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03/07/94

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A better way to track heavy metal

STANFORD -- Researchers at Stanford and Tufts universities have developed a novel system that may drastically reduce the cost of measuring heavy metal contaminants in drinking water and groundwater. Instead of sending samples to a laboratory for analysis, investigators will be able to get accurate results, on site and in minutes.

The new system uses a tiny silicon sensor that is only a centimeter long, a few millimeters wide and half a millimeter thick and costs only pennies to manufacture. Yet, it can measure concentrations of the key heavy metals lead, cadmium and copper down to parts per billion. Details of its construction and characteristics were reported in the Feb. 1 issue of the journal Analytical Chemistry.

In addition, the successful miniaturization of the sensor's control electronics into a single, inexpensive integrated circuit that can replace laboratory equipment costing as much as $20,000 was reported by graduate student Richard Reay Feb. 17 at the International Solid State Circuits Conference, held in San Francisco.

The microelectronic sensor and controller, when plugged into a laptop computer, are designed to provide ultra-precise measurements of the concentrations of key heavy metals in the field, said Gregory T. A. Kovacs, assistant professor of electrical engineering at Stanford's Center for Integrated Systems, who is leading the effort with Professor Samuel P. Kounaves of Tufts University.

Currently, water must be sent to a laboratory for analysis of its heavy metal content. Typically, the pen-sized electrode-sensors used are only accurate in controlled laboratory conditions and the control electronics are not portable.

"With our new system, you will be able to put the sensor in a glass of water and, within minutes, get a display showing the heavy metal concentrations," Reay said.

Contamination of drinking water and groundwater by heavy metals is a serious and continuing health problem. Many heavy metals can be highly toxic. Because it is widespread and can have detrimental effects on children at very low concentrations, lead is the greatest public health concern.

"It is very important that we do a better job of identifying the sources of lead exposure than we have done so far. A portable instrument of this type can be of real assistance," said Fernando S. Mendoza, an associate professor of pediatrics at the Stanford University Medical School who studies the effects of lead on children.

One of the goals of the Environmental Protection Agency funded project was to develop a heavy metal sensor that could be placed underground to detect the presence of these contaminants and monitor how they move through groundwater. Heavy metal contamination of groundwater comes from mining operations, landfills, deforestation and agriculture, among other sources. Attempts to monitor this type of contamination have been limited by the lack of a system that can measure heavy metals directly in groundwater.

"Laboratory testing indicates that we are on the right track for a sensor that will work in field conditions," Kovacs said.

The researchers also plan to test the system's usefulness for monitoring internal corrosion of large industrial machinery by measuring heavy metal levels in the coolant. They also have a joint project with Intel Corp. to determine if the sensors can be used to detect the levels of heavy metals in the process fluids used in computer chip manufacturing.

The research is funded by the EPA's Northeast Hazardous Substance Research Center, EG&G Princeton Applied Research Corp., the National Science Foundation, and the family of the late Robert Noyce.

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