**2. Immunotoxins and their impact on aquatic invertebrates**

Immunotoxins are chemical compounds that can modulate the immune-related parameters and can adversely affect the biological and physiological functioning of the immune system of organisms including human. The freshwater ecosystem of India is being contaminated by diverse groups of xenobiotics of known and unknown chemistry. Ray et al. (2011) reported mineral acids, alkalis, detergents, metalloids and pesticides as major environmental contam‐ inants of the Indian freshwater ecosystem [1]. Scientists reported [2] the toxic effects of pyrethroids, cypermethrin and fenvalerate in aquatic molluscan invertebrates and claimed them as immunotoxins for their adverse effect on the immune parameters of host animal. Toxicity of these pyrethroid pesticides on non-target aquatic invertebrates appears to be detrimental and can seriously affect their survival efficacy and reproductive success. Arsenic, another metalloid and a potent immunotoxin, bears toxic effects on aquatic invertebrates and can modulate the histopathology and immune parameters of freshwater mollusc [3] and estuarine mud crab [4]. Biopesticide azadirachtin has been recently identified as an immuno‐ toxin due to its potential to affect the immunofunctioning of mussels. Moreover, during monsoon and flood, pesticide-laden agricultural runoff often contaminates the freshwater ecosystem and poses serious threat to its inhabitants. Washing soda, chemically known as anhydrous sodium carbonate, is an important aquatoxin that can alter the selected physiolog‐ ical parameters of diverse groups of invertebrates. Mukherjee et al. (2015b) reported the toxicity of washing soda in a freshwater sponge of India with reference to its phagocytic and cytotoxic status [5]. Altered functioning of the immune system may lead to opportunistic invasion of environmental pathogens and parasites into the body of host and increase the vulnerability of these biofilter species in polluted environment.

The nature and magnitude of immunotoxicity depend on multiple parameters including the concentration of toxin, type and span of exposure and route of entry to the host. Immunotoxins invertebrates [7].

are difficult to identify as they can cause a wide magnitude of adversity on the immune status of organisms. Immunotoxicology deals with the assessment of toxicological response in an organism by estimating the responsiveness and reactivity of its immunological parameters. Immunotoxicology of invertebrates, in recent times, has been gaining a special scientific attention for its efficacy in monitoring the health of environment – both aquatic and terrestrial. Accuracy and precision of selected toxicological responses of aquatic invertebrates enabled a few species to function as suitable biomonitoring agents of water pollution [6]. Several effective immunomarkers of aquatic pollution have recently been established in model invertebrates [7].

system may lead to opportunistic invasion of environmental pathogens and parasites into the

the concentration of toxin, type and span of exposure and route of entry to the host.

Immunotoxins are difficult to identify as they can cause a wide magnitude of adversity on the

immune status of organisms. Immunotoxicology deals with the assessment of toxicological

response in an organism by estimating the responsiveness and reactivity of its immunological

parameters. Immunotoxicology of invertebrates, in recent times, has been gaining a special

scientific attention for its efficacy in monitoring the health of environment – both aquatic and

terrestrial. Accuracy and precision of selected toxicological responses of aquatic invertebrates

enabled a few species to function as suitable biomonitoring agents of water pollution [6]. Several

effective immunomarkers of aquatic pollution have recently been established in model

The nature and magnitude of immunotoxicity depend on multiple parameters including

body of host and increase the vulnerability of these biofilter species in polluted environment.

**Figure 1.** Attributes of cell-mediated immune responses of invertebrate immunocytes exposed to various aquatic pol‐ lutants.
