A single strand of hair from the head of an Indian woman in Norway has helped scientists refine a technique to assess past exposure to toxic metals, revealing a new tool to explore connections between the environment and illness.

Researcher Kristin Gellein at the Norwegian University of Science and Technology has shown that exposure to varying levels of metals over periods of months or even years show up as unique patterns of metal residues in hair.

Blood analysis for metals will yield only a snapshot of exposure at a specific point in time. But substances in blood also end up in hair. And since hair typically grows at about one centimetre a month, a 10-cm strand will allow scientists to analyse the exposure to metals over a 10-month period. “The longer a strand of hair, the further back in time we can probe,” Gellein told KnowHow.

Scientists have long known that ingested substances can accumulate in hair. Gellein was studying metal residues in the hair of an Indian woman, who had lived in Norway for several years, when she encountered a peculiar pattern of residues of a metal called strontium. The part of the strand closest to the head — and thus the youngest — had lower levels of strontium than the segments closer to the tip of the hair.

It’s a signal of changing levels of exposure to the metal, Gellein said.

Strontium levels in drinking water are far higher in India than in Norway, she said, although even moderate levels of exposure are not known to cause any harm. Water samples in India have about 1,300 micrograms strontium per litre, compared to 27 micrograms in Norway. “The Indian woman’s hair was 36cm long and provided us three years of information about exposure,” Gellein said.

In another person’s hair, which was 26cm long, she found huge differences in the levels of mercury and selenium. The highest concentrations appeared along specific segments, sandwiched between zones of low concentration. On questioning, the researcher found that the hair owner was an enthusiastic fisherman and ate a lot of marine fish in summer — a possible explanation for the variations.

“The new thing with her method is that we can measure many trace elements at the same time, and at extremely low levels,” said Tore Syversen, a neuroscientist at the Faculty of Medicine, Norwegian University of Science and Technology.

Gellein said the technique that uses a special instrument to pick up low concentrations of metal residues in the hair could be used to detect virtually any metal. The process involves the breaking down of all organic matter, and then examining the metal residues.

“We could use this to examine the history of arsenic exposure,” Gellein said.

But biochemists warn that hair, after all, is not the best indicator of exposure to pollutants. “It’s an interesting, non-invasive alternative to blood tests, provided the hair is not directly exposed to pollutants through external sources such as hair dyes or oils,” said Thuppil Venkatesh, head of biochemistry at St John’s Medical College, Bangalore.

Blood and spinal fluids provide the best results of exposure analysis, said Venkatesh. “Hair and nails are exposed to various substances in the environment and may not always reflect the true levels of exposure.”