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→Biological classification of elements
Trace elements are those elements that have concentrations far below 0.1% in the body; they are needed in the body only in parts per million (ppm). They are essential to plant and animal lives only in trace amounts. Such trace elements are called essential trace elements (Christine et al, 2000). They are highly variable in their abundance in various rocks (Table 1, Khandare, 2012 ).
Trace elements are those elements that have concentrations far below 0.1% in the body; they are needed in the body only in parts per million (ppm). They are essential to plant and animal lives only in trace amounts. Such trace elements are called essential trace elements (Christine et al, 2000). They are highly variable in their abundance in various rocks (Table 1, Khandare, 2012 ).
{| class="wikitable"
|-
|+ Table 1: Average abundances of selected elements in bedrock, all values in ppm ( after Khandare, 2012).
|-
! Element !! Ultrabasic Rock !! Basalt !! Granite !! Shale !! Limestone
|-
| As || 1 || 2 || 1.5 || 15 ||2.5
|-
| Cd || - || 0.2 || 0.2 || 0.2 || 0.1
|-
| Co || 150 || 50 || 1 || 20 || 4
|-
| Cr || 2000 || 200 || 4 || 100 | 10
|-
| Cu || 10 || 100 || 10 || 50 || 15
|-
| Pb || 0.1 || 15 || 20 || 20 || 8
|-
| Se || - || 0.05 || 0.05 || 0.6 || 0.08
|-
| U || 0.001 || 0.6 || 4.8 || 4 || 2
|-
| W || 0.5 || 1 || 2 || 2 || 0.5
|-
| Zn || 50 || 100 || 40 || 100 || 25
|}
Deficiency of these elements in the soil results in their low abundance in plants. Sequel to this, plants –as primary producers –would decline in supplying them to animals and humans– the consumers. Deficiency of these nutrients brings negative health effects to humans and animals. A typical example is iodine deficiency which leads to goiter, which is caused by ‘shortage’ of iodine in the rocks. On the other hand, over-abundance of any of these elements causes toxicity problems (Table 2). For instance, excess arsenic is known to cause lesion of the skin in some Asian countries such as Bangladesh and China (Bunnell et al, 2007).
Deficiency of these elements in the soil results in their low abundance in plants. Sequel to this, plants –as primary producers –would decline in supplying them to animals and humans– the consumers. Deficiency of these nutrients brings negative health effects to humans and animals. A typical example is iodine deficiency which leads to goiter, which is caused by ‘shortage’ of iodine in the rocks. On the other hand, over-abundance of any of these elements causes toxicity problems (Table 2). For instance, excess arsenic is known to cause lesion of the skin in some Asian countries such as Bangladesh and China (Bunnell et al, 2007).