Bioaccumulation And Biodegradation Of Environmental Androgens By Freshwater Microalgae

Environmental androgens are a class of typical endocrine disruptors that can adversely affect the organism through interfering with the development,function,and elimination of endogenous androgens in the organism.Environmental androgens have been widely detected in different environmental media throughout the world,and cause serious threat to environment.As the primary producer of aquatic ecosystems,microalgae are widely distributed in water and can rapidly bioaccumulate and biodegradate pollutants in water.As the foundation of the aquatic food web,microalgae can also affect the environmental behavior of pollutants.However,there are still few studies on the interaction between microalgae and environmental androgens.The transportation and transformation of environmental androgens in food webs are also unclear.In this paper,the tolerance of three freshwater microalgae(Chlorella vulgaris,Cyclotella sp.,Microcystis aeruginosa)to four different environmental androgens(testosterone,androstenedione,trenbolone,methyltestosterone)were investigated.On this basis,a typical natural environmental androgen(testosterone)and a synthetic environmental androgen(Trenbolone)were selected to study the bioaccumulation and biodegradation ability of three microalgae on them.Furthermore,the kinetics of degradation of environmental androgens by microalgae were briefly discussed.The main research results are as follows:1.The tolerance of microalgae to environmental androgensThree species microalgae(Chlorella vulgaris,Cyclotella sp.,M.aeruginosa)were highly tolerant to four environmental androgens.Different microalgae cells have different tolerance to the same environment androgen.The results showed that the tolerance of the three microalgae to testosterone was Cyclotella sp.>Chlorella vulgaris>M.aeruginosa.In the tolerance experiment for androstenedione and trenbolone,the tolerance of Cyclotella sp.was significantly higher than that of the other two microalgae,and Chlorella vulgaris and M.aeruginosa showed similar tolerance to androstenedione,and to trenbolone.The tolerance of the three microalgae to methyltestosterone was as follows: M.aeruginosa > Cyclotella sp.>Chlorella vulgaris.The same microalgae also had different tolerance to different environmental androgens.The results showed that there was no significant difference for the tolerance among the four kinds of environmental androgens in Chlorella vulgaris.The tolerance of Cyclotella sp.to the four kinds of environmental androgens was as follows: when the androgen concentration was 10 mg/L,there was no significant difference among the environmental androgens.In the concentration groups of 20 mg/L and 40 mg/L,the tolerance of Cyclotella sp.to trenbolone was significantly higher than that of the other three environmental androgens.As for the tolerance of androgens to M.aeruginosa,when the androgens concentrations at 10 mg/L and 20 mg/L,there was no significant difference among the four kinds of environmental androgens.At 40 mg/L,the tolerance of M.aeruginosa to methyltestosterone was significantly higher than that of the other three environmental androgens.2.Bioaccumulation and biodegradation of environmental androgens by microalgaeAll three kinds of microalgae could significantly accumulate and degrade environmental androgen.Different androgen concentration had a certain effect on the bioaccumulation and biodegradation of microalgae,but the general trend were similar.And to the same androgen,different kinds of microalgae had different bioaccumulation and biodegradation ability.The bioaccumulation ability of different microalgae to testosterone was: M.aeruginosa > Cyclotella sp.> Chlorella vulgaris.Moreover,microalgae have different biodegradation ability to different kinds of androgen.This study found that Cyclotella sp.had significant biodegradation ability to testosterone and Trenbolone.Under the same conditions,the biodegradation ability of Cyclotella sp.to testosterone was greater than that of trenbolone.3.Degradation kinetics of environmental androgen in microalgaeThis study briefly discussed the biodegradation kinetics of environmental androgens in microalgae.After using different kinetic equations to fit the experiment data,the results showed that the degradation process of environmental androgens in microalgae was mainly affected by the species of microalgae,the number of algae cells involving in the degradation process,the growth rate of algae(r)and the concentration(C)of environment androgens in water.In the case of algae density increasing,when the concentration of environmental androgens in the algae-water system was high,the biodegradation rate of environmental androgen in microalgae was mainly affected by the number of algae cells(N)and the growth rate(r)of algae.Thus,the biodegradation kinetics was in accordance well with the second-order kinetic equation: dC/dt=KNr(K is a constant).As the biodegradation process progresses,the number of algal cells continued to increase,and the concentration of environmental androgens in the algae-water system continued to decrease.At this circumstances,the biodegradation rate was less affected by the number of algae cells N,and biodegradation process(relative to N and r)is a mixed phase reaction,which was approximately a first-order or zero-order kinetic equation: dC/dt=Kr or dC/dt=K(K is a constant).When the density of algal cells density was constant,r was approximately equal to zero,and the concentration of environmental androgens in the algae-water system was low.In this case,the biodegradation process of environmental androgens in microalgae was mainly affected by the number of algae cells involving in the degradation process and followed the exponential decay model.The degradation rate was the first-order kinetic equation d C/dt=?C which was relative to the concentration of environmental androgens in the algae-water system.(? is a constant).