Abstract:
recent decades. Ultramafic environments lead to potential risks to the agricultural products and, subsequently, to
human health. This unique review presents geochemistry of ultramafic soils, TM fractionation (i.e. sequential
and single extraction techniques), TM uptake and accumulation mechanisms of ultramafic flora, and ultramaficassociated
health risks to human and agricultural crops. Ultramafic soils contain high levels of TMs (i.e. Cr, Ni,
Mn, and Co) and have a low Ca:Mg ratio together with deficiencies in essential macronutrients required for the
growth of crops. Even though a higher portion of TMs bind with the residual fraction of ultramafic soils, environmental
changes (i.e. natural or anthropogenic) may increase the levels of TMs in the bioavailable or extractable
fractions of ultramafic soils. Extremophile plants that have evolved to thrive in ultramafic soils present
clear examples of evolutionary adaptations to TM resistance. The release of TMs into water sources and accumulation
in food crops in and around ultramafic localities increases health risks for humans. Therefore, more
focused investigations need to be implemented to understand the mechanisms related to the mobility and
bioavailability of TMs in different ultramafic environments. Research gaps and directions for future studies are
also discussed in this review. Lastly, we consider the importance of characterizing terrestrial ultramafic soil and
its effect on crop plants in the context of multi-decadal plans by NASA and other space agencies to establish
human colonies on Mars.
