**1. Introduction**

Environmental pollution by heavy metal is a wide ranging problem due to the urbanization and industrial development. For recent years, scientific world had shown the great interest in heavy metals as they had detrimental effect on atmosphere, aquatic and terrestrial environment [1]. Heavy metals are important class of pollutant with mass density greater than 4 g/cm3 or more such as, lead (Pb), chromium (Cr), cadmium (Cd), mercury (Hg), copper (Cu), zinc (Zn), arsenic (As) nickel (Ni) and manganese (Mn) [2]. These are discharged in the surroundings as an outcome of industrial activities, agricultural practices and atmospheric deposition.

Metals have important physiological and biochemical role in organism, symbolized as carcinogenic and toxic when concentration increased the required level as enlisted in **Table 1**. For instance, iron, copper and zinc have essential role in maintaining the structure of organism but show acute toxicity when exceed the concentration as in certain genetic disorders. Some heavy metals are not essential even in small concentration such as arsenic, mercury and lead become carcinogenic. For example, ingestion of arsenic, generally occur as arsenate, may cause cancer of various part of human body [10]. Lead and mercury are responsible for the autoimmunity thus


### **Table 1.**

*Effect of heavy metal on insects.*

leading to disease state of nervous system, renal, circulatory system and arthritis [11]. Cadmium exposure might cause kidney issues [12]. Exposure to mercury also causes various psychological and neurological damage such as panic, irregular sleep wake cycle and restlessness [12].

According to the report of WHO (World Health Organization), a million of people died every year in developing countries due to pollution induced diseases [13, 14]. The agricultural soil is contaminated by metal pollutant as a result of industrial product used in modern farming including insecticides, fertilizers, herbicide and sewage [15, 16]. Meanwhile, the pollutants are uptake to plant tissue from roots in soil therefore contaminated crop consumption becoming hazardous to living organism [17]. Pollutants toxicity has impacted the biological processes

**Figure 1.**

*Various means of heavy metal pollution and their transfer to insects.*

as well as biotic interaction among living organism such as ecological structure, parasitism and predator prey relationship [18] as shown in **Figure 1**.
