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Copper Pollution in South San Francisco Bay: A Brake Researcher's Perspective. Part 4 of 4

By: Arnold Anderson

What are the Expected Consequences of Automotive Brake Lining Copper on the Bay?

Total Copper

The expected contribution of automotive brake lining copper wear particulate on the Bay in general, and the South Bay in particular, is essentially zero-the same as airport brake wear copper particulate. The flat shape of copper brake wear particulate makes them stable and difficult to remove once they are deposited. This is understood by anyone who has tried to wash metallic brake wear debris off a wheel or tire.

WCC estimated brake copper wear in the South Bay area to be 7717 pounds, for 80% of the urban nonpoint load. Several compounded errors remove all credibility from the WCC estimate. The entirety of each disc brake lining was assumed to be completely worn off at the time of replacement. Original equipment brake linings were assumed, although replacement brake linings were shown to have much lower copper levels and constitute about 70% of total usage. These assumptions made the WCC estimate of disc brake pad copper wear more than two times too high.

Then WCC assumed, with no supporting data, that copper brake wear particulate is readily removed by stormwater. It is fairly well known that airborne dust can be removed by stormwater. Such particulate matter may be designated as PM-10, for particulate under ten microns in size, or PM-2.5 for particulate under 2.5 microns in size. Such dust particles are known to come from many sources. Included are ashes and other products of combustion. These, and small particulate that may be attached, are quite readily removed by stormwater. Their open and porous structure holds small air bubbles that aid in their floatation and removal. Fibers, both organic and mineral, similarly can be removed by stormwater.

Some portion of all dust is removed by stormwater. The WCC reference study (Kobriger and Geinopolis, 984) estimated that 52% to 57% of the particulate mass on highway I-94 near Milwaukee is carried away with storm water. WCC assumed copper brake pad wear dust would do the same. Copper brake wear particulate is flat, dense, and large. It clearly would not behave like other dust components. Perhaps 1% might be washed away, not 55% as WCC assumed. Correcting these estimation errors reduces the brake copper loading from 7717 pounds to about 70 pounds.

What are the Expected Consequences of Automotive Brake Lining Copper on the Bay?

Dissolved Copper

There are no studies in the literature that even suggest that copper brake wear particulate is soluble in freshwater or saltwater.

The 1994 WCC study assumed that 55% of copper brake wear particulate will be carried off by stormwater, based on reported street and highway data. The 1996 WCC study (and their reference sources) said copper solubility in stormwater runoff from parking lots was 50% to 90%. It is not unreasonable to find this high copper solubility. It is unreasonable to assume that this soluble copper comes from brake linings. Brake wear copper particulate is known to be under 0.1 percent of the total deposited dust, higher in some places, lower in others. Brake wear copper particulate is not soluble in water. Copper platelets from brake wear remain where they land. The reported soluble copper apparently came from the vast majority of particulate matter (dust) that was not from brakes.

Both WCC reports were cited by the Brake Partnership. If accepted as valid, then the majority of copper brake lining wear is carried off in stormwater, and that copper is predominantly in solution. High soluble copper [much of which reportedly is organically complexed] is recognized as a South Bay problem. In the past, copper-bearing brake wear dust has been tested for heavy metals solubility. In practical terms it was zero. A recent brake dynamometer composite wear sample was sent to the Brake Pad Partnership Technical Committee for their evaluation. Presumably this also will have no soluble copper.

If a valid basis for copper removal is found, and copper were to be removed, the economic and highway safety consequences would be sensitive to the timing requirements. Accelerated reformulation of OEM and aftermarket brake linings would have a direct cost in the millions of dollars and require thousands of man hours by the friction material manufacturers. Many additional millions would be required to perform brake and vehicle manufacturer product acceptance tests, along with mandated federal motor vehicle safety tests. By the time that these tests are completed for all car and truck models, the total cost would be in the hundreds of millions of dollars. While it might be accomplished by the aftermarket industry in two years, OEM brake lining conversion would take at least twice as long.

A gradual phase-out would cost far less but would take over twelve years to complete. New brake systems could be developed with essentially no added cost. However, it is inconceivable that a copper­ free program would be acceptable to the world's vehicle manufacturers without a sound scientific basis for it. Credible test documentation also would be required.

Final Comments

Santa Clara Valley Non-Point Source Pollution Control Program clearly has a problem. Nine metals, one being copper, are found at excessive levels in the South Bay. Of these, only copper is used in brake linings.

Copper, nickel, mercury, silver, and selenium also are 'pollutants of concern.' All are metals found in the soil around the Bay. All have been used by businesses in the region The four stream sampling stations in the South Bay area find, during the critical wet season, about the same amounts of chromium and copper, much more nickel, and still more zinc in solution. The Program's own report (WCC '96) indicates erosion of copper and nickel from natural soil deposits is a significant source, and that their estimated load of these metals was questionable.

Technically flawed and superficial work by WCC has been used by the Program to lay blame upon the automotive industry in general and the friction material industry in particular. Such unsubstantiated and incorrect reporting does nothing to solve the problem. It does distract attention from major pollution sources. Thus, it also delays their management.

Much of the information that has been sent out through the Brake Pad Partnership has been partisan and self-serving to local government and industry. For example, the Copper, Brake Pads & Water Quality Briefing Packet was not prepared nor reviewed by the brake industry representatives. It was "Developed by the City of Palo Alto and Common Ground for the Environment." This document package contains patently false and misleading statements. For example, the Briefing Packet overstated the copper levels from the WCC report for two aftermarket brake linings by a factor often. Numerous other errors were noted-mostly unfavorable to the brake industry, and many revealing a lack of brake knowledge by the writer. This briefing packet appears to have been written more to arouse environmental activists against copper in brake linings than to inform partnership members. Blatant bias such as this has caused Common Ground for the Environment to lose credibility with most of the automotive industry.

Based on unsupported allegations and sophomoric research, the friction material industry has been asked to remove, or significantly reduce, copper content by the Brake Pad Partnership. To what end? No percentage reduction of brake lining copper will help the Estuary and the South Bay, unless brake lining copper wear particulate actually reaches the bay in soluble form.

The fundamental need for the Brake Pad Partnership is to identify and quantify the true contribution of brake lining copper to the South Bay. Good research makes problem resolution and environmental responsibility achievable. Good documentation of this research should help others to address complex metal pollution problems in a logical and technically correct manner. When this is done, vehicle manufacturers and friction material suppliers everywhere will act responsibly.

AEA 4/19/97

Arnold Anderson, known as Arne in the brake technology world, has devoted most of his professional life to studies in tribology, the science of friction and wear. Much of this was done as a researcher at the Scientific Laboratory of Ford Motor Company. After his retirement in 1987, Arne was a consultant to vehicle manufacturers, brake manufacturers, and regulatory groups. He recently retired after having accumulated 12 patents, 42 technical papers, as he performed diagnostic studies of car, truck, aircraft, and aerospace brakes and clutches.


Sep 05, 2022

With all due respect to the author's expertise on brake pad design, the information in this posting is not scientifically correct descrption of environmental science, nor is it a procedurally correct description of the Brake Pad Partnership scientific work underlying the development of US nationwide measures addressing copper in vehicle brake pads to protect aquatic life. The Brake Pad Partnership (a joint industry/government/NGO collaboration) did not use the Woodward Clyde study. Instead, it obtained >$1Million in government grants plus contributions from the brake pad industry, other industries that use copper (e.g., computer manufacturers), and government agencies and foundations and to conduct a series of studies to address the very questions raised in this blog post, leading to the joint (amo…


Jun 10, 2022

Great information... and 4 series post. Good read!


Brake Academy
Brake Academy
Jun 07, 2022
  • Gerald Dreisewerd Question: The copper issue was something that interested me when I encountered California’s Better Brake Law. I wondered if the rivers and tributaries that feed San Francisco Bay pass through major copper deposits. What I found was that North America has sizable copper deposits and all the rivers and bays on the West Coast pass through these deposits. So I’m left with the question whether the copper in San Francisco Bay are due to natural processes or human activity. The bureaucrats administering the Better Brake Law will of course solemnly assure us that this is caused by human activity. I’m from Missouri. You’ll have to show me.

Arnold Anderson Response:

I am not up to date on almost anything…

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