As a result of human activities, a lot of substances get into the sea. Precipitation transports combustion products through the air and into the sea. Heavy metals, pesticides, PCBs, disinfectants, household cleaners, and other synthetic chemicals come from industrial outflows and sewage. These gather in the surface film and marine sediment, particularly estuarine mud, where they become concentrated.
Due to the large number of substances involved and the lack of information on their biological effects, the outcome of all this contamination is largely unknown. Copper, lead, mercury, cadmium, and zinc are the heavy metals of greatest concern because they may bioaccumulate in marine organisms and travel up the food chain.
Rather than biodegrading, a lot of floating plastic waste disintegrates over time and eventually breaks down to the molecular level. For years, rigid plastics may float. In the focal point of the Pacific gyre there is a long-lasting drifting gathering of for the most part plastic waste and there is a comparative trash fix in the Atlantic. Sea birds that forage for food, like the petrel and albatross, may mistake debris for food and build up indigestible plastic in their digestive systems. Fishing line and plastic bags have been found in the stomachs of whales and turtles. Microplastics might sink, undermining channel feeders on the seabed.
Cities and industry are the primary sources of oil pollution in the sea. Oil is perilous for marine creatures. It can get stuck in the feathers of sea birds, making them less insulating and making them more buoyant. It can also get into the birds when they groom themselves to get rid of the contaminant. Marine mammals are less affected than land animals, but they can be chilled by losing their insulation, blinded, dehydrated, or poisoned.
When oil sinks, the food chain is disrupted, fish become poisoned, and benthic invertebrates are swamped. Oil spills have a short-term negative impact on wildlife populations, leisure activities, and the livelihoods of people whose lives are dependent on the sea. Since the marine environment is self-cleaning, oil from the sea will be removed over time by naturally occurring bacteria. Oil-eating bacteria are already present in the Gulf of Mexico, so it only takes a few days for them to consume spilled oil.