The occurrence and transport of microplastics: The state of the science

Microplastic (MP) particles have been observed in most environments and concentrations are expected to increase over the coming decades given continued and increased production of synthetic polymer products. The expected increase in plastic pollution (including MPs) may elevate the risk posed by these synthetic particles to both environmental and human health. The purpose of this review is to provide a review of the state of knowledge regarding the occurrence and transport of MPs in and across three of the Earths subsystems, specifically, the lithosphere, atmosphere, and hydrosphere. Evidence is presented that shows the lithosphere includes substantial MP accumulation (e.g. approximately 25 particles L^-1 in landfill leachate), the impacts of which remain poorly understood. The atmosphere plays an important role in MP transport, with increased occurrence and higher transport concentrations noted in more densely populated areas (e.g. 175 to 313 particles m^-2 d^-1 in Dongguan China). In the hydrosphere, freshwater ecosystems alternate between MP transport (e.g. rivers) and deposition (e.g. lakes) with flow rate being identified as a key factor determining the movement and fate of MPs. Conversely, marine ecosystems act as a major sink for MP pollution (e.g. MP comprise 94%, approximately 1.69 trillion pieces, of plastic pieces in the Great Pacific Garbage Patch), driven by direct deposition or by transport via the atmosphere or freshwater conveyance systems (e.g. streams, rivers, or ice sheets). Once ingested by organisms, the trophic transfer and bioaccumulation of MPs has been confirmed with the polymer particles potentially accumulating in or impacting fauna, flora, microbes, and humans. Finally, 16 areas are identified in which future MP research efforts should be focused, with the goal of accurately identifying the scope and potential risks posed by synthetic polymer pollution. This review serves as a valuable steppingstone for future research and researchers wishing to address MP research gaps across various environmental settings in the coming decades.

Transfer of trace elements in the ocean-atmosphere-continent system as a factor in the formation of the elemental composition of the Earth's soil cover

The dynamics of global flows of matter in the biosphere has been studied. The general law of redistribution of average elemental compositions in the biosphere between the solid and liquid phases (lithosphere-hydrosphere) is established. In these processes, the main role is played by "living matter." The most active processes of redistribution of mean elemental compositions in the biosphere take place in the places of "life thickening" (biogeochemical barriers) such as ocean-atmosphere, river-sea and hydrosphere-lithosphere. The result of these processes is a general relative increase in the concentrations of trace elements in the environment of living organisms. A new methodological approach is proposed to study the role of the transfer of trace elements in the ocean-atmosphere-continent system as a factor in the formation of the elemental composition of the Earth's soil cover.

Integrating connectivity theory within watershed modelling part I: Model formulation and investigating the timing of sediment connectivity

Integrating connectivity theory within watershed modelling is one solution to overcome spatial and temporal shortcomings of sediment transport prediction, and Part I and II of these companion papers advance this overall goal. In Part I of these companion papers, we present the theoretical development of probability of connectivity formula considering connectivity's magnitude, extent, timing and continuity that can be applied to watershed modelling. Model inputs include a high resolution digital elevation model, hydrologic watershed variability, and field connectivity assessments. We use the model to investigate the dependence of the probability of connected timing and spatial connectivity on sediment transport predictors. Results show the spatial patterns of connectivity depend on both structural and functional characteristics of the catchment, such as hillslope gradient, upstream contributing area, soil texture, and stream network configuration (structural) and soil moisture content and runoff generation (functional). Spatial connectivity changes from catchment-to-catchment as a function of soil type and drainage area; and it varies from event-to-event as a function of runoff depth and soil moisture conditions. The most sensitive connected pathways provide the stencil for the probability of connectivity, and pathways connected from smaller hydrologic events are consistently reconnected and built upon during larger hydrologic events. Surprisingly, we find the probability of connected timing only depends on structural characteristics of catchments, which are considered static over the timescales analyzed herein. The timing of connectivity does not statistically depend on functional characteristics, which relaxes the parameterization across events of different magnitudes. This result occurs because the pathway stencil accumulates sediment from adjacent soils as flow intensity increases, but this does not statistically shift the frequency distribution.

Multimedia fate and transport simulation of perfluorooctanoic acid/ perfluorooctanoate in an urbanizing area

Strong global demand leads to significant production of fluoropolymers (FP) in China which potentially release large quantities of perfluorooctanoic acid/perfluorooctanoate (collectively called PFOA/PFO) to the environment. Modelling the fate and transport of PFOA/PFO provides an important input for human health risk assessment. Considering the effects of urbanization and existing forms of PFOA/PFO, this study used the modified multispecies Berkeley-Trent-Urban-Rural model to simulate the transfer behavior of PFOA/PFO in the Bohai Rim, China. Spatial distributions of PFOA/PFO emissions during the year 2012 for the study area were illustrated. About two thirds of the total amount of PFOA/PFO was estimated to be released into fresh water, and the total releases to rural areas were 160-fold higher than those to urban areas due to the location of fluorochemical industrial parks. The simulations predicted that hydrosphere was the fate of PFOA/PFO, followed by soil and vegetation, which was consistent with field data. The highest PFOA/PFO concentration was modeled in the Xiaoqing River basin with a value of 32.57 μg/L. The PFOA/PFO concentrations in urban soils were generally higher than those in rural soils except for grids 1, 3 and 46. In addition, it was estimated that the total flux of PFOA/PFO entering into the Bohai Sea was 24.57 ton/year, 100-fold higher than that of perfluorooctane sulfonates (PFOS).

Iodine isotopes (129I and 127I) in the hydrosphere of Qinghai-Tibet region and South China Sea

The radioactive isotope ¹²⁹I, with a half-life of 1.57 × 10⁷ years, is widely used as a tracer to assess nuclear safety, to track environmental and geological events and to figure out the details of the stable iodine geochemical cycle. This work investigated the ¹²⁹I and ¹²⁷I distribution in water samples collected from the terrestrial (rivers, lakes and springs) and marine water systems (estuary and sea) in China. The measured ¹²⁹I concentrations of (1-51) × 10⁶ atoms/L and ¹²⁹I/¹²⁷I ratios of (0.03-21) × 10^-10 shows the variability of ¹²⁹I level in the water systems. The local permafrost and seasonal frozen environment play a key role in groundwater recharge in the Qinghai-Tibet region, which is reflected in the ¹²⁹I distribution in surface water. The depth distribution of ¹²⁹I in the water column of the South China Sea reflects the effluence of different currents. The results also indicate that the hydrosphere of China contains one to three orders of magnitude less ¹²⁹I compared to those reported in Europe. Despite the large distance, the European nuclear fuel reprocessing facilities represent the major source of ¹²⁹I in the hydrosphere of China through atmospheric transport. The contribution of the Fukushima nuclear accident to ¹²⁹I levels in the hydrosphere of China was negligible.