Microplastics are a major form of anthropogenic pollution, and over time, the sediment at the bottom of aquatic environments becomes the sink for the denser of these particles. By mapping and analyzing sediment from lake and estuary systems, this study aimed to find spatial relationships between water and sediment dynamics at stream-to-slack-water transitions and resulting microplastic sediment accumulation characteristics. Sediment was collected along transects extending from the stream mouth to open water depositional environments at four unique study sites. After a series of separations from collected sediment, microplastics were weighed to map longitudinal variations in plastic concentration. At all study sites, the highest concentrations of microplastics (up to 14% dry weight) in sediment were found to focus in spatial hotspots peaking 600–700 m down gradient from the transition to a low-energy environment in intertidal freshwater estuary systems, and 150 m downstream in a lake system, all being associated with environments of clay-dominated sediment deposition. The dominant types of plastics identified were cellophane and polydimethylsiloxane. We hypothesize these spatial hotspots of microplastic accumulation may result from the unique diversity of density ranges for microplastic sediment, ranging from just above 1 g/cm³, but below the 2.7 g/cm³ common for natural mineral sediment, thus creating plastic depositional locations that are spatially offset from those of common mineral grains.

Methane, a potent greenhouse gas, has gained prominence due to its significant contribution to global climate change. Beyond its climate impact, this review recognizes methane’s dual role in influencing local and regional air quality, underscoring its growing concern in the context of contemporary environmental issues. The paper aims to provide an overview of methane sources, geographic distribution, long-term health effects, interactions with other pollutants, and the pivotal role of integrated monitoring systems in effective pollution control strategies. The review delves into the primary sources of methane emissions, including anthropogenic and natural processes. Geographically, it identifies high-risk areas, with substantial emissions concentrated in North America, Europe, and Asia. Prolonged exposure to elevated methane levels in urban and industrial settings is associated with respiratory, cardiovascular, and neurological health issues. Furthermore, methane’s interaction with other pollutants leads to the formation of secondary organic aerosols and ground-level ozone, exacerbating air quality challenges. Efficient pollution control hinges on integrating satellite and ground-based data into monitoring systems, ensuring accurate and timely information. Managing methane emissions presents a complex dilemma, impacting both local air quality and global climate. Addressing this dual challenge necessitates a comprehensive approach encompassing legislative reforms, technological advancements, increased public awareness, and international collaboration. A swift response is imperative to mitigate the adverse effects of methane emissions on the environment and human health.