Uncertainties in Pollution and Risk Assessments of Heavy Metals in Lake Sediments Using Regional Background Soils in China.

Background soils are frequently utilized as a surrogate to assess pollution levels and environmental risks of heavy metals in Chinese lakes. However, there remains a lack of understanding regarding the reliability and uncertainty of such assessments. Here, we determined heavy metals (As, Cd, Co, Cr, Cu, Hg, Ni, Pb, and Zn) in sediment cores from five rural lakes in North China to evaluate the reliability and uncertainty of the assessments using background soils by comparing them with assessments based on background sediments. Comparative studies reveal large uncertainties in the assessments using background soils. Among these metals, uncertainties for Hg and Cd are relatively large, whereas those for the other metals are minor. This discrepancy is due to the considerably higher natural variability of Hg and Cd in soils and sediments in comparison to the other metals. Generally, assessments utilizing background soils underestimate pollution levels and risks of Hg but overestimate those of Cd in these lakes. Despite limited human activities around the lakes, they still received a considerable influx of heavy metals via regional atmospheric transport. Assessments of the nine metals indicate moderate to considerable ecological risks in these lakes. The risks are contributed primarily (78-89%) by Hg and Cd. This study underscores the substantial uncertainties in assessing heavy metal pollution and risks using regional background soils and emphasizes the importance of controlling atmospheric emissions of Hg and Cd to mitigate pollution in rural and remote water bodies in China.

Two-century sediment records of atmospheric mercury variations in North China and their relations with regional and global emissions.

Sedimentary mercury (Hg) records from remote areas are significant for revealing historical variations of regional Hg and understanding the influence of regional and global Hg emissions. In this study, sediment cores were retrieved from two subalpine lakes in Shanxi Province in North China and employed to reconstruct atmospheric Hg variations over the last two centuries. The two records show similar anthropogenic Hg fluxes and evolution trends, corresponding with that they were affected mainly by regional atmospheric Hg deposition. Before ~1950, the records show negligible Hg pollution signals. Atmospheric Hg in the region had increased rapidly since the 1950s, lagged more than a half-century compared to the global Hg. This indicates that they were seldom affected by Hg emissions dominated by Europe and North America after the industrial revolution. The Hg increases since the 1950s in the two records corresponded well with rapid industrial developments in and around Shanxi Province after the founding of the China, implying the dominant contribution of domestic Hg emissions. By comparing other Hg records, we find that widespread increases in atmospheric Hg in China likely occurred post ~1950. This study rouses to re-examine historical variations in atmospheric Hg at various settings, which is significant to understanding global Hg cycling in the industrial era.

Sediment records of black carbon variations over the last two centuries in North China.

Reconstructing historical black carbon (BC) variations based on sedimentary records are significant for understanding long-term BC emissions, tracing sources, and establishing effective strategies for pollution control. By comparing BC profiles between four lake sediment cores, historical BC variations were reconstructed on the southeastern Mongolian Plateau in North China. Except one, the other three records show close fluxes and similar temporal trends of soot, indicating their repetitiveness on revealing historical variations at a regional scale. Unlike soot, char and BC in these records, derived mainly from local sources, reflected the occurrence of natural fires and human activities near the lakes. Before the ∼1940s, these records showed no well-established anthropogenic BC signals except some occasional natural-related increases. This was different from the global BC increased since the Industrial Revolution, indicating a negligible influence of transboundary BC on the region. Anthropogenic BC in the region had increased since the 1940s-1950s ascribed to emissions from Inner Mongolia and nearby provinces. The increases were moderate in the 1950s-1970s, corresponded with the initial development of industry after the founding of the P.R. China. The most pronounced BC increases occurred in 1980s-2016, commensurate with rapid socio-economic development after the Reform and Opening-up in 1978. Different from model estimations on Chinese BC emissions, our records show unexpected BC increases in recent two decades caused by pollutant emission rises in this undeveloped region. This suggests that BC emissions in relatively small cities and rural areas in China were likely underestimated and their role on national BC cycling needs to be reassessed.

Sediment records of global and regional Hg emissions to the atmosphere in North China over the last three centuries.

Reconstructing the long-term Hg history in major emission countries is important for understanding the global Hg cycle and controlling Hg pollution. In this study, the atmospheric Hg history was reconstructed over the last three centuries based on three lacustrine sediment records from southeastern Inner Mongolia in North China, and its relationship with global and regional Hg emissions was revealed. These records show little Hg pollution in the 18th and 19th centuries. This implies a limited influence of Hg emitted from Europe and North America in this region, which is confirmed by their different Hg trends during the two World Wars and the post-1970s. Atmospheric Hg in the region had increased gradually since the 1900s, primarily contributed by emissions from the former Soviet Union in Lake Dalihu (DLH) and Lake Zhagesitai (ZGST) and from the Beijing-Tianjin-Hebei region in Lake Kulunnao (KLN). In the last century, two decreases in Hg fluxes occurred in the KLN core due to the economic recession in the 1960s-1970s and reduced energy consumption and industrial production in the 1990s. In the DLH and ZGST cores, only one decrease occurred, corresponded with the dissolution of the Soviet Union in the 1990s. Although atmospheric Hg emissions in China had stabilized or even decreased in the last decade, atmospheric Hg continued to increase, particularly in KLN, because of emissions from small cities in the region. This study can help understand Hg sources and control Hg pollution in North China and supplement the understanding of the global Hg cycling.

Spatiotemporal trends of atmospheric Pb over the last century across inland China.

Sedimentary records from remote regions contain pollutants derived dominantly from atmospheric input, and thus have the potential to trace past atmospheric pollution history. Based on seventeen sediment records from relatively remote areas of China, atmospheric Pb pollution history during the last century was studied. These records suggest only occasionally slight pollution before ~1950 and display synchronous Pb enrichment processes since the 1950s, implying the start of widespread atmospheric Pb pollution in China. This corresponded well with the beginning of socio-economic development after the establishment of the People's Republic of China. However, owing to the Chinese Cultural Revolution, a roughly unchanged atmospheric Pb status was found in the 1960-70s except on the Qinghai-Tibetan Plateau, where atmospheric Pb still increased gradually caused by long-range atmospheric transport of pollutants from southwest Asia. In ~1980-2000, atmospheric Pb experienced the greatest increase, resulting from rapid development of extensive economy after the Reform and Opening-up in 1978. After ~2000, atmospheric Pb generally stopped increase due to the phasing out of leaded gasoline, but it remained high, with the highest in Southwest China, medium in Northeast China, central North China and the Qinghai-Tibetan Plateau, and the lowest in the southeast Mongolia Plateau and West China. This study reveals spatio-temporal variations of atmospheric Pb in inland China under the influence of recent human activities, providing an important supplement for understanding global Pb pollution in the Anthropocene.

Effect of Molybdenum on Plant Physiology and Cadmium Uptake and Translocation in Rape (Brassica napus L.) under Different Levels of Cadmium Stress.

This study investigated the beneficial effect of molybdenum (Mo) application on rape plants (Brassica napus L.) grown in a soil polluted by cadmium (Cd). A pot experiment was conducted to determine how different concentrations of exogenous Mo (0, 50, 100, and 200 mg/kg) affect plant physiology, biomass, photosynthesis, cation uptake, and Cd translocation and enrichment in rape plants under Cd stress (0.5 and 6.0 mg/kg). Under single Cd treatment, plant physiological and biochemical parameters, biomass parameters, leaf chlorophyll fluorescence parameters, and macroelement uptake of rape plants decreased, while their malonaldehyde content, proline content, non-photochemical quenching coefficient, and Cd uptake significantly increased, compared to those of the control group (p-values < 0.05). High-Cd treatment resulted in much larger changes in these parameters than low-Cd treatment. Following Mo application, the accumulation of malondialdehyde and proline decreased in the leaves of Cd-stressed plants; reversely, the contents of soluble protein, soluble sugar, and chlorophyll, and the activities of superoxide dismutase and glutathione peroxidase, all increased compared to those of single Cd treatment (p-values < 0.05). Exogenous Mo application promoted shoot and root growth of Cd-stressed plants in terms of their length, fresh weight, and dry weight. The negative effect of Cd stress on leaf chlorophyll fluorescence was substantially mitigated by applying Mo. Exogenous Mo also improved the uptake of inorganic cations, especially potassium (K+), in Cd-stressed plants. After Mo application, Cd uptake and accumulation were inhibited and Cd tolerance was enhanced, but Cd translocation was less affected in Cd-stressed plants. The mitigation effect of Mo on Cd stress in rape was achieved through the immobilization of soil Cd to reduce plant uptake, and improvement of plant physiological properties to enhance Cd tolerance. In conclusion, exogenous Mo can effectively reduce Cd toxicity to rape and the optimal Mo concentration was 100 mg/kg under the experimental conditions.

Historical variation of black carbon and PAHs over the last ~200 years in central North China: Evidence from lake sediment records.

As the largest coal-producing province in China, the coal production of Shanxi Province accounts for one third of the country's total. Thus it is of great importance to study the pollution history of typical pollutants in Shanxi Province and their links with energy usage in North China. Sediment cores from two relatively remote lakes in central North China were retrieved to investigate historical evolutions of black carbon (BC) and polycyclic aromatic hydrocarbons (PAHs) in the last ~200 years. The two records show several-fold increases in both concentrations and depositional fluxes of BC, char, soot, and PAHs in recent five decades, which were associated with the influence of anthropogenic activities resulting from socio-economic development in Shanxi Province. However, after ~2000 their fluxes decreased sharply due to China's effort on environmental protection. These changes indicate that atmospheric BC and PAHs loads in the region were affected significantly by recent anthropogenic activities and environmental policies. Ratios of individual PAHs and char/soot indicate pyrogenic sources of these increased pollutants in recent decades, with coking industry and coal combustion as the two major sources. Significant positive correlations between BC and PAHs were observed in both cores of Lake Gonghai and Lake Mayinghai, indicating that they were likely co-transported by BC particles from similar sources. This study provides new and important understanding of the atmospheric pollution history of BC and PAHs in North China.

One-century sediment records of heavy metal pollution on the southeast Mongolian Plateau: Implications for air pollution trend in China.

Historical records of heavy metals from remote areas are important for assessing temporal pollution trends of the regional atmosphere. Based on comparison analyses of heavy metals, Pb isotopes, and total carbon in sediment cores from two relatively remote lakes on the southeast Mongolian Plateau, atmospheric heavy metal pollution trends during ∼1900-2016 were reconstructed. The current anthropogenic fluxes of Zn, Cd and Pb in the region are 11.7, 0.104 and 2.44 mg m-2 yr-1, respectively, close to those in Lake Sayram in West China, but lower than most other records in China. Anthropogenic metal fluxes and 206Pb/207Pb ratios suggest that (1) before ∼1950 atmospheric metal pollution was negligible in the region; (2) since ∼1950, the pollution became detectable but was relatively slight until ∼1980, corresponded with the beginning of socio-economic development after the foundation of China in 1949 and the rapid development after the Reform and Opening-up in 1978; and (3) since ∼2000, atmospheric Pb stopped increasing because of the phasing out of leaded gasoline. Based on comparison and fitting analyses with other sediment records, a similar four-stage evolution picture of atmospheric heavy metals in China over the last century was uncovered. This study indicates rapid increase trends of atmospheric heavy metals in China since ∼1980 associated with economic development.

Sedimentary biogeochemical record in Lake Gonghai: Implications for recent lake changes in relatively remote areas of China.

Owing to rapid socio-economic development and climate warming, lakes even in remote areas have experienced marked changes in the last century. However, there are few studies revealing the multi-faceted biogeochemical changes and disentangling impacts of human and climate in relatively remote lakes in China. In this study we reconstructed historical changes of geochemistry, nutrition, primary production, ecology, and pollution in an alpine lake (Gonghai) in central North China, and revealed coherent changes and drivers in relatively remote Chinese lakes by compiling other records. Results show that Lake Gonghai has experienced considerably biogeochemical changes since the 1980s induced mainly by increased regional human activities, with detected human-related changes occurring in the 1950s-70s. The most important change is a shift of diatom primary producers in the 1980s, caused mainly by an increase of regional atmospheric N and P deposition associated with rapid socio-economic development. Another remarkable change is the increase of pollution levels since the 1980s, represented by heavy metals, also caused by atmospheric deposition. Compiled sediment records demonstrate similar biogeochemical changes in most lakes from relatively remote areas of China since the 1970s-80s, associated closely with increased inputs of human-induced atmospheric N, P and pollutants, whereas the influence of climate warming is likely limited. This study highlights markedly human-related biogeochemical changes in relatively remote Chinese lakes during the Anthropocene epoch.

Heavy Metal Pollution in Settled Dust Associated with Different Urban Functional Areas in a Heavily Air-Polluted City in North China.

Understanding variations of heavy metals in atmospheric particles between different functional areas is significant for pollution control and urban planning in cities. To reveal pollution and spatial distribution of heavy metals in atmospheric particles from different urban functional areas in Shijiazhuang in North China, 43 settled dust samples were collected over the main urban area and heavy metal concentrations were determined in their <63 µm fractions using an ICP-OES. The results suggest that Cr, Mn, Fe, Co, Ni, and V in the dust are not or slightly enriched and their concentrations vary slightly between different sites, implying their natural origins; whereas Cu, Zn, Cd, and Pb are often notably enriched and their concentrations vary significantly between different functional areas, indicating their anthropogenic sources. Integrated pollution indexes (IPIs) of the ten heavy metals are 2.7-13.6 (5.7 ± 2.2), suggesting high or very high pollution levels of most dust. Relatively lower IPIs occur mainly in the administration-education area, the commercial area, and other unclassified sites; while peaks occur mainly in the North Railway Station, the northeastern industrial area, and some sites near heavily trafficked areas, implying the significant influence of intensive industrial (including coal combustion) and traffic activities on atmospheric heavy metal accumulation. These results suggest a clear need of mitigating atmospheric heavy metal pollution via controlling emissions of toxic metals (especially Cd and Pb) from industrial and traffic sources in the city.

Preliminary Assessment of Health Risks of Potentially Toxic Elements in Settled Dust over Beijing Urban Area.

To examine levels, health risks, sources, and spatial distributions of potentially toxic elements in settled dust over Beijing urban area, 62 samples were collected mostly from residential building outdoor surfaces, and their <63 µm fractions were measured for 12 potentially toxic elements. The results show that V, Cr, Mn, Co, Ni, and Ba in dust are from predominantly natural sources, whereas Cu, Zn, As, Cd, Sb, and Pb mostly originate from anthropogenic sources. Exposure to these elements in dust has significant non-cancer risks to children but insignificant to adults. Cancer risks of Cr, Co, Ni, As, and Cd via inhalation and dermal contact are below the threshold of 10(-6)-10(-4) but As via dust ingestion shows a tolerable risk. The non-cancer risks to children are contributed mainly (75%) by As, Pb, and Sb, and dominantly (92%) via dust ingestion, with relatively higher risks mainly occurring in the eastern and northeastern Beijing urban areas. Although Cd, Zn, and Cu in dust are heavily affected by anthropogenic sources, their health risks are insignificant. Source appointments suggest that coal burning emissions, the dominant source of As, are likely the largest contributors to the health risk, and traffic-related and industrial emissions are also important because they contribute most of the Pb and Sb in dust.