Role of Helminth Parasites as Bioindicators of Heavy Metal Pollution in Environment

Abstract

Heavy metals pose a threat to the environment and living organisms because they are highly toxic, cannot be broken down by natural processes, bioaccumulates and biomagnifies in the food chain and can damage organs and disrupt vital biological functions even at extremely low concentrations. Thus, there is need for constant monitoring and removal of these toxic heavy metals from the environment. Because of their diverse responses to anthropogenic pollution, particularly heavy metal pollution, helminth parasites are gaining attention from parasite ecologists as possible markers of environmental quality. These parasites are strong bioindicators  in two different ways. Firstly, they are "effect indicators" and help to monitor the changes in whole population structure of parasites depending on the pollution of the environment. Secondly, they are "accumulation indicators" and help to  monitor the chemical state of their environment through their ability to concentrate environmental toxins within their tissues which is usually higher than the host tissues . The  majority of research revealed that helminth parasites, particularly cestodes and acanthocephalans, are more constant and trustworthy indicators of metal pollution due to their massive capacity to accumulate heavy metals which surpasses that of  most known free living bioindicators. The presence of parasite also have a significant impact on reduction of heavy metal accumulation in the host which help in their detoxification. Thus, parasites are advantageous to the both, environment as bioindicator of heavy metal pollution and to its host in reducing the amount of heavy metal from its tissue by accumulating in itself. Therefore, this review summarises the present knowledge on the role of helminth parasites as a bioindicator (biological indicators) in assessing the concentration of heavy metals in terrestrial and aquatic (marine, coastal and freshwater) environment and presents their role as sensitive indicators for environmental monitoring purposes.