Forsøksdyr: Digestion and transfer of microplastic contaminants in fish larvae

Godkjenningsdato 16.04.2018

Plastics represents the most abundant pollutant of the oceans. Ingested plastics by marine organisms is not digested, potentially leading to blockage in the gastrointestinal tract (GI-tract), inflammations and erroneous satiety signalling leading to malnutrition or starvation. Plastics also functions as a vector for contaminants, which potentially becomes released from the plastics and absorbed by biological tissues to a various degree upon ingestion.

This RCN funded project PlastiCod studies the vector capacity and kinetics of microplastics saturated with pollutants in the marine ecosystem and within Atlantic cod (Gadus morhua). The focus of the current section of the project is the release of polychlorinated biphenyls (PCB) added a 14C-tracer from ingested microplastics in Atlantic cod larvae at environmentally low, medium and high concentrations of PCB in plastics reported at worldwide locations.

Contaminated microplastic spheres (microspheres) will be tube-fed to sedated fish larvae as described in Rønnestad et al. (2001) allowing the microspheres being delivered directly into their GI-tract with minimal handling. After recovery, the larva is incubated in a small well of thermostated seawater to enable the microplastics to evacuate the gut (>24hours). Once the gut is empty, the larvae are euthanized by a MS 222 overdose.

The concentration of PCB in the microspheres prior to feeding, the larval body after feeding, and the evacuated microspheres will be analysed using a liquid scintillation counter. The in vivo results will be incorporated in a biodynamic modelling tool to i) describe the residence time of microspheres in the GI-tract and ii) trace the PCB in different compartments (larval body and water) at different time points and iii) retrieve a dose-response curve for PCB in the larvae. These results will increase our understanding of the transfer kinetics of conatminant substances between microplastics and marine organisms hence our knowledge of pollution management and marine environmental health and guide the policymakers in formulating better policies.

Regarding selection of model animal. Depending upon welfare indicators assessment (humane endpoints) after tube-feeding in a pilot study, the project may switch to Atlantic herring (Clupea harengus) as a model. Herring has previously been shown to be very resilient to handling, including tube-feeding (Koven et al., 2002, Conceição et al., 2002, Rojas-García et al., 2016). The data acquired for this marine teleost will give an equally valuable set of data to assess the challenges with the transfer of contaminants to fish larvae from microplastics. If herring is not available/suitable, Zebrafish (Danio rerio) is an alternative, a very resilient fish available whole year at UiB.

Regarding the 3R, live animals are needed to determine the transfer of contaminants from microplastics ingested by fish to esstablish the biodynamic model and "Replacement" is not possible. Regarding the “Reduction”, the minimum number of animals will be used to assess the effects of the treatments with statistical significant detection of tracer in the samples (based on pilot study). Concerning “refinement”, various measures will ensure minimal impact before and during treatment with frequent monitoring, use of anaesthesia, and well-defined humane end-points where animals will be euthanized immediately.