Nanotechnology and Health.

: Potential adverse health effects associated with exposure to engineered or synthesized nanomaterials have not been reported in humans; however, there is accumulating evidence from animal studies that exposure to some nanomaterials is harmful. While there is uncertainty as to the likelihood, frequency, and intensity of exposures experienced by those working around engineered nanoparticles, the American College of Occupational and Environmental Medicine has developed this guidance document for occupational medicine physicians and their colleagues to offer prudent preventive recommendations on the topics of exposure monitoring, exposure controls, and medical surveillance.

Persistence of mercury-induced motor and sensory neurotoxicity: systematic review of workers previously exposed to mercury vapor.

Elemental mercury (Hg0) is a well-recognized neurotoxicant, but it is uncertain whether and for how long its neurotoxicity persists. Among studies that evaluated previously-exposed workers, only one examined workers during and also years after exposure had ceased. The objective of this review is to create a series of 'synthetic' longitudinal studies to address the question of persistence of Hg0 neurotoxicity in occupationally exposed workers. We systematically reviewed studies describing objective motor and sensory effects in previously-exposed mercury workers. Data from physical examination (PE), neurobehavioral (NB) tests, and electrophysiological studies (EPS) were extracted into structured tables and examined for their consistency and dose-relatedness and then compared with the corresponding results from studies of currently exposed workers. We identified six cohorts that described neurological findings in 1299 workers, examined an average of 4.8-30 years after the cessation of exposure. Historical group mean UHg levels ranged from 23 to >500 µg/L, with UHg levels >6000 µg/L in some individuals. Overall, few findings were significant; most were inconsistent across the previous-exposure studies, and in comparisons between studies of previously and currently exposed workers. The results of this systematic review indicate that Hg0-related neurotoxic effects detectable on PE, NB testing, and EPS are substantially reversed over time. To the extent that such effects do persist, they are reported principally in workers who have had very high-dose exposures. In addition, based on the limited available data, those effects reported to persist have been described as having little or no functional significance.

Mercury-induced motor and sensory neurotoxicity: systematic review of workers currently exposed to mercury vapor.

The neurotoxicity of elemental mercury (Hg0) is well-recognized, but it is uncertain whether and for how long neurotoxicity persists; among studies that evaluated previously exposed workers, only one examined workers during and also years after exposure ceased. The aim of this review is to document the type, frequency, and dose-relatedness of objective neurological effects in currently exposed mercury workers and thereby provide first approximations of the effects one would have expected in previously exposed workers evaluated during exposure. We systematically reviewed studies of neurotoxicity in currently exposed mercury workers identified by searching MEDLINE (1950-2015), government reports, textbook chapters, and references cited therein; dental cohorts were not included. Outcomes on physical examination (PE), neurobehavioral (NB) tests, and electrophysiological studies were extracted and evaluated for consistency and dose-relatedness. Forty-five eligible studies were identified, comprising over 3000 workers chronically exposed to a range of Hg0 concentrations (0.002-1.7 mg/m3). Effects that demonstrated consistency across studies and increased frequency across urine mercury levels (<50; 50-99; 100-199; ≥200 µg/L) included tremor, impaired coordination, and abnormal reflexes on PE, and reduced performance on NB tests of tremor, manual dexterity and motor speed. The data suggest response thresholds of UHg ≈275 µg/L for PE findings and ≈20 µg/L for NB outcomes. These results indicate that PE is of particular value for assessing workers with UHg >200 µg/L, while NB testing is more appropriate for those with lower UHg levels. They also provide benchmarks to which findings in workers with historical exposure can be compared.

Mortality disparities in Appalachia: reassessment of major risk factors.

OBJECTIVE: To determine the predictive value of coal mining and other risk factors for explaining disproportionately high mortality rates across Appalachia. METHOD: Mortality and covariate data were obtained from publicly available databases for 2000 to 2004. Analysis employed ordinary least square multiple linear regression with age-adjusted mortality as the dependent variable. RESULTS: Age-adjusted all-cause mortality was independently related to Poverty Rate, Median Household Income, Percent High School Graduates, Rural-Urban Location, Obesity, Sex, and Race/Ethnicity, but not Unemployment Rate, Percent Uninsured, Percent College Graduates, Physician Supply, Smoking, Diabetes, or Coal Mining. CONCLUSIONS: Coal mining is not per se an independent risk factor for increased mortality in Appalachia. Nevertheless, our results underscore the substantial economic and cultural disadvantages that adversely impact health in Appalachia, especially in the coal-mining areas of Central Appalachia.

Methyl methacrylate and respiratory sensitization: a critical review.

Methyl methacrylate (MMA) is a respiratory irritant and dermal sensitizer that has been associated with occupational asthma in a small number of case reports. Those reports have raised concern that it might be a respiratory sensitizer. To better understand that possibility, we reviewed the in silico, in chemico, in vitro, and in vivo toxicology literature, and also epidemiologic and occupational medicine reports related to the respiratory effects of MMA. Numerous in silico and in chemico studies indicate that MMA is unlikely to be a respiratory sensitizer. The few in vitro studies suggest that MMA has generally weak effects. In vivo studies have documented contact skin sensitization, nonspecific cytotoxicity, and weakly positive responses on local lymph node assay; guinea pig and mouse inhalation sensitization tests have not been performed. Cohort and cross-sectional worker studies reported irritation of eyes, nose, and upper respiratory tract associated with short-term peaks exposures, but little evidence for respiratory sensitization or asthma. Nineteen case reports described asthma, laryngitis, or hypersensitivity pneumonitis in MMA-exposed workers; however, exposures were either not well described or involved mixtures containing more reactive respiratory sensitizers and irritants. The weight of evidence, both experimental and observational, argues that MMA is not a respiratory sensitizer.

Five classic articles in public health.

In this brief review, Dr. Jonathan Borak comments on five seminal papers that helped shape the fields of epidemiology and public health. These papers include Hill's criteria for inferring causality; the first proof of the multistage theory of cancer; the first evidence that subclinical lead exposures can cause neurobehavioral impairment in children; a simple yet robust study that had a major influence on setting current air pollution policies; and a landmark review of the general public's perception of risk in relation to actual public health hazard.

How clean is "clean"? Regulations and standards for workplace clothing and personal protective equipment.

OBJECTIVE: To compile current regulations and advisory recommendations on cleanliness of worker clothing and personal protective equipment and to evaluate the adequacy of criteria for determining whether cleanliness has been achieved. METHODS: Systematic review of information provided by federal agencies (eg, OSHA, MSHA, and NIOSH), nongovernmental advisory bodies (eg, ACGIH, AIHA, and ANSI), and manufacturers of protective clothing and equipment. RESULTS: We identified an array of terms describing "cleanliness" and the processes for achieving "cleanliness" that were almost never defined in regulations and recommendations. We also found a general lack of criteria for determining whether cleanliness and/or sterility have been achieved. CONCLUSIONS: There is need to harmonize cleanliness-related terminology, establish best practices for equipment cleaning and sterilization, implement a signage systems to provide equipment-specific cleaning instructions, and adopt objective criteria for determining what is "clean."

An examination of cancer epidemiology studies among populations living close to toxic waste sites.

BACKGROUND: Toxic waste sites contain a broad range of suspected or confirmed human carcinogens, and remain a source of concern to many people, particularly those living in the vicinity of a site. Despite years of study, a consensus has not emerged regarding the cancer risk associated with such sites. METHODS: We examined the published, peer-reviewed literature addressing cancer incidence or mortality in the vicinity of toxic waste sites between 1980 and 2006, and catalogued the methods employed by such studies. RESULTS: Nineteen studies are described with respect to eight methodological criteria. Most were ecological, with minimal utilization of hydrogeological or air pathway modeling. Many did not catalogue whether a potable water supply was contaminated, and very few included contaminant measurements at waste sites or in subjects' homes. Most studies did not appear to be responses to a recognized cancer mortality cluster. Studies were highly variable with respect to handling of competing risk factors and multiple comparisons. CONCLUSION: We conclude that studies to date have generated hypotheses, but have been of limited utility in determining whether populations living near toxic waste sites are at increased cancer risk.

Particle size distribution and particle size-related crystalline silica content in granite quarry dust.

Previous studies indicate that the relationship between empirically derived particle counts, particle mass determinations, and particle size-related silica content are not constant within mines or across mine work tasks. To better understand the variability of particle size distributions and variations in silica content by particle size in a granite quarry, exposure surveys were conducted with side-by-side arrays of four closed face cassettes, four cyclones, four personal environmental monitors, and a real-time particle counter. In general, the proportion of silica increased as collected particulate size increased, but samples varied in an inconstant way. Significant differences in particle size distributions were seen depending on the extent of ventilation and the nature and activity of work performed. Such variability raises concerns about the adequacy of silica exposure assessments based on only limited numbers of samples or short-term samples.

Studies of self-pollution in diesel school buses: methodological issues.

Considerable interest has focused on levels of exhaust emissions in the cabins of diesel-powered school buses and their possible adverse health effects. Significantly different policy and engineering issues would be raised if compelling evidence found that inc-cabin contamination was due to self-pollution from bus emissions, rather than ambient pollution, neighboring vehicles, and/or re-entrained road dust. We identified 19 reports from 11 studies that measured diesel exhaust particulate in the cabins of 58 school bus of various type. Studies were evaluated in light of their experimental design, their data quality, and their capacity to quantify self-pollution. Only one study had a true experimental design, comparing the same buses with and without emission controls, while four others used intentional tracers to quantify tail pipe and/or crankcase emissions. Although definitive data are still lacking, these studies suggest that currently available control technologies can nearly eliminate particulate self-pollution inside diesel school buses.

Biological stress response terminology: Integrating the concepts of adaptive response and preconditioning stress within a hormetic dose-response framework.

Many biological subdisciplines that regularly assess dose-response relationships have identified an evolutionarily conserved process in which a low dose of a stressful stimulus activates an adaptive response that increases the resistance of the cell or organism to a moderate to severe level of stress. Due to a lack of frequent interaction among scientists in these many areas, there has emerged a broad range of terms that describe such dose-response relationships. This situation has become problematic because the different terms describe a family of similar biological responses (e.g., adaptive response, preconditioning, hormesis), adversely affecting interdisciplinary communication, and possibly even obscuring generalizable features and central biological concepts. With support from scientists in a broad range of disciplines, this article offers a set of recommendations we believe can achieve greater conceptual harmony in dose-response terminology, as well as better understanding and communication across the broad spectrum of biological disciplines.

Seafood arsenic: implications for human risk assessment.

Concerns about the adverse effects of chronic arsenic exposure have focused on contaminated drinking water and airborne workplace exposures; the risks of naturally occurring arsenic in foods have received less attention. About 90% of the arsenic in US diets comes from seafood, of which only a small proportion occurs in inorganic forms; the great majority consists of complex organic compounds that generally have been regarded as non-toxic. However, recent studies of seafood have documented formation of metabolites carcinogenic in some rodents. To calculate the risks of ingested seafood arsenic, therefore, it is necessary to identify the nature and quantity of arsenic species present and the metabolites formed by expected metabolic activities. We review the nature and quantities of the various arsenical compounds found in dietary seafood and discuss their metabolic processing and fate. Based on conservative dose estimates and the likelihood that arsenic's carcinogenic mechanisms follow sub-linear dose-response curves, we estimate a margin of exposure of at least 10(3)-10(4) between carcinogenic doses used in rodent studies and those expected after human consumption of large quantities of seafood.

Use of beryllium lymphocyte proliferation testing for screening of asymptomatic individuals: an evidence-based assessment.

OBJECTIVE: We reviewed published data describing use of beryllium lymphocyte proliferation testing (BeLPT) to determine the appropriateness of BeLPT for screening asymptomatic individuals. METHODS: Published studies were identified by computerized literature searches and hand searches of relevant bibliographies and cited references. Critical assessment of evidence focused on five elements essential to judging effectiveness of preventive services: 1) burden of suffering, 2) accuracy and reliability of screening tests, 3) effectiveness of early detection, 4) harms of screening, and 5) benefits outweighing harms. RESULTS: Important gaps and deficiencies in the evidence were found. The prevalence of beryllium sensitization and chronic beryllium disease in asymptomatic individuals are unknown. The accuracy and reliability of BeLPT are uncertain. Marked intra- and interlaboratory variability has been reported. The clinical benefits of early intervention have not been confirmed or quantified in asymptomatic individuals. CONCLUSIONS: There is currently insufficient scientific evidence to support the use of BeLPT for routine screening of asymptomatic individuals.