微藻不同光合荧光参数对氯化消毒副产物毒性响应特性

Response Characteristics of Different Photosynthetic Fluorescence Parameters of Microalgae to Toxicity of Chlorinated Disinfection By-products

以淡水微藻中的蛋白核小球藻为受试生物,以典型毒性氯化消毒副产物氯乙酸及三氯乙腈为研究对象,采用荧光动力学方法研究了4种光合荧光参数F_(v)/F_(m)、F_(v)/F_(o)、F_(m)/F_(o)(F_(o)为初始荧光强度,F_(m)为最大荧光强度,F_(v)=F_(m)-F_(o))及PI_(ABS)对两种消毒副产物的响应规律,并分别从对低质量浓度与等质量浓度消毒副产物响应性能、10%效应质量浓度(EC_(10))与50%效应质量浓度(EC_(50))值4个方面对比了4个光合荧光参数的响应灵敏性。结果表明:4个参数对两种消毒副产物都具有质量浓度响应特性,抑制率与消毒副产物质量浓度之间都具有较好的Logistic曲线型剂量-效应关系,修正相关系数R^(2)_(adj)均大于0.993,其中PI_(ABS)的R^(2)_(adj)最大;4个参数对两种消毒副产物毒性的响应灵敏性从大到小的排序均为PI_(ABS)、F_(v)/F_(o)、F_(m)/F_(o)、F_(v)/F_(m),因此PI_(ABS)是基于荧光动力学方法检测水体氯化消毒副产物毒性较为灵敏的响应指标。该研究结果为发展水体消毒副产物毒性的现场快速检测方法与技术提供了重要参考。

Objective Due to the advantages such as good inactivation effect on pathogenic microorganisms and low usage cost,chlorinated disinfectants have been widely employed for disinfection in various aspects.However,the large amount of chlorinated disinfection by-products produced by chlorinated disinfectants have biological toxicity,and they will have toxic effects on aquatic organisms and pose potential threats to the aquatic ecosystem once entering aquatic environment.Therefore,the development of on-site and rapid detection methods for the toxicity of chlorinated disinfection by-products in water is of significance for ensuring the aquatic environment safety.As the main primary producers and energy converters in aquatic ecosystems,microalgae play an important role in maintaining the balance and stability of aquatic ecosystems and indicating the water environment quality.Additionally,the microalgae photosynthesis has a rapid response characteristic to the toxicity of pollutants in water.Based on this,fluorescence kinetics technique which could rapidly and non-destructively detect the photosynthetic status of living plants has good development prospects in rapid toxicity detection of chlorinated disinfection by-products in water.However,at present,it is still unclear which photosynthetic fluorescence parameter obtained based on fluorescence kinetics technique can serve as the optimal response indicator for rapidly and sensitively detecting the toxicity of chlorinated disinfection by-products.Therefore,we study the response characteristics of different photosynthetic fluorescence parameters to the toxicity of chlorinated disinfection by-products for determining the optimal response indicator with sensitive response characteristics to chlorinated disinfection by-products.This is of practical significance for the development of on-site and rapid detection methods for the toxicity of chlorinated disinfection by-products based on fluorescence kinetics technology.Methods We employ a common freshwater microalgae Chlorella pyrenoidosa as the test organism,and two typical toxic chlorinated disinfection by-products chloroacetic acid and trichloroacetonitrile as the research objects.Meanwhile,we first investigate the change rule of photosynthetic activity of Chlorella pyrenoidosa with incubation time and the influences of algal cell density and environmental temperature on the response sensitivity of Chlorella pyrenoidosa to the toxicity of two chlorinated disinfection by-products to determinate the optimal experimental conditions for the response of Chlorella pyrenoidosa to chlorinated disinfection by-products toxicity. The fluorescence kinetics method is adapted to study the response of four photosynthetic fluorescence parameters F_(v)/F_(m), F_(v)/F_(o), F_(m)/F_(o), and PIABS to different mass concentrations of chloroacetic acid and trichloroacetonitrile, and then the dose-response relationships between each photosynthetic fluorescence parameter and each chlorinated disinfection by-product are constructed. On this basis, the response sensitivities of four photosynthetic fluorescence parameters to chlorinated disinfection by-products are compared in four aspects. The aspects include response performance to low mass concentration of chlorinated disinfection by-products,inhibition degree by equal mass concentration of chlorinated disinfection by-products, 10% effective mass concentration (EC10), and 50% effective mass concentration (EC50) values.Results and Discussions By studying the change of photosynthetic activity of Chlorella pyrenoidosa with incubation time, the results show that when Chlorella pyrenoidosa is cultured to the third to fourth days, all the four photosynthetic fluorescence parameters F_(v)/F_(m), F_(m)/F_(o), F_(v)/F_(o), and PIABS are at a high level (Fig. 1), which indicates that Chlorella pyrenoidosa has the best photosynthetic activity at this time. Therefore, the best growth period of Chlorella pyrenoidosafor studying the response characteristics of different photosynthetic fluorescence parameters to the toxicity of chlorinated disinfection by-products is the third day to the fourth day during culture. The results of influences of algal cell density and environmental temperature on PIABS inhibition ratio of Chlorella pyrenoidosa exposed to chloroacetic acid and trichloroacetonitrile demonstrate that when the algal cell density is in the range of 0. 5×10^(5)-100×10^(5) cells·mL^(-1), PIABSinhibition ratio is at a high level and tends to stabilize [Fig. 2 (a)]. Under the environmental temperature of 25 ℃ , the inhibition ratio of PIABS is the maximum [Fig. 2 (b)]. Therefore, 0. 5×10^(5)-100×10^(5) cells·mL^(-1) and 25 ℃ are the optimal algal cell density and the optimal environmental temperature for the response of Chlorella pyrenoidosa to chlorinated disinfection by-products toxicity respectively. In the optimal toxicity response conditions, when the exposure time is 2 h,all the four photosynthetic fluorescence parameters F_(v)/F_(o), F_(m)/F_(o), F_(v)/F_(m), and PIABS values gradually decrease with the mass concentration increase in chloroacetic acid and trichloroacetonitrile (Figs. 3 and 4). When the mass concentrations of chloroacetic acid and trichloroacetonitrile are in the ranges from 5. 06 to 36. 80 mg·L^(-1) and from 1. 55 to 19. 32 mg·L^(-1)respectively, all the inhibition ratios of F_(v)/F_(o), F_(m)/F_(o), F_(v)/F_(m), and PIABS show good Logistic curve relationships with the mass concentrations of chloroacetic acid and trichloroacetonitrile, and the adjustive correlation coefficients R^(2)adj are all greater than 0. 993 (Figs. 5 and 6). These results indicate that all four photosynthetic fluorescence parameters could be adopted as response indicators for quantitative toxicity detection of chlorinated disinfection by-products. F_(o)r low mass concentrations of chloroacetic acid and trichloroacetonitrile, PIABS has the most sensitive response performance compared to F_(v)/F_(o), F_(m)/F_(o), and F_(v)/F_(m) (Figs. 3 and 4). Meanwhile, by comparing the inhibition ratios of F_(v)/F_(o), F_(m)/F_(o), F_(v)/F_(m), and PIABS by equal mass concentration chloroacetic acid and trichloroacetonitrile at the exposure time of 2 h, the inhibition degree order of the four photosynthetic fluorescence parameters is PIABS>F_(v)/F_(o)>F_(m)/F_(o)>F_(v)/F_(m). This indicates that compared with the other three photosynthetic fluorescence parameters, PIABS is the most sensitive to the toxicity of chlorinated disinfection by-products at the same mass concentration. Additionally, the EC10 and EC50 values of chloroacetic acid and trichloroacetonitrile calculated according to F_(v)/F_(o), F_(m)/F_(o), F_(v)/F_(m), and PIABS are further compared. The results show that the photosynthetic fluorescence parameters corresponding to the EC10 and EC50 values of chloroacetic acid and trichloroacetonitrile in descending order are F_(v)/F_(m)>F_(m)/F_(o)>F_(v)/F_(o)>PIABS (Table 2). This indicates that the sensitivity of the four photosynthetic fluorescence parameters to the toxicity of chloroacetic acid and trichloroacetonitrile is PIABS>F_(v)/F_(o)>F_(m)/F_(o)>F_(v)/F_(m).Conclusions All the photosynthetic fluorescence parameters F_(v)/F_(m), F_(v)/F_(o), F_(m)/F_(o), and PIABS of Chlorella pyrenoidosahave mass concentration-dependent response characteristics to two chlorinated disinfection by-products chloroacetic acid and trichloroacetonitrile. The four photosynthetic fluorescence parameters have good logistic curve dose-response relationships with the mass concentration of chloroacetic acid and trichloroacetonitrile, which could be utilized for quantitative toxicity detection of chlorinated disinfection by-products in water. In addition, among the four photosynthetic fluorescence parameters, PIABS exhibits the most sensitive response characteristics to chloroacetic acid and trichloroacetonitrile. Therefore, it is a suitable response indicator for rapidly and sensitively detecting the toxicity of chlorinated disinfection by-products. We provide a more suitable toxicity response parameter for the development of on-site and rapid detection methods and technologies for disinfection by-products toxicity based on fluorescence kinetics technique.