By Nicole Fitzgerald, Ph.D., James Hatton, and William DiGuiseppi, M.SAME
Encompassing more than 5,000 individual compounds, per- and polyfluoroalkyl substances (PFAS) are able to withstand high temperatures and acidic and basic conditions, making them ideal candidates for use in manufacturing processes, such as metal electroplating. PFAS are persistent and, once released to the environment, do not readily degrade. They are also associated with adverse human health effects. Some PFAS can cause increased cholesterol, low infant birth weights, immune system effects, specific cancers, and thyroid disruption.
The Department of Defense has been proactive in identifying locations where PFAS have been used. These primarily are related to aqueous film-forming foams (AFFF), which were used in emergency response, firefighter training, and fire suppression systems. Secondary locations where PFAS may be present at military installations include landfills, wastewater treatment facilities, and chromium plating shops.
While the environmental impacts from these potential secondary source areas are not presently known, it is anticipated they will be substantially less extensive than those from AFFF, simply due to the number of locations and quantities of PFAS-containing materials handled at them. However, that does not diminish the potential risk to human health and the environment where they are found. Some states, notably Michigan and California, have recently identified chromium plating facilities as potential sources of PFAS, forecasting an increase in attention on these facilities in the future.
CHROMIUM PLATING CONTROLS
Chromium has been linked to skin lesions, nasal ulcers, nasal perforation, respiratory tract irritation, and lung cancer. The Occupational Safety & Health Administration regulates chromium emissions through permissible exposure limits that were last updated in 2006. The Environmental Protection Agency has regulated hard chromium plating, decorative chromium plating, and chromium anodizing operations since 1995. Hard chromium plating facilities are required to meet emissions standards, while decorative chromium plating and chromium anodizing facilities have the option to either meet a chromium emission standard or adhere to surface tension limits in their baths.
While the environmental impacts from these potential secondary source areas are not presently known, it is anticipated they will be substantially less extensive than those from AFFF, simply due to the number of locations and quantities of PFAS-containing materials handled at them. However, that does not diminish the potential risk to human health and the environment where they are found.
Emissions Concerns. A variety of chemical and engineering controls, such as ventilation, covers, and the addition of a fume suppressant, are used to control chromium plating emissions—although covers are less common because of the potential for hydrogen gas to accumulate underneath and because hexavalent chromium can coat the underside, creating a hazard when workers remove it. Fume suppressants control mist formation by chemically lowering the surface tension of the plating bath. As the surface tension is reduced, the bubbles produced in the bath become smaller, which are slower to rise. When they surface, they have less energy and are less likely to form a mist. The foam used on the surface of a chromium plating bath has a characteristically yellow-orange color from entrained chromate.
Plating processes for other metals yield negligible emission levels. In fact, emission levels from other metals plating operations in uncontrolled scenarios are estimated to be comparable to controlled emissions from chromium plating and anodizing operations. As a result, fume suppressants are not commonly used and are generally not a regulatory requirement for plating other than chromium plating and chromium anodizing. However, it is possible that other materials used other plating processes, such as wetting agents, may contain PFAS.
Early fume suppressants were hydrocarbon-based, but these were reactive and had to be replenished frequently. Chromium plating operators turned to PFAS fume suppressants around the mid-20th century. Fluorinated fume suppressants overcame the problems associated with early fume suppressants. By the 1980s, formulations containing perfluorooctane sulfonate (PFOS) were widely used.
Wastewater Presence. Chromium plating facilities using PFAS-containing fume suppressants can be a source to wastewater. In 2007, a chromium plating facility in Brainerd, Minn., caused elevated PFOS in the local wastewater treatment plant (PFOS was detected at greater than 150,000-ng/L throughout the wastewater treatment plant). Of the 11 chromium plating facilities that were sampled a year later, 10 had detectable PFOS concentrations in their wastewater, with concentrations from 31.4- to 39,000-ng/L.
In 2012, the Environmental Protection Agency mandated that fume suppressants containing PFOS be phased out by 2015. Newer formulations were sampled in 2019 and did not contain detectable levels of PFOS or PFOS-precursors. The active ingredient in all sampled formulations was 6:2 fluorotelomer sulfonate.
Perfluoroalkyl phosphinic acids, perfluoroalkyl carboxylates, perfluoroalkane sulfonyl fluoride-based substances, perfluoroalkane carbonyl fluoride-based substances, and perfluoropolyether-based substances may also be used in fume suppressants.
Residual Detection. The State of Michigan released a study concerning PFAS used in chromium plating in 2020—after PFOS had been phased out of fume suppressants for five years. This study found that despite the ban, PFOS was still detected in the wastewater of 10 out of 11 chromium plating facilities at concentrations ranging from 15- to 51,700-ng/L. It was concluded that residual amounts of PFOS from prior to 2015 were likely still sorbed to the piping and tanks in the facilities.
KEEPING CLOSE WATCH
While PFOS-containing fume suppressants are no longer used by chromium plating facilities, residual PFOS can still contaminate waste streams. Additionally, 6:2 fluorotelomer sulfonate is now prevalent in chromium plating. Other plating operations such as those for gold, silver, zinc, and nickel are more efficient, where less bubbling occurs. This negates the need for PFAS-containing fume suppressants. These other plating operations are generally not regulated; therefore, mandates for the use of fume suppressant foams among non-chromium plating operations are limited.
These facilities may be a secondary source for PFAS and PFOS, but should not be ignored. As the Department of Defense makes strides to clean up PFAS from AFFF sites, chromium plating facilities should also warrant a watchful eye.
Nicole Fitzgerald, Ph.D., is Environmental Specialist, James Hatton is Senior Engineer, and William DiGuiseppi, PG, M.SAME, is Principal Hydrogeologist, Jacobs Engineering. They can be reached at email@example.com; firstname.lastname@example.org; and email@example.com.
[This article first published in the January-February 2021 issue of The Military Engineer.]