Team 2

Microplastics (MPs) are becoming increasingly prevalent in our world today and serving as a global environmental challenge. They are found everywhere, from our drinking water and food to clothing and the air we breathe. Evidence shows that not only can MPs cross our physiological borders, but they can also cross the placenta during pregnancy (Ragusa et al. 2021). MPs can also be found in other reproductive tissues like the placenta, semen, and ovarian follicular fluid (Zhang, et al. 2024). This raises risks of introducing toxic chemicals to fetuses. MPs can harm humans by disrupting molecular and cellular processes. Numerous studies have shown several mechanisms that indicate the exertion of toxicity: the activation of oxidative stress, triggering of inflammatory pathways, and uptake of cells through endocytosis. While the exact physiological mechanisms that demonstrate toxicity, such as long-term exposure in humans, dose-thresholds, and physical abnormalities, have not been fully studied, this review demonstrates that these mechanisms are well-articulated in studies regarding animal and cell-based models.  (Khan & Jia, 2023). The brain is one of the first (and most important) organs to be formed in an embryo. Observing the size of the brain during development has long been used to determine the health of the brain and nervous system (Watanabe, et al. 2021). 

The Chicken Embryo Model

To better gain knowledge on this phenomenon, chicken embryos can be used to emulate the development of a human fetus. Human and chicken brains share similarities in the early developmental stages of life. Chicken embryology has been deeply studied and there is a vast amount of information about every stage of development (Hamburger & Hamilton, 1951). The study of MPs has not been widely introduced in avian biology; therefore, it is important to increase the research in this area.

Key Observations:

The primary focus is to observe the size and growth abnormalities of the brain. However, secondary observations will include other physical abnormalities, such as eye size, to provide a more complete picture of systemic developmental impact.

   A total of 62 chicken eggs were utilized to determine the effect of microplastics on neurological development of an embryo. The largest average brain mass was observed in the treatment group (n = 39), which received microplastics treatment (Figure 1). Eggs that received microplastics had a significantly heavier average brain mass than those in the control group (t= 3.9, df = 61, p < 0.01).

Figure 1. Comparison of day 10 chicken embryos in control versus microplastic treated groups in relation to brain mass in mg (A), brain size in mm (B), and red discoloration (C), eye size in mm (D). The treatment group had a higher average brain mass in mg (t= 3.9, df= 61, p<0.01), a larger average brain size in mm (t= 3.2, df= 61, p= <0.01), no differences in discoloration (t= 1, df= 61, p= 0.31), and no differences in eye size (t= 0.71, df= 61, p=0.48).

In this study, we examine the effects of microplastics on the neurological development of chicken embryo brains. Microplastics have become a recent issue in our world today. They can be found in all types of water, tap water, bottled water, and ocean water. They can also be found in food, clothing, air, and more. Evidence shows that not only can microplastics cross our physiological borders, but they can also cross the placenta during pregnancy (Zhang, et al. 2024).  

We found that on average, the brains of the microplastic treated group had a larger brain mass and size than the control group. The treated group was 27.91% heavier than the control and 14.88% larger in size. One limitation of the project was the low sample size. With a larger sample size, we would have been able to perform more experiments and formulate a more credible conclusion. While the sample size was the main issue. Our equipment was also outdated and small. Another limitation was the inexperience of working with chicken embryos and the fragility of their tissues. It was easy to accidentally tear tissues while manipulating the positions of the embryos. More practice with embryos would be helpful in decreasing these mishaps.  

Other studies on micro plastics have highlighted their effect and not only animal, but also human health. In both males and females, toxicity in the developmental stages of an embryo may be caused by the chemicals that reside in micro plastics. Oxidative stress, epigenetic changes, and the inflammation all occur with microplastics present in the bloodstream (Zhang et. Al, 2024). In future studies, the question of whether the swelling of the brain is caused by a blockage of microplastics in small vessels or an increase of water retention should be asked. 

The entire group worked together to designed the experiment. A.T. led the data collection efforts during lab. R.K. organized the data and conducted the data analysis using image J. C.O. did data analysis and prepared the figures. We collectively wrote the first draft of the assignment and all edited and formatted it.