Oil spills can have a detrimental effect on sea life, fishing and tourism industries, and the environment, but only 12 percent of the oil contaminating seas comes from spills each year. Nearly 40 percent of this type of marine pollution comes from runoff and waste from cities and industry. Many coastal areas are plagued by fertilizer runoff originating from lawns and farms. Algal blooms that are exposed to the excess nutrients emitted by fertilizers are killed, reducing the amount of dissolved oxygen in the water. As a result, marine life is suffocated and can no longer survive. Enormous dead zones caused by fertilizers have been observed around the world, including in the Baltic Sea and the Gulf of Mexico.
Many of the Earth’s oceans have become garbage dumps filled with solid rubbish like plastic bags, glass bottles, packaging materials and cans. In some areas of the Pacific Ocean, floating garbage debris goes 90 feet deep. In other areas, plastic outnumbers plankton by six times. Many marine animals confuse the waste with food, and high concentrations of plastic have been found in the stomachs of many ocean species, including dolphins, whales and turtles.
Sewage also makes its way into the world’s oceans, and much of it is untreated. For instance, 80 percent of the sewage flowing into the Mediterranean Sea is untreated. The influx of sewage kills marine life and can also cause diseases in humans.
Almost all marine life is contaminated with chemicals like pesticides and those used in common products. Until the 1970s, toxic materials were often disposed of in oceans, and although toxic dumping has since been outlawed in most of the world, the practice still continues today. Other chemicals contribute to marine pollution through leaks, improper disposal and from manufacturing processes that emit chemicals into the air and soil.
Once in the oceans, these chemicals are absorbed by tiny organisms like plankton. The chemicals accumulate to high concentrations in the plankton’s bodies, which are eventually consumed by other animals. Each step in the marine food chain results in a higher concentration of the chemicals. For instance, polar bears can have contamination levels that are three billion times higher than the surrounding environment.