| Spirulina is known as "the most ideal food in the 21st century" because of its high nutrient contents.However its safety has received more attention with the development of health products made of Spirulina.In recent years,arsenic?As?content in some Spirulina health products exceeded food quality standards.Previous research on As pollution in Spirulina has been mostly focused on the detection of total As content in algae powder,as well as the analysis of the As pollution sources for this algae.However,the effects of phosphate?P?concentration on arsenate?As????,arsenite?As????adsorption,absorption and transformation in Spirulina are still rarely reported.P may influence the uptake and biotransformation of As,thus it is possible to reduce the accumulation of this toxic element by manipulating P concentration in the culture.To test this hypothesis,we first set up different As???or As???treatments for 7 days to analyze the As adsorption and absorption characteristics of Spirulina platensis.Then the P concentration of the culture was decresed to study the effects of normal and low P levels on the growth,the As???or As???uptake,adsorption and biotransformation of this algae.The main results are summarized as follows:1.Effects of different P concentrations on the growth of Spirulina platensisIn laboratory cultures,we set up various P treatments(1/200P?P,nomal P concentration is 88.9 mg·L-1)to investigate the effects of P on the biomass,phycobiliprotein and chlorophyll content of Spirulina platensis.The results showed that 1/10,1/25,1/50P treatments have little impact on the growth of Spirulina platensis,compared with the normal P level.The phycobiliprotein content significantly reduced,but the chlorophyll content increased at 1/100P level.When the P concentration was decreased to 1/200,the biomass,phycobiliprotein,chlorophyll content decreased,indicating the growth of Spirulina platensis was affected significantly.2.Effects of different As???,As???concentrations on the growth and As enrichment of Spirulina platensisWe treated Spirulina platensis with different As???(50,100,150,200,250,300?g·L-1)or As???(50,100,200,300 ?g·L-1)concentrations to compare the difference of growth,As adsorption,absorption of this microalgae.The results showed that,compared with control,different concentrations of As???almost had no effect on the biomass of Spirulina pltensis.An increase of biomass was observed after As???treatment,but the change was not significant.The As adsorption,absorption and total arsenic content of Spirulina platensis rose significantly by increasing As concentration in the culture medium.At the same treatment concentration,the uptake and total As content of this algae treated by As?III?were all higher than As???treatment,whereas the amount of adsorbed As had little difference.There had no As absorption in Spirulina platensis exposed at 50 and 100?g L-1 As???,but the accumulated As reached 0.242 and 0.300 mg·kg-1 when the algae was treated with As???.Therefore,this algae had a stronger ability to accumulate As???at the same concentrations.When the As???concentration was 150 ?g·L-1,the As accumulation of Spirulina platensis reached 1.006 mg·kg-1,exceeding the limit value of As in health care products(1.0 mg·kg-1).The phenomenon was more serious in the algae treated by 200 and 300 ?g·L-1 As???,which may cause a risk to human health.But most of the As was adsorbed on the cell surface,and therefore using phosphate buffer solution?PBS?can significantly reduce the total arsenic content of this algae.In addition,only As???occurred in Spirulina platensis with As???exposure.As???and As???were found in the algae treated As???,but the latter was the main form.3.Effects of various P concentrations on As?V?or As???adsorption,absorption and conversion of Spirulina platensisUnder lower and normal P concentrations?1/50P?P,no growth reduction was found for Spirulina?,we cultivated this algae with As???(300 ?g·L-1)or As???(200,300?g·L-1)to compare the effects of P concentrations on the As???or As???adsorption,absorption and intracellular As species.The absorbed As content were 0.202 and 0.802 mg·kg-1 in Spirulina platensis treated with 300 ?g·L-1 As???or As???under normal P condition,respectively.When P concentration was 1/25 P,the As uptake significantly increased to 1.369 and 2.181 mg·kg-1.What's more,the absorbed As increased to 1.457 and 2.672 mg·kg-1 by algae when P was changed to 1/50P.The findings indicated that reducing P concentration in the medium will promote the absorption of algae,increasing the risk of As accumulation in Spirulina platensis.In addition,As reduction,methylation and efflux processes were promoted by lower P concentrations under As???treatment.When treated with As???,decreasing P concentration also promotes the above process because of the strong As???oxidation of Spirulina platensis.In 300 ?g·L-1 As???treatment,dimethylarsinic?DMA?produced in this algae when the P level was reduced to 1/50P.Nevertheless,DMA was detected in algae exposed As???at 1/25P,and the more DMA was produced in 1/50P.Nevertheless,the proportion of DMA in As???treated algae was 37.35%of total absorbed As,only 5.58%was found in the As???treatment algal cells.It indicated that lower P concentration in the culture medium may lead to more methylated As in the algae exposed As???,but the capability of methylation seemed higher for Spirulina in the As???treatment. |
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