The USGS has not looked for paraquat
contamination of groundwater, so very little data
are available. However, it has been detected in
drinking water wells in at least two US states
(US 1997). One out of 399 samples taken in
California in 2006 did contain a low level (0.24 ppb) of paraquat (US EPA 2009). In Thailand it
has been found in groundwater at levels up to
18.9 µg/L (Amondham et al 2006