Biomarkers of occupational manganese toxicity

Abstract

Manganese (Mn) is an essential trace element that is required for maintaining normal function in the human body. However, excessive exposure to Mn has been associated with Parkinson-like symptoms of a disease called manganism. Mn exposure is occurred in different occupational settings such as mining, steel and alloy production, welding and dry cell battery manufacturing. Biological monitoring of chemical exposure in the workplace has become increasingly important in the assessment of health risk as an integrating part of the overall strategy in the occupational health and safety. This activity requires accurate sampling and analysis with correct interpretation of results. Biological monitoring is an important tool in the prevention of occupational diseases related to those exposed to chemicals such as manganese on a regular basis. Particularly, when there may be multi-route exposures (inhalation, skin and ingestion) or abnormal exposures. No reliable biomarker has been established to evaluate the effects of Mn exposure. A complete scientific understanding of the mechanism of Mn induced toxicity remains undiscovered. Over the past decade, extensive researches using animal models and human communities have led to several potential indicators of Mn exposure and biological effects. The present study aimed to identify reliable biomarkers of Mn exposure and toxicity. Using keywords such as biomarkers and manganese toxicity in the available databases, the relevant papers published from 1990 to 2014 were found and those having our criteria were selected. The results were obtained by analyzing the collected data. The biomarkers of Mn exposure such as Mn concentration in biological fluids (blood, urine and saliva) and some parts of body (hair and nail) were investigated. Mn of blood and urine are not good markers to evaluate the exposure. Although Mn in blood is different in group comparison of those having active exposure than those not exposed to it, it is not valid for the individuals. Biomarkers related to Mn poisoning effects including variation in Mn to Iron Ratio (MIR), variation in iron and regulatory proteins of iron, serum prolactin, auric acid (ROS) Reactive Oxygen Species, and MRI were investigated. Regarding criteria for a good biomarker, each investigated biomarker had a number of advantages and disadvantages. Therefore, further researches are required to introduce an appropriate biomarker for Mn exposure and effects to prevent manganism in workers exposed to Mn. Mn-exposed biological indicators such as Mn concentration in biological fluids (blood, urine and saliva) and some parts of body (hair, nail and bone) are studied. Mn of blood and urine are not good indicators to evaluate the exposure. However, Mn in blood for group comparison of current exposure is good but not for the discrimination of an individual. Biological indicators related to effects are Mn to Iron Ratio (MIR), variation in iron and regulatory proteins of Iron, serum prolactin, auric acid, (ROS) Reactive Oxygen Species, and MRI. Concerning the criteria for a good indicator, every mentioned indicator has a number of advantages and disadvantages. Thus, it is indispensable to conduct additional researches to introduce an appropriate indicator in order to prevent manganism in workers.