In vitro digestion and DGT techniques for estimating cadmium and lead bioavailability in contaminated soils: influence of gastric juice pH

A sensitivity analysis was conducted on an in vitro gastrointestinal digestion test (i) to investigate the influence of a low variation of gastric juice pH on the bioaccessibility of Cd and Pb in smelter-contaminated soils (F_B, using the unified bioaccessibility method UBM) and fractions of metals that may be transported across the intestinal epithelium (F_A, using the diffusive gradient in thin film technique), and (ii) to provide a better understanding of the significance of pH in health risk assessment through ingestion of soil by children. The risk of metal exposure to children (hazard quotient, HQ) was determined for conditions that represent a worst-case scenario (i.e., ingestion rate of 200 mg day^− 1) using three separate calculations of metal daily intake: estimated daily intake (EDI), bioaccessible EDI (EDI-F_B), and oral bioavailable EDI (EDI-F_A). The increasing pH from 1.2 to 1.7 resulted in: (i) no significant variation in Cd-F_B in the gastric phase but a decrease in the gastrointestinal phase; (ii) a decrease in soluble Pb in the gastric phase and a significant variation in Pb-F_B in the gastrointestinal phase; (iii) a significant decrease in Cd-F_A and no variation in Pb-F_A; (iv) no change in EDI-F_B and EDI-F_A HQs for Cd; (v) a significant decrease in EDI-F_B HQs and no significant variation in EDI-F_A HQ for Pb. In the analytical conditions, these results show that risk to children decreases when the bioavailability of Pb in soils is taken into account and that the studied pH values do not affect the EDI-F_A HQs. The present results provide evidence that the inclusion of bioavailability analysis during health risk assessment could provide a more realistic estimate of Cd and Pb exposure, and opens a wide field of practical research on this topic (e.g., in contaminated site management).     

一种应用在自耦变压器中的带偏压绕组的有载调压方式

本文中作者介绍了一种应用在三相自耦变压器中的带偏压绕组的有载调压方式,论述了其设计原理及结构布置,并将其与常规的有载调压方式进行了对比。     

Lead,Cadmium And Zinc Accumulation On Soil And Vegetation Along Some Selected Major Roads Of Eastern Cape

Surface soil and grass samples were collected in triplicates from seven locations perpendicular to three major roads in Eastern Cape. Total and available lead, cadmium and zinc were determined in the soil samples and total elements were determined in grass. Lead, cadmium and zinc concentrations declined with distance from road traffic. Significant correlation was also established between available elements in soil and in grass. Levels of total and available elements in the soils ranged from 1167-10834 v µg v g m 1 and from 200-" 5734 v µg v g m 1 , respectively. The levels of the element in grass varied between 200 v µg v g m 1 and 3900 v µg v g m 1 . Total and available cadmium levels in soil although lower than the levels are also significant with values ranging from 17-"2833 v µg v g m 1 and from 27 v µg v g m 1 and from 27-1867 v µg v g m 1 , respectively. The cadmium levels in grass varied between 7 v µg v g m 1 and 1100 v µg v g m 1 . The total and available zinc levels in soil ranged from 2833-8334 v µg v g m 1 and from 533-3600 v µg v g m 1 . The levels in grass varied between 0 and 2800 v µg v g m 1 . The degree of pollution measured would constitute a threat to livestock. Motor traffic appears to be the main source of the elements.     

Water treatment with silicofluorides and lead toxicity

Toxic metals like lead, manganese, copper and cadmium damage neurons and deregulate neurotransmitters like serotonin and dopamine (which are essential to normal impulse control and learning). Earlier studies show that — controlling for socio‐economic and demographic factors — environmental pollution with lead is a highly significant risk factor in predicting higher rates of crime, attention deficit disorder or hyperactivity, and learning disabilities. Exposure and uptake of lead has been associated with industrial pollution, leaded paint and plumbing systems in old housing, lead residues in soil, dietary habits (such as shortages of calcium and iron), and demographic factors (such as poverty, stress, and minority ethnicity). We report here on an additional “risk co‐factor” making lead and other toxic metals in the environment more dangerous to local residents: the use of silicofluorides as agents in water treatment. The two chemicals in question — fluosilicic acid and sodium silicofluoride — are toxins that, despite claims to the contrary, do not dissociate completely and change water chemistry when used under normal water treatment practices. As a result, water treatment with siliconfluorides apparently functions to increase the cellular uptake of lead. Data from lead screening of over 280,000 children in Massachusetts indicates that silicofluoride usage is associated with significant increases in average lead in children's blood as well as percentage of children with blood lead in excess of 10μg/dL. Consistent with the hypothesized role of silicofluorides as enhancing uptake of lead whatever the source of exposure, children are especially at risk for higher blood lead in those communities with more old housing or lead in excess of 15 ppb in first draw water samples where silicofluorides are also in use. Preliminary findings from county‐level data in Georgia confirm that silicofluoride usage is associated with higher levels of lead in children's blood. In both Massachusetts and Georgia, moreover, behaviors associated with lead nurotoxicity are more frequent in communities using silicofluorides than in comparable localities that do not use these chemicals. Because there has been insufficient animal or human testing of silicofluoride treated water, further study of the effect of silicofluorides is needed to clarify the extent to which these chemicals are risk co‐factors for lead uptake and the hazardous effects it produces.     

Technopathogenology: technology and non-evident risks – a contribution to prevention

The concentration of lead in the scalp hair of 257 school children within the age range of 6–12, living in the Manzini region in Swaziland, was measured using a graphite furnace atomic absorption spectrometer. Mean lead concentration ranged between 7.75–9.19 μ.g/g, and 4.95–5.95 μg/g for the urban and rural schools, respectively. The mean lead concentrations in the hair for urban school children were significantly higher than those of the rural school children. The rapid industrialization within the city centre with increasing number of vehicles using leaded petrol may be a contributing factor to the observed levels. Although the mean lead concentration was higher in girls (7.59 μg/g) than in boys (6.62 μg/g), this difference was not statistically significant.     

隧道下穿红线渠施工技术分析

岭西隧道在下穿浅埋、地表河流水量大的红线渠全~强安山玢岩地段时,先以超前地质预报对前方围岩状况进行预判,后以洞身超前大管棚注浆预支护、环形开挖预留核心土法开挖、全断面径向注浆辅以监控量测,成功穿过浅埋、地表河流水量大的全~强安山玢岩地段,获得良好的效果。     

Development of a convective diffusion model for lead pipe rigs operating in laminar flow

As part of achieving lower lead standards water undertakers are utilising lead pipe rigs to quantify the benefit of treatment measures. A convective diffusion model is developed for lead pipe rigs operating in laminar flow, and applied to the three operating steps of flushing, sampling and stagnation. The model is used to determine the appropriate time-scales for each stage, and the sensitivity of the measure to variations in flow-rate. In contrast to rigs operating in turbulent flow the average lead observed leaving the pipe and that in the pipe, after a period of stagnation, are substantially different. Equations are derived for both, and take into account the residual distribution of lead left in the pipe after flushing. It is shown that the lead concentration observed leaving the pipe is well approximated by a single exponential term in contrast to the concentration within the pipe. Predictions are made on the residual lead concentration that can be achieved through flushing, and its dependence on flow-rate. The relevance of the laminar flow model to that in domestic lead pipes is discussed.     

Mobilization of adsorbed copper and lead from naturally aged soil by bacterial extracellular polymers

Sorption of pollutants is a dominant phase transfer process affecting the fate and transport of metals through the subsurface. The movement of contaminants is retarded by sorption to the stationary subsurface porous media and can seriously hinder remediation efforts. Research has shown that the binding of adsorbed metals becomes more pronounced the longer the contaminant is in the subsurface and the release rates of aged metal contaminants have not received the research attention given to freshly added metals in laboratory studies. Metal release rates are also influenced by the presence of dissolved ligands that compete with mineral soil surfaces by providing binding sites. Dissolved organic matter such as bacterial extracellular polymers are common in natural soil solutions and the metal binding properties of bacterial polymers are well established. Therefore, binding of metals to dissolved biopolymers may result in mobilization of an adsorbed metal. This is important for cases where the metals are assumed to be relatively immobile such as in the case of land applied biosolids. In addition, naturally occurring adherent bacteria commonly produce extracellular polymers and thus may modify the bioavailability of meal contaminants at the point of their attachment. In this study samples from three sites, one a land applied sludge test site, were used to investigate the ability of bacterial extracellular polymers to release metals from soils with long-term exposures. The presence of ?200mg/L bacterial extracellular polymer was found to increase the short-term (less than 350h) release of Cu and Pb by a factor of 2-4-fold.     

Comparison of a static and a dynamic in vitro model to estimate the bioaccessibility of As, Cd, Pb and Hg from food reference materials Fucus sp. (IAEA-140/TM) and Lobster hepatopancreas (TORT-2)

Bioaccessibility, the fraction of an element solubilized during gastrointestinal digestion and available for absorption, is a factor that should be considered when evaluating the health risk of contaminants from food. Static and dynamic models that mimic human physiological conditions have been used to evaluate bioaccessibility. This preliminary study compares the bioaccessibility of arsenic (As), cadmium (Cd), lead (Pb) and mercury (Hg) in two food certified reference materials (CRMs) (seaweed: Fucus sp., IAEA-140/TM; Lobster hepatopancreas: TORT-2), using two in vitro gastrointestinal digestion methods: a static method (SM) and a dynamic multicompartment method (TIM-1). There are significant differences (p < 0.05) between the bioaccessible values of As, Cd, Pb and Hg obtained by SM and TIM-1 in the two CRMs. The specific form in which the elements studied are present in the CRM may help to explain the bioaccessibility values obtained.     

风电叶片部件疲劳试验机跟随控制策略研究

针对风电叶片部件疲劳试验过程中实际载荷与期望载荷跟随效果差的问题,提出一种超前自校正与改进线性自抗扰(LADRC)相结合的同步控制策略。该方法通过对实际载荷进行自校正补偿与系统误差以及外部扰动一起输入到改进线性自抗扰控制器,从而实现加载力和频率的有效控制。对疲劳试验机油电液伺服系统控制算法进行仿真分析,并通过搭建现场试验平台对同步控制策略进行有效性验证。仿真及试验结果表明：在较大载荷疲劳试验过程中,该控制策略显著提升系统的快速响应性和抗干扰能力,载荷误差控制在1%以内,相对于传统ADRC控制算法同步误差减小了56.14%,有效实现了风电叶片部件疲劳试验载荷的精确控制。