Mercury Spill Clean-Up
Liquid Mercury is a proven neurotoxin. While Mercury salts are toxic by ingestion, the prime toxicity of Liquid Mercury is in the form of vapor. OSHA regulations limit the amount of Mercury vapor to less than 0.1mg/m3. Yet concentrations of Mercury vapor of up to 20mg/m3 can go unnoticed for considerable periods of time. Liquid Mercury is found in thermometers, blood pressure devices, switches, and a host of other industrial and household equipment. Containers of Mercury are used in industrial processes from gold mining to Chlorine production. Despite government regulations restricting and reducing the amount of Mercury in our environment, it remains a ubiquitous item all around us.
Cleaning up Liquid Mercury usually involves one or both of two chemical processes; insolubilization and/or amalgamation. Both turn Liquid Mercury into a nonvaporizing form. Insolubilization most often involves turning the Mercury into a sulfide. Amalgamation combines Liquid Mercury with metal powder to produce a solid, non-mobile form.
First Response. The minimum protection required for working with Mercury spill cleanups involves equipment specially designed for mercury exposures, including respirators, gloves, goggles, and shoe covers. In some cases, full body protection may be required. Other equipment includes gold film-type mercury-vapor detectors, probably the most sensitive and efficient available for Mercury cleanups are those manufactured by Arizona Instrument Corp.. The use of a high intensity Halogen lamp will often reveal Liquid Mercury to the eye. If the mercury spill is in a confined area it should be ventilated immediately. Indoor heating systems should be shut off to reduce vaporization. If an amalgamating powder is not available immediately, responders can cover the suspected area with polyethylene sheeting or spray, and apply an acrylic wash over the surface.
Humans and animals that may have been contaminated should be washed using an alkaline soap and a paste of water and flowers of sulfur-which generally can be found in garden shops and will turn some of the mercury into an insoluble sulfide-then rinsed. All wash water should be collected and concentrated. Liquid Mercury is not absorbed by the body to any great degree and generally passes through; thus if any Liquid Mercury has been ingested, feces should be collected and disposed properly. The individuals and animals should then be tested for residual Mercury. The presence of Mercury can be detected with a sodium sulfide solution, which can be obtained from a chemical supply house. After reducing the solution to 0.5% in water, it may be sprayed on affected part (except for eyes, mucous membranes and the mouth). Any Mercury present will show up as dark, reddish-brown stains. Residual Mercury then can be removed using vinegar wash, followed by hydrogen peroxide to combat the hydrogen sulfide odor. An alternate method is to wipe the area with a vinegar-soaked swab, then a peroxide wipe. All wipes contaminated with Mercury should be disposed properly. First responders should collect any metal objects that have come in contact with the spill. Coins, jewelry, and many other metals with amalgamate with Mercury. Metal objects can be decontaminated by distilling off the Mercury.
Area Cleanup. One of the most efficient, economical methods for cleaning up Mercury spills is to use an amalgamating powder, which consists of various metal powders combined with a mild acid. For example, a single package containing a ferrous-nucleating agent simply requires a small quantity of water to be effective. The powder not only turns the liquid Mercury into a solid while reducing its vapor pressure, but allows the mercury to be picked up with a common magnet. All amalgamating powders may be picked up by sweeping or using an approved vacuum for mercury cleanup.
Horizontal surfaces can be treated effectively by broadcasting the powder uniformly over the contaminated area, then lightly misting with potable water. Small areas may be scrubbed by hand with a plastic scouring pad, which ensures complete contact, while larger areas may be scrubbed with a stiff floor brush.
When using a magnetic amalgamating powder, a hand magnet (or, for large areas, a wheeled magnet) may be be used to pick up the substance. A plastic bag turned inside out or sheet plastic placed over the magnet also enables easy removal and collection.
Vertical areas such as walls, can be decontaminated by mixing the amalgamating powder with water to form a thick paste, then scrubbing the paste into the surface with brush or pads. The paste may be picked up with magnets. Soft surfaces, such as carpeted floors or cloth coverings, can be treated similarly. Only using more water to produce a sloppy slurry which can be scrubbed into the surface and picked up.
Soil Contamination. Soils vary in type and consistency. In most soil contamination cases, the Mercury is at or close to the surface. The contaminated soil should be excavated to 50% beyond the depth of contamination to ensure complete removal. The excavated soil can be taken off site, and the Mercury removed through distillation or through magnetic means, using amalgamating powder. The latter process involves slurring the contaminated soil in water and stirring in the magnetic powder. In some cases, a mild acid may have to be added to maintain a pH of no less than 4 or higher than 6. After adequate mixing, the amalgamated Mercury can be removed using as plastic covered magnet as described previously.
The soil should be tested on site for any remaining Mercury. In all procedures, the use of corrosive-resistant, plastic equipment should be employed.
Cleaning Equipment. Any equipment not testing Mercury free can be sent to a recycling facility. Equipment that can be recycled includes plastic swimming pools, plastic tubs and containers, and plastic scrub brushes.
Plumbing fixtures such as sinks, commodes and floor drains, are special concerns during a Mercury spill. These systems must be dismantled or decontaminated with magnetic powder. Nearly every plumbing system contains traps located just after the drain. The magnetic powder can be poured into the drain, then forced into the trap by gently pumping a plumber's helper. This should be done slowly and gently to avoid forcing the Liquid Mercury or the amalgamating powder further into the system. After a short while, the solid amalgam can be removed using a plastic covered magnet on the end of a plumber's snake. Prefabricated magnets, about 18 inches, can be used.
Collected wash water can be decontaminated and concentrated by filtering it through layers of fine sand and amalgamating powder. Several one inch thick layers of sand and powder usually remove all the Mercury. The powder will solidify the Liquid Mercury and fine sand will collect any insoluble mercury sulfide. A simple gravity filter with suitable plastic container or a common, stainless steel swimming pool filter are usually sufficient. In all cases, effluent water and all equipment used in the cleanup should be tested using sodium sulfide or other Mercury test before disposal. Used filter media can be retained and sent to a recycling facility.
OMNI/Ajax, 3 Cemetery Road, P.O. Box 161, Great Meadows, NJ 07838-0161. Tel: 908-637-4315; Fax: 908-637-8455.