Much attention from regulators is focused on the metal finishing industry. When USEPA and state technical assistance providers look to target specific industrial sectors for extra attention, metal finishing is among the top selections. Several federal, state, and local programs are geared toward preventing the pollution that these shops produce. In fact, several such programs are described in this issue of CLEARWATERS. Why have metal finishers attracted all this attention? This article looks at some of the health and environmental effects of the wastes that metal finishing shops produce.

Black zinc computer components are removed from one of many water rinses used in the plating process. Copious water is required. (Photo courtesy of Anoplate Corp.)

Counting metal finishers

The U.S. Department of Commerce collects data about businesses in the United States. To organize this information, businesses are classified by their primary product or service into four-digit Standard Industrial Classification (SIC) codes (six-digit NAICS codes will soon replace the old SIC codes). The SIC code that best describes most metal finishing businesses is 3471: electroplating, plating, polishing, anodizing, and coloring. Some metal finishers might be classified as 3479: coating, engraving, and allied services, not elsewhere classified. These codes capture the majority of independent metal finishing shops.

Beyond SIC 3471 and 3479 Metal finishing processes are also part of many metal-related manufacturing and service businesses, and a company that manufactures and then finishes a metal product is classified under the SIC code for that product. Some of the businesses that may use metal finishing processes include those classified under SIC codes 33xx: primary metal industries; 34xx: fabricated metal products, except machinery and transportation; 35xx: industrial and commercial machinery and computer equipment; 37xx: transportation equipment; 7532: automotive top, body, and upholstery repair shops and paint shops; and 7631: watch, clock, and jewelry repair.

The U.S. Department of Commerce reported that nationwide, 5603 metal finishing shops (SIC codes 3471 and 3479) employed more than 65,000 workers, and 267 of these shops were located in New York State (data from 1992). Almost half of these shops had fewer than 10 employees. Less than 10% of all metal finishing shops had more than 50 employees. No firm figures are available to tell us the extent of metal finishing activities in New York State manufacturing plants or service businesses, but the sites may number in the thousands. These figures - and extrapolations - reveal that most metal finishing wastes come from many small sources located throughout the State, not from a small number of large well-known sources as is characteristic of many other industrial sectors.

Environmental risk

How much harm any particular environmental release causes cannot be fully known. Risk can be described as "the likelihood of harm occurring from a particular situation." In an environmental context, risk can be thought of as the product of a substance's potential to do harm (toxicity) and the amount and location of the substance in the environment (exposure). Toxicity is often estimated through controlled scientific studies on animals, epidemiological studies, or clinical studies that link chemical exposure to an adverse effect in humans. Toxic effects can include cancer, neurological effects, liver and kidney damage, or a number of other health problems. Different people may have different reactions to the same chemical. Moreover, the quality and quantity of available toxicity information varies greatly among chemicals.

Exposure is harder to predict than toxicity. The degree to which people are exposed to a given chemical release depends upon their proximity to the source, the weather, the volume of air breathed and water and food consumed, and many other factors. Environmental chemical concentrations vary from place to place and day to day. Chemicals in the environment can travel far from where they are released, and tracing a particular contaminant back to its source may be impossible.

Risk can be characterized by summarizing what is known about the possible health and environmental effects of a release and by describing the level of uncertainty of these effects. The risks from any single metal finishing shop could be described in these terms, even though releases can vary over time as jobs and processes fluctuate. The risks from the metal finishing industry as a whole, however, can only be characterized in very broad terms.

Metal finishing waste streams

No one is sure just how much waste is generated by metal finishing shops. A primary source of information about environmental releases in New York State is the Toxics Release Inventory (TRI). The TRI requires businesses to report annually releases from any of more than 600 specific hazardous substances to the State.

TRI data can be sorted by SIC code to give a picture of the waste generation patterns for a given industry. The 1992 Census of Manufactures lists 267 businesses in SIC codes 3471 and 3479 for New York State. However, only 29 of these businesses were large enough to report their releases under the TRI in 1998 (smaller businesses are not required to report under the TRI). These 29 businesses collectively released 315,156 pounds of hazardous substances to the environment. No release data is available for the other 238 establishments. Many businesses in other SIC codes conduct some metal finishing activities, but when these businesses report their releases under the TRI, they report only the total quantity of each chemical that is released, and it is impossible to tell from their reports how much of the release resulted from metal finishing.

Atomic absorption analysis is used to monitor metals levels in effluent as well as to trace metal contaminant levels in plating baths (courtesy of Anoplate Corp.)

Complex wastes

Metal finishers differ widely in the types of items that are finished and in the types of plating or finishing that they do. Each variation in the finishing process results in a different waste stream and, in fact, no two metal finishers will generate exactly the same types of waste. Yet, some waste streams are commonly found: solvents for cleaning the parts, plating baths with metals, cyanide or acid solutions, rinse waters, stray air emissions, and others. These wastes contain solvents, metals, cyanide, acids, and other toxic components.

Although metals are the most obvious of the toxic waste products from metal finishing operations, many other hazardous substances are released as well. Solvents are most often used to clean the metal parts before they are finished, and acids or bases are often a component of the plating baths. These chemicals tend to be volatile and can contribute to environmental damage like ozone layer depletion as well as cause human health effects.

What happens if these materials are not handled responsibly? They enter the environment and disperse, making it difficult or impossible to remove them in the future. Airborne particles can travel over short or long distances before eventually breaking down or settling on the land or water in a remote site. While airborne, they may be inhaled by humans or animals. Through air deposition or direct discharges to land or water, they can enter food sources or drinking water and cause health problems in humans.

Web extra: Many hazardous releases result from metal finishing. See details.

Conclusion

Although the health and environmental risks from metal finishing activities cannot be quantified, the activity definitely poses the potential for significant environmental harm. The small shops that make up much of the metal finishing industry may find that it is very costly to manage properly the wastes that result from their processes. This is why pollution prevention techniques can be so beneficial. P2 can make a big difference in the volume and toxicity of waste generated and can save significant amounts of money. Sometimes even minor process changes can lead to big benefits for the environment.
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Sharon A. Rehder, PE is an environmental engineer with the NYSDEC Pollution Prevention Unit.

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