The Toxic Effects Of Pesticides Rac-metalaxyl, R-metalaxyl And Heave Metal Cd On Earthworm

IntroductionSoil contamination is one of global ecological environmental problems, especially stress of heavy metals and pesticides. Earthworm is the representative organism in soil animals, which has become a bio-indicator of soil pollution. Recently, earthworm eco-toxicological test is widely used in eco-toxicological diagnosis of soil environmental pollution, and relevant methods and appraisal indices are developed. About quarter of currently used pesticides are chiral. A chiral pesticide has two or more enantiomers, which have the difference in internal activity, metabolism, toxicity and environmental durability. Metalxayl,a chiral fungicide,has been widely used throughout the world. R-metolachior of Metalxayl has more activity to sterilize than rac- metolachior. Metalaxyl-M is the first light-active fungicide made in Novartis Corporation, its major component is R-metolachior of Metalxayl. The commodity rac-Metalxayl on the market has been replaced by Metalaxyl-M (R-Metalaxyl) gradually, but the data of ecological safety evaluation still used. A comparative toxicity assessment of rac- and R-metolachlor was discussed through their effects on the acute toxicity, subacute toxicity and avoidance behavior of Eisenia foetida, in order to provide more reference of ecological safety evaluation on enantioselective.Combined contamination is a new hot topic in eco-toxicological studies. The studies on effects of heavy metals and pesticides combined have not enough report inChina and abroad. An initial toxicity of Cadmium (Cd) and rac-Metalxayl was discussed through their effects on the acute toxicity and enzymatic activities of Eisenia foetida, in order to provide a basis on appraise and control of Cd and rac-Metalxayl Combined pollution, and more reference of ecological safety evaluation on heavy metals and pesticides combined pollution.Methods1. The acute toxicity of rac-Metalxayl and R-Metalaxyl on earthworms (Eisenia foetida) was studied by the methods of contact filter paper test, artificial soil test and nature soil test. The acute toxicity of Cd and rac-Metalaxyl respectively or combined on earthworms was studied by the methods of artificial soil test.2. The excluding rate and avoidance behavior of rac-Metalxayl and R-Metalaxyl on earthworms was studied by the facilities for avoidance behavior response test. (two part) The subacute toxicity of rac-Metalxayl and R-Metalaxyl on earthworms was studied by the indices of weight change rate.3. Effects on activity of cellulase, catalase(CAT), superoxide dismutase(SOD) of Cd and rac-Metalaxyl respectively or combined on earthworm were studied by the methods of CMC saccharification, ultraviolet spectrophotometry and xanthine oxidase.Results1. The acute toxicity of rac-Metalxayl and R-Metalaxyl on earthworms (Eisenia foetida) was studied by the methods of contact filter paper test, artificial soil test and nature soil test. The value of their LC50 were 107.41μg·mm-2, 98.97μg·mm-2 (contact filter paper test 48h); 178.56 mg·kg-1 ,158.67mg·kg-1 (artificial soil test 14d ) ; 134.99 mg·kg-1, 110.86 mg·kg-1(nature soil test 14d).2. The acute toxicity of Cd on earthworms was studied by the methods of artificial soil test. The value of its 14d LC50 was 908.58 mg·kg-1. The acute toxicity of rac-Metalxayl combine with Cd at low, medium and high concentration on earthworms was studied and the value of their 14d LC50 were 203.85 mg·kg-1, 289.64mg·kg-1 and 220.69 mg·kg-1. The acute toxicity of Cd combine with rac-Metalxayl at low, medium and high concentration on earthworms was studied and the value of their 14d LC50 were 1072.78 mg·kg-1, 1261.77 mg·kg-1 and 588.68 mg·kg-1. 3. In the avoidance response, the excluding rate of the earthworms treated with R-Metalaxyl were much higher than those of rac-Metalaxyl treatment both in artificial soil and nature soil. The earthworms have no response at agricultural concentration.4. In the subacute toxicity test, the weight change rate of earthworms decreased obvious with the concentration increment of rac-metalaxyl and R-metalaxyl. The weight change rate of earthworms treated with R-metalaxyl was less than that of rac-metalaxyl treatment. In artificial soil, the weight change rate treated with rac-metalaxyl and R-metalaxyl was significantly lower than that in nature soil all the concentration groups.5. The respective pollution of Cd and rac-metalaxyl can be caused by a variety of enzymatic activity changes on earthworms. Compared with the control group, cellulose activity has the most significant difference. Each change of Cd and rac-metalaxyl in treatments was significant different compared with the control at the same duration of exposure time. The activity of CAT was not show the significant order all the experimentation, but the activity of SOD and cellulose increased at first, and then decreased. In the experiments of combined pollution, the activity of SOD was more activity than single experiment but activity of cellulose was weaker than single experiment.ConclusionsThe results showed that there were no huge differences between the LC50 of rac-metalaxyl and R-metalaxyl by the methods of contact filter paper test, artificial soil test and nature soil test, both of which were low toxicant based on the classification standard of toxicity. Cd at all concentration, it could decrease the toxicity of rac-metalaxyl. Rac-metalaxyl at low and medium concentration,it could decrease the toxicity of Cd, but at high concentration, it could increase the toxicity of Cd slitely. The weigh of earthworms implied that R-metalaxyl had induced more toxicity on earthworm than rac-metalaxyl. There was more affect when earthworm treated in nature soil than in artificial soil. In the experiments of single pollution of Cd and rac-metalaxyl, the activity of CAT was not show the significant order all the experimentation, but the activity of SOD and cellulose increased at first, and then decreased. In the experiments of combined pollution, the activity of SOD was more activity than single experiment but activity of cellulose was weaker than single experiment.