Uptake of Metals from Soil into Vegetables - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 325

Chapter 8
Uptake of Metals from Soil into Vegetables

Mike J. McLaughlin, Erik Smolders, Fien Degryse, and Rene Rietra

Abstract The consumption of locally-produced vegetables by humans may be an
important exposure pathway for soil contaminants in many urban settings and for
agricultural land use. Hence, prediction of metal and metalloid uptake by vegetables
from contaminated soils is an important part of the Human Health Risk Assessment
procedure. The behaviour of metals (cadmium, chromium, cobalt, copper, mercury,
molybdenum, nickel, lead and zinc) and metalloids (arsenic, boron and selenium)
in contaminated soils depends to a large extent on the intrinsic charge, valence
and speciation of the contaminant ion, and soil properties such as pH, redox sta-
tus and contents of clay and/or organic matter. However, chemistry and behaviour
of the contaminant in soil alone cannot predict soil-to-plant transfer. Root uptake,
root selectivity, ion interactions, rhizosphere processes, leaf uptake from the atmo-
sphere, and plant partitioning are important processes that ultimately govern the
accumulation of metals and metalloids in edible vegetable tissues. Mechanistic mod-
els to accurately describe all these processes have not yet been developed, let alone
validated under field conditions. Hence, to estimate risks by vegetable consump-
tion, empirical models have been used to correlate concentrations of metals and
metalloids in contaminated soils, soil physico-chemical characteristics, and concen-
trations of elements in vegetable tissues. These models should only be used within
the bounds of their calibration, and often need to be re-calibrated or validated using
local soil and environmental conditions on a regional or site-specific basis.