Accumulation of mercury in Indo-Pacific bottlenose dolphin

In 2015, Johns Hopkins environmental scientists collaborated with the Animal Health team at Resorts World Sentosa (RWS), to learn more about if and how mercury accumulates in the bodies of Indo-Pacific bottlenose dolphins.

Indo-Pacific bottlenose dolphins are found in tropical and temperate waters of the Indian and western Pacific Oceans. Found almost exclusively over the continental shelf, they appear to prefer shallow, near shore waters, hunting at night and foraging over reefs or soft bottoms to capture their prey. Top of the aquatic food web, these dolphins are known to consume a variety of bony fish and squids.

Mercury and its dangers

Mercury (also commonly known as quicksilver) is considered one of the most toxic chemical elements worldwide. Found naturally in air, water and soil, it is also a contaminant produced from human industry such as coal-fired power plants.

Once in the atmosphere, mercury is widely distributed and can circulate for years before settling in the oceans. Bacteria in the water take up mercury from the surrounding environment and convert it into a highly toxic organic soluble form known as methylmercury.

These methylmercury-containing bacteria may be consumed by the next higher level in the food chain. Organisms accumulate methylmercury faster than they can get rid of it, causing the toxin to be collected and stored in a process known as bioaccumulation.


As one organism eats another, the toxin moves up through the food chain and the concentration increases, an effect known as biomagnification. Consuming organisms containing methylmercury, over a prolonged period of time, is known to affect the development of the nervous system.

Fish now accounts for almost 17 percent of the global population’s intake of protein. Once caught, commercial fish species are often transported around the world, to locations far removed from their origin. At RWS, dolphins are fed ‘human grade’ seafood, which means it is fit for human consumption and is also being supplied to people in restaurants and supermarkets.

The process of bioaccumulation of toxins in the aquatic environment

Blood tests have a wide range of uses and are one of the most common types of medical tests. To ensure the utmost care for the dolphins, the Animal Health team at conducts regular health checks, which include taking blood samples. The results of which are stored in a database.

These collected blood samples results over a five-year period will allow researchers to investigate any change in mercury levels over time. The information is critical to allow us to better understand the rate of accumulation and impact of methylmercury in organisms at the top of food chains.

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