Berkeley ESPM H196 - Addressing the Environmental Mercury Problem in Watersheds

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Addressing the Environmental Mercury Problem in Watersheds: Remediation in the Guadalupe River Watershed, San Jose, California Amanda Fuller Abstract Mercury pollution in watersheds has become an urgent problem and within the last thirty years, has been identified as a serious risk for human health. Mercury can be converted to methyl mercury by bacteria in waterway sediments. Methyl mercury is up to a thousand times more toxic than elemental mercury due to its ability to cross cell membranes and interact in biological systems, causing brain damage, paralysis and even death in humans. Remediation of elemental and methyl mercury within watersheds is currently being addressed as a major priority in water quality management, but there are several legal and technical obstacles to mercury clean up. This paper reviews current remediation methods for mercury contamination, and then evaluates these methods as possible means of cleaning up the heavily mercury-polluted Guadalupe River Watershed in San Jose, California. Parameters influencing decisions to implement different remediation methods are discussed, along with key factors influencing successful remediation.Introduction Uses of Mercury Mercury and its principal ore, cinnabar (HgS), have been utilized by human cultures for over three thousand years. It has been used by ancient Chinese, Hindu, Egyptian, Greek and Roman civilizations for a variety of purposes including as a medicine, an aid in religious ceremonies and as a pigment or dye. Mercury was identified as having a toxic nature by a number of ancient authors such as Hippocrates, Pliny, Galen and Avicenna (D’Itri 1972). Mercury found in the environment comes from two major sources. First, there are sources that originate in the earth’s crust and account for naturally occurring background levels of mercury in the environment and exist as part of a global geo-chemical cycle. This mercury is transported to surface waters by soil erosion and is circulated into the atmosphere by a natural degassing of the Earth’s crust and oceans (D’Itri 1972, Merian 1991). The second source of mercury is from rocks that have been extracted from the Earth and redistributed globally as a direct result of anthropogenic activities. Anthropogenic activities have resulted in the release of various types of both inorganic and organic mercury into the environment. The electrical industry, chloralkali industry, and the burning of fossil fuels release elemental mercury into the atmosphere (D’Itri 1972, Merian 1991). Metallic mercury has also been released directly into fresh water by chloralkali plants, and both phenylmercury and methylmercury compounds have been released into fresh and sea water – phenylmercury by the paper and pulp industries, and methylmercury by chemical manufacturers (Merian 1991). Perhaps the most important source of human influenced mercury pollution is the mining industry, which will be discussed in detail (D’Itri 1972, Merian 1991). The Chemistry of Mercury Environmentalists and toxicologists have not always drawn distinctions between the various chemical forms (speciation) of mercury although each form exhibits a very different environmental behavior, bioavailability, and effect on exposed organisms. Different species of mercury also have different types of interactions with other substances. It is generally accepted that metallic mercury, mercury vapor, inorganic mercury (I) and (II), alkyl mercury, and phenyl mercury must be distinguished from one another in order to most accurately and efficiently address the complex reactivity of mercury pollution (Merian 1991). The most important forms of mercury to which living organisms are exposed can beplaced into three broad categories having different pharmokinetic properties with regard to absorption, bodily distribution, accumulation and toxic hazards (Merian 1991), and they are summarized in Table 1. TYPE OF MERCURY FORM OF MERCURY RISK LEVEL HEALTH EFFECTS LOCALE IN THE ENVIRONMENT Elemental Vapor in atmosphere; metallic as a liquid Low to medium Usually converted to ionic or organic form to be toxic; causes headaches, loss of memory In the atmosphere as a vapor Hg2+ (mercuric salts); Hg+ (mercurous salts) Ionic combinations in general; HgS is cinabar Medium to High; Hg2+ more risky because readily complexes with organic ligands Corrosive to skin and mucous membranes, nausea, kidney and liver dysfunction Hg2+ prominent in marine and fresh water Organic Mercury Compounds Arylmercurials (phenylmercury) Alkoxyalkyl mercury Alkylmercurials (methyl, dimethyl and ethyl mercury) Medium to High; Form salts with organic and inorganic acids and reacts readily with biologically important ligands High to Extremely High; Pass easily across biological membranes; 1000 times more toxic than elemental Hg Health effects are similar to those for the salts because they are quickly metabolized by organisms in biological systems Visual impedment, ataxia, dysarthria, paralysis and death In sediment/soil, water column In sediment/soil, water column and bioaccuumulated in fish and other wildlife Table1. Types of Mercury in the Environment. Information in this table is from Merian 1991, Porcella 1994, D”Itri 1972, Clarkson 1994. Mining for Mercury Historic hydraulic mining and the use of mercury has left many watersheds of the Western United States with a legacy of eroding hillsides, heavy mercury loads and excess sediment. The United States Geological Survey (USGS) estimates that up to 8 million of the 26 million pounds of mercury used in the gold mining in the Sierra Nevada Mountains may have been “lost” to the environment during gold recovery. Mercury was integral to the process of gold mining. Usually, the mercury was mined in the Coastal ranges of the Western United States and then exported to the Central ranges where the gold was mined. As a result, mercury pollution in both the central and coastal mountain ranges of the Western United States is widespread. In most California mines, the mercury was extracted from the cinnabar ore by a process called calcination (Abu-Saba 2000). After the ore was mined, it was crushed and roasted in the presence of air where the mercury sulfide decomposed, and the sulfur was removed while theheat volatilized the mercury. The mercury vapors were then condensed into a liquid in a series of water-cooled condensers, and the resulting liquid


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