Assessment of exposure to lead through air and biological monitoring in a lead and zinc mine

 Background and aim: Lead is ubiquitous and one of the earliest metals discovered by the human. This metal is widely used in different industries due to its important physico-chemical properties like softness, high malleability, ductility, low melting point and resistance to corrosion. Lead absorbed in body with several routs and when transfer in blood is primarily in red blood cells. Human exposure to this toxic metal and its compounds occurs mostly in lead related occupations and also non-occupational exposures can acccure. Lead and lead compounds are not beneficial or necessary for human health, and can be harmful to the human body.The health effects of lead are directly related to the concentration of lead in the affected organe. Lead can affect on various organs in the body and it is one of the causes of problems and health conditions, including effects on central nervous system and cuses anemia, abnormal behavior, depression, nausea, fatigue, Lead colic, high blood pressure, joint and muscle pain and headache. Also researchs show that Lead causes other health problems such as toxicity of the liver and kidneys system. Initial symptoms of lead poisoning are non-specific and some factors such as age, the amount of lead, whether the exposure is over a short-term or a longer period will influence what symptoms or health effects are exhibited. Due to the toxicity of this metal, it is necessary to investigate exposures of this toxic heavy metal in different environments. Lead exposure at mines is a concern therefore to determine the concentration of lead in air and blood samples of miners; air and blood sampling were down with specific methods. Another part of the study was the estimate of miners skin exposure that for this porpuse, DREAM (Dermal exposure assessment method) model was used. Methods: This study is a cross-sectional, descriptive-analytic research that was conducted on workers of a lead and zinc mine in Isfahan province. This research includes workers with at least one year of work experience. The oncentration of lead in the respiratory air of 46 workers was measured and of these, 40 blood samples were taken. In order to sampling and analysis of respiratory air samples, NIOSH7082 method was used that in this method for Lead sampleing the cellulose ester membrane filter was fitted into a holder and the calibrated individual sampling pump with a flow rate of 2 liters per minute was connected to the filter holder. After completion of the sampling, analysis was carried out using an atomic absorption spectrophotometere, flame. Biological monitoring of lead was performed on the basis of NIOSH8003 method after obtaining informed consent from the personnel and a complete explanation of the sampling steps. After collecting blood samples and preparing of them, analysis was performed using atomic absorption device. At the other stage of the research after extracting work information, the DREAM model was designed by the authors in Excel 2016 software. DREAM model, consists of an inventory and an evaluation part so the inventory part comprises a questionnaire with some modules consist of  exposure, department(the observer indicates whether exposure to chemical or biological substances is likely to occur), company(general information on the company), job(job titles are defined and information on workers’ hygiene is obtained), agent( physical and chemical properties of substances are collected) and task(information is obtained on frequency and duration of task performance). Key items of the exposure module are assessment of probability and intensity of three dermal exposure routes: emission, deposition and transfer. Emission involves mass transport of substances by direct release from a source onto skin or clothing, deposition on skin or clothing describes mass transport from air, ransfer is defined as the transport of mass from contaminated surfaces onto skin or clothing. In DREAM model, exposure assessment for nine different body parts takes place at the task level to assessing both potential dermal exposure(Skin-PTASKBP) and actual dermal exposure(Skin-ATASK.BP). Potential dermal exposure is defined as exposure on clothing and uncovered skin, whereas actual dermal exposure is about exposure on skin. The potential exposure estimate (Skin-PBP) for a certain body part comprises the sum of dermal exposures due to three different exposure routes: emission (EBP), transfer (TBP) and deposition (DBP).  Finally after collecting data statistical analysis of the data was performed using SPSS 22 software and related statistical tests. Results: In this research the average age of mining workers is 35.5 years, the average weight is 51.72 kg and the mean of height is 172.54 cm. According to the results of this study, mean blood lead in different age groups is not the same so that the level of blood leads in the age group of 22 to 38 years old was lower than the age group of 39 to 53years. The results of this study showed that the average blood lead of workers in mining tunnels was 24.7μg/dl ±3.36 and the average blood lead concentration of workers outside the tunnel was 23.57μg/dl ± 5.80. The mean air lead of the respiratory region within the tunnels is 0.0205 ± 0.015 mg/m3 and the mean air lead of the respiratory air region outside the tunnels is 0.0201 ± 0.017 mg /m3. Independent T-test showed that workers were not homogeneous in terms of blood lead variable and there was a significant difference between the mean of blood lead (P <0.001). Results show that although, with increasing work history, the level of blood lead in individuals has increased, but this increase is not statistically significant (P = 0.224). Comparison of the results obtained from the control and main samples showed that the mean and standard deviation of blood lead in the main and control samples are 24.5±5.43 and 17.08± 3.85 respectively. According to the results of the correlation test, there was no significant correlation between the Lead concentration of the respiratory air region, the concentration of leed in blood samples and the actual skin exposure that comes with the DREAM model with a significant level of Pvalue = 0.806 and Pvalue = 0.193, respectively. The mean of lead concentration in respiratory air was compared with occupational exposure limit in Iran so that the average results of the respiratory air lead were 0.02 mg / m3, which is less than the limit specified. According to the results of this study, the mean blood lead of workers was 24.5 μg/dl, which is less than biological exposure indices. DREAM model analysis show that 15.2% of miners had a low exposure rating with lead, 4.3% ranked average, 13% high, 37% very high and 30.4% had very high exposure rating. Conclusion: Regarding the porpuse of this study, after careful observation of the process and the different sections and working areas, the level of Lead in the blood respiratory air were measured and analyzed. According to the results of this research workplaces are the most important factor in increasing and reducing blood lead. It is almost impossible to remove lead completely from the human body; therefore reduction and prevention of lead exposure are very important. The use of appropriate personal protective equipment, the correct use of them, establishment of appropriate time table between drilling and extraction, the use of rubbing non-petroleum products are recommended in order to exposure control to lead. Occupational hygiene has traditionally focused on inhalation exposures to chemical and biological agents and during the last decade, dermal exposure assessment has received more attention. Different approaches are used to estimate dermal exposure that in this research DREAM model was used. Results show that DREAM model is flexible and can be used for dermal exposure characterization for all kinds of scenario and because of its hierarchical structure; it takes on average 15–30 min only to assess exposure for one person carrying out one task. According to the present study the DREAM is a simple and inexpensive model which is well suited to investigate exposure to lead in the mine. This model supplies an estimate for exposure levels on the skin and outside clothing layer, and gives insight in the distribution of dermal exposure over the body of exposued workers to pollutants. In addition to the advantages, the model also has some limitations, for example since few studies have been done on skin exposures, the values are presented hypothetically. In order to expand this study and provide more definitive views on the DREAM model, it is recommended that in addition to measuring the concentration of lead in air and blood samples in different working conditions, researchers use skin sampling techniques and compare the results with this model.In this study researchers suggested that skin and clothing sampling methods be used to increase the accuracy of determining the amount of lead exposure to skin. Also, the identification and risk assessment of lead exposure in workplace is recommended to determine maximum and minimum of risk level