Validating hair as a biomarker of manganese exposure
By Bailey Schug
Epidemiologists have long struggled to establish reliable noninvasive methods to predict human exposure to chemicals. A new study by NIEHS grantee Donald Smith, Ph.D., from the University of California, Santa Cruz, describes a process to accurately and noninvasively determine levels of manganese (Mn) exposure in children and adults, as a tool for better evaluating health risks from exposure.
According to Smith, there is clear evidence that elevated Mn exposure in children and adults can lead to neurological deficits, including problems with cognitive, behavioral, and neuromotor function. However, the Achilles heel of environmental epidemiology is exposure assessment. Researchers have long struggled with the challenge of developing standardized methods to measure internalized dose from exposure over longer time frames.
This study contributes to the ongoing effort, by describing and testing a protocol for cleaning hair of exogenous contamination, and then measuring levels of Mn incorporated into hair during metabolism with high-resolution inductively coupled plasma mass spectrometry (ICP-MS).
Hair levels reflect exposure over time
Studies have suggested that levels of Mn in blood or urine may not reliably reflect environmental exposure. However, since hair grows relatively slowly, and since Mn is incorporated from blood into hair during hair growth, hair may reflect and integrate changes in body Mn levels from exposure over a period of several months.
As Smith explained, “In the simplest terms, hair Mn levels may reflect environmental Mn exposure over the period of hair growth better than other commonly used exposure biomarkers, such as urine or blood.”
High tech methods to measure Mn in hair
Smith’s group developed a hair analysis method using ICP-MS, scanning electron microscopy, and laser ablation. Exogenous metal contamination on hair that was untreated or intentionally contaminated with dust or Mn-contaminated water was removed using a sequential sonification cleaning method that does not alter the morphology of the hair, employing a laboratory detergent and weak nitric acid before rinsing in ultrapure water. Analyses were performed in a standard trace-metal clean room environment.
The cleaning method was then used on hair samples from 121children, which were collected as part of an on-going epidemiologic study of health effects of environmental Mn exposure from a ferroalloy plant operation in northern Italy. Studies have documented elevated air, dust, and soil Mn levels in the homes and schools near historically or currently active ferroalloy plants.
“Using this cleaning method, hair Mn levels were found to be significantly higher in children living in the vicinity of active, but not historic, ferroalloy plant emissions,” the authors concluded, “substantiating the use of hair Mn levels as a biomarker of environmental Mn exposure in children.”
Citation: Eastman RR, Jursa TP, Benedetti C, Lucchini RG, Smith DR. 2013. Hair as a biomarker of environmental manganese exposure. Environ Sci Technol 47(3):1629-1637.
(Bailey Schug studies health promotion at Appalachian State University. She is an intern with the NIEHS Office of Communications and Public Liaison.)