206)Pb/(207)Pb = 1.1.38-1.167) from Athens residents is mostly comparable to that of urban soil suggesting that exterior soil particles are transferred into homes. As a result, anthropogenic Pb in house dust from Athens urban environment principally originated from soil particles containing Pb from automobile emissions (former use of leaded gasoline).

Arsenic stress after the Proterozoic glaciations.

Protection against arsenic damage in organisms positioned deep in the tree of life points to early evolutionary sensitization. Here, marine sedimentary records reveal a Proterozoic arsenic concentration patterned to glacial-interglacial ages. The low glacial and high interglacial sedimentary arsenic concentrations, suggest deteriorating habitable marine conditions may have coincided with atmospheric oxygen decline after ~2.1 billion years ago. A similar intensification of near continental margin sedimentary arsenic levels after the Cryogenian glaciations is also associated with amplified continental weathering. However, interpreted atmospheric oxygen increase at this time, suggests that the marine biosphere had widely adapted to the reorganization of global marine elemental cycles by glaciations. Such a glacially induced biogeochemical bridge would have produced physiologically robust communities that enabled increased oxygenation of the ocean-atmosphere system and the radiation of the complex Ediacaran-Cambrian life.