Diagram showing the commonly used methods for extracting plastics from environmental samples. The methods used are dependent on the types of samples taken and budget for the project. Samples for OSIMAP will be from oysters, crabs, seawater, and sediments and make use of all steps listed here except mass spectroscopy. Diagram taken from Nguyen et al. 2019.
The amount of microplastics in water, sediment, and animals can all be determined by filtering the sample through a flat circular filter called a membrane filter. Sediment samples must first have a very salty solution added to them that causes the less dense particles (the microplastics) to float out from the denser sediment. Any organic matter around the microplastic is then dissolved using a high pH potassium hydroxide solution. The water containing the microplastic then goes through a filter by vacuum suction. The microplastics that were in the water remain on the filter. The filter is then examined under the microscope so a count of the plastics can be taken. Fluorescent stains and lights are used to make the plastics glow and thus easier to spot. In a different microscope, a laser in then applied to the plastic and the resulting light information is then used to figure out what types of plastics are on the filter (Bessa et al., 2019; Frias et al., 2019; Gago et al., 2018). Researchers make sure these methods work in their lab by spiking a sample with a defined amount of microplastic and checking to see if they can recover close to 100% of the microplastic at the end of the analysis. Blank sample are also to assess how much plastic contamination is coming from the laboratory.
Bessa et al., (2019). Harmonized protocol for monitoring microplastics in biota. JPI-Oceans BASEMAN project.
Frias et al., (2018). Standardised protocol for monitoring microplastics in sediments. JPI-Oceans BASEMAN
Gago et al., (2018). Standardised protocol for monitoring microplastics in seawater. JPI-Oceans BASEMANproject.
Nguyen, B., Claveau-Mallet, D., Hernadez, L.M., Xu, E.G., Farner, J.M., Tufenkji, N. (2019) Separation and analysis of microplastics and nanoplastics in complex environmental samples. Accounts of Chemical Research 52.