Estimating global marine surface microplastic abundance: systematic literature review.

Toxicity and persistence of microplastics (MP) in the marine environment has a potential to disturb the ecological balance of the planet. To evaluate the gravity of the situation, continuity in research of MP abundance is required. In this work for the first time a systematic literature review was conducted to build abundance datasets of MP at marine surface waters that were used to estimate average MP abundance and produce maps. Due to non-Gaussian distribution of the data, non-parametric statistics were used. The results show that an estimated average of approximately 6300 MP km MP float at the surface of the oceans. Additionally, observations of drawbacks in MP research that hamper inter-research comparability were made and these mainly include heterogeneity of methods and poor reporting practice. Basic guidelines to improve future research comparability were devised. Results provided here can be beneficial to research that requires a reliable and comparable MP abundance datasets sourced in a transparent and rigorous manner. These datasets are made available to the readers.