Topic 4. pollutants and contaminants and their potential impacts on human health and ecosystems

MARINE DEBRIS AND PELAGIC ECOSYSTEMS Wood, pumice, drifting kelp, and other natural marine debris have long played important roles in marine ecosystems. Today, oceanic “litter” generated by human activities, notably plastics, constitutes the majority of marine debris and is mostly harmful to those ecosystems. In the twentieth century, plastic became a symbol of technological development and globalization of the world’s economy. Cheap, durable, and long-lasting, with a broad variety of properties that are attractive for an array of human uses, plastic penetrated all parts of business and everyday life. In recent decades, growing demand exponentially increased plastic production. Ironically, the negative environmental impacts of plastic are in part an extension of some of the very properties that make it popular, such as its durability and wide availability. Plastic degrades with time into microscopic particles that have been found in every corner of the natural world—on land, in lakes and rivers, and in the ocean. This phenomenon has led to a new description of the present era as the Plasticene: “an era in Earth’s history, within the Anthropocene, commencing in the 1950s, marked stratigraphically in the depositional record by a new and increasing layer of plastic” (Haram et al., 2020). A significant fraction of plastic in the ocean has sources located on land. Depending on chemical composition, some plastic entering the ocean sinks instantly, but the majority is buoyant and remains floating at the ocean’s surface for various durations. The fate of marine debris depends on ocean currents, winds, and waves, which together move floating objects and can transport them over long distances. Some debris released into the ocean transits between distant locations and pollutes remote