Background and aims: One of the major health issues in developed countries is the workplace air pollution. Cement factories are one of the industries where many workers worked in them. Workers in this industry are exposure with many harmful factors, such as ergonomics factor, physical factors, and in particular various chemical agents, during their job. The most important factors that threaten the health of workers in the cement industry are dust and respirable particles of cement. Respirable particles of cement contains some elements such as arsenic, calcium, aluminum, cadmium, lead, cobalt, zinc, iron, and chromium. Recent studies concluded that the concentrations of arsenic, chromium, lead, and cadmium within the particles are higher than the other metals.
Exposure to heavy metals within cement respirable particles can lead to some adverse health effects among exposed workers. Expanding of industries and emission of respirable particles containing heavy metals in the workplace ambient causes higher exposure for workers within various industries and therefore has become a major problem in these industries, including the cement industry. To arrive the health goal that is protection of the workers, exposure to chemicals and the dangers of exposure to these substances need to be scrutinized. Risk assessment is defined as the process of assessing the risks arising from risks in the workplace by taking control measures and deciding whether or not to accept them. Risk assessment is a basic action for evaluation of danger in the workplace and the first step for risk management.
Quantitative health risk assessment for different chemical agents in industries is necessary to decide on control of risk and management measures to reduce risk and determine risk level of these substances. This process combines scientific information about the toxic properties of chemicals as well as the results of chemical measurements in the workplace can provide comprehensive information on the measure of risk and how best to deal with these potential risks. The aim of this study was to assess the risk level of workers occupational exposure to heavy metals (lead, chromium, cadmium) within cement respirable particles for exposed workers in a cement factory.
Methods: This cross-sectional study was conducted in one of the cement industries during warm and cold air condition during 3 months (March 2016 to May 2016). In this study, the concentration of respirable particles within the breathing zone of 70 workers who were working at different production worksites of a cement factory (Packing worksite, Cement mill, Grill and Greater cooler, kiln, blending, Raw material storage and Mine and crushing) was evaluated. The standard method of 0600 recommended by the National Institute of Occupational Safety and Health (NIOSH) was use to evaluate time weighted average (TWA) of workerschr('39') exposure to respirable cement particles. Workerchr('39')s exposure was measured using a personal sampling pump (SKC, model 224-44MTX, UK) with a 2.5 L.min-1 flow rate, air was passing through an aluminum cyclone (SKC, UK) with a 37 mm 2 micrometer pore size poly vinyl chloride (PVC) filter (SKC, UK) bedding on a plastic cassette. The filters were placed in the desiccator for 24 hours before sampling time. To weigh the filters, a microbalance accurate to 6 decimal places (1 µg sensitivity Sartorius, Model ME5, Germany) was used. Critical orifice was used to keep the flow constant during sampling period. Workers personal sampling carried out continuously during a complete shift time. A blank filter was used for each batch of samples to eliminate sampling errors. To evaluate workerschr('39') exposure to heavy metals including lead, chromium and cadmium within the cement respirable particles, the standard method of ID121 recommended by the Occupational Safety and Health Administration (OSHA) was applied. Each filter was dissolved separately at 100 ° C in concentrated nitric acid and perchloric acid until its metals were dissolved in the solution phase. Then, the solution obtained with deionized water was diluted to the lowest level of detection (LOD). The US-made FAAS Model VARIAN 240FS atomic absorption device was used for analysis. Firstly the standard curve was obtained using standard solutions with different concentrations of meals. Samples were then transferred to the atomic absorption apparatus to determine the concentration of the metals within solution. By measuring the sample absorption rate and comparing with the calibration curve and using Bier Lambertchr('39')s law, the amount of metal elements in the unknown sample was obtained. Semi quantitative risk assessment of heavy metals among exposed workers was carried out using a standard method provided by the Institute of the occupational health and Safety in Singapore. Finally, the risk level for each of the heavy metals (lead, chromium and cadmium) in the respirable cement particles was obtained. The degree of exposure (ER) for all parts of the plant was obtained. Since the mean concentrations of these metal in the air of all sections of the cement plant were below the exposure limit recommended by the Iranian Occupational Health Technical Committee (OEL) and the (TLV) recommended by the ACGIH, the E/OEL ratio was lower than one. The hazard rating (HR) of the chemicals was determined using a standard table. Then, the exposure rating (ER) was calculated and determined using air monitoring results using E that is the weekly exposure in milligram per cubic meter or parts per million, F is the number of exposures per week, D is the average time of each exposure in hours, M is the exposure rate in parts per million or milligram per cubic meter, W is the average working hours per week (40 h). Finally, the risk rate (RR) was calculated using the chemical hazard risk (HR) and exposure rate (ER) values.
Results:
This study showed that the mean concentrations of cadmium, lead and chromium elements were measured as 2.41, 10.39, and 1.36 microgram per cubic meter respectively. The highest average exposure to lead metal in the respirable cement particles was 15.09 ± 4.45 µg / m3 and the lowest mean was 8.48 ± 3.11 µg / m3. The highest mean chromium concentration in cement respirable particles was 2.27 ± 1.15 µg / m3 and the lowest mean was 1.11 ± 0.48 µg / m3. The highest mean concentration of cadmium in the cement respirable particles was 2.78 ± 0.62 µg / m3 and the lowest mean was 2.17±0.37 µg / m3.
Most workers in the various cement worksites were exposed to heavy metals less than the OEL suggested by the Iranian Occupational Health Technical Committee and the TLV recommended by the ACGIH. Due to the toxicity of lead metal, the grade 3 risk was considered for this metal. According to the E / OEL ratio, the exposure rate (ER) for all parts of the plant was 1, and since the concentration of this metal in all parts of the cement plant was less than the OEL designed by the Iranian Occupational Health Technical Committee and the TLV recommended by the ACGIH. the risk score for all parts of the plant was 1.73, and finally the risk score for lead in all parts of the plant was low. Due to the toxicity level of chromium metal, the hazard rate (HR) for this metal was considered 5. According to the E / OEL ratio, the exposure rate (ER) for all parts of the plant was obtained 1and since the concentration of this metal in all parts of the cement plant is less than the OEL designed by the Iranian Occupational Health Technical Committee and the TLV recommended by the ACGIH, the risk score was 2.23 in all parts of the plant. And the risk rating for chromium metal was low in all parts of the plant. Due to the toxicity level of cadmium metal the (HR) was considered 4 for this metal. Risk score was obtained in all parts of factory number 2 and as a result the risk rating for cadmium metal in all parts of factory was low. Since all workers in a section are exposed to cement respirable particles and therefore exposed to lead, chromium and cadmium metal elements in these particles are different. The risk of exposure to workers exposed to the highest concentrations of the studied metals in the three sections of kiln, blending, and Cement mill was calculated separately. The results showed that workers exposed to cadmium and lead metals were in the medium risk exposure kiln and blending worksites, respectively and workers exposed to chrome metal working in the cement mill were also at low risk.

Conclusions:
According to the present study, concentrations of chromium, cadmium and lead in the respirable cement particles were lower than the exposure limit set by the Occupational Health Technical Committee of Iran (OEL) and (TLV) recommended by the ACGIH. Exposure to lead, chromium and cadmium elements in cement respirable particles were at a low risk rates for all worksites of the plant However, some workers in the kiln silo and milling materials that exposed to higher particle concentrations containing cadmium and lead had an average risk rate. Therefore, engineering and management control strategies for heavy metal exposure in those sectors are recommended to reduce the risk and prevent injury to these workers.