The Effects of Regulated and Unregulated Plastic Additives on Aquatic Organisms using Invertebrate and Vertebrate Models

  • Bidemi Mariam Green-Ojo

Student thesis: Doctoral Thesis

Abstract

Plastic additives have been found in freshwater and marine systems globally, and there is increasing concern regarding their long-term impact on aquatic organisms and by extension, their indirect effects on humans. The effects of pollution arising from plastic additives on ecosystem health and function are understudied, particularly in marine amphipods, and their effects on freshwater vertebrates are not fully understood. Regulations governing use, disposal, and maximum allowable limits in the environment are constantly changing, although not proactively, to protect the environment. Two of the selected plastic additives (N-butyl benzenesulfonamide (NBBS) and triphenyl phosphate (TPHP)) in this study are currently unregulated, classified on the international watchlist for evaluation, and have no set environmental quality standards (EQS). The other two are regulated plastic additives (diethylhexyl phthalate (DEHP) and dibutyl phthalate (DBP)), although banned, are persistent and found in the environment. This study aimed to assess the ecotoxicological impact and underlying mechanism of action of unregulated (NBBS and TPHP) and regulated (DEHP and DBP) plastic additives in the marine amphipod Echinogammarus marinus and freshwater vertebrate zebrafish (Danio rerio). This was achieved by exposing E. marinus to environmentally relevant concentrations of NBBS, TPHP, DEHP, and DBP to assess physiological (mortality, moulting, swimming activity, and startle response) and reproductive (sperm count and pairing behaviour) endpoints. There was a significant increase in mortality and impaired moulting in the tested compounds aside from DEHP while only TPHP and NBBS concentrations significantly impaired swimming activity and startle response of E. marinus. Assessing reproductive endpoint, TPHP significantly decreased sperm count. At the same time, precopulatory pairing behaviour was affected such that contact time (unsuccessful pairing attempt) and re-pairing time (successful pairing) were significantly prolonged in low environmental concentration (0.5 µg/l) of all the tested plastic additives. This was followed by studies on early life development of zebrafish exposed to NBBS, TPHP, DEHP, and DBP from embryos to 4 dpf to investigate their effects on development, locomotion, and underlying mechanisms of action by examining the expression of antioxidant genes (GST, GSR, GTPx, Cu/Zn-SOD, and p53) and acetylcholinesterase (AChE) activity. All tested compounds significantly decreased survival and hatching success and increased malformation. Swimming activity significantly reduced in 0.5 µg/l of all the tested compounds during dark conditions.
There was a significant upregulation and downregulation of the tested genes based on the compound and concentration of exposure, whereas no effects were found on AChE activity. This study is the first to demonstrate that plastic additives can have physiological effects on marine amphipods by impairing behaviour and reproduction at concentrations found in the environment, as well as the use of 4dpf old zebrafish to investigate NBBS and assess molecular endpoints of all the tested compounds. The findings of our study showed that unregulated plastic additives (NBBS and TPHP) had more detrimental effects on physiological and molecular endpoints than their regulated counterparts (DEHP and DBP), as tested in both vertebrate and invertebrate model species at concentrations found in the environment. This is a major concern, as there is no current set EQS for these compounds, thus presenting potential evidence of the risk they pose to aquatic animals. Further studies are needed to fully understand the mode of action of these selected plastic additives in non-target aquatic animals.
Date of Award9 May 2024
Original languageEnglish
Awarding Institution
  • University of Portsmouth
SupervisorAlex Ford (Supervisor), Matthew Parker (Supervisor) & Lena Grinsted (Supervisor)

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