From the perspective of biogeochemical prospecting (i.e. concerning
ppb concentrations of Au in plant tissues), Kovalevskii and Kovalevskaya [5] classified plant species and organs into four
groups:
(i) Non barrier bio-objects which give quantitative information on
the Au concentration in the growth medium.
(ii) Semi-non barrier bio-objects with high concentration limits of
3–300 times the Au concentration in the growth medium.
(iii) Barriers having concentration limits of 3–30 giving only qualitative
information on the concentration of Au in the growth
medium.
(iv) Background barriers which provide neither quantitative nor
qualitative information on Au concentration in the growth
medium.
Kovalevskii and Kovalevskaya [5] recommended the inner, middle
and outer bark of trees as non-barriers and confirmed them
as the main organs of trees which can reflect deeply buried Au
deposits based on a study of 33 separate species. Kovalevskii and
Kovalevskaya’s barrier concept states that every plant and plant
organ offers varying degrees of resistance to metal uptake. Thus,
when prospecting for an element, the focus of analysis has to be on
specific plants and plant organs.
More recently, researchers have reported inordinately large
concentrations (e.g. ppm to %-wt) of metals in some plants [12].
To this end, Baker and Brooks [13] classified plants into three categories:
(i) excluders; plants which do not take up metals, (ii)
hyperaccumulators; those which take up abnormally large quantities
of metal and (iii) indicators; those which take up metal
in proportion to its quantity in the soil. Hyperaccumulators of
From the perspective of biogeochemical prospecting (i.e. concerningppb concentrations of Au in plant tissues), Kovalevskii and Kovalevskaya [5] classified plant species and organs into fourgroups:(i) Non barrier bio-objects which give quantitative information onthe Au concentration in the growth medium.(ii) Semi-non barrier bio-objects with high concentration limits of3–300 times the Au concentration in the growth medium.(iii) Barriers having concentration limits of 3–30 giving only qualitativeinformation on the concentration of Au in the growthmedium.(iv) Background barriers which provide neither quantitative norqualitative information on Au concentration in the growthmedium.Kovalevskii and Kovalevskaya [5] recommended the inner, middleand outer bark of trees as non-barriers and confirmed themas the main organs of trees which can reflect deeply buried Audeposits based on a study of 33 separate species. Kovalevskii andKovalevskaya’s barrier concept states that every plant and plantorgan offers varying degrees of resistance to metal uptake. Thus,when prospecting for an element, the focus of analysis has to be onspecific plants and plant organs.More recently, researchers have reported inordinately largeconcentrations (e.g. ppm to %-wt) of metals in some plants [12].To this end, Baker and Brooks [13] classified plants into three categories:(i) excluders; plants which do not take up metals, (ii)hyperaccumulators; those which take up abnormally large quantitiesof metal and (iii) indicators; those which take up metalin proportion to its quantity in the soil. Hyperaccumulators of
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