This group includes elements that are used as nutrients by only a limited number of plant species.  When high concentrations of an element, not commonly found in most plants, is seen in a particular species, it raises the possibility that the element is essential for that species.  The plants may use these for non-nutritional purposes.  It is thought that species where these elements are present may use them for protection against invading bacterii.  For example, Barium is found in brazil nuts; Aluminum in tea; Chromium, Nickel and Cobalt in gramineae; Silicon in rice and cucumbers.

BARIUM  (Ba) 137.33 Atomic Weight

(Essential Trace Element?)

Barium is not recognized as a plant nutrient, although it is found in certain plant species.  It constitutes 0.04% of the earth’s crust, totally in combinations with other mineral elements. Barium is widely used in the medical and manufacturing industries.  Though Barium minerals are very dense, barium itself is comparatively light.  Barium and all its mineral compounds that are soluble are toxic, so it is not known why some plant species survive with the levels of Barium present.

BROMINE  (Br ) 79.90 Atomic Weight

(Essential Trace Element?)

Bromine is a rare element dispersed throughout the earth’s crust in compound form.  In sea water, it constitutes 65 parts per million by weight.  It combines readily with many elements. With the exception of a few plant species, Bromine has no known biological role.  It is a toxin that is sometimes used in the control of nematodes and other invading microbes in the soil.  Its main uses are in the medical and fossil fuel industries.  It is not known why certain plant species contain significant levels of  Bromine.

NICKEL  (Ni) 58.70 Atomic Weight

(Essential Trace Element?)

Nickel in its elemental form occurs sparingly in terrestrial and meteoric deposits.  In compounds, it constitutes approximately 0.007% of the earth’s crust, twice as abundant as copper.  Its primary use is in the manufacture of metals and as a protective coating.  It has properties that are resistant to oxidation and corrosion.  The biological role of Nickel in uncertain, as it is carcinogenic or toxic, depending upon its compound form.  It is not known why certain species of plants contain higher levels of Nickel.