Background and aims: Nowadays, artificial insulators such as fiberglass and rock wool are used as sound absorbers in developing countries. The present study is performed to introduce new sound absorbing materials used in developed countries and discuss their acoustical characteristics. It also aims to look at the efficiency of sound absorber natural materials (green materials) as an alternative to commercial materials with a synthetic base used in different places. Methods: In order to identify new porous absorbents, their mechanism of action and various applications, a search was conducted by using keywords such as "Sound Absorbent", "Natural Noise Absorbent" and "Passive Absorber" in PubMed, Scopus, Science Direct, ProQuest, Springer, Web of Knowledge, Magiran, SID, IranMedex and Google Scholar. We selected 48 review and original research papers that were about natural and recycled absorbents. Results: Most recent research includes production and optimization of sound absorbers using natural and recycled materials. The aim of all of these researches was producing green absorber materials in accordance with environmental regulations. In order to properly use these materials, in addition to knowing the benefits and suitability of absorbers for use in the intended environment, the effective factors in sound absorption such as fiber size, air flow resistance, porosity, curve, thickness and density of absorbers were considered. Conclusion: In comparison to old absorbents, new materials are safer and lighter and enjoy a more efficient technology. It seems like environmental friendly, degradable, recyclable and green noise absorbents will play on important role in the market of noise absorbents in the future. Also because of the place and different uses of absorbent materials, specialists should consider the limitations of the environment and the acoustic characteristics of the absorbents.

<p><strong>Background: </strong>There are a few studies about the health effects of steady magnetic fields. This study was performed in order to evaluate some of the mental effects of exposure to steady magnetic fields in the copper electrolysis unit.<strong></strong></p><p><strong>Methods: </strong>This cross-sectional descriptive and analytical study was performed at the electrolysis unit of a Copper Complex in Kerman Province in 2013. The populations under study were ninety workers exposed to steady magnetic fields chosen as the exposed group and 90 workers without exposure chosen from the concentration unit and similar to the exposure group in regard to working conditions. The intensity of steady magnetic field was measured in different parts of the saloon and in the head, waist and feet position. Measuring mental signs was performed by the General Health Questionnaire GHQ-28. Data analysis was performed through SPSS19 and the Mann-Whitney U, one way ANOVA, Chi-square test and Regression analysis was used.</p><p><strong>Results: </strong>In this study the mean intensity of the steady magnetic field in the exposed group was 2.5 mT. The mean rank of mental health in the exposed group was 102.04 and in the unexposed group was 78.96 and the difference was statistically significant (p=0.003). Also there were statistical differences between the two groups in anxiety and sleep disorder (p=0.001) and depression (p=0.007) dimensions.</p><p><strong>Conclusion: </strong>It appears that exposure to static magnetic fields can cause psychological complications. Therefore, more research is recommended to improve the safety of workers exposed to these fields.<strong></strong></p>

The health effects of environmental and occupational exposure to steady magnetic fields is a matter of concern. The aim of this study was to evaluate the hematologic effects of exposure to steady magnetic fields at the electrolysis unit of a Copper complex. The population under study was the workers of the electrolysis unit of the copper refinery. The average steady magnetic field in the exposure group was 2.5 mT. The blood indices of workers exposure to steady magnetic fields after adjusting for confounders showed decreased white blood cells (except neutrophils) and increase in the number and volume of platelets. Red blood cells did not show any significant difference. Exposure to steady magnetic fields even in proposed safe limits may have hematologic effects on humans. There is a necessity for more research about the safe doses of exposure to magnetic fields.