Potential sources of microplastic contamination in laboratory analysis and a protocol for minimising contamination

Measurements of microplastics in environmental and biological samples can be overestimated because of contaminants introduced during the analytical process. Knowledge of the potential sources and frequency of contamination during analysis is required to develop a protocol to prevent analytical errors. In this study, potential sources of contamination in the laboratory analysis of biological samples were evaluated, and reliable, inexpensive measures to prevent contamination were tested. Glass fibre filters, water samples, air samples, and chemicals [Fenton's reagent (H2O2 and FeSO4), and ZnCl2] were tested for the presence of contaminants. Particulate contamination, including microplastics, was found in all samples when tested before application of any preventative measures. The following measures were evaluated for preventing contamination: (1) filtration of the water and chemical solutions using a glass fibre filter, (2) pre-combustion of the glass fibre filters, and (3) use of a clean booth for experimental work. The preventative measures reduced the levels of microplastics in all samples by 70-100%. The dominant polymers identified by Fourier transform infrared spectroscopy were polyethylene terephthalate, cellulose fibre (rayon), polystyrene, polyacrylonitrile, and polyethylene. With the preventative measures, the number of microplastics in the laboratory blanks was low enough to set the limit of detection to < 1. This limit of detection would be suitable for examination of microplastics contamination at the individual organism level, even at trace levels. Preventative countermeasures are essential to reduce overestimation of microplastics in biological samples and can be implemented at low cost.