EWG's Tap Water Database — 2019 UPDATE


Heptachlor epoxide

Mcconnell S/d

Heptachlor epoxide is a breakdown product of heptachlor, a highly toxic and carcinogenic pesticide banned in the U.S. since the 1980s.





Samples exceeding legal limit (MCL)


Samples exceeding
health guidelines

Testing results - average by year

YearAverage resultSamples takenDetectionsRange of results
20120.0563 ppb110.0563 ppb
20130.0379 ppb110.0379 ppb
20140.0618 ppb110.0618 ppb
20150.0220 ppb110.0220 ppb
20160.0270 ppb110.0270 ppb
20170.0187 ppb32ND - 0.0280 ppb

ppb = parts per billion

State and national drinking water standards and health guidelines

EWG Health Guideline 0.006 ppb

The EWG Health Guideline of 0.006 ppb for heptachlor epoxide was defined by the California Office of Environmental Health Hazard Assessment as a public health goal, the level of a drinking water contaminant that does not pose a significant health risk. This health guideline protects against cancer.

EPA Maximum Contaminant
Level (MCL) 0.2 ppb

The legal limit for heptachlor epoxide, established in 1991, was based on analytical detection limits at the time that the standard was set. This limit may not fully protect against the risk of cancer.

ppb = parts per billion

All test results

Date Lab ID Result
2012-05-29C202064-010.0563 ppb
2013-04-29C302442-010.0379 ppb
2014-04-08C402912-010.0618 ppb
2015-04-010.0220 ppb
2016-04-18CZ02809-010.0270 ppb
2017-04-11CA02671-010.0280 ppb
2017-08-08CA10733-010.0280 ppb