Low level lead inhibits the human brain cation pump.

The impact of low level lead exposure on human central nervous system function is a major public health concern. This study addresses the inhibition of the cation pump enzyme Na, K-ATPase by low level lead. Human brain tissue was obtained at autopsy and frozen until use. Brain homogenates were preincubated with PbCl2 for 20 min at 0 degrees C. Inhibition of K-paranitrophenylphosphatase (pNPPase), a measure of the dephosphorylation step of Na,K-ATPase, reached steady state within 10 min. K-pNPPase activity, expressed (mean +/- SEM) as a percentage of control (45.2 +/- 2.7 nmol/mg/min), fell to 96.3 +/- 0.9% at 0.25 uM [PbCl2] to 82.0 +/- 1.6% at 2.5 uM [PbCl2] in homogenates prepared from normal brain. Similar results were obtained with homogenates prepared from brains of patients with a history of alcohol abuse and of those with other miscellaneous conditions. Since the mean blood level of lead in the United States has ranged recently from 9.2 to 16.0 ug/dl (0.44 to 0.77 uM), these results indicate that current in vivo levels of lead exposure may impair important human brain function.     

Low level radiation exposure the radiobiologist's challenge in the next millennium

A formal definition for low level exposure does not exist. This has arbitrarily been defined here as exposures from 0 to 5 cGy. The health implications of exposures within this dose range are highly controversial since the effects are exclusively stochastic. As such, the effects can only be detected in large populations. The Oxford Survey of Childhood Cancers (OSCC) established leukaemia as a predominant effect. After the chernobyl nuclear disaster, studies in European countries have correlated perinatal mortality with radioactive contaminations which could only have raised the radiation burdens by levels which are currently regarded as negligible. The reported risk indices for childhood leukaemia arising from low level exposures are generally comparable to those ascertained for high exposures, thus posing an enigma to radiobiologists. This paper reviews the progress in various areas of radiobiological research and attempts to make a synthesis of the facts with the view to provide an explanation. The purpose is also to stimulate an understanding of multifactorial biological mechanisms. Environmental radiation exposures must be expected to be concomitant with other toxic agents which must be taken into account in risk assessment. The challenge in the future will be to realise this goal.     

Effects on the prostate of environmental cadmium exposure--a cross-sectional population study in China.

To explore possible effects of environmental cadmium exposure on prostate in humans, and the possible relationship of serum sex hormones to occurrence of clinic signs of tissue changes in the prostate, a case-control study was undertaken in the southeast part of China in 1998. A total of 297 male volunteers from a control area and two cadmium-polluted areas were included as subjects in this study. All the subjects were required to answer a questionnaire and to undergo a complete physical examination including digital-rectal examination (DRE). Blood and urine samples were collected. Serum total prostate specific antigen (PSA), total serum testosterone (T), follicle stimulating hormone (FSH) and luteinizing hormone (LH) were measured by radioimmunoassay and enzymeimmunoassay method, respectively. The data of urinary cadmium (U-Cd) and blood cadmium (B-Cd) were obtained by atomic absorption spectrometry (AAS) as an indicator of cadmium body burden. Statistical analysis was applied to investigate a possible relation between cadmium exposure and prostate pathological changes. The results show that there is a clear dose-response relationship between cadmium exposure and the prevalence of cases with abnormal PSA. The blood cadmium content in cases with positive DRE was significantly higher than that of subjects with negative DRE (P < 0.05). Significant differences in the level of FSH between cases with positive DRE and the normal subjects were also noted (P < 0.05). These results indicate that chronic environmental cadmium exposure is associated with injuries to human prostate. A possible relationship to changes in circulating sex hormones needs further investigation.     

Low doses of lead

The effects of exposure to high doses of lead on reproduction and development have been established, but not so those caused by low lead doses or the influence that life stage at which contact with the metal takes place might have. The aim of this work was to study the effects of 200 and 400 ppm lead acetate in drinking water on reproduction and development as well as on renal and hepatic parameters of rats at different life stages, from gestation to 3 mo postweaning. The results indicate a dose-dependent effect on reproduction, with variations in the number of births and in pups' weight. Development was mostly affected at the weaning stage, with hemoglobin levels and erythrocyte numbers significantly decreased. The lead levels in tissues, blood, urine, and feces along with selected renal and hepatic parameters (blood urea nitrogen, creatinine, alanine aminotransferase, aspartate aminotransferase, and alkaline phosphatase) were determined. There were histological, blood urea nitrogen, alanine aminotransferase, and alkaline phosphatase changes in the first month postweaning. After 3 mo, these changes are no longer evident, possibly because of metabolic adaptation.     

赞比亚的人类发展与环境挑战

由于赞比亚社会经济及人民生活水平较低,赞比亚人民为了生存,不得不依靠掠夺性地开发自然生态系统和破坏环境来获得资源。赞比亚有60%以上的人民是农村居民,直接靠自然环境资源维持生存,对当地的自然环境造成了很大的影响。这种人类对环境的压力包括森林的毁坏,农田覆土的不断流失,土壤侵蚀以及气候的多变性造成的周期性干旱等。而人口的快速增长,当地社会经济的长期疲软以及大气、水、土地资源的污染更是给原本脆弱的生态环境雪上加霜。本文受统计数据的可获得性限制,部分结论尚未定量化,但其反映的人类发展与环境保护之间的矛盾却是客观存在的。     

Doctors accept a challenge: self-assessment exercises in continuing medical education.

A new approach to continuing medical education by distance learning has been implemented. A series of six patient-management problems or challenges were posted to 20 000 doctors throughout Britain. Each doctor had to decide on the diagnosis, investigations, and treatment of the patients described. The challenges covered problems that were important in the doctor''s day-to-day work and were designed so that he could obtain immediate feedback about his decisions and compare his own responses with those of a specialist and those of his colleagues. Additional information was available by telephone and by post on request. The series has been well received and is being widely used.     

Overcoming the challenge of venous occlusion for lead implantation

Vein stenosis or occlusion is a frequent finding in patients with previously-implanted transvenous leads. This editorial describes the different techniques that may be used to overcome this hurdle in case a new lead needs to be implanted, and discusses two case reports in this issue of the journal.     

Scaling up: the next challenge in environmental microbiology

Great strides have recently been made in identifying and characterizing the staggering diversity of microorganisms conducting primary and secondary production, nutrient transformation and mineralization processes that underlie ecosystem and regional biogeochemical, trophodynamic and ecological change. We are now faced with the challenge of assigning and coupling function to structure in highly complex and interactive microbial communities mediating such change. Previous and ongoing ecophysiological work has shown that microbial processes controlled by environmental variables and limiting resources are highly specific in terms of what, when, where and why they are active, not to mention how they impact ecosystem dynamics. As such, it is imperative that we assess the activities and roles of key microbial 'players' along the appropriate environmental scales and gradients catalysing ecological change. Here, we discuss conceptual and technical challenges for some key microbially mediated environmental processes, problems and extremes that require synthesizing our growing knowledge of microbial community structure with emerging knowledge of function in aquatic ecosystems. We emphasize the importance of assessing ecological change over a range of relevant time scales that vary from minutes to millennia and spatial scales that range from microscale aggregates to ocean basins.     

Biocalcification through time: environmental challenge and cellular response

A concept explaining biocalcification as a form of calcium detoxification is advanced using geochemical and paleontological criteria. The first appearence of calcareous skeletons at the turn of the Precambrian/Cambrian is interpreted as a biotic response to a gradual rise of Ca²⁺ in world ocean resulting in Ca²⁺ stress environments in shelf areas. Periodic appearance in the Phanerozoic record of heavily calcified marine biota, absent or relic in modern seas, suggests considerable temporal fluctuations of calcium concentrations in the ancient ocean. Temporal changes in Ca²⁺ and mineral nutrient contents in the environment can thus be seen as overriding factors in the evolution of organisms.