RESPONSE AND RECOVERY OF THE MACROPHYTES ELODEA CANADENSIS AND MYRIOPHYLLUM SPICATUM FOLLOWING A PULSE EXPOSURE TO THE HERBICIDE IOFENSULFURON-SODIUM IN OUTDOOR STREAM MESOCOSMS

摘要

Interest in stream mesocosms has recently revived for higher tier aquatic macrophyte risk assessment of plant protection products mainly because 1) the highest predicted environmental concentrations for the assessment of effects are frequently derived from stream scenarios, and 2) they allow an effect assessment using stream-typical pulse exposures. Therefore, the present stream mesocosm study used an herbicide pulse exposure and evaluated the responses of Elodea canadensis and Myriophyllum spicatum. Macrophytes were exposed for 24h to 1g/L, 3g/L, 10g/L, and 30g/L of the herbicide iofensulfuron-sodium with a subsequent recovery period of 42d. Biological endpoints were growth rates of the main, side, and total shoot length, the shoot number, the maximum root length, and the dry weight. The total shoot length was identified as the most sensitive endpoint; the growth rate of the total shoot length was inhibited by up to 66% and 45% in M. spicatum and E. canadensis, respectively. The lowest no observed effect concentrations (NOECs) were observed at day 7 and/or day 14 after herbicide treatment and were 1g/L for M. spicatum and 3g/L for E. canadensis. The no-observed-ecologically-adverse-effect concentrations (NOEAECs) were 10g/L and 30g/L for M. spicatum and E. canadensis, respectively. Such or similar mesocosm designs are useful to simulate typical stream exposures and estimate herbicide effects on aquatic macrophytes in stream systems. (C) 2016 SETAC