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Trace levels of herbicide detected in Oahu water systems


Trace levels of the chemical bromacil, an herbicide used for weed control, were recently detected in water samples collected in Waipahu and Mililani. 

However, Hawaii Department of Health officials are advising consumers they should not be alarmed as levels were well below the Environmental Protection Agency Lifetime Health Advisory Level for drinking water, and bromacil is filtered out through the Honolulu Board of Water Supply’s Granular Activated Carbon treatment facilities before delivery to drinking water supplies.  

The water samples were drawn from one Waipahu I pump and one Mililani I pump, according to a news release issued by the state Department of Health.

In addition, trace levels of boron were recently detected in water from several Waipahu GAC treatment facilities and water from the Waialua GAC treatment facility. The levels of boron found were also well below the EPA Lifetime Health Advisory Level for drinking water. 

Boron, present naturally in rocks and soil, enters the environment through weathering. Bromacil is used or weed control in pineapple fields and citrus crop areas.

The Honolulu Board of Water Supply tests for the presence of these chemicals as part of its regular monitoring schedule and reported these latest findings to the DOH. 

“We are confident that these trace levels do not pose a public health threat,” Gary Gill, the DOH’s deputy director for Environmental Health, said in the release. 

“These chemicals had not previously been detected at these sampling points. The Department of Health will continue to work with the Honolulu Board of Water Supply, so that tests for these chemicals continue as part of its regular monitoring schedule to ensure that public health is not compromised.” 

The EPA’s Lifetime Health Advisory Level for bromacil is 70 parts per billion, which is measured in micrograms per liter. By contrast, the bromacil level detected at a Waipahu I pump was 0.46 parts per billion and at a Mililani I pump was 0.66 parts per billion.

State Health official Ann Zane said 0.66 parts per billion would be comparable to distributing less than one drop of bromacil among 250 55-gallon drums of water. 

The Honolulu Board of Water Supply also reported very low levels of boron at three Waipahu granulated activated charcoal treatment facilities and at the Waialua Wells granulated activated charcoal treatment facility, ranging from 0.092 to 0.15 milligrams per liter or parts per million. These levels were also well below the EPA Lifetime Health Advisory Level for boron in drinking water of 6 parts per million and do not represent a health threat.

Zane said bromacil and boron are not EPA-regulated with “maximum contaminant levels” because they haven’t posed problems as contaminants.

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