[Toxicological assessment of nanostructured silica. III. Microecological, hematological indices, state of cellular immunity]

This paper is the third in a series of publications on the experimental study of subacute oral toxicity of nanostructured silicon dioxide (SiO2). We used commercial nanostructured SiO2, obtained by hydrolysis of tetrachlorosilane in the gaseous phase, with the size of the primary nanoparticles (NPs) of 5-30 nm. The aqueous dispersion of SiO2 after treatment with ultrasound was administered to rats with initial weight of 80 +/- 5 g for the first 30 days by intragastric gavage and further for 60 days with diets in doses of 0.1; 1.0; 10 and 100 mg/kg body weight per day. Animals of the control group were treated with deionized water. The amount of basic and transient populations of gut microbiocenosis, hematological indexes were measured using standard methods. Specific content of the B-lymphocytes (CD45RA+), total T-lymphocytes (CD3+), T-helper cells (CD4+), T-cytotoxic cells (CD8+), NK-cells (CD161a+) in general population of lymphocytes was evaluated byflow cytometry; serum cytokine levels of TNF-alpha, IL-6, IL-10 were determined by ELISA. No significant changes in the qualitative and quantitative composition of the intestinal microbiota populations regardless of the dose of administered nanomaterial have been found. This gave reason to believe that the postulated mechanism of the toxic effects of the NPs of SiO2, mediated by modification of the composition of the intestinal microflora and the corresponding changes in its functional activity, apparently, is not realized. The main target of nanostructured SiO2 was the T-cellular system of the immune system of animals, that was manifested in the significant decrease of the number of leukocytes (33%), number of T-helper cells (13%), CD4/CD8 ratio (27%) and increasing the number of cytotoxic lymphocytes (19%) and the level of TNF-alpha (590%). The value of the maximum dose (NOAEL) of nanostructured SiO2, has no effect on T-cell immunity was not more than 100 mg/kg body weight per day.

Interleukin-1β-mediated suppression of microRNA-101 and upregulation of enhancer of zeste homolog 2 is involved in particle-induced lung cancer

Lung cancer may be a result of complex factors. Small mineral particle is the well-known inducer of lung cancer. Previous study revealed the high morbidity of lung cancer in Xuan Wei in China, and the main cause of lung cancer is the use of smoky coal there. And it is generally accepted that chronic inflammation induced by small mineral particle may be a cause of lung cancer. But the relationship between chronic lung inflammation and lung cancer is largely unknown. In the present study, we found that silica particle was able to induce the secretion of interleukin-1β from a Xuan Wei lung cancer cell line, XWLC-05. At the same time, microRNA-101 (mir-101) was found to be downregulated by the treatment of silica particle. Interestingly, the interleukin 1 receptor antagonist and interleukin-1β antibody can reduce silica particle-induced downregulation of mir-101. Twenty-four Xuan Wei lung tumor tissues were collected to detect the expression level of mir-101 and enhancer of zeste homolog 2 (EZH2), which is the potential target of mir-101. The results showed that mir-101 was down-regulated and EZH2 were upregulated. Subsequently, the roles of mir-101 and EZH2 in tumor growth and progression in vitro were tested. Overexpression of mir-101 mimics was able to suppress the expression of EZH2 in XWLC-05 cells. And this resulted in the inhibited tumor cell growth and attenuated cell migration. The results in the present study showed that particle can induce the secretion of interleukin-1β. Interleukin-1β subsequently induces the downregulation of mir-101, which may result in the upregulated level of EZH2, and occurrence of lung cancer. We for the first time proposed the role interleukin-1β-mir-101-EZH2 axes in the particle-induced lung cancer. Further study may be needed to decipher the detailed mechanism involved.

Evaluation of workplace exposure to respirable crystalline silica in Italy

BACKGROUND

Crystalline silica is a human carcinogen and its use is widespread among construction, mining, foundries, and other manufacturing industries.

PURPOSE

To evaluate occupational exposure to crystalline silica in Italy.

METHODS

Data were collected from exposure registries and descriptive statistics were calculated for exposure-related variables. The number of potentially exposed workers was estimated in a subset of industrial sectors. Linear mixed model analysis was performed to determine factors affecting the exposure level.

RESULTS

We found 1387 cases of crystalline silica exposure between 1996 and 2012. Exposure was most common in construction work (AM = 0·057 mg/m(3), N = 505), and among miners and quarry workers (AM = 0·048 mg/m(3), N = 238). We estimated that 41 643 workers were at risk of exposure in the selected industrial sectors during the same period.

CONCLUSIONS

This study identified high-risk sectors for occupational exposure to crystalline silica, which can help guide targeted dust control interventions and health promotion campaigns in the workplace.

Exposure to silica nanoparticles causes reversible damage of the spermatogenic process in mice

Environmental exposure to nanomaterials is inevitable, as nanomaterials have become part of our daily life now. In this study, we firstly investigated the effects of silica nanoparticles on the spermatogenic process according to their time course in male mice. 48 male mice were randomly divided into control group and silica nanoparticle group with 24 mice per group, with three evaluation time points (15, 35 and 60 days after the first dose) per group. Mice were exposed to the vehicle control and silica nanoparticles at a dosage of 20 mg/kg every 3 days, five times over a 13-day period, and were sacrificed at 15, 35 and 60 days after the first dose. The results showed that silica nanoparticles caused damage to the mitochondrial cristae and decreased the levels of ATP, resulting in oxidative stress in the testis by days 15 and 35; however, the damage was repaired by day 60. DNA damage and the decreases in the quantity and quality of epididymal sperm were found by days 15 and 35; but these changes were recovered by day 60. In contrast, the acrosome integrity and fertility in epididymal sperm, the numbers of spermatogonia and sperm in the testes, and the levels of three major sex hormones were not significantly affected throughout the 60-day period. The results suggest that nanoparticles can cause reversible damage to the sperms in the epididymis without affecting fertility, they are more sensitive than both spermatogonia and spermatocytes to silica nanoparticle toxicity. Considering the spermatogenesis time course, silica nanoparticles primarily influence the maturation process of sperm in the epididymis by causing oxidative stress and damage to the mitochondrial structure, resulting in energy metabolism dysfunction.

Pulmonary function tests in stone crushers

A cross-sectional type of observational study was conducted at 7 various stone crusher units on 120 male stone crushers and 120 healthy male controls. Values of FEF25-27% and PEFR were recorded on computerized spirometer and were compared between workers and age matched controls group. The value of FEF25-75% and PEFR was significantly reduced in stone crushers as compared to controls. Also as the duration of exposure increases the values of flow rates goes on decreasing among workers. Stone crushers of Marathwada region of Maharashtra exposed to silica dust were prone to develop lung disorders as indicated by reduced value of FEF25-75% and PEFR.

Occupational exposure to solid chemical agents in biomass-fired power plants and associated health effects

Occupational exposure to aluminium, arsenic, lead, cadmium, and manganese can increase the risk of numerous neurophysiological changes in workers, and may lead to conditions resembling Parkinson's and Alzheimer's disease. However, although the health hazard aspect of these agents has been examined, biomass-fired power plant workers' exposure to them remains a neglected issue. The purpose of this study was to measure maintenance and ash removal workers' multiple exposures to inhalable dust, metals, and crystalline silica during their work tasks in biomass-fired power plants. Maintenance and ash removal workers were exposed to high inhalable dust concentrations inside biomass-fired boilers. The median air inhalable dust concentration in workers' breathing zones were 33 mg m(-3) and 120 mg m(-3) in ash removal and maintenance tasks, respectively. The median concentration of manganese (0.31 mg m(-3)) exceeded the occupational exposure limit in worker's breathing zone samples in maintenance tasks. The most evident exposure-associated health risk from multiple exposures to metals was that of cancer, followed by central nervous system disorders, lower respiratory tract irritation, and finally upper respiratory tract irritation. To avoid the above mentioned health effects, powered air respirators with ABEK+P3 cartridges and carbon monoxide gas detectors are recommended as the minimum requirement for these work tasks. A compressed air breathing apparatus is the best form of protection for the most demanding work phases inside boilers in biomass-fired power plants.

Aspects of renal-pulmonary pathogenic replationships in chronic kidney disease and chronic pulmonary diseases--a less-known connection

The kidneys, as an integral part of the body, are in close functional relationship with other organs. Dysfunction of the relationship with one organ will affect the kidney. Chronic kidney disease (CKD) leads in time to alteration of the relationship of the kidney with other organs, sometimes with severe consequences. Thus, cardiovascular involvement in CKD leads to increased severity of CKD, with an increase in mortality rate. At present, the relationship between the kidney and the lung has been less studied. Many aspects of this relationship are still unknown. The objective of the present paper is to analyze the main situations of the alteration of the kidney-lung relationship in clinical pathology, with special reference to chronic kidney disease. The pulmonary-renal syndrome is at the forefront. This pathology--well known in practice--refers mainly to the kidney-lung relationship in vasculitis, systemic lupus erythematosus and Goodpasture's syndrome. The relationship between the kidney and the lung is not limited to this syndrome. Many systemic diseases like sarcoidosis and amyloidosis alter the lung-kidney binomial. Likewise, the association in some patients of an important disorder primarily affecting the lung, such as silicosis, with concomitant renal involvement, highlights the relationship between the lungs and kidneys in clinical pathology. It is very important to know heart-kidney relationships via the lung in pulmonary arterial hypertension. In-depth knowledge of the patient with chronic kidney disease also requires thorough analysis of the lung-kidney relationship. This relationship is very evident in haemodialysed patients, taking into consideration that the pulmonary circulation is influenced by the dialysis membranes, in patients on peritoneal dialysis and especially in transplanted patients whose kidney-lung relationship has a favorable outcome. Although little dealt with, the relationship between the kidneys and the lungs requires more attention, as it can have important consequences, and appropriate therapy.

Radiation dose to workers due to the inhalation of dust during granite fabrication

There has been very little research conducted to determine internal radiation doses resulting from worker exposure to ionising radiation in granite fabrication shops. To address this issue, we estimated the effective radiation dose of granite workers in US fabrication shops who were exposed to the maximum respirable dust and silica concentrations allowed under current US regulations, and also to concentrations reported in the literature. Radiation doses were calculated using standard methods developed by the International Commission on Radiological Protection. The calculated internal doses were very low, and below both US occupational standards (50 mSv yr(-1)) and limits applicable to the general public (1 mSv yr(-1)). Workers exposed to respirable granite dust concentrations at the US Occupational Safety and Health Administration (OSHA) respirable dust permissible exposure limit (PEL) of 5 mg m(-3) over a full year had an estimated radiation dose of 0.062 mSv yr(-1). Workers exposed to respirable granite dust concentrations at the OSHA silica PEL and at the American Conference of Governmental Industrial Hygienists Threshold Limit Value for a full year had expected radiation doses of 0.007 mSv yr(-1) and 0.002 mSv yr(-1), respectively. Using data from studies of respirable granite dust and silica concentrations measured in granite fabrication shops, we calculated median expected radiation doses that ranged from <0.001 to 0.101 mSv yr(-1).

Evaluation of respirable crystalline silica in high school ceramics classrooms

Air concentrations of respirable crystalline silica were measured in eleven (11) high school ceramics classrooms located in Salt Lake County, UT, USA. Respirable dust was collected on PVC filters using precision flow pumps and cyclone samplers (n = 44). Filters were subsequently analyzed for respirable dust and percent crystalline silica content. The geometric mean of the silica concentrations was 0.009 mg/m³ near the teacher’s work station and 0.008 mg/m³ near the kilns. The number of students in the classroom was correlated to the silica concentration in the ceramics classroom, but no correlation was found between the silica concentrations and either the size of the classroom or the age of the building. Results from this study indicate that ceramics teachers may be at an increased risk of exposure to crystalline silica based on the ACGIH TLV of 0.025 mg/m³, with an exceedance of 21%.

Respiratory disease mortality among US coal miners; results after 37 years of follow-up

OBJECTIVES

To evaluate respiratory related mortality among underground coal miners after 37 years of follow-up.

METHODS

Underlying cause of death for 9033 underground coal miners from 31 US mines enrolled between 1969 and 1971 was evaluated with life table analysis. Cox proportional hazards models were fitted to evaluate the exposure-response relationships between cumulative exposure to coal mine dust and respirable silica and mortality from pneumoconiosis, chronic obstructive pulmonary disease (COPD) and lung cancer.

RESULTS

Excess mortality was observed for pneumoconiosis (SMR=79.70, 95% CI 72.1 to 87.67), COPD (SMR=1.11, 95% CI 0.99 to 1.24) and lung cancer (SMR=1.08; 95% CI 1.00 to 1.18). Coal mine dust exposure increased risk for mortality from pneumoconiosis and COPD. Mortality from COPD was significantly elevated among never [corrected] smokers and former smokers (HR=1.84, 95% CI 1.05 to 3.22; HRK=1.52, 95% CI 0.98 to 2.34, respectively) but not current smokers (HR=0.99, 95% CI 0.76 to 1.28). Respirable silica was positively associated with mortality from pneumoconiosis (HR=1.33, 95% CI 0.94 to 1.33) and COPD (HR=1.04, 95% CI 0.96 to 1.52) in models controlling for coal mine dust. We saw a significant relationship between coal mine dust exposure and lung cancer mortality (HR=1.70; 95% CI 1.02 to 2.83) but not with respirable silica (HR=1.05; 95% CI 0.90 to 1.23). In the most recent follow-up period (2000-2007) both exposures were positively associated with lung cancer mortality, coal mine dust significantly so.

CONCLUSIONS

Our findings support previous studies showing that exposure to coal mine dust and respirable silica leads to increased mortality from malignant and non-malignant respiratory diseases even in the absence of smoking.

Health effects of occupational exposure to crystalline silica in the light of current research results

Crystalline silica is commonly found in the work environment. Possible health effects of occupational exposure continue to be the subject of extensive research. The aim of this paper was to analyze the recent findings concerning the health effects of exposure to crystalline silica, taking into account different levels of exposure. This work is based on the relevant information from the papers retrieved from the following databases: EBSCO, Scopus, ScienceDirect, and Web of Science, using the following keywords: crystalline silica, quartz, health effects. The review of the results confirms the multi-faceted harmful effects of crystalline silica. Prolonged occupational exposure, apart from silicosis and non-cancer respiratory diseases, may also result in the development of lung cancer, and autoimmune and chronic kidney diseases, the pathogenesis, which has not been completely explained yet. The exposure to the crystalline silica at concentrations close to the current occupational exposure limit value does not exclude the risk of the following pathologies: silicosis, lung cancer, other lung diseases and renal diseases. It is not feasible to completely eliminate the crystalline silica dust from the work environment. The best way to reduce the health effects of the exposure is to minimize the concentrations of silica dust. Further progress in clarifying the true mechanisms of interaction between silica dust and lung cells, the determination of the importance of surface properties of the silica particles in the pathogenic processes and explaining the effects of co-morbid dust in the work environment may help to prevent the harmful effects of silica dust.

Silica: a lung carcinogen

Silica has been known to cause silicosis for centuries, and evidence that silica causes lung cancer has accumulated over the last several decades. This article highlights 3 important developments in understanding the health effects of silica and preventing illness and death from silica exposure at work. First, recent epidemiologic studies have provided new information about silica and lung cancer. This includes detailed exposure-response data, thereby enabling the quantitative risk assessment needed for regulation. New studies have also shown that excess lung mortality occurs in silica-exposed workers who do not have silicosis and who do not smoke. Second, the US Occupational Safety and Health Administration has recently proposed a new rule lowering the permissible occupational limit for silica. There are approximately 2 million US workers currently exposed to silica. Risk assessments estimate that lowering occupational exposure limits from the current to the proposed standard will reduce silicosis and lung cancer mortality to approximately one-half of the rates predicted under the current standard. Third, low-dose computed tomography scanning has now been proven to be an effective screening method for lung cancer. For clinicians, asking about occupational history to determine if silica exposure has occurred is recommended. If such exposure has occurred, extra attention might be given to the early detection of silicosis and lung cancer, as well as extra emphasis on quitting smoking.

Exposures and cross-shift lung function declines in wildland firefighters

Respiratory problems are common among wildland firefighters. However, there are few studies directly linking occupational exposures to respiratory effects in this population. Our objective was to characterize wildland fire fighting occupational exposures and assess their associations with cross-shift changes in lung function. We studied 17 members of the Alpine Interagency Hotshot Crew with environmental sampling and pulmonary function testing during a large wildfire. We characterized particles by examining size distribution and mass concentration, and conducting elemental and morphological analyses. We examined associations between cross-shift lung function change and various analytes, including levoglucosan, an indicator of wood smoke from burning biomass. The levoglucosan component of the wildfire aerosol showed a predominantly bimodal size distribution: a coarse particle mode with a mass median aerodynamic diameter about 12 μm and a fine particle mode with a mass median aerodynamic diameter < 0.5 μm. Levoglucosan was found mainly in the respirable fraction and its concentration was higher for fire line construction operations than for mop-up operations. Larger cross-shift declines in forced expiratory volume in one second were associated with exposure to higher concentrations of respirable levoglucosan (p < 0.05). Paired analyses of real-time personal air sampling measurements indicated that higher carbon monoxide (CO) concentrations were correlated with higher particulate concentrations when examined by mean values, but not by individual data points. However, low CO concentrations did not provide reliable assurance of concomitantly low particulate concentrations. We conclude that inhalation of fine smoke particles is associated with acute lung function decline in some wildland firefighters. Based on short-term findings, it appears important to address possible long-term respiratory health issues for wildland firefighters. [Supplementary materials are available for this article. Go to the publisher's online edition of Journal of Occupational and Environmental Hygiene for the following free supplemental resources: a file containing additional information on historical studies of wildland fire exposures, a file containing the daily-exposure-severity questionnaire completed by wildland firefighter participants at the end of each day, and a file containing additional details of the investigation of correlations between carbon monoxide concentrations and other measured exposure factors in the current study.].

[Toxicological assessment of nanostructured silica. I. Integral indices, adducts of DNA, tissue thiols and apoptosis in liver]

Nanostructured amorphous silica (SiO2) is widely used in food additives, pharmaceuticals and cosmetics. Available data on the oral toxicity of this nanomaterial (NM) in vivo, obtained in acute and subacute experiments are contradictory. The purpose of this study is evaluation of some parameters of toxicity of nanostructured SiO2 when orally administered to rats for 3 months. We used commercial SiO2 preparation, obtained by gas-phase hydrolysis of tetrachlorosilane with a size of the primary nanoparticles close to 5-30 nm, which was characterized as NM by several independent methods. SiO2 in the form of sonicated aqueous dispersion was administered to male rats with initial weight of 80 +/- 4 g for the first 30 days by intragastric gavage and then for 62 days with consumed diets in daily dose of 0,1; 1,0; 10 and 100 mg/kg body weight. The control animals received vehicle--deionized water. Weight gain, relative mass of internal organs, intestinal permeability to protein macromolecules (determination of ovalbumin level in blood serum by solid-phase bivalent immunoassay), urinary excretion of oxidative degradation product of DNA 8-oxo-2-deoxyguanosine (8-oxo-G) (by reversed phase HPLC), the level of thiol compounds in liver (spectrophotometrically), liver cell apoptosis (flow cytometer), fixing efficiency of passive avoidance (CRPA) have been measured. It has been shown that three-month administration of nanostructured SiO2 in all doses resulted in animal body weight decrease by 10-15%; a significant increase in adrenal weight was noticed under doses of 1 and 10 mg/kg and urinary 8-oxo-G excretion was significantly reduced at the dose 10 mg/kg. At the maximum dose of NM, 100 mg/kg, after 2 months of administration the number of animals decreased that entered the dark compartment of the experimental setup at initial testing of CRPA. The rest of the studied indices did not experience any significant changes depending on the dose of NM. It is concluded that no toxic effect were expressed in indices studied under the influence of nanostructured SiO2 in rats at daily doses up to 100 mg per kg body weight for 3 months.

Assessment of nanoparticle exposure in nanosilica handling process: including characteristics of nanoparticles leaking from a vacuum cleaner

Nanosilica is one of the most widely used nanomaterials across the world. However, their assessment data on the occupational exposure to nanoparticles is insufficient. The present study performed an exposure monitoring in workplace environments where synthetic powders are prepared using fumed nanosilica. Furthermore, after it was observed during exposure monitoring that nanoparticles were emitted through leakage in a vacuum cleaner (even with a HEPA-filter installed in it), the properties of the leaked nanoparticles were also investigated. Workers were exposed to high-concentration nanosilica emitted into the air while pouring it into a container or transferring the container. The use of a vacuum cleaner with a leak (caused by an inadequate sealing) was found to be the origin of nanosilica dispersion in the indoor air. While the particle size of the nanosilica that emitted into the air (during the handling of nanosilica by a worker) was mostly over 100 nm or several microns (µm) due to the coagulation of particles, the size of nanosilica that leaked out of vacuum cleaner was almost similar to the primary size (mode diameter 11.5 nm). Analysis of area samples resulted in 20% (60% in terms of peak concentration) less than the analysis of the personals sample.

Pre-exposure of Mycobacterium tuberculosis-infected macrophages to crystalline silica impairs control of bacterial growth by deregulating the balance between apoptosis and necrosis

Inhalation of crystalline silica (CS) particles increases the risk of pulmonary tuberculosis; however, the precise mechanism through which CS exposure facilitates Mycobacterium tuberculosis (Mtb) infection is unclear. We speculate that macrophage exposure to CS deregulates the cell death pathways that could explain, at least in part, the association observed between exposure to CS and pulmonary tuberculosis. We therefore established an in vitro model in which macrophages were exposed to CS and then infected with Mtb. Expression of surface markers was analyzed by flow cytometry, JNK1/2, ASK1, caspase 9, P-p38, Bcl-2 and Mcl-1 were analyzed by Western blot, and cytokines by ELISA. Our results show that exposure to CS limits macrophage ability to control Mtb growth. Moreover, this exposure reduced the expression of TLR2, Bcl-2 and Mcl-1, but increased that of JNK1 and ASK1 molecules in the macrophages. Finally, when the pre-exposed macrophages were infected with Mtb, the concentrations of TNFα, IL-1β and caspase-9 expression increased. This pro-inflammatory profile of the macrophage unbalanced the apoptosis/necrosis pathway. Taken together, these data suggest that macrophages exposed to CS are sensitized to cell death by MAPK kinase-dependent signaling pathway. Secretion of TNF-α and IL-1β by Mtb-infected macrophages promotes necrosis, and this deregulation of cell death pathways may favor the release of viable bacilli, thus leading to the progression of tuberculosis.

Exposure-response analysis and risk assessment for lung cancer in relationship to silica exposure: a 44-year cohort study of 34,018 workers

Crystalline silica has been classified as a human carcinogen by the International Agency for Research on Cancer (Lyon, France); however, few previous studies have provided quantitative data on silica exposure, silicosis, and/or smoking. We investigated a cohort in China (in 1960-2003) of 34,018 workers without exposure to carcinogenic confounders. Cumulative silica exposure was estimated by linking a job-exposure matrix to work history. Cox proportional hazards model was used to conduct exposure-response analysis and risk assessment. During a mean 34.5-year follow-up, 546 lung cancer deaths were identified. Categorical analyses by quartiles of cumulative silica exposure (using a 25-year lag) yielded hazard ratios of 1.26, 1.54, 1.68, and 1.70, respectively, compared with the unexposed group. Monotonic exposure-response trends were observed among nonsilicotics (P for trend < 0.001). Analyses using splines showed similar trends. The joint effect of silica and smoking was more than additive and close to multiplicative. For workers exposed from ages 20 to 65 years at 0.1 mg/m(3) of silica exposure, the estimated excess lifetime risk (through age 75 years) was 0.51%. These findings confirm silica as a human carcinogen and suggest that current exposure limits in many countries might be insufficient to protect workers from lung cancer. They also indicate that smoking cessation could help reduce lung cancer risk for silica-exposed individuals.

Silicosis and industrial bronchitis by exposure to silica powders and cement

OBJECTIVE

to identify the association between the exposure of workers to inorganic dust in a quarry and a cement factory and pulmonary diseases.

METHODS

a transverse study on data from 32 quarry workers (QWs) and 57 cement production line workers (CFWs) to inorganic-dust exposure was performed. Pulmonary function tests and chest X ray were done in both groups.

RESULTS

there were differences between QWs and the CFWs; QWs were younger, shorter and thinner. The number of sick individuals might be considered significantly different, showing a smaller proportion on the cement production line. The quarry workers have been on the company for a shorter period of time and, in the end, they present more serious pulmonary problems with an average of 3 years working.

CONCLUSIONS

the amount of free-silica that is managed on the quarry affects the workers in some way, even when literature states that the evolution of industrial bronchitis and silicosis have a period development of approximately 10 years.

[Hemoptysis in a young man smoking cannabis]

The respiratory toxicity of cannabis is well known today. Along with the classic cannabis 'joint', there are other ways of consuming it, which should be known. Smoking cannabis that has been cut with micro-particles of silicon dioxide may cause hemoptysis. We will describe here the case of a young 16-year-old man who was in the hospital because of hemoptic expectoration. The etiologic investigation was negative, in particular a thoracic scan and a bronchial fiberscope. Questioning the patient afterwards allowed us to discover the inhalation of cannabis 2 h before the hemoptysis, cannabis mixed with micro-particles of silicon dioxide. Stopping inhalation stopped the symptoms. Pediatricians should be familiarized with such practices. Silicon dioxide particles cause ENT problems or bronchial ones (coughing, spitting, hemoptysis, wheezing). Over the long term, the risk of silicosis cannot be excluded, although a longer and more complete exposure is necessary.

Silicosis exposure-response in a cohort of tin miners comparing alternate exposure metrics

BACKGROUND.: The detailed lung radiographic response to silica exposure has not been described. In estimating the exposure-response relationship in silicosis with statistical models, the absence of baseline (unattributable) risk can disable relative-rate estimation or produce widely varying estimates. This obstructs identification of optimum exposure metrics and invalidates comparisons and meta-analyses, which assume a common background rate. METHODS.: A cohort of 3,000 Chinese tin miners with more than 1,000 cases of silicosis was analyzed for the period 1961-1994. Regular surveillance documented three stages of silicosis. To examine the exposure-response relationship, the intercept in relative-rate models was fixed to correspond to 1% of the observed silicosis rate. Exposure metrics for contributions in different time-windows were simultaneously evaluated, as were burden and cumulative burden metrics. RESULTS.: Silica exposures that most contributed to silicosis onset occurred in the period 5-10 years prior (excess annual rate per 10 mg-year/m(3) , ER = 0.158, 95% CI = 0.125-0.192, or 16% per year). During 10-20 year prior, the excess rate contribution was much smaller (ER = 0.048, 95% CI = 0.037-0.060) but larger again during 20-30 year prior to onset (ER = 0.112, 95% CI = 0.098-0.126). For advanced silicosis, all time periods contributed about equally to the rate of onset. CONCLUSIONS.: Reliable estimates of parameters were observed, demonstrating exposure contributions over time. Burden metrics with different half-lives suggested some reversibility for silicosis onset with a half-life of 20 years. Advanced silicosis was best predicted with a cumulative burden metric which was consistent with prior observations that previously deposited silica continues to cause pulmonary damage.