Article Preview
Top1. Introduction
Birds have been known to be important species for ecotoxicological analysis. Choice of a suitable bird for ecotoxicological study depends on the diversity, ecology, behavior, reproduction system and origin of the species (Stokes, 2004). Again, a variety of diverse factors, together with migratory abilities, worldwide distribution, diverse for aging habits, conspicuous nature, and their sensitivity to environmental pollutants, contaminant exposure has been better documented in birds than in any other terrestrial vertebrate group. This makes them vital species for a defined toxicity study (Smith et al., 2007). Endocrine disrupting chemicals (EDCs) have been associated with adverse effects on development and reproduction in birds and other wildlife species. Due to rapid industrialization, there is an emergence of continuous development of new EDCs which are affecting not only wildlife but humans too. The endocrine system of birds is comparable to mammals according to many aspects of the anatomy, physiology, and biochemistry which make them good species for ecotoxicity modeling (Ritchie and Pilny, 2008). Therefore, in vivo and in silico modeling of EDC’s toxicity to birds can help to fill up the data gaps for higher taxonomy animals also. Anas platyrhynchos, commonly known as Mallard duck is one of the common avian test species recommended by Organization for Economic Cooperation and Development (OECD) (OECD, 2010) and United States Environmental Protection Agency (US EPA) (EPA, 2012) and has been traditionally used in acute oral toxicity tests, the 50% lethality from oral dose (LD50).
The EDCs include organochlorine pesticides, polychlorinated biphenyls (PCBs), phthalates and brominated flame retardants that can interfere with the hormone homeostasis in the body (Jiménez et al., 2007). Disruption of hormone systems affect the thyroid system, reproductive hormones, immune system and neurological behavioral development. A good number of studies showed adverse effects in wildlife and also amplified the anxiety about potential endocrine disruptive effects in humans (Stokes, 2004). The aim of ecotoxicological research is to examine and predict the fate of the environmental contaminants in the environment, their bioavailability, uptake in diverse organisms, toxicokinetics, and potential effects. Ecotoxicological risk assessment is an important part of current legislative frameworks regarding chemical production and use. Again, due to limitation of animal studies, there is also much emphasis on the use of in vitro models as well as alternatives to animal testing like chemometric tools and/or in silico models (Kar et al., 2106). Among the alternatives, quantitative structure-activity relationship (QSAR) models are the front runners and most acceptable among the regulatory bodies over the world. The application of a QSAR model is recommended for risk assessment and management of environmental hazards by regulatory agencies like European Centre for the Validation of Alternative Methods (ECVAM) of the European Union, European Union Commission's Scientific Committee on Toxicity, US EPA, and the Agency for Toxic Substances and Disease Registry (ATSDR).