NEW YORK — The following is the first of four articles by Arnold Anderson posted on the Brake Academy’s website concerning the interaction between copper pollution in South San Francisco Bay and emissions from brake components.
Copper Pollution in South San Francisco Bay: A Brake Researcher’s Perspective
Background: South San Francisco Bay was declared an impaired water body by the California State Water Resources Control Board in 1989 under Section 304(1) of the federal Clean Water Act. USEPA water quality criteria were periodically exceeded for nine heavy metals (cadmium, chromium, copper, lead, mercury, nickel,selenium, silver, and zinc). Recent data (Chen ’96) shows that the South Bay has high total and dissolved copper levels, especially in the winter. Copper concentrations throughout the estuary are known to rise with distance from the ocean, both North and South. However, south of the Dumbarton Bridge (toward Silicon Valley), copper measurements rise sharply.
Water districts in the impaired region have reduced copper levels from point sources. USGS monitoring data indicates a 90% decrease of wastewater copper between 1980 and 1990. Non-point sources of copper remain a problem. The Santa Clara Valley Non-Point Source Pollution Control Program funded studies which estimated in 1994 that 7,717 pounds of copper enters the South Bay each year from disc brake pad wear (WCC ’94). If correct, this would be quite significant since the estimated total copper load from all sources was 14,600 pounds (WCC ’91) and 17,400 pounds (Lacy ’93). In February of 1994, an agreement was reached that required non-point source runoff controls which would reduce copper loadings into the bay by 20%, with an extra 950 pounds of reductions for South Bay loadings.
The 950-pound copper reduction was targeted through stormwater controls.
The entire bay area has had protracted problems with heavy metals, some dating back to the gold rush era. Copper levels in the Bay are known to vary with time and location. For example, high dissolved copper levels are endemic to the South Bay, primarily in the winter. North Bay regions have much lower dissolved copper. Some North Bay locations at times have higher levels of suspended copper. Copper concentration data (e.g., time, form, and distribution) does not appear to have been used to diagnose possible brake lining copper effects.
Introduction: It is essential to have some understanding of where copper is used in friction materials, why it is used, and what happens to copper in the wear processes. Copper-containing friction materials are employed in brakes and clutches of vehicles and machinery used everywhere. However, three applications produce most of the copper wear particulate in the region surrounding the Estuary. These are sintered aircraft disc brakes, heavy duty drum brakes, and passenger car/light truck disc brakes.
Applications that may use copper-containing friction materials, but with minimal annual wear, are motorcycle brake linings, light aircraft organic disc brake linings, light rail disc brake linings, and heavy-duty clutch facings. Other friction material applications, such as railroad tread brake shoes, have inconsequential copper content. These will not be discussed.
To provide a basis for discussion, a description of the three main applications follows, then reasons why copper is used in these friction materials, and finally what happens to the copper, or copper-containing constituents, during friction and wear processes. Existing reports are reviewed, then consequences of friction material wear on copper level are discussed for the entire region, but with primary focus on the South Bay.
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