Abstract:
Trace elements (TEs) may have toxic effects to plants and humans; thus, countries and organizations impose maximum
allowable regulation limits of their concentrations in soils. Usually such limits are placed in different categories
according to soil use, soil properties or based on both attributes. However, some countries have regulation limits
irrespective of differentiation in soil properties. In this review, we aimed at collecting TE regulation limits in soils
from major countries and organizations around the globe, and critiquing them by assessing potential human health
risks in the case of soils attaining the maximum allowable values. We explored the soil-to-human pathway and
differentiated among three major exposures from TEs, i.e., residential, industrial and agricultural. We observed the
existence of problems concerning TE regulation limits, among which the fact that limits across countries do not
regulate the same TEs, not even a minimum number of TEs. This indicates that countries do not seem to agree on
which regulation limits of TEs pose a high risk. Also, these regulation limits do not take into account TE mobility to
neighbouring environment interphases such as plant, especially edible, and water matrices. Moreover, limits for same
TEs are vastly diverse across countries; this indicates that those countries have conflicting information concerning TErelated
health risks. Subsequently, we addressed this problem of diversity by quantifying resultant risks; we did that
by calculating human health risk indices, taking into consideration the cases in which the highest allowable TE limits
are attained in soil. Arsenic limits were found to generate a relatively high hazard quotient (HQi, accounting for
human intake over the maximum allowable oral reference dose for that same TE), indicating that its risk tends to be
underestimated. Other TE limits, such as those of Cd, Cu, Ni, Pb, and Zn typically result in low HQi, meaning that
limits in their cases are rather overprotective. Our approach reveals the need of reducing diversity in regulation limits
by drafting soil legislations of worldwide validity, since risks are common across countries. We suggest that new
directions should strategically tend to (a) reduce limits of TEs with underestimated contribution to health risk (such
as As), (b) cautiously increase limits of TEs that currently cause minor health risks, (c) quantify TE risks associated
with uptake to edible plants and potable water, and (d) consider multi-element contamination cases, where risks are
cumulatively enhanced due to TE synergism.
