Research On The Spatial Distribution Of The Marine Microplastics

Microplastics are small plastic fragments formed by biodegradation,or sun exposure,weathering and other abiotic processes after plastics enter the environment.Conventionally,microplastics are defined as the one with particle size less than 5mm.Due to the negative impacts of microplastics on wildlife,the plastic pollution attracts more and more attentions.It is one of the hot spots in marine ecological environment research.With more and more of the production and use of plastic products,the number of microplastics is also increasing.It finally goes into the ocean through either the surface runoff or other ways,thus causes serious harm to the marine ecology.Due to its small size,it is difficult to sample and detect.One of the consequences is that there are very few public data sets.In this paper,the microplastics data published in various journals are collected to construct the spatial distribution data set.From the perspective of fluid mechanics,the point particle model and continuum model of microplastics movement in fluid are discussed.It is concluded that due to the interaction between microplastics and fluid,the clustering will be emerged in both small scale and large scale.As a result,the spatial distribution of microplastics should obey a power-law against the spatial scales.In this paper,the second order structure function S2(r)=<|C(i+r)-C(i)|2)was applied to collected data sets.The power-law behavior was confirmed experimentally.Based on the fact that the marine microplastics are mainly from land,analogy with the boundary layer theory,the distance again the land dependence is assumed for the concentration of the marine microplastics.Qualitatively,with the increasing of the distance,the concentration is decreasing.Experimentally,the power law decaying is observed.These findings support the idea that microplastics follow ocean currents as passive scalars.