Toxicological impacts of persistent organic pollutants on avian physiology: A scientometric and systematic analysis

Abstract

Persistent organic pollutants (POPs), primarily from industrial and agricultural sources, pose significant risks to birds due to their environmental pervasiveness, bioaccumulation, and toxicological impacts. Bird's trophic position and ecological traits make them vulnerable to POP exposure while also serving as bioindicators of environmental contamination. This review aims to systematically evaluate the global occurrence and bioaccumulation of POPs in birds, focusing on exposure pathways, non-invasive and tissue-based monitoring, species-specific sensitivity, and long-term toxicological impacts on avian physiology, behaviour, reproduction, and neural development. A systematic literature review was conducted following PRISMA guidelines, using peer-reviewed articles and international reports. Key themes and trends were analyzed using VOSviewer for keyword clustering and network visualization, allowing assessment of POP exposure in avian populations. POPs were widespread with higher bioaccumulation in seabirds and passerines than freshwater and terrestrial species, reflecting biomagnification through the food web. Notably, terrestrial birds accumulate hydrophobic POPs more readily than aquatic birds due to reduced elimination efficiency and dietary differences. Bioaccumulation was most pronounced in tissues such as liver, blood, preen gland oil, feathers, and eggs, reflecting species-specific, ecological, and migratory variations. Non-invasive matrices provide valuable tools for long term monitoring. POPs exposure in birds leads to multiple behavioral and physiological disruptions, primarily affecting endocrine and immune systems, influencing growth, survival, and reproductive success. POPs activate aryl hydrocarbon receptor (AHR) and disrupt the hypothalamus-pituitary-thyroid axis, causing prenatal hypothyroidism, delayed hatching, impaired ovarian steroidogenesis, reproductive failure, and reduced eggshell thickness through altered calcium transport and bioavailability. POPs can cross the blood-brain barrier, leading to neural effects including spinal cord dysmyelination, cerebral asymmetry, oxidative stress, disrupting dopaminergic, cholinergic, and serotonergic neuronal pathways, ultimately disrupting navigation, spatial behaviour, and cognitive function. Temporal trends indicate a decline in some legacy POPs following regulatory measures, though contamination persists in high trophic species, reflecting complex global contamination patterns. These findings emphasize the importance of monitoring POPs in birds and underscore the need for stringent restrictions and regulations to mitigate ecological risks and protect wildlife.