**5. Quantification of trophic transfer**

The degree or extent of accumulation of HMs in biota has been quantified using some terminology. Bioconcentration factor (BCF), bioaccumulation factor (BAF), bioaccumulation coefficient (BAC) and so on are some of these quantitative terms. Below, some of these terms are discussed.

#### **5.1 Bioconcentration factor (BCF)**

Bioconcentration Factor is representative of the degree of heavy metal enrichment in an organism as opposed to that in its habitat. The ratio of the concentration of a heavy metal in the tissue of an organism to its concentration in the abiotic medium is known as' (water and sediments).

It is calculated by the following equation [60]:

$$B \text{CF} = \mathbf{C}\_{\text{organism tissue}} / \mathbf{C}\_{\text{abblotic medium}} \tag{1}$$

Where, *C*organism is the metal concentration in the organism tissue and *C*abiotic medium is the metal concentration in the abiotic medium.

The alternative words transfer factor (TF), metal transfer factor (MTF), accumulation factor (AF), bioaccumulation factor (BAF), and biota sediment accumulation factor (BSAF) are used by some writers and measured accordingly. All these indexes, however, indicate the extent of a heavy metal's accumulation in the organism compared to that in the world where it grows/lives.

#### **5.2 Bioaccumulation coefficient (BAC)**

Bioaccumulation Coefficient is calculated by the following equation [61]:

$$\mathbf{BAC} = \mathbf{C}\_{\text{plant}} / \mathbf{C}\_{\text{soll}} \tag{2}$$

Where, Cplant is the metal concentration in plant and Csoil is the metal concentration in soil.

The values of BCF, BAF, BAC, etc. are obviously dependent on the concentration of the HM in the organism and the environmental medium in question. In view of the fact that the values of these indices are inversely related to the concentration of metals in the environmental medium (water, sediments and soil), the values of these indices should be used with caution to measure the contamination of heavy metals in biota. For example, because of the lower metal content in the environment of the former fish, the BCF value of a heavy metal in the muscles of a fish living in less polluted water may be higher than that of a fish living in more contaminated water. The bio-concentration factor (BCF) values of seven common HMs in crop grains have been shown to decrease exponentially with average soil metal concentrations [62].
