The world’s lakes, seas and oceans have been, and are being affected by human activity. Only recently has it been realised that they are finite resources which are vulnerable to growing populations and industrialisation. Sewage discharge, agricultural runoff, toxic waste disposal, oil spillages and overfishing have all adversely affected marine ecosystems. Global warming is implicated in the destruction of coral reefs.
Marine litter, also known as marine debris, refers to human-made solid waste that ends up in coastal and marine environments. It includes wood, fibres, paper, glass, metal and plastics. Objects most commonly discarded worldwide include cigarette butts (most common and not biodegradable!), plastic or paper bags, food wrappers/containers, eating utensils, plastic bottles, drink cans and straws, ropes. Plastics are generally not biodegradable.
About 80% of marine litter originates from land. People discard litter, deliberately or accidentally, which is carried to the sea by wind or rivers. Rain washes litter off streets into drains. Poorly-maintained waste disposal facilities, rubbish bins and refuse trucks fail to contain the litter which often finds its way to the sea. Ships can lose cargoes and fishing boats can lose nets and equipment by accident or in storms. Tsunamis and hurricanes result in millions of tonnes of marine debris. Warfare and economic collapse generate sunken or abandoned ships, planes and weapons.
At an immediate level, litter fouls any environment and lowers its aesthetic value. This affects life quality and can also be a health hazard as litter attracts vermin. Litter at sea has fouled ship propellers and interfered with water intake. Ships abandoned in waterways can affect currents and increase shading – this can alter the ecosystem. As they disintegrate, metals, oil and toxic materials enter the water. Conversely, ships and rigs can be deliberately sunk to create artificial reefs.
Much litter sinks in the ocean where it interferes with coral reefs and can cause injury to animals. The effects on benthic organisms have not yet been properly determined. Nets entrap birds, fish and seals. Ingested plastics have blocked animals’ tracts leading directly to suffocation and starvation. Large quantities of ingested plastics have given animals a feeling of being full so they cease eating.
More subtly, chemicals from plastic have mimicked the effect of hormones such as estradiol, possibly disrupting the physiology of animals. Wood, paper and plastics are often coated with polish or preservatives which are released into the water.