*2.1.1 On the basis of mode of action*

**Accumulative bioindicators:** A type of bioindicators of environment that accumulate single or more element and chemical compound are called as accumulative bioindicators.

**Sensitive bioindicators:** A type of bioindicators that represent certain modification due to chemicals or elements exposure are called as sensitive bioindicators. The modifications may be related to tissue, morphology, cytology and organism or population behavior.

**Figure 2.** *Schematic illustration of classification of bioindicators.*
