Toxic Effects Of Lanthanum Compounds And Modified Materials On Aquatic Organisms And Their Application In Phosphorus Removal From Pond Aquaculture Water

Phosphorus is the key factor leading to eutrophication of aquaculture water body,and it is also the key index of pollution control of aquaculture tail water.Therefore,phosphorus pollution in aquaculture water becomes a subject to be increasing noticed.Due to the variety of existing phosphorus styles in aquaculture water,the treatment effect that obtained from technology is not very stable,which may result in low treatment efficiency.However,there are existing many influencing factors affecting the treatment effect.So,how to improve the purification effect of phosphorus deserves consideration and needs more research.This study attempted to draw lanthanum,a rare earth element with the function of purifying phosphorus pollution,into the treatment system.The present study tested the purification capacity and influencing factors of different lanthanum containing substances on phosphorus removal,based on the comprehensive evaluation of the biological safety of different lanthanum containing substances to different ecological groups in aquatic ecosystem.This study was to select appropriate treatment materials and methods to improve the phosphorus removal efficiency,which provided technical support for sustainable aquaculture.The results were as follows:1.This study tested the toxic effects of three lanthanum containing substances（lanthanum chloride,lanthanum oxide and lanthanum modified attapulgite）with different characteristics（solubility,adsorption,etc.）on six different ecological groups of organisms（fish,shrimp,algae,aquatic plants,benthos,microorganisms）,and obtained the safe application concentration of lanthanum containing substances in the breeding ecosystem.（1）The LC₅₀ of LaCl₃,La₂O₃,La@ACP to zebrafish were 3.24 mg·L^-1,3.94 mg·L^-1and 10.39 mg·L^-1 at 48 h,while 2.35 mg·L^-1,2.05 mg·L^-1 and 5.48 mg·L^-1 at 96 h.LaCl₃and La₂O₃ were moderately toxic to zebrafish,while La@ACP was a low toxic substance.The safe concentrations of LaCl₃,La₂O₃,La@ACP to zebrafish were 0.31 mg·L^-1,0.77mg·L^-1 and 1.16 mg·L^-1,respectively;（2）The LC₅₀ of LaCl₃,La₂O₃,La@ACP to Macrobrachium nipponense were 5.51mg·L^-1,7.29 mg·L^-1 and 12.80 mg·L^-1 at 48 h,while 2.45 mg·L^-1,2.83 mg·L^-1 and 5.39mg·L^-1 at 96 h.LaCl₃ and La₂O₃ were moderately toxic to M.nipponense,while La@ACP showed low toxic.The safe concentrations of LaCl₃,La₂O₃,La@ACP to M.nipponense were 0.49 mg·L^-1,1.07 mg·L^-1 and 2.55 mg·L^-1,respectively;（3）The LC₅₀ values of the three lanthanum containing substances to Procambarus clarkii in 24-96 h were more than 5000 mg·L^-1 and the safe concentration was more than500 mg·L^-1,which suggested three lanthanum containing substances to P.clarkii slightly toxic or non-toxic.The LC₅₀ values of the three lanthanum containing substances to Oncomelania sinensis in 24-96 h were more than 10 mg·L^-1 and the safe concentration was more than 3 mg·L^-1,which suggested three lanthanum containing substances to O.sinensis low toxic;（4）The toxicological effects of three lanthanum containing substances on Chlorella vulgaris in 96h revealed as the promotion in the lower group,while as the inhibition in the higher group.The growth of C.vulgaris increased under 10 mg·L^-1,which was negatively correlated with the concentration of lanthanum.The growth of C.vulgaris inhibited up to10 mg·L^-1 or more,which was positively correlated with the concentration.The EC₅₀ values of three lanthanum containing substances on C.vulgaris was>100 mg·L^-1 and the safe concentration was≥10 mg·L^-1;（5）The growth of Oenanthe javanica was not affected by the three lanthanum containing substances below 5.0 mg·L^-1,but inhibited when the concentrations above 5.0mg·L^-1.The inhibition ability ordered as LaCl₃>La@ACP>La₂O₃;（6）The EC₅₀ values of three lanthanum containing substances to Bacillus subtilis and Vibrio parahaemolyticus in 24-48 h were>100 mg·L^-1,and the safe concentration was≥10 mg·L^-1;（7）LaCl₃ with more than 1.0 mg·L^-1 can affect the activity of ACC,SOD and EROD enzyme in zebrafish muscle tissue within 96 hours,and among those enzymes,ACC revealed as:“ascending-descending-rising”,SOD decreased,EROD showed as“descending-ascending”.It suggested LaCl₃ produced oxidative damage effect on zebrafish muscle cells.In order to protect the safety of all levels of organisms in aquatic ecosystem,when we used LaCl₃,La₂O₃ and La@ACP in the aquaculture pond,the concentration of these products should be controlled below 0.30 mg·L^-1.2.Under the safe concentration(≤0.30 mg·L^-1),this study also tested the removal efficiency and influencing factors of different lanthanum containing substances on phosphorus pollution in aquaculture water environment.The results showed that the purification effect of phosphorus by LaCl₃,La₂O₃ and La@ACP,is related to the concentration of total phosphorus,the proportion of soluble phosphate in total phosphorus,the concentration of lanthanum and water temperature.（1）In the range of TP content of 0～2.0 mg·L^-1,the removal rates of soluble PO₄^3-and TP were 22.9～66.0%and 4.5～22.4%.Firstly in the range of TP content of 0.5～2.0mg·L^-1,the removal rates of TP and PO₄^3-by LaCl₃ were higher than those of the other two lanthanum containing substances.Secondly,when the TP content was in the range of 0～0.5 mg·L^-1,the removal rate of PO₄^3-by LaCl₃ was still higher than that of the other two substances,but the removal rate of TP was lower than that of the other two substances.The removal rate of TP by LaCl₃ depended on the proportion of soluble phosphorus in TP,which showed a positive correlation and revealed as a certain dose-dependent relationship.The application concentration of 0.3 mg·L^-1 was better than that of 0.1 mg·L^-1;（2）The three lanthanum containing substances had a certain time-dependent effect on the removal of phosphorus in aquaculture water environment.LaCl₃ was relatively fast and took effect mainly within 24 hours after the use,while La₂O₃ and La@ACP had a certain time-dependent effect on the removal of phosphorus within 24～48 hours after the use;（3）The results showed that the appropriate change and fluctuation of p H value in the range from the weak alkaline to the alkaline,had no significant effect on the phosphorus removal efficiency of the three lanthanum containing substances,while the phosphorus removal efficiency became significantly increased with the increased water temperature.To conclude,the results show that the three lanthanum containing substances（LaCl₃,La₂O₃ and La@ACP）had a certain purification effect on phosphorus removal within the safe concentration range in aquaculture water environment together with the tail water.When we used lanthanum containing substances as an auxiliary means of phosphorus purification in aquaculture water,La@ACP was suitable based on the use cost and cost performance,while LaCl₃ was more suitable for rapid onset.