Fig. 14.1 shows how plastic waste enters and accumulates in the marine environment. Plastic pollution is one of the most significant environmental challenge...

(a) Microplastics are tiny pieces of plastic less than 5 mm in size, formed either by the breakdown of larger plastic items through UV light, wave action and physical abrasion, or manufactured as small particles (e.g. microbeads in cosmetics and cleaning products). [1]

(b) How plastic waste from land enters the marine environment: [3]

1. Plastic waste that is not properly collected, recycled or disposed of is dumped in landfill sites, left as litter on streets and in parks, or blown by wind into streams and rivers. Inadequate waste management infrastructure, particularly in developing countries, is a major source. [1]
2. Rivers act as conveyor belts, carrying plastic waste from urban and rural areas to the coast and out to sea. Surface runoff during storms washes additional plastic debris from land into waterways. [1]
3. Approximately 80% of ocean plastic originates from land-based sources via this route. The remaining 20% comes from maritime activities: discarded fishing nets and lines (known as "ghost gear"), shipping waste and offshore platforms. [1]

(c) Effects of plastic pollution on marine organisms: [4]

• Ingestion: Marine animals such as sea turtles, seabirds and whales mistake plastic bags and fragments for food (turtles confuse plastic bags with jellyfish, for example). Ingested plastic blocks the digestive system, creates a false feeling of fullness and can lead to starvation and death. [1]
• Entanglement: Animals become trapped in plastic debris such as discarded fishing nets, six-pack rings and packing straps. Entanglement restricts movement, prevents feeding and can cause drowning in marine mammals and turtles that need to surface to breathe. [1]
• Habitat damage: Plastic debris that sinks to the ocean floor or accumulates on beaches smothers benthic habitats (coral, seagrass beds), blocking light and preventing organisms from feeding and growing normally. [1]
• Chemical toxicity: Plastics contain additives (such as BPA and phthalates) that leach into the water. These chemicals are endocrine disruptors that interfere with the hormonal and reproductive systems of marine organisms, potentially reducing population viability. [1]

(d) Why microplastics are particularly dangerous in the marine food chain: [3]

• Microplastics are small enough to be ingested by organisms at the base of the food chain, including zooplankton, larval fish and filter-feeding shellfish (mussels, oysters). These organisms cannot distinguish microplastics from their normal food. [1]
• When these small organisms are eaten by predators, the microplastics (and the toxic chemicals adsorbed onto their surfaces) accumulate in body tissues. This process is called bioaccumulation. As energy and material pass up the food chain, the concentration of microplastics and toxins increases at each trophic level, a process called biomagnification. [1]
• Top predators (tuna, sharks, marine mammals) and ultimately humans who eat seafood are therefore exposed to the highest concentrations of plastic-associated toxins, posing potential risks to human health including hormonal disruption and cellular damage. [1]