ing large amounts of Cu when the pH was above this
value. The CaCl2-extractable Cu was correlated with the
concentration of Cu in the aerial parts of maize,
although it was shown that the relationship was rather
weak (see the scattering of the experimental points in
Fig. 2, especially so for acid soils). In fact, pH and total
Cu had comparable eects in the same order of impor-
tance for explaining CuCacl2
content and Cu concentra-
tion in the aerial parts of maize (Table 7). In addition,
CuCacl2
content was found to be correlated with Cu
concentration in aerial parts of wild plants growing in
situ in vineyard plots in soils with acidic to neutral pH
(Brun et al., 1998). These results suggest that this
extraction method may be used for ecotoxicological
purposes, in order to assess the risk for Cu to enter the
food chain and to monitor food quality (consumption
of aerial parts of plants by herbivorous animals and
human beings).
Collecting roots from plants which have grown in
soils, even in a pot experiment, is an extremely long and
tedious procedure which cannot be carried out routinely
at the laboratory level. It requires careful washing to
avoid any overestimation that could arise because of
incomplete removal of soil particles adhering to the
roots. In addition, recovering the whole root system is
an almost impossible task for species with ®ne roots
such as tomato (Brun, 1998). However, for overcoming
such diculties the experimental device proposed by
Guivarch et al. (2000) and successfully applied to Cu by
Cherrey et al. (1999) appear as a potential alternative.
This technique that provides an easy access to the roots
by preventing them to grow into the contaminated soil
with a nylon mesh would need to be applied to a larger
range of soils and plant species in order to ascertain the
conclusions of the present work.