The Ecological Effects Of Inorganic Arsenic On Typical Zooplankton Under The Influence Of DOM

Arsenic is a kind of poisonous metal element which exists widely in nature.With the discharge of a large number of arsenic compounds,arsenic pollution in water bodies poses a threat to humans and aquatic organisms in different regions of the world.Dissolved organic matter(DOM)exists widely in water environment.It can change the existence form of heavy metals by combining with heavy metals in water bodies,and then affect the bioavailability of heavy metals.The presence of DOM increases the complexity of the environmental effects of arsenic.As the primary trophic level in the food chain,zooplankton is widely distributed in freshwater ecosystems and plays a very important regulatory role in the process of material circulation and energy transfer.In this study,Tetrahymena thermophila and Daphnia magna were selected as the test organisms to explore the biological effects of two kinds of inorganic arsenic(arsenite(As(III))and arsenate(As(V)))on two typical species of zooplankton in the presence of different compositions and concentrations of DOM(humic acid(HA)and fulvic acid(FA)).The main results are as follows:(1)To investigate the toxic effect of the presence of inorganic arsenic on the T.thermophila under different DOM conditions.The results showed that whether or not DOM was added to the medium,the cells concentration of T.thermophila decreased with increaseing concentrations of inorganic arsenic,wherein the toxic effect of As(III)on T.thermophila was more larger.The addition of HA and FA improved the tolerance of T.thermophila to As(III)and As(V).The higher concentration of DOM added,more obvious effect of inhibiting toxic effect of two inorganic arsenic on T.thermophila.In addition,with increased of DOM molecular weight,its inhibitory inorganic arsenic had a stronger toxic effect on T.thermophila.(2)In the enrichment kinetics experiment of T.thermophila,bioaccumulation of arsenic in T.thermophila was positively correlated with the inorganic arsenic concentrations in the solution.The addition of DOM in the medium could inhibit the accumulation of arsenic in T.thermophila to a certain extent.Which the inhibitory effect of accumulation gradually increased with increase of DOM concentration.The greater molecular weight,the stronger inhibitory effect of accumulation.(3)To explore the influence of different DOM conditions on the toxic effects of inorganic arsenic to D.magna.The results showed that whether or not DOM was added to the medium,the survival rate of D.magna was positively correlated with the inorganic arsenic concentrations.Compared to As(V),As(III)had a greater toxic effect on D.magna.As(III)and As(V)had certain toxic effects on the body length and reproductive system of D.magna.As the concentration of inorganic arsenic increases,its body length shortened,the first reproductive time was delayed,and the total number of reproduction decreased.Adding both HA and FA to the culture medium both improved the tolerance of D.magna to inorganic arsenic.(4)In the enrichment kinetics experiment of D.magna,bioaccumulation of arsenic in D.magna was positively correlated with the inorganic arsenic concentrations in the solution.Compared to As(III),D.magna had a higher degree of accumulation of arsenic in the As(V)solution.After adding DOM to the culture medium,on the one hand,the accumulation of arsenic in D.magna was inhibited under the waterborne exposure.On the other hand,at the dietborne exposure accumulation of arsenic in D.magna was promoted.Besides,with the increaseing of DOM molecular weight,the effect was strengthened.Based on the above study,the toxic effects of As(III)and As(V)on T.thermophila and D.magna in the presence of two kind of DOM were clarified.Beyond that,bioaccumulation of arsenic in T.thermophila and D.magna organisms were also elaborated.These results provide relevant scientific data for a more reasonable evaluation of the toxic effects of inorganic arsenic on aquatic organisms under the regulation of DOM,and also provide theoretical references for more accurate arsenic risk assessment in the future.