Diquat
City of Tigard
NOTE: City of Tigard purchases water from Lake Oswego - Tigard Water Supply which is required to test for diquat. Sample information shown below was taken by Lake Oswego - Tigard Water Supply.
Diquat is a herbicide used on potato crops and aquatic weeds.
Samples
Samples exceeding legal limit (MCL)
Samples exceeding
health guidelines
Testing results - average by year
| Year | Average result | Samples taken | Detections | Range of results |
|---|---|---|---|---|
| 2018 | ND | 2 | 0 | ND |
| 2019 | N/A | 0 | 0 | N/A |
| 2020 | ND | 5 | 0 | ND |
| 2021 | ND | 1 | 0 | ND |
| 2022 | ND | 1 | 0 | ND |
| 2023 | ND | 1 | 0 | ND |
ppb = parts per billion
State, National, and Health Guidelines for Drinking Water
EWG Health Guideline: 6 ppb
The EWG Health Guideline of 6 ppb for diquat 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 cataracts.
EPA Maximum Contaminant
Level (MCL): 20 ppb
The legal limit for diquat, established in 1992, was based on a toxicity study in laboratory animals conducted in the 1980s.
ppb = parts per billion
All test results
NOTE: City of Tigard purchases water from Lake Oswego - Tigard Water Supply which is required to test for diquat. Sample information shown below was taken by Lake Oswego - Tigard Water Supply.
| Date | Lab ID | Result |
|---|---|---|
| 2021-10-27 | 202110280645-S | ND |
| 2022-01-19 | 202201200820-S | ND |
| 2023-10-04 | 23-60552-S | ND |