Abstract
Large quantities of herbicides are used in paddy fields, so that there is much concerned about contamination of herbicides in water. The contamination of eight different compounds of herbicides was investigated in run-off waters from paddy fields and drainager river located around the southern basin of Lake Biwa.
Adsorption of the herbicides on suspended solids was found to increase with decrease in solubility of them in water. It is confirmed that the run-off of herbicides from paddy fields is influenced by the time of scattering herbicides, rainfall after scattering and inappropriate control of water in the paddy fields.
Although water in the paddy fields was not intentionally discharged during application of herbicides, the run-off of herbicides was found to frequently occur by rainfalls and inappropriate control of water in the paddy fields.
High peaks of concentration of herbicides that decreased rapidly in water were detected in the drainage river waters during application of the herbicides in paddy fields.
On the other hand, herbicides that could remain in paddy fields for a long time, were detected even after a long time in the drainage river waters.
