Chemical Pollution

Plants and animals produce countless chemical substances as part of their life processes. For the purposes of the Ocean Health Index, ‘chemical’ refers to a  compound or substance that has been purified or manufactured by human sources.

More than 100,000 chemicals are used commercially (Daly 2006), and many enter the marine environment via atmospheric transport, runoff into waterways, or direct disposal into the ocean.

Three general categories of chemicals are of particular concern in the marine environment: oil, toxic metals, and persistent organic pollutants.

Chemical Pollution Infographic
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Which Goals Does This Affect?

How Was It Measured?

It is not yet, and may never be, possible to measure actual concentrations of the numerous substances found throughout the ocean, so the following proxy measures were used. Pollution from land-based organic chemicals was modeled from data on agricultural pesticide use. Pollution from land-based inorganic chemicals was modeled by estimating runoff from impervious surfaces. Ocean-based pollution was modeled from data on commercial shipping tracks and ports.

These models only provide rough estimates of pollution intensity. They do not represent all chemicals and they do not distinguish between chemicals that are more or less toxic. Focal studies at the country level may be able to use more detailed data, but they do not yet exist at the global level.

Details about the models used are provided in online Supplementary Information for Halpern et al. (2012).


The total amount of oil entering the ocean has been estimated, but global data on the size and geographic distribution of oil spills are not available, so oil pollution could not be included as a separate category within the Ocean Health Index.  However, oil would be among the substances contained in runoff from impervious surfaces and released by shipping and ports.

‘Oil’ is the general term for any thick, viscous, typically flammable liquid that is  insoluble in water but soluble in organic solvents. Plants and animals produce a variety of natural oils, but the Clean Waters goal is primarily concerned with oil derived from geological deposits of petroleum (crude oil) for use as a fuel or lubricant.

Natural oil makes up 47% of the oil in the ocean. About 600,000 metric tonnes of oil enters the ocean naturally each year by seepage through many cracks in the seafloor (NRC 2003), but input from each is typically slow (Wells 1995) and natural seepage is not considered to be pollution.

The other half of the oil comes from anthropogenic sources, including boats, land-based runoff and, to a lesser degree, oil spills. These sources pose a greater threat to marine environments as the oil enters the ocean in concentrated areas at a high rate of flow.

The largest sources of human oil pollution are urban-based runoff and operational discharge of fuel from boating traffic and port operations. Discharge associated with boats constitutes 24% of the total amount of oil in the ocean (UNEP/GPA 2006).

Only 8% of overall oil ocean pollution is a result of spills during transportation or production. However, the toxicity levels of these spills tend to persist over time and have been linked to highly visible local and regional disasters.

After 20 years, oil pollution from the 1989 Exxon Valdez spill persists and, in some areas, is nearly as toxic as initial levels (Exxon Valdez Trustee Council 2009; Raloff 2009).

What Are The Impacts?

Oil pollution can degrade or destroy marine ecosystems.

Oil pollution can elevate concentrations of toxic elements (ex. arsenic).

Oil pollution can kill marine life through ingestion, inhalation, absorption and loss of insulation.

Oil pollution can have long-term effects on spawning grounds and fish stock recovery.
Oil pollution can harm those who consume contaminated water or seafood or have contact with polluted waters through recreation and clean-up activities.

Symptoms can include chest pain, coughing, dizziness, headaches, respiratory distress and vomiting.
Responding to the ecological impacts of oil pollution can result in significant economic costs.

Response to the Deepwater Horizon oil spill cost BP US $13 billion dollars. Litigation and compensation for claims cost BP an additional US $15 billion (Telegraph 2011).

Local economies have to deal with costs resulting from contaminated or diminished fish stocks.

The BP Deepwater Horizon oil spill caused Louisiana to lose 50 percent of its seafood production, a US $2.4 billion dollar industry in Louisiana that supplied as much as 30 percent of the domestic seafood for the continental U.S. (Nawaguna-Clemente 2011).

Find Out More

Woods Hole Oceanographic Institution [WHOI]
A diagram detailing the route of oil as it travels from the seafloor through the water column. 

U.S. Senate Committee on Environment & Public Works
A policy brief on the Oil Pollution Act of 1990 by David Lungren 

National Oceanic and Atmospheric Administration [NOAA]
Six fact sheets evaluating the effect of the Gulf oil spill on Marine Mammals and Sea Turtles, Seafood Safety, Hurricane, South Florida, Restoration Efforts, and Cumulative Impacts on Wildlife.

Toxic Metals

Metals are chemical elements that are typically hard, shiny, malleable, fusible, and ductile, with good electrical and thermal conductivity. Metals are toxic if they change the structure and function of proteins and enzymes (GESAMP 2001).

Metals found in the ocean that are highly toxic on their own include mercury, cadmium, lead, arsenic, tin, copper, nickel, selenium, and zinc. Mercury, cadmium, and lead can become even more highly toxic in combination with organic compounds. For example, mercury can form neurotoxic compounds such as methylmercury (CH3Hg), when combined with carbon.

Arsenic, copper, nickel, selenium, tin, and zinc are not highly toxic by themselves but are able to react with organic materials, creating very toxic compounds (UNEP 2006).

Many metals occur naturally in the environment, but anthropogenic emissions from industrial and mining activities can increase concentrations of many to toxic levels.

96% of mercury enters the ocean via atmospheric input (GESAMP 2001).

While some metals are deliberately dumped in the ocean, most are found downstream from their sources, including waste dumps, industrial areas, mining operations and metal processing areas.

What Are The Impacts?

Mercury Pollution Cycle
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Results of laboratory studies can demonstrate the effects of one or several pollutants on growth, reproduction or other physiological processes in test organisms. Chemical analyses can also reveal the concentrations of pollutants in the tissues of marine organisms collected in the wild. However, limited information is available on how wild marine plants, animals, microorganisms and ecosystems respond to sub-lethal exposure to the many pollutants they encounter, and how other factors such as temperature or pH affect those responses. 
Certain metals, such as zinc, are essential to life in very small amounts, but are toxic in higher concentrations. Others, such as mercury or cadmium, are not used in normal metabolism and are harmful when taken into the body. Ingesting toxic metals can have serious effects on the kidney, liver, immune system, central nervous system and other organs.

Over 90% of methylmercury exposure occurs through the ingestion of contaminated fish and shellfish (USGS 2 2009).

In the past 20 years, mercury concentrations in the Pacific Ocean have increased 30 percent due to increases in human atmospheric emissions from industries and are estimated to rise 50 percent by the year 2050 (Sunderland 2009).
In 2004, the U.S. Environmental Protection Agency (EPA) released recommendations for weekly fish consumption so that high levels of mercury ingestion could be avoided (EPA 2010).

Expenses can be incurred from health problems attributed to mercury ingestion.

An estimated 637,233 children in the United States are born each year with cord blood mercury levels greater than 5.8 mg/L, a level linked to decreased IQ and other birth defects (Trasande et al 2005).

Find Out More

United States Environmental Protection Agency [EPA]    
Fact sheet on mercury content in fish and shellfish.

Turtle Island Restoration Network
Fact Sheet on mercury in seafood.

European Health and Environment Alliance (HEAL)
Fact Sheet on fish and mercury consumption.

Persistent Organic Pollutants [POPs]

Persistent Organic Pollutants (POPs) are chemical compounds that are toxic to humans and wildlife.

POPs include pesticides such as DDT, herbicides, PCBs (a component found in many coolants, flame-retardants, adhesives), and BPA (a compound found in plastics – primarily in plastic bottles).

What Are The Impacts?

The beluga whale population in Canada’s St. Lawrence estuary has declined from about 5,000 at the beginning of the 1900s to about 650 animals today. They have one of the highest rates of cancer known in any wild population, as well as some of the highest levels of POPs and toxic metals. (Lyons, 2008; Martineau et al. 2002).

POP concentrations increasingly accumulate at each stage in the food web. The highest concentrations are found in ‘apex’ predators that feed at the top of the food web (at a high trophic level).

Low temperatures cause POPs to break down more slowly and accumulate in higher concentrations than in more temperate zones.
POPs can cause birth defects, increase cancer risks, disrupt hormone functions and cause reproductive, behavioral, immune system, and neurological problems in humans.

Inuit populations that consume large amounts of whale and seal fat have health-threatening, heightened blood levels of POPs, including industrial chemicals such as PCBs and pesticides such as DDT, even though such products were made and used thousands of miles away (Kirby, 2008). 
Because POPs are versatile and inexpensive to manufacture, many countries continue to allow their use.  However, the economic costs to deal with the resultant pollution can be high.

An estimated 2.8 billion dollars has been spent on dredging and processing POP contaminants from PCB manufacture in the Rhine Delta since 1997.  

In the United States, the General Electric company (GE), which dumped polychlorinated biphenyl (PCB) used in manufacturing capacitors, will have to pay an estimated total of 1.4 billion dollars to remove PCB-contaminated sediments from the Hudson River (Greenpeace, 2011).

Get More Information

Blue Voice
Policy brief-fact sheet on Persistent Organic Pollutants (POPs).    

World Health Organization
Policy brief-fact sheet addressing country-based implementation of the Stockholm Convention

Webpage for the Stockholm Convention on Persistent Organic Pollutants 

World Bank
Informational paper on Persistent Organic Pollutants Country Strategy Development: Experiences And Lessons Learned Under the Montreal Protocol

World Bank
A guidebook from the World Bank on Persistent Organic Pollutants: Backyards to Borders

World Bank
A fact sheet on Persistent Organic Pollutants (POPs) 

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PHOTO(S): © Keith A. Ellenbogen
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