Eichhornia crassipes(Mart.)Solms,also known as water hyacinth,is a perennial herb.water hyacinth originated from South America,has invaded more than 60 countries and regions in the world.It has been badly threatened to ecological environment,agriculture,livestock and health of citizen and waterway transportation.It is one of the most serious invasive aquatic plants in the world.Pistia stratiotes Linn,also called Water Lettuce,is a perennial herb,water hyacinth originated from South America-Brazil,has been distributed in tropical,subtropical regions and affected seriously,such as the East China and South China.It has caused great harm to the ecological environment,the water conservancy irrigation and the use of the waterway,is listed for 100 most dangerous invasive species in China with water hyacinth.In order to screen the low toxicity and high efficiency herbicides in controlling the water lettuce and water hyacinth and assess the environmental safety after using.The study is consist of four main section to discuss,including the result of herbicides screening and LC50 determination,determination of acute toxicity on zebrafish and selenastrum capricoinutum and environmental safety assessment of herbicide,digestion of herbicides in natural light conditions in water and the dynamic distribution of herbicide in water lettuce and water hyacinth,qualitative and quantitative analysis of the metabolites of herbicides in water under the natural light conditions.The conclusion are as follows:1.mesotrione,bentazone and fomesafen were screened as the low toxicity,rapid and high efficacy herbicides of controlling against water lettuce and water hyacinth,And the toxicity test result of water hyacinth show that after foliar herbicide application 10 d,the inhibitory effect of 3 herbicides on the new root of water hyacinth was stronger than other parts,which mesotrione has the best inhibitory effect on the new root of water hyacinth with value of LC50 is 14.22 mg/kg,0.32 times of the value of LC50 of bentazone;But the mesotrione has the worst effect on fresh weight with value of LC50 is 4091 mg/kg,which is 287.69 times of the value of LC50 of inhibitory effect on the new root of water hyacinth;After herbicide foliar application 30 d,the control effects of 3 herbicides on water hyacinth leaves,petioles and fresh weight were greater than 55%,among which the control effects of bentazone reached 100%on the new root and fresh weight of water hyacinth at the pesticide concentration of 48 mg/kg,and the control effect of mesotrione and fomesafen also reached 100%on new root at the pesticide concentrations of 25 mg/kg and 50 mg/kg respectively.As to the toxicity test result of water lettuce,which illustrate that mesotrione has the best control effect on the new root with the value of LC50 is 7.21 mg/kg,and the control effect is 8.8 times higher bentazone;However,the bentazone has the best control effect on fresh weight with the value of LC50 is 3.49 mg/kg,which the control effect is 206.38 times higher than fomesafen;After herbicide foliar application 20 d,The inhibitory effects of 3 herbicides on new roots were up to 100%,at the pesticide concentration of 10 mg/kg,96 mg/kg,125 mg/kg respectively.What’s more,The inhibitory effects of mesotrione and fomesafen on fresh weight also reach 100%at the pesticide concentration of 10 mg/kg and 24mg/kg,however the control effect of all the 3 kinds of herbicides on leaves of water lettuce is less than 75%.2.The acute toxicity test results of 3 kinds of herbicides and its technical material indicate that the toxicity on zebrafish and selenastrum capricoinutum,fonnulations is much higher than technical material.On the zebrafish,the toxicity of 10%mesotrione dispersible oil suspension is the highest,LC50=7.18 mg a.i./L(6.22～8.06),which is 13.9 times of mesotrione technical material.And the toxicity of 480 g/L bentazone aqueous solution is the lowest,LC50≥100 mg a.i./L.on the selenastrum capricoinutum,the toxicity of 480 g/L bentazone aqueous solution is lower than other two herbicides,the EyC50 and ErC50 is 15.47 mg a.i./L(10.26～26.18)and 18.66 mg a.i./L(9.51～60.68)respectively.10%mesotrione dispersible oil suspension has higher toxicity on the selenastrum capricoinutum,the EyC50 and ErC50 is 0.10 mg a.i./L(0.07～0.14)and 0.17 mg a.i./L(0.10～0.28),which is 49.9 and 115.9 times of mesotrione technical material.3.Compared the speed of digestion of 3 kinds of herbicides in water covered by water lettuce and water hyacinth or not under the same natural light conditions.The results illustrate that under the condition of being covered by water lettuce and water hyacinth,the digestion of mesotrione and fomesafen is more rapid,and the half life of mesotrione is 30.02 time shorter than without being covered by the plant.During the observation period of 180 d,the digestion cycle of mesotrione is shortest,the half-life is 6.04 d and the bentazone has the longest digestion cycle with the Digestion rate 47.32%and half-life is 187.34 d,which is 31 times longer than mesotrione.Without being covered by water lettuce and water hyacinth,the bentazone has the shortest of digestion cycle,the half-life is 49.16 d and fomesafen has the longest digestion cycle with the Digestion rate 8.7%during the observation period of 180 d.The results of the distribution of herbicides in plant body showed that with the passage of experiment time,the concentration of herbicide on the blade became higher and became less on the roots.The rate of uptake and movement of different herbicides in plant body was different,which mesotrione has the fastest rate uptaked and movement,the concentration of mesotrione most concentrate on the blade after 3 d,however,fomesafen need>7 d achieve it.4.Compared the water sample and the chemical standard of metabolite of mesotrione(MNBA)and bentazone(6-hydroxy bentazon)by UPLC-ESI-QQQ-MS.In different conditions(plant coverage or not)of mesotrione and bentazone water samples,the two metabolites MNBA and 6-hydroxy bentazon were detected by UPLC-ESI-QQQ-MS after enrichment respectively.The quantitative results show that without being covered by the plant,the concentration of the MNBA and 6-hydroxy bentazon is higher than with the plant,and the concentration of 6-hydroxy bentazon is increasing,maximum concentration reach 13.55 μg/L and MNBA reach the highest concentration at 105d,is 219.58 μg/L,during the observation period of 180d.Being covered by plant,6-hydroxy bentazon increase to the highest concentration 5.39 μg/L in 21 d,and decrease to 0.59 μg/L at 180 d and MNBA increase to the highest concentration at 5 d with 4.68 μg/L,in 180 d,the concentration decrease to 0.48 μg/L.