Bioaccumulation of Metals in Lichens and Mosses Understanding Atmospheric Deposition, Metal-induced Modifications and their Suitability as Biomonitors and Bioremediators

Abstract

Heavy metals (HM) make up a significant fraction of particulate air pollutants, which are of epidemiological concern. They easily accumulate in living organisms and have detrimental effects on various components of the ecosystem and human health that call for bioremediation methods to mitigate environmental contamination. The accumulation of heavy metals in biota (bioaccumulation) has been investigated for ages. Lower plant groups have been extensively used in bioaccumulation studies, more commonly the lichen and moss. Despite lichens and mosses being two unrelated groups of cryptogamic organisms, they have many common features that facilitate heavy metal accumulation, making them potential biomonitors and bioremediators. They lack true roots and thick waxy cuticles and alternately have a high surface-to-mass ratio to absorb nutrients from the atmosphere that makes them suitable for the cause. Biomonitoring studies using lichens and mosses date back to 1866 and 1970, respectively. Lichens often accumulate higher concentrations of atmophile elements and mosses higher concentrations of lithophile elements. Heavy metals are persistent in nature and can alter physiological processes like inhibition of photosynthesis, membrane damage, increase in reactive oxygen species (ROS), etc. Hence, monitoring and mitigating them are a necessity. Lichens and moss are to be investigated as biomonitors to evaluate atmospheric deposition and as bioremediators to correct environmental contamination to prevent HM from entering the food chain.