BAR TODAY || Official Quarterly Publication of the Bureau of Agricultural Research

Mercury contamination in Agusan river?
by Ma. Lizbeth J. Baroña

October-December 2003
Volume 5 No. 4

Agusan River

Going to the market for the family's week-long fish diet is not a difficult task. Only one thing concerns you: freshness. And you have the eyes and meat of the fish to indicate that. But for one to determine whether the fish has mercury in it, what can a hapless mother do?

Mercury is a well-known and dangerous environmental pollutant. Studies have demonstrated that fish and other wildlife from various ecosystems have mercury of toxicological levels that they get from mercury-containing emissions from human-related activities. Human health concerns arise when fish and wildlife from these ecosystems are consumed by humans. Mercury is easily absorbed by the respiratory tract that can result to permanent health damage, particularly brain damage.

Humans can take in mercury in two ways: as methyl mercury from fish consumption, and as vaporous mercury from the air. The vital question whether or not the Agusan River in Butuan that flows out to the Butuan Bay is contaminated with mercury, was the concern of the study conducted by the Mindanao State University, led by Ms. Elnor Roa.

How does mercury contaminate our waters?
Mercury is the only metal that can exist both as liquid and volatile form at ambient temperatures (Sadiq,1992). This trait makes it easy for the compound to form alloys with metals like gold, silver, and tins, which are called amalgams.

The discovery of gold in the 1980s intensified the gold mining operations in northeastern Mindanao. It provided livelihood to 200,000 people in the region. Little did they know that harm is already piling up from metal processingwastes from these gold mines.

It took a news article on the Bulletin Today in 1987 to raise alarm of possible mercury contamination in the bodies of water in Surigao del Sur, Davao del Sur, and Agusan del Norte, where gold mining is a major source of livelihood in the area.

Later, it was confirmed by the Bureau of Mines and Geosciences (BMG) that the mercury waste dumped on creeks and rivers by the major gold mine sites in the said areas flowed through the Agusan River, out towards Butuan Bay. A 1999 report by the Department of Health supported the findings of the BMG after it revealed that the mercury content of sediment from the Agusan River has exceeded a level that allows for "unpolluted" sediments.

Toxin from the river to dinner plates
Fishes, and other aquatic organisms in the river ingest this contaminants through water exchange and feeding. If one had been ingesting mercury- contaminated food for years, even at small doses, danger is never far. This is because mercury becomes toxic through a process called bioaccumulation. Bioaccumulation is the process by which organisms, including humans, can take up contaminants more rapidly than their bodies can eliminate them, thus the amount of mercury in their body accumulates over time, and toxicity builds up.
Agusan River, being one with many creeks and tributaries, is a depository of wastes from Naboc River, a river that receives the wastes from Mt. Diwalwal, the biggest mining area in that part of the region.

Testing the river water, sediment, and organisms
Researchers from Mindanao State University (MSU) led by Ms Elnor Roa tested the levels of mercury contamination in Agusan River. Water, sediment, fish, and plant samples were gathered for testing. Water samples were pre-treated with 5ml of nitric acid per 500ml of sample and kept in containers washed and rinsed with water and nitric acid. Sediment was kept in a Styrofoam box. The plant samples were washed and stored in polyethylene bags, while the fishes were transported in an ice chest.

The fish samples were Johnius vogleri ("guama"), Gobius guirus, and Ambassis commersonii ("ibis"), and S. sihama ("aso-os"), while the plant samples were Lumnitzera sp., Eichornia crassipes or water hyacinth, and Cyperus alternifolius or umbrella plant. All samples were oven-dried at 600C to constant weight before they were analysed for mercury content.

How bad is contamination in the river?
Mercury level in the water has exceeded the permissible amount of concentration for fish propagation.

The sediment, where precipitated toxic compounds ultimately would reside, was also found to have high levels of mercury content. This finding qualified the sediments in the river to a "polluted" category.

Among the three plants, E.crassipes had the highest level of mercury contamination and is recommended for total elimination from the river. C. alternifolius had the second highest level of contamination, while the Lumnitzera sp, had the lowest.

Mercury was also detected in the four species of fish. Although G. gurius and J. vogleri are still fit for human consumption, the levels of the mercury content detected in A. commersonii and S. sihama have exceeded the standards of what is safe for humans to eat.

The study recommended the salvaging of the three contaminated plants through bioremediation, the branch of biotechnology that uses biological process to overcome environmental problems. The people in the area are encouraged to plant more of the species for remediation purposes.

Source: Mercury content of some species of fish and aquatic in Agusan River and Estuary by Elnor C. Roa, Mindanao State University. www.solucorpltd.com www.thefreedictionary.com
www.water.usgs.gov