Last week, this column covered the Great Barrier Reef and the loss of more than half its coral cover over the past 30 years. With supportive financing for massive coal projects in Queensland, Australia, the potential exists for still more harm to our world’s reefs, oceans and wildlife, all of which will influence human health.

When coal is burned, mercury is released into the environment. Coal-burning power plants are the largest human-caused source of mercury emissions in the air. The U.S. Environmental Protection Agency has estimated that about one-quarter of U.S. emissions from coal-burning power plants are deposited within the contiguous U.S. and the rest enters the global cycle. Current estimates are that less than half of all mercury deposits within the U.S. comes from U.S. sources.

Mercury tends to build up in living organisms. Nearly all fish contain at least trace amounts of methylmercury, which accumulates more in larger predatory fish with longer life spans in a process known as biomagnification.

There are no metabolic functions in the body that require mercury, and the presence of this metal is considered toxic at any level. High concentrations of mercury can result in damage to vital organs including the heart, liver and kidneys. In addition, the neurological system is highly susceptible to damage from chronic mercury exposure. Initial symptoms often include depression, fatigue, headaches, dizziness, irritability, lack of concentration, memory lapses and nervousness.

Over time, exposure to high levels of mercury can result in significant neurological damage in the form of trembling hands, numbness in the hands and feet, loss of muscle coordination, and impaired hearing and vision. The level of toxicity and adverse effects vary among individuals. Of all age groups affected by mercury toxicity, children are at greatest risk due to high growth rates and low body mass. Others at high risk for toxicity include pregnant women, women of reproductive age and the elderly.

At Manakai, we routinely screen for heavy metals in those who consume seafood regularly. Over the years, we have noticed increasingly high levels in our patients, especially who are heavy seafood eaters.

This trend is consistent with a recent study on yellowfin tuna caught near Hawaii over the past half-century. It found that the concentration of mercury in these fish is increasing at a rate of at least 3.8 percent a year. This rate of increase is consistent with the human sourcing of mercury in the North Pacific Ocean, which suggests that mercury concentrations in fish are keeping pace with current load increases in the oceans.

Both the EPA and the U.S. Food and Drug Administration recommend fish intake to be 8 to 12 ounces per week. Mercury levels and beneficial omega-3 fatty acids vary widely from one seafood variety to the next.

There are several other sources of seafood besides salmon that are low in mercury but high in healthy omega-3’s such as anchovies, herring, mussels, sardines and trout. The fish that contain the highest levels of mercury include shark, swordfish and mackerel and should be avoided completely. Tuna and ahi should be limited to no more than 6 ounces weekly. Smaller tuna, also known as "shibi," especially those under 30 pounds in weight, are better options for limiting mercury exposure.

Another recommendation is to rotate seafood choices as opposed to ordering ahi at every opportunity.

Richard Branson, the billionaire entrepreneur and owner of Virgin America airline, recently backpedaled on comments opposing coal mining development in Australia to protect the Great Barrier Reef from damaging impacts, most likely in part due to political and business pressure. Australia’s environmental minister is expected to make a ruling on the proposed industrial expansion in the second half of the year.

Coal is the least efficient method of burning fossil fuels for energy. In contrast, liquefied natural gas is a better option because it releases less greenhouse gas per unit of energy produced. Still, the health of our oceans and the human population depends on sustainable energy. Let’s continue to work at reducing the use of all fossil fuels.

Ira Zunin, M.D., M.P.H., M.B.A., is medical director of Manakai o Malama Integrative Healthcare Group and Rehabilitation Center and CEO of Global Advisory Services Inc. Please submit your questions to info@manakaiomalama.com.