不同磷浓度对钝顶螺旋藻吸附、吸收和转化砷酸盐的影响

Effects of Phosphorus at Various Concentrations on Adsorption, Uptake and Transformation of Arsenate by Spirulina platensis

采用室内培养实验,首先用0~300μg·L-1砷酸盐[As(Ⅴ)]处理钝顶螺旋藻(Spirulina platensis),分析了螺旋藻对As(Ⅴ)的吸附和吸收特性,并在300μg·L-1 As(Ⅴ)处理下,研究了不同磷浓度(P正、1/10 P正、1/25 P正、1/50 P正)对螺旋藻吸附、吸收和转化As(Ⅴ)的影响。结果表明,在本研究As(Ⅴ)处理范围内,螺旋藻的干重与对照没有显著差异。随着As(Ⅴ)浓度的升高,藻体富集的总砷含量增加,当As(Ⅴ)处理浓度为150~300μg·L-1时砷富集量为1.006~1.569 mg·kg-1,超过了国家保健(功能)食品的砷污染限量1.0 mg·kg-1(GB 16740—1997)。随着培养基中磷浓度的降低,螺旋藻体内吸收的砷含量呈现增多趋势。在正常磷(P正)和1/10 P正条件下,螺旋藻体内的砷均为As(Ⅴ);当磷浓度降低至1/25 P正时,藻细胞中的砷有3.28%为As(Ⅲ);当磷浓度降低为1/50 P正时,螺旋藻吸收的砷增加至1.457 mg·kg-1,其中有9.24%和37.35%分别转化为As(Ⅲ)和二甲基砷(DMA),表明降低培养基中磷浓度促进了螺旋藻体对As(Ⅴ)的吸收、还原和甲基化,但藻细胞中砷的主要形态仍为As(Ⅴ)。在正常磷浓度培养下,藻体富集的砷以藻细胞表面吸附为主,通过磷酸盐缓冲液脱附可去除95%以上螺旋藻富集的砷。

Arsenic(As)accumulation in Spirulina platensis may reduce the quality of health products produced from this microalga. Phosphorus(P)may influence the algal uptake and biotransformation of As. Thus it would be possible to reduce the accumulation of As in algae by manipulating P concentrations in growth media. To test this, we first sat up an experiment to examine the As(Ⅴ)adsorption and absorption characteristics of S. platensis under 0~300 μg·L-1As(Ⅴ), and then conducted another experiment to study the effects of normal and low P levels on the As(Ⅴ)uptake, adsorption and biotransformation by S. platensis at 300 μg·L-1As(Ⅴ). Algal biomass was not significantly affected by As(Ⅴ)treatments, compared with the control. However, arsenic accumulation increased with As(Ⅴ)levels in the growth media. At 150~300 μg·L-1As(Ⅴ), S. platensis contained 1.006 to 1.569 mg·kg-1, which exceeded the national standard(GB 16740—1997)for health(functional)foods(1.0 mg·kg-1). The As absorption was reduced by increasing P concentrations. At P levels of 1/10 normal or higher, P did not change As speciation in S. platensis, whereas only 3.28% of As was transformed to As(Ⅲ) at 1/25 normal P level.When P concentration was lowered to 1/50 of normal P level, As uptake increased significantly to 1.457 mg·kg-1, of which 9.24% and37.35% were converted to As(Ⅲ)and DMA, respectively. In conclusion, decrease in P supply promoted the uptake, reduction and methylation of As(Ⅴ), though As(Ⅴ)was still the main As species in the microalgae. The majority of As was adsorbed on the surface of algal cells,suggesting that more than 95% of As in the S. platensis could be removed by washing with phosphate buffered saline(PBS)solution.