Mercury waste

The toxic nature of mercury and its compounds has caused concern over environmental pollution, and governmental agencies have imposed severe restrictions on release of mercury compounds to waterways and the air (see Mercury). Methods of precipitation and agglomeration of mercurial wastes from process water have been developed. These methods generally depend on the formation of relatively insoluble compounds such as mercury sulfides, oxides, and thiocarbamates. MetaUic mercury is invariably formed as a by-product. The use of coprecipitants, which adsorb mercury on their surfaces facihtating removal, is frequent. 

Tokuyama Bay, Japan, received 6.6 metric tons of mercury wastes between 1952 and 1975 in wastewater from two chloralkali plants, although sediment analysis suggests that as much as 380 tons of mercury were released (Nakanishi et al. 1989). Unlike Minamata Bay, however, there were no human sicknesses reported, and the hair of residents contained 0 to 5 mg Hg/kg FW vs. 15 to 100 mg Hg/kg FW in Minamata residents. In 1970, a maximum concentration of 3.3 mg total Hg/kg FW was reported in tissues of Squilla, a crustacean. In 1973, a health safety limit was set of 0.4 mg total Hg/kg FW in edible fish and shellfish tissues with a maximum of 0.3 mg methyl-mercury/kg FW permitted at least five species of fish had more than 0.4 mg total Hg/kg FW, and fishing was prohibited. Contaminated sediments (>15 mg total Hg/kg) were removed by dredging and reclamation between 1974 and 1977. By 1979, the mercury content of all fish, except one species, was less than 0.4 mg total Hg/kg FW fishing was prohibited. By 1983, all fish and shellfish contained less than 0.4 mg Hg/kg FW and fishing was allowed (Nakanishi et al. 1989). 

Four courses of action now seem warranted. First, toxic mercurials in agriculture and industry should be replaced by less toxic substitutes. Second, controls should be applied at the point of origin to prevent the discharge of potentially harmful mercury wastes. Third, continued periodic monitoring of mercury in fish and wildlife is needed for identification of potential problem areas, and for evaluation of ongoing mercury curtailment programs. And fourth, additional research is merited on mechanisms of mercury accumulation and detoxification in comparatively pristine ecosystems. 

The Universal Demercurization Process, or UNIDEMP , is an ex situ process for removing mercury from a variety of solid and aqueous mercury waste streams such as metals, concrete, soils, asbestos, plastic, and cable as well as amalgams and mercury compounds. The process can also treat polychlorinated biphenyls (PCBs) and halogenated organics. UNIDEMP is a mobile system that volatizes and condenses mercury in a countercurrent rotating furnace at temperatures from 550 to 650°C. Celsius. 

One strategy for avoiding these problems is to use the services of a mercury recycler such as Quicksilver Products, Inc. of Brisbane, CA This company is an EPA licensed handler of mercury wastes that is able to extract the mercury from fluorescent tubes and mercury vapor lamps, as well as from batteries, switches, thermometers, contaminated soil, and other sources. 

A widely used method for removing mercury from polluted water is addition of sodium sulfide. Insoluble mercuric sulfide (HgS), which forms is removed as a sludge (Price et al. 1972) that is then landfilled. It has been assumed that HgS remains permanently insoluble, thus preventing movement of mercury into the surrounding environment. Mercury waste has been treated and buried in this manner for many years. 

To clean a mercury spill, consolidate the droplets with a piece of cardboard. Then suck the mercury into a filter flask with an aspirator. A disposable Pasteur pipet attached to a hose makes a good vacuum cleaner. To remove residual mercury, sprinkle elemental zinc powder on the surface and dampen the powder with 5% aqueous H2S04 to make a paste. Mercury dissolves in the zinc. After working the paste into contaminated areas with a sponge or brush, allow the paste to dry and sweep it up. Discard the powder as contaminated mercury waste. This procedure is better than sprinkling sulfur on the spill. Sulfur coats the mercury but does not react with the bulk of the droplet [D. N. Easton, Management and Control of Hg Exposure, Am. Lab., July 1988, p. 66],... 

Fig. 7.4. Mercury pickup devices, (a) Vacuum pickup device. Collected mercury is trapped in the flask for recycling or disposal. (b) Amalgamated copper wire pickup device. The wire is first cleaned in nilric acid, then dipped into a solution of mercuric nitrate to give a thin coating of mercury. Droplets of mercury readily cling to the spiral and may be shaken off into a mercury waste container.

The most notorious incident of widespread mercury poisoning in modem times occurred in the Minimata Bay region of Japan during the period of 1953 to 1960. Mercury waste from a chemical plant draining into the bay contaminated seafood consumed regularly by people in the area. Overall, 111 cases of poisoning with 43 deaths and 19 congenital birth defects were documented. The seafood was found to contain 5 to 20 ppm of mercury. 

Reproduced by permission p. 82 Landfill with aluminum drum for mercury waste, photograph. Recio/Greenpeace. Reproduced by permission p. 83 Ritalin tablets, photograph. Photo Researchers, Inc. Reproduced by permission p. 85 Lothar von Meyer, Julius, photograph. Photo Researchers, Inc. Reproduced by permission p. 86 Millikan, Robert A., photograph. The Library of Congress p. 88 Stratas of banded liassic limestone and shale on a seacliff by... 

Thus, the synthesis of triphenylscandium is a salt-elimination reaction (or metathesis) whilst the route for the lanthanide phenyls involves a redox reaction. The former has the problem of producing LiCl, which is often significantly soluble in organic solvents and contaminates the desired product, whilst the latter involves disposal of mercury waste, as well as handling toxic organomercury compounds. 

Most data is confined to MMM which can be generated from inorganic mercurial wastes by plankton and then progressively bioaccumulated. The final concentration in animals higher up the food chain can be several orders of magnitude higher than those present in the original water. Bacterial synthesis of DMM also takes place in marine and estuarine environments. It is present there at very low levels since it is rapidly hydrolyzed to MMM or vented into the atmosphere. 

It is noteworthy that muscle from two species of recreationally inportant fish spotted seatrout (Cynoscion nebulosus, red drum, Sciaenops ocellatus) collected from coastal bays in Texas considered minimally impacted by mercury exceeded the current recommended value in the U.S. of 0.3 mg total Hg/kg FW muscle. And walleye (Stizostedium vitreum vitreum) collected from Clay Lake, Ontario - a water body heavily contaminated by mercury wastes from a chloralkali plant between 1962 when discharges began and 1970 when the plant closed - contained 2.7 mg... 

---