Non-invasive samples for biomonitoring heavy metals in terrestrial ecosystems.

As highly relevant environmental contaminants, metals and metalloids have been extensively evaluated for decades in biomonitoring programs, due to their potential toxicity at low levels and high persistence in many ecosystems. When considering chemical analysis, metal quantification has been carried out through conventional methods, based on the determination of their levels in internal organs, such as the liver and kidneys. Nevertheless, non-invasive methods constitute an alternative response regarding trace elements biomonitoring studies. Specifically, keratinized tissue from terrestrial mammals (such as hair, nails, or spines) presents a high accumulation rate, giving relevant information about heavy metal dynamics at internal levels and, most particularly, a chronic exposure. This critical review focuses on the use of non-invasive tissues, mainly hair and spines, as adequate tools on heavy metals assessment, specifically mercury (Hg) and lead (Pb), in biomonitoring studies performed in terrestrial wild mammals.