The effects of 9 herbicides in 5 different families on the growth of Lemna sp. were studied through 7-day exposure. The treated plant was transferred to fresh medium to observe recovery from inhibition. Inhibition and the recovery of growth were estimated on the basis of frond number and area, and expressed as the relative growth rate (RGR) compared with the untreated control. Patterns of RGR in exposure and recovery periods showed a tendency corresponding to the different families of herbicides. Considering the recovery potential of Lemna sp. from inhibition by chemicals and the large difference in RGRs between exposure and recovery periods, it is appropriate to take them into account for ecotoxicological risk assessment of chemicals.
2008 Pesticide Science Society of Japan