Aquatic Plants: Water Shield and Arrowhead
Abnormalities were found in the leaves of two aquatic plants growing in Japan. One is the water shield ( Brasenia schreberi). This has oval leaves which float on the water surface. The other is the arrowhead ( Sagittaria trifolia).
Malformed Leaves in Paddy Fields
The malformed leaves were seen at the middle or end of May, and were caused by an inflow of low-density sulphonylurea herbicide into the irrigation water of paddy fields.
Biological Indicators of Herbicide Residues
The appearance of these abnormal leaves became a biological indicator of herbicide residues in the water from paddy fields. Although herbicide sprayed on the paddy field should not escape into rivers, this in fact often occurs, especially when transplanting begins and just after it has ended.
Sensitivity to Herbicides
Since the water draining from paddy fields is recycled as irrigation water and water for general use, this is a simple method of detecting herbicide in runoff. It is made possible by the fact that these two species of aquatic plants react sensitively to a low density of sulphonylurea herbicide.
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