In early October 2010, Hungary declared a state of emergency in three western counties after a massive and deadly industrial spill of highly alkaline, redcolored, toxic sludge from a ruptured industrial reservoir flooded nearby towns and flowed into tributaries leading to the Danube River.
The industrial reservoir ruptured on October 4, 2010, releasing at least 35 million cubic feet (1 million cubic meters) of toxic mud-like waste created during the refining of bauxite into alumina. Bauxite is a naturally occurring mixture of aluminum hydroxide minerals. Often extracted by strip mining, bauxite is then mixed with industrial strength and highly caustic sodium hydroxide under high temperature (400°F, 200°C) and pressure to release alumina. Alumina is an industrially produced crystalline aluminum oxide used in smelting aluminum. Alumina is also used in many ceramic products. During filtering, a red mud or red sludge is removed to evaporation tanks or reservoirs. A precipitate containing aluminum hydroxide then forms as the filtered solution cools. The precipitate is then purified and heated again to form aluminum oxide. The red mud or red sludge typically has high concentrations of caustic, alkaline sodium hydroxide mixed with variable amount of silicon and titanium. The sludge may also be slightly radioactive and can contain varying concentrations of heavy metals such as arsenic, lead, cadmium, and chromium.
Efforts to contain the massive spill initially failed to prevent contaminated sludge from reaching the Danube, Europe's second longest river. Polluted runoff into feeder streams also thwarted containment efforts. Waterways near the broken reservoir, including streams near Kolontar, the village nearest the spill and about 45 miles (70 km) from the Danube, reported massive fish kills. Observers also reported massive kills in all forms of aquatic life in the Marcal River, a smaller river that flows into the Raba River, which in turn, flows into the Danube.
An acidic environment is rich in hydrogen ions, whereas a basic environment is relatively depleted of hydrogen ions and, in an aqueous environment, is rich in OH— ions. Mathematically, pH is calculated as the negative logarithm of the hydrogen ion concentration. For example, the hydrogen ion concentration of distilled water is 10—7 and hence, pure or distilled water has a pH of 7. In comparison, a pH of 0 corresponds to 10 million more hydrogen ions per unit volume, and a pH of 14 corresponds to one ten-millionth as many hydrogen ions per unit volume.
As the sludge mixed with water (with a neutral pH of 7), dilution reduced the highly alkaline sludge, By the time the sludge reached the Danube, investigators and environmental officials recorded pH levels of 9.4 in contaminants entering the river. The diluted sludge was more than 1,000 times less alkaline than the sludge at the source. Investigators remained uncertain, however, as to the heavy metal content of the sludge.
Emergency response teams also poured plaster and vinegar (a dilute form of acetic acid) into the sludge as part of efforts to neutralize the deadly alkalinity.
The day after diluted sludge was detected in the Danube, sporadic losses of fish were reported. Water pH near areas where the Raba flows into the Danube measured 9.1. Fish and many forms of vegetation cannot survive in such alkaline conditions. Industrial pollution in the Danube routinely creates pH levels of 8.0 to 8.4.
Experts continued to test waters for impacts on microbial life. Microorganisms can tolerate a spectrum of pHs, while individual microbes usually have an internal pH close to that of distilled water. The surrounding cell membranes and external layers (e.g., the glycocalyx) help buffer the cell membrane and offer protection from pH extremes in the surrounding environment.
Ten deaths were attributed to the Hungarian spill, with between 120 and 150 people also treated for chemical burns and other injuries. Exposure to highly alkaline or acidic substances can result in chemical burns that manifest hours or days after exposure. Deep tissue burns are also possible.
By mid-October, World Health Organization (WHO) personnel, who continuously tested waters downstream of the spill, declared water quality to be adequate and within expected ranges of pollution established prior to the spill. Local drinking water supplies were also cleared for use. WHO officials announced plans for long-term monitoring for pH fluctuations and heavy metal contamination. Public health officials continued to warn against contact, inhalation or ingestion of the highly alkaline industrial sludge.
See also Hazardous waste ; Water pollution .
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K. Lee Lerner