Water to five West Marin conmunities last month was overdosed accidentally with up to eight times the accepted level of fluoride for about two weeks, it was disclosed Thursday.

The excessive concentration of the chemical, a health hazard according to its critics even at normal levels, was injected into water pumped from Marin Municipal Water District’s San Geronimo treatment plant. Advocates of fluoridation argue it helps protect teeth from decay.

The district’s staff defended distribution of this water to customers even after the overdose was discovered, arguing it would have been undesirable to dump the water in a drought year.

District directors and its general manager said the staff didn’t notify them of the problem. Several directors argued the public should have been informed as well.

The plant usually serves the Ross Valley and Terra Linda as well-but because these areas are getting their water over the Richmond-San Rafael Bridge, the plant is serving only Woodacre, San Geronimo, Forest Knolls, Lagunitas and Nicasio.

The problem came to light in a staff report issued late Wednesday for the board’s meeting 1 p.m. this coming Wednesday in the district’s Corte Madera office. The report was sought by the president of the district board, Dr. William J. Filante.

He said he had learned of the incident from Dr. John Lee of Mill Valley, who, in turn, had been told about it by someone in the state Department of Public Health.

Dr. Lee is an opponent of fluoridation.

The staff of the district notified the state department on Oct. 28 that the accident had been discovered the day before. The overdose apparently began sometime after Oct. 22, the last recorded time the plant was found in normal action.

A laboratory technician performing routine chemical analyses of weekly sampling noted on October 27 that a sample from the plant indicated a fluoride level of 5.4 parts per million. The accepted level is .7 of a part per million.

Immediate steps were taken to dilute the concentration in the water supply already fluoridated.

A sample taken the next day at the county fire station in Woodacre found a level of 3.9. Despite dilution and a halt to fluoridation the level had risen to 4.1 at the fire station by Oct. 30.

The staff report does not indicate sampling at any other point. The 4.1 count was the maximum reported outside the plant.

The fire station count included in the report was 1.4 on Nov. 2. It concluded that “fluoridation was resumed on Nov. 9 at a treatment level of .7.”

The failure was caused by a breakdown of a valve, and was not detected sooner because one device that would have found it was being moved and the other was in Massachusetts for servicing.

A back-up system will be installed to prevent another such failure, the staff said.

Filante argued “it’s not as bad as it looks,” and defended as adequate the staff’s notification of the state department. Noting state officials had not suggested public notice, he reported “we also notified the Environmental Protection Agency, and again there was no direction to make further notification.”

Asked why the county health department had not been notified, Filante said “apparently that is not something we’re supposed to do You have to follow some kind of rule. And the rule is to notify the state. ”

A sharply contrasting reaction came from director K. C. Bishop 111, who lives in Woodacre and drank the water – as did his wife and their two children, age 1 1/2 and 3 1/2.

Calling the staff’s failure to notify the board and the public “just incredible,” Bishop repeatedly said “I can’t believe I was not told that it happened, especially since some concern remains about health. By God, it better not happen again.”

As a resident of the affected area, he added, “I am kind of angry, even though state health said we were not required to give notice, that we weren’t even given any chance to make a decision on our own whether to drink it. That’s something that should not have been done.”

Recalling voter approval of fluoridation in 1972, Bishop said “people were assured we would not get higher doses than safe.” Hazards probably come with longer exposures to the chemical, he said, “but it shouldn’t be risked even for a short time without telling the people. ”

The staff’s performance in the matter, Bishop declared, is “just stunning.” As for his children getting the overdosed water, he said, “I am not particularly enthralled with the idea of them drinking it.”

Director Richard Fox also argued “it might have been best to notify the public.” Noting that as a citizen he voted against fluoridation in 1972, he said, “I just don’t think it’s a good idea.” People who want the chemical should take it on their own, he said.

Director Pamela W. Lloyd said she, too, was “very surprised” the staff had failed to notify the board about the problem. “We need to decide whether to give public notice,” she said.

General Manager J. Dietrich Stroeh said he had not yet seen the report because he has been on vacation. He said he knew nothing about the incident, which occurred two weeks before he went on vacation.

The staff report conceded that mottling of teeth can occur when concentrations are more than 1.5 to 2 parts per million, and that bones and joints can be affected when the level rises above 3 parts per million.

It stressed, however, there is a “lack of data relating to these concentrations to short-term exposures.”

Lethal doses, it observed, are some 500 times the levels counted during the breakdown.

Fluoridation of district water began in December 1973 after opponents failed to block it in court action and through an appeal to the state Department of Health.

Dr. Lee, chairman of the Marin Medical Society’s committee on the environment, said in May 1976 that “it is time for a reappraisal of fluoridation in Marin.” He cited recent studies and reports he said show a correlation between intake of the chemical and cancer, kidney ailments, bone damage, teeth mottling and other maladies.

He said children already get the optimal amount of fluoride through food and untreated water without addition of more of the chemical.

Fox reported this past January that a new study by the University of Missouri found small amounts of fluoride in drinking water can cause genetic damage to mice –