The Effect of Hexavalent Chromium on the Incidence and Mortality of Human Cancers: A Meta-Analysis Based on Published Epidemiological Cohort Studies

Background: Hexavalent chromium [Cr(VI)] is an occupational carcinogen that can cause lung and nasal cancers, but its association with mortality and incidence in many other cancers is unclear.Objectives: In this meta-analysis, we aimed to evaluate the relationship between exposure to Cr(VI) and the mortality and incidence of human cancers.Methods: We performed a search of the literature and extracted the standardized mortality ratios (SMRs), standardized incidence ratios (SIRs), and their corresponding 95% confidence intervals (CIs), to estimate risk values. Subgroup analyses were conducted by sex, occupation, and types of cancer to identify groups that were at high-risk or predisposed to certain cancers.Results: A total of 47 cohort studies covering the period 1985–2016 were included (37 studies reporting SMRs and 16 studies reporting SIRs). The summary SMR for all studies combined was 1.07 (95% CI: 1.01–1.15). Summary SMRs were higher among chromate production workers, chrome platers, and masons, and especially male workers. In the subgroup analysis, Cr(VI) exposure was related to a higher risk of death owing to lung, larynx, bladder, kidney, testicular, bone, and thyroid cancer. The meta-SIR of all studies combined was 1.06 (95% CI: 1.04–1.09). Summary SIRs were elevated among cement industry workers and tanners. Cr(VI) exposure was related to an elevated risk of respiratory system, buccal cavity, pharynx, prostate, and stomach cancers.Conclusions: Cr(VI) might cause cancers of the respiratory system, buccal cavity and pharynx, prostate, and stomach in humans, and it is related to increased risk of overall mortality owing to lung, larynx, bladder, kidney, testicular, bone, and thyroid cancer. In addition, there was a strong association between incidence and mortality risk of cancers and concentration of Cr(VI) in the air and the exposure time

Modeling Hidden Nodes Collisions in Wireless Sensor Networks: Analysis Approach

This paper studied both types of collisions. In this paper, we show that advocated solutions for coping with hidden node collisions are unsuitable for sensor networks. We model both types of collisions and derive closed-form formula giving the probability of hidden and visible node collisions. To reduce these collisions, we propose two solutions. The first one based on tuning the carrier sense threshold saves a substantial amount of collisions by reducing the number of hidden nodes. The second one based on adjusting the contention window size is complementary to the first one. It reduces the probability of overlapping transmissions, which reduces both collisions due to hidden and visible nodes. We validate and evaluate the performance of these solutions through simulations

Persistent sulfate formation from London Fog to Chinese haze

Sulfate aerosols exert profound impacts on human and ecosystem health, weather, and climate, but their formation mechanism remains uncertain. Atmospheric models consistently underpredict sulfate levels under diverse environmental conditions. From atmospheric measurements in two Chinese megacities and complementary laboratory experiments, we show that the aqueous oxidation of SO2 by NO2 is key to efficient sulfate formation but is only feasible under two atmospheric conditions: on fine aerosols with high relative humidity and NH3 neutralization or under cloud conditions. Under polluted environments, this SO2 oxidation process leads to large sulfate production rates and promotes formation of nitrate and organic matter on aqueous particles, exacerbating severe haze development. Effective haze mitigation is achievable by intervening in the sulfate formation process with enforced NH3 and NO2 control measures. In addition to explaining the polluted episodes currently occurring in China and during the 1952 London Fog, this sulfate production mechanism is widespread, and our results suggest a way to tackle this growing problem in China and much of the developing world

4-Methyl-24-Ethylcholestane in Upper Permian Fossil Conifer Wood from Paleo-Midlatitude of NE Pangea, Wutonggou Low-Order Cycle, Southern Bogda Mountains, NW China

The use of C30 4-methylsteranes as an indicator of source organic matter relies on accurate identification of the compounds from their isomers and distribution of their precursors (i.e. sterols) in contributing organisms. C30 4-methylsteranes have been reported in many Mesozoic and pre-Mesozoic samples but not in Permian rocks. They may be produced from dinoflagellates or aquatic plants or methylotrophic bacteria. Significant amount of C30 4-methylsteranes was detected in preserved materials in two Upper Permian fossil conifer stems. The 4- methylsteranes have a 4-methyl-24-ethylcholestane structure, without 4α, 23, 24-trimethylcholestanes (also known as dinosteranes). The preservation of C30 4-methylsteranes with C29 steranes and absence of C27-28 steranes with rare hopanes suggest that the 4-methyl sterols produced by conifers may be an important potential precursor for 4-methylsteranes. Alternative sources include freshwater dinoflagellates or methylotrophic bacteria in the environments where the conifers lived, transported, and deposited. Significant amount of C30 4-methylsteranes in Permian fossil conifer in fluvial-lacustrine environments shows that regarding the 4-methylsteranes as an indicator of diagnostic marine input can lead to erroneous conclusions. The rarity of this biomarker in geological records makes it an effective proxy for nonmarine sequence stratigraphic correlation and oil-oil and oil-source rock correlation