Microplastic Pollution as a Driver of Immune Dysregulation in Marine Mammal Populations

Abstract

Introduction: Microplastic (MP) pollution is now an important environmental issue, especially in marine environments, where it endangers marine mammals. The bioaccumulation of MPs in the food web causes different biological effects on apex predators like the marine mammals. MPs have the capacity to disrupt immune homeostasis through oxidative stress, inflammation, and immune dysfunction. The review is a synthesis of existing studies on how MPs affect the immune systems of marine mammals and the pathways of the immune system dysregulation, i.e., oxidative stress, chronic inflammation, and cytokine imbalance. Materials and Methods: This review combines experimental toxicology, mechanistic research, and environmental evaluation regarding exposure to microplastics in the marine environment. It concentrates on the rodent, fish, and aquatic invertebrate models because they are related to marine mammal immune systems. Such important techniques as the measurement of oxidative stress, inflammatory cytokines, and immune function should be mentioned. Also, the review brings out the effects of movements of toxic chemicals such as heavy metals and persistent organic pollutants (POPs) by MPs, which aggravate the immune dysfunction of exposed organisms. Results and Discussion: MP exposure leads to the dysregulation of the immune system by way of elevated reactive oxygen species (ROS), diminished antioxidant defense, and stimulation of the inflammatory cytokines. The level of ROS increased up to 50%, cytokines such as TNF-α, IL-6, and IL-1β B were increased by 30-60% in experimental models. There is impaired lipid metabolism and gut microbiota in marine mammal models, which further impair the immune system. The MPs are also the transporting agents of heavy metals and persistent organic pollutants, which enhance the immune disruptions. Marine mammals are most prone to chronic exposure data whereby MPs are found in major body parts such as liver, gastrointestinal tract and lungs. Conclusion: The health of marine mammals is increasingly endangered by the microplastic pollution that causes dysregulation of the immune system and predisposes them to disease. Due to the long-term exposure and bioaccumulation of the marine ecosystems, additional studies on the immunotoxicology of MPs on marine mammals are critical to the effective conservation and mitigation measures.