Carrying on from the last post, we will be discussing the effects of marine plastic pollution on human health. I’m sure that many of you have heard of the message from the World Wildlife Fund International that we could be eating up to a credit card worth of plastic every week. Reuters Graphics also visualised the amount of microplastics we could be eating in a different way, which I found to be more visually shocking.
Visualisation of the amount of microplastic we could be ingesting through the use of dinnerware (adapted from Reuters Graphics)
To be fair, 5g is the upper estimation of the mass of microplastic ingested per week. Senathirajah et al. (2020) had actually estimated 0.1g-5g. Hence the actual amount of microplastic we are ingesting is likely somewhere in between those numbers. The consumption of seafood is one of the pathways for human exposure to microplastics, as they can be found in many species of fish, bivalves and crustaceans. Other products made from water or salt extracted from seawater, such as beer and honey, were also found to contain microplastics (Smith et al., 2018).
Our bodies are able to remove more than 90% of ingested microplastics and nanoplastics via the excretion of faeces (EFSA Panel on Contaminants in the Food Chain (CONTAM), 2016). However, some microplastics remain and those that >150µm may result in inflammation and immunotoxicity (Hirt & Body-Malapel, 2020). Microplastics that are smaller than 150µm may translocate across the intestinal epithelial cells, resulting in systemic exposure (Lusher et al., 2017). They are able to enter cells, the blood-brain barrier and even the placenta (Barboza et al., 2018). What happens after this? Exposure of microplastics to our cells may lead to oxidative stress, DNA damage, necrosis, or apoptosis, where the cells essentially self-destruct (Lusher et al., 2017).
The risk of exposure to chemicals from plastics is also worrying. Chemical additives in plastics, such as phthalates, bisphenol A (BPA) and polybrominated bisphenols, have been found to exhibit endocrine-disrupting properties (Lusher et al., 2017). Endocrine-disrupting chemicals disrupt hormonal activity, which can result in adverse impacts on reproductive health and cancer development in adults, as well as the development of the brain and immune system in foetuses (Darbre, 2020).
Lastly, marine plastic debris may serve as vectors for pathogens. Microbial communities have been found to colonise microplastics (Barboza et al., 2018). Microplastics may also accelerate the transfer of antibiotic resistance genes in bacteria through the depolymerization chemicals it leaches (Yuan et al., 2021). However, the impact that this may have on humans had not been well-documented and would require more data to ascertain.
In general, communities that rely heavily on seafood to meet their dietary requirements are at higher risk of experiencing these effects on their health. Understanding the impact of microplastics on their food security is an area that requires greater research focus.
References
Barboza, L.G.A., Vethaak, A.D., Lavorante, B.R.B.O., Lundebye, A.K. & Guilhermino, L. (2018). Marine microplastic debris: an emerging issue for food security, food safety and human health. Marine Pollution Bulletin, 133: 336-348.
Darbre, P.D. (2020). Chemical components of plastics as endocrine disruptors: overview and commentary. Birth Defects Research, 112(17): 1300-1307.
EFSA Panel on Contaminants in the Food Chain (CONTAM) (2016). Presence of microplastics and nanoplastics in food, with particular focus on seafood. European Food Safety Authority Journal, 14(6).
Hirt, N. & Body-Malapel, M. (2020). Immunotoxicity and intestinal effects of nano- and microplastics: a review of the literature. Particle and Fibre Toxicology, 17: 57.
Lusher, A., Hollman, P. & Mendoza-Hill, J. (2017). Microplastics in fisheries and aquaculture: status of knowledge on their occurrence and implications for aquatic organisms and food safety. FAO Fisheries and Aquaculture Technical Paper: 615.
Senathirajah, K., Attwood, S., Bhagwat, G., Carbery, M., Wilson, S. & Palanisami, T. (2020). Estimation of the mass of microplastics ingested – a pivotal first step towards human health risk assessment. Journal of Hazardous Materials, 404(Pt B): 124004.
Smith, M., Love, D.C., Rochman, C.M. & Neff, R.A. (2018). Microplastics in seafood and the implications for human health. Current Environmental Health Reports, 5(3): 375-386.
Yuan, Q., Sun, R., Yu, P., Cheng, Y., Wu, W., Bao, J. & Alvarez, P.J.J. (2021). UV-aging of microplastics increases proximal ARG donor-recipient adsorption and leaching of chemicals that synergistically enhance antibiotic resistance propagation. Journal of Hazardous Materials, 427: 127895.