The Study Of Glyphosate Toxicity To The Daphnia Magna And Pomacea Canaliculata

Glyphosate is one of the most commonly used herbicides worldwide. It is an organophosphorus compound, which is adopted to kill annual broadleaf weeds and grasses that compete with crops. The release of glyphosate from agricultural product will inevitably contaminant aquatic environment and consequently pose a potential risk to non-selective species. As(?), release of artificial or natural factors, is listed as one of the most toxic and carcinogenic effects of chemical elements. These two materials may coexist in the natural aquatic environment due to surface run off after applications that may has potential harm to the ecological rice paddies and pond through soil and water migration.Therefore, this study aimed to elucidate influence of the herbicide glyphosate and As(?) to aquatic ecosystem while two organism models were employed. One is a small planktonic crustacean Daphnia magna who inhabits in a variety of freshwater environments and is broadly distributed throughout the northern hemisphere. It has been subject of biological research since the 18 th century and widely used in ecological studies and ecotoxicology. The other is a species of large freshwater snail Pomacea canaliculata, an aquatic gastropod mollusk with origin from South American. This species is regarded to be in the top 100 of the �World's Worst Invasive Alien Species�. Different methodologies were conducted inclusive of acute(joint) toxicity, productive toxicity as well as physiological development of target species. Results showed that: 1. The 24 h- and 48 h-LC50 of glyphosate and As(III)were 54.12, 51.12 mg/L and 7.47, 6.07 mg/L to D. magna, respectively. Based on the concentration�response curves of individual glyphosate and As(III)as well as the concentration of mixture effect curve, logit function model and the response surface model were used to predict the single factor effect and the joint toxicity of the two chemicals in equivalent toxic concentration ratios. Two response surface models of Loewe Parametric Response Surface(CARS) model and Response Additive Response Surface(RARS) model were used to estimate the joint toxicity of the two materials, and the result showed that the interaction was antagonistic. 2. Egg hatching rate of the snail P. canaliculata was 43.00 % in the control while treatments of glyphosate exposures(10, 50, 100, 150, 200, 300 mg/L for 10 seconds) showed hatchability at 38.75 %, 25.00 %, 32.50 %, 18.75 %, 13.75 % and 12.50 %, individually. Results from acute toxicity in 24-h P. canaliculata newborns resulted in the LC50 at 178.50 and 175.00 mg/L after exposure of 24 h and 48 h, respectively. Generally, higher concentrations over 50 mg/L of glyphosate demonstrated an increasing trend in egg hatching inhibition. Relatively high levels of glyphosate had a significant effect in physiological response of P. canaliculata such as enhanced oxygen consumption rate. The varied oxygen/nitrogen ratio in the exposure solution would definitely affect physiological parameters of the model organism. However, it is interesting to note that low level of 10 mg/L of glyphosate shorted incubation period though hatching rate was slightly decreased, which might avoid hunting by natural enemies or damage by accidental events. Glyphosate at environmental concentration of 2 mg/L can significantly improve the growth and feeding in P. canaliculata. Continuous exposure of glyphosate for 5 days in P. canaliculata led to a significant reduction in the activity of lipase and an increase in that of amylase while no significant change presented in the activity of cellulose. It worth noting that the increased activity of amylase(by 52.79 %) represented stress acclimation of the model organism to glyphosate exposure.This project was working on the impact of the herbicide glyphosate to aquatic environment by taking daphnia and snail as model organisms. Generally speaking, glyphosate showed low toxicity(LC50 at mg/L level) to either D. magna or P. canaliculata at the environmental concentrations. To some extent, such environmental level of glyphosate would short hatching period in P. canaliculata although hatching rate was a little decreased relative to the experimental control. On the other hand, relatively high concentration of glyphosate is another story. It would affect physiological development or even mortality of aquatic species if glyphosate was present in high levels. In addition, joint toxicity of glyphosate with other agricultural pesticides or herbicides should draw more attentions during agricultural production.