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State and trends


PCBs, which are also chlorinated hydrocarbons, were banned in the US in 1979. Canada prohibited the import and sale of PCBs, and restricted their use in 1977. PCBs include more than 200 congeners with differing numbers of chlorines on different locations on the biphenyl structure, and have a range of toxicity. Polychlorinated biphenyls were used in industrial and commercial applications including electrical equipment; as plasticizers; in pigments and copy paper; and other applications. The entered the environment during their manufacture as well as use. They can still be released into the environment from poorly-maintained hazardous waste sites, leaks from electrical transformers and disposal of PCB-containing products into landfills.


Chlorinated hydrocarbons are highly persistent and remain in the environment, especially in sediments, so they continue to be found long after being banned (King et al. 2004). Resistant to microbial degradation, they remain for long periods, cycling between air, water and soil. PCBs are carried long distances and have been found far away from where they were released. Like chlorinated pesticides and methylmercury, PCBs biomagnify. Animals higher on the food chain have higher concentrations than smaller ones. Levels are decreasing following the ban on use. Figure 2.5.6 shows reductions in PCBs in harbour seals in Canada (Ross et al. 2013).


Noise pollution


Noise pollution in the ocean is another emerging concern. Many marine species have specialized hearing, communication skills and echo-location abilities. Human activities such as commercial shipping, exploration and extraction of oil and minerals, air guns used for seismic exploration, sonar and even jet skis contribute to the increased level of underwater noise. Sound travels four times faster in water than in air, 1 230 metres per second as opposed to 340 metres per second, so it travels further under water and as water is denser than air, sound waves travel though water at higher energy levels and are hence louder. As a result, high-intensity sound in the oceans can travel for thousands of kilometres and have lethal and sub-


lethal effects (André et al. 2011). Animals are alarmed by the sounds, which may damage internal organs, especially ears, and cause a panic response. Normal communication between marine animals can be disrupted by noise. The death of animals, especially cetaceans, often occurs hours after exposure to extreme underwater noise (Peng et al. 2015) – for example, whales die after beaching themselves shortly after a tactical sonar exercise; this is a rather common occurrence and has been reported in the coastal US areas where sonar exercises are common. Since ships are getting larger, it is likely that noise pollution is increasing but data on this trend could not be identified.


Nutrients and eutrophication


Nutrient enrichment due to excessive amounts of nitrogen is the main cause of impaired coastal waters worldwide, including North America. Sewage, even after treatment, contains high levels of nutrients, while excess nitrogen flows from agricultural fields, suburban lawns and stockyards, entering freshwater and going down to estuaries along streams and rivers. It is also released from septic tanks and reaches water bodies through groundwater, and comes from the atmosphere in precipitation. These nutrients cause algal blooms and when the algae die and sink to the bottom, bacterial decay uses up oxygen, resulting in hypoxia (low oxygen) in deeper waters. Seasonal occurrences of dead zones with no oxygen have expanded in many areas, and are abundant and increasing along the coasts of North America, the largest being in the Gulf of Mexico.


Studies by the US EPA in the 1980s established that excess nitrogen and phosphorus were the main source of pollution in the Chesapeake Bay. This finding led to the formation of the Chesapeake Bay Programme (CBP), which is a regional partnership made up of federal and state agencies, local governments, non-governmental organizations and academic institutions, with the mission of directing Chesapeake Bay restoration and protection. The CBP Executive Council includes the governors of Maryland, Pennsylvania and Virginia, the Administrator of the US Environmental Protection Agency, and the Mayor of the


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