Ecotoxicology and Environmental Safety 120 (2015) 468–472
Contents lists available at ScienceDirect
Ecotoxicology and Environmental Safety journal homepage: www.elsevier.com/locate/ecoenv
Response to the Commentary on “Arsenic mobility in the arsenic-contaminated Yangzonghai Lake in China”
art ic l e i nf o Keywords: Arsenic distribution Stratification Microorganism Sediment Arsenic release
a b s t r a c t This is the response to “Commentary on ‘Arsenic mobility in the arsenic-contaminated Yangzonghai Lake in China’ by Changliang Yang et al. [Ecotoxicology and Environmental Safety, 107(2014)321-327]” (by Jing Chen et al.). To doubts and questions raised by Chen et al., we give further explanations and provide more relevant evidences. The water temperature stratification existed in Lake Yangzonghai in summer, and affected by which arsenic concentration with water depth was uneven and peaked in the bottom layer in summer. In the case of adding carbon source (glucose) and maintaining anerobic state, enhanced microbial activity promoted the release of arsenic from sediment to water which was observed in the laboratory experiments. Errors might exist in sampling, determination and calculation, but they would not change the main conclusions of the article. & 2015 Elsevier Inc. All rights reserved.
We would like to thank Professor Jing Chen and his research team for their commentary on our article “Arsenic mobility in the arsenic-contaminated Yangzonghai Lake in China” (Liu et al., 2014). As the responsible person who proposed and implemented the project of purifying arsenic pollution with the flocculants of ferric trichloride in Lake Yangzonghai, Professor Jing Chen has been paying special attention on any publication related to the arsenic pollution of the lake. We would like to show our respect to him for his efforts and contribution to the arsenic removal from water of the lake. After reading the commentary carefully, we realize that there are some misunderstandings and some misinterpretations in the commentary which we would like to clarify as follows:
1. About the concentration distribution of As in the lake To understand the spatial distribution of As in Yangzonghai Lake, we made two thorough field investigations on August 31, 2012, and January 8, 2013, respectively. Among 31 sampling sites in the lake, we chose five sites (A-E) (Fig. 1) to collect samples at different depths (from the first one at 0.5 m below the surface to the last one at 0.5 m from the bottom, a sample every other meter down along the water column). The water temperature, pH, and dissolved oxygen (DO) at each depth were recorded simultaneously by a multi- functional parameters instrument (YSI Inc). Distinct water temperature stratification was observed on August 31, 2012, but not found on January 8, 2013. We noticed that total arsenic concentration changed with depth, which showed little difference from 0.5 m to 10.5 m depth, but increased beyond 10.5 m and peaked at the bottom (Fig. 2). As now well known, water temperature stratification of lakes generally forms in http://dx.doi.org/10.1016/j.ecoenv.2015.06.026 0147-6513/& 2015 Elsevier Inc. All rights reserved.
summer and disappear in winter. The commentators try to deny the fact that total arsenic concentration changed with depth in their commentary by quoting the investigation results of Wang et al. (2010). Unfortunately, none of the four investigations made by Wang et al. were in the same month as we did. It is inappropriate to compare the investigation results obtained in different seasons and different years, especially comparing the investigation results obtained before and after the remediation (Wang et al. made the investigations before September 2009, and the remediation took place between October 2009 and December 2011). And furthermore, Wang et al. did find that arsenic concentration increased with water depth at some sampling sites ( Figs. 3 and 4), but the commentators did not draw attention to this. According to the article by Wang et al., all the water samples were filtered before acidation and determination, which means they examined the dissoluble arsenic in water column when they investigated the changes of arsenic concentration with water depth. As for other evidence the commentators quoted (data from Kunming Environmental Monitoring Center and Professor Jing Chen’s research team), we decline to comment on them since they are not from publications.
2. About microorganisms role in As release Our conclusions in the article that “In the case of glucose supplementation, microbial activity promoted the release of As from sediment to solution, resulting in authigenic secondary As pollution.” was derived based on the experiments which were done under the following conditions: maintaining the incubators an aerobic condition and enhancing microbial activity by adding a
S. Li et al. / Ecotoxicology and Environmental Safety 120 (2015) 468–472
469
Fig. 1. Schematic graph of the sampling sites in Lake Yangzonghai in southwest China (Liu et al., 2014).
carbon source (glucose). It does not imply by any means that the release of As is happening or will certainly happen in the natural system of Lake Yangzonghai in the same way as the experiments showed, which we should have made clearer. However, despite the different conditions between laboratory experiment and the natural system, one cannot deny that the microorganisms plays an important role in the transformation and mobilization of As from sediment to water, which has been widely accepted now. It is generally thought that the microbially mediated reductive dissolution of iron-bearing minerals in water environments leads to the release of As. The amount released depends on the valence state of As and the mineralogical characteristics of Fe within the environment (Islam et al., 2004; Campbell et al., 2006). Most researchers believe that, as the carrier of As in sediment, the catalytic reduction of iron (hydr)oxide minerals in an anaerobic environment is the main driver of As release (Smedley and Kinniburgh, 2002; Islam et al., 2004). Both the microbially mediated reductive dissolution of iron (hydr)oxides and the direct reduction of As by microorganisms can lead to the activation of As, resulting in an increase in As concentration in water (Islam et al., 2004). Our experiments arrived at the same conclusions.
3. About sampling and determination Firstly, sampling water with a suction pump in a deep lake like Yangzonghai Lake is practical and feasible when a large amount of water is needed. The local environmental monitoring institution employs the same method to investigate the arsenic concentration distribution with depth. We noticed the possible disturbance of the sediment when we took the sample from the bottom of the lake. We had taken necessary measures to avoid sucking the sediment. We should point out that the arsenic concentration
changed little in hypolimnion compared with that in thermocline. The hypolimnion occurred from 16.5 m depth to the bottom of the lake. Since the arsenic concentrations from 16.5 m depth to the bottom changed little, the disturbance effect from the sampling was quite slight. Concerning the determination of As, we made a mistake in our article when we described the water sample treatment. Actually, we displayed only total arsenic in this study, and all the arsenic concentrations in the article refer to total arsenic. We are very sorry about the mistake which has confused readers. The determination method of total arsenic in our study is so called Atomic Fluorescence Spectrum (AFS) which is widely used to detect arsenic in water and waste water in environmental monitoring sector in China. The limit of detection of the method is 0.1 μg L-1. To determine the total arsenic in water sample from Yangzonghai Lake, 20 ml well-mixed water sample without filtration pretreatment was put into a 50 ml beaker, and was mixed evenly with 3 ml HCL (1 mol/l) and 2 ml 10% thiocarbamide. After 20 minutes, 5 ml solution was taken from the beaker with bottletop dispenser and was injected into hydride-generator of AFS. After adding 4 ml 0.7% potassium borohydride (PBH), the water sample was detected with AFS. In the study, we added a little HNO3 into the water sample to adjust the pH o2, which is the common method to preserve water sample, and should not affect the determination of total arsenic.
4. About arsenic reserve in the lake Since the water level of the lake changed day by day, and the distribution of the arsenic concentrations in the lake water in summer was uneven, the accurate calculation of the arsenic reserve in the lake water was not easy, and further verification will be needed. The arsenic reserve was not the important question
470
S. Li et al. / Ecotoxicology and Environmental Safety 120 (2015) 468–472
Fig. 2. The ranges of As concentration, water temperature, pH, and DO at sample sites A, B, C and E at various water depths in Lake Yangzonghai (Liu et al., 2014).
which we aimed to answer in our study, and the possible error in the calculation did not affect the main conclusions of the study.
5. About competitive anion exchange In our study, based on the research findings of others, we
discussed the functions of the competitive anion, and concluded that “although studies have confirmed that the presence of competing anions promoted As leaching from sediment, whether competitive anions promote desorption of As on iron(oxy)(hydr) oxides in the sediment of a lake contaminated by As and then treated with a flocculent such as Yangzonghai Lake requires verification”. It is an obvious misinterpretation to say that “the
S. Li et al. / Ecotoxicology and Environmental Safety 120 (2015) 468–472
471
Fig. 3. Map of sampling sites in Yangzonghai (▲ lake water and sediments; ◆ soil; ● well water and spring water) (Wang et al., 2010).
Fig. 4. Relation between arsenic concentrations and depth of lake water in Yangzonghai (Wang et al., 2010).
authors attribute the As release in summer to the high concentration of HCO3- without any support of experimental data”.
6. Summary Based on investigations of total arsenic distribution in vertical direction in Lake Yangzonghai, we found that the total arsenic concentration increased with depth and peaked at the bottom layer because of water temperature stratification in summer, but the same phenomenon was not found in winter. The same
phenomenon of the lake was discovered and reported by other researchers. Laboratory experiments displayed that in the case of adding a carbon source (glucose) and maintaining an anerobic state, enhanced microbial activity promoted the release of arsenic from sediment to water, which implied that microorganism played an important role in the mobilization of As in the sediment. Besides microorganism’s function, whether competitive anions also promoted desorption of As on iron(oxy)(hydr)oxides in the sediment of the lake needs further verification.
472
S. Li et al. / Ecotoxicology and Environmental Safety 120 (2015) 468–472
Shiyu Li, Changliang Yangn Engineering Technology Institute, Yunnan University, Kunming 650091, Yunnan Province, PR China E-mail address: [email protected] (C. Yang)
References Campbell, K.M., Malasarn, D., Saltikov, C.W., Newman, D.K., Hering, J.G., 2006. Simultaneous microbial reduction of iron(III) and arsenic(V) in suspensions of hydrous ferric oxide. Environ. Sci. Technol. 40 (19), 5950–5955. Islam, F.S., Gault, A.G., Boothman, C., Polya, D.A., Charnock, J.M., Chatterjee, D., 2004. Role of metal reducing bacteria in arsenic release from Bengal delta sediments. Nature 430, 68–71. Liu, R.B., Yang, C.L., Li, S.Y., Sun, P.S., Shen, S.L., Li, Z.Y., Liu, K., 2014. Arsenic mobility in the arsenic-contaminated Yangzonghai Lake in China. Ecotoxicol. Environ. Saf. 107, 321–327. Smedley, P.L., Kinniburgh, D.G., 2002. A review of the source, behavior and distribution of arsenic in natural waters. Appl. Geochem. 17, 517–568. Wang, Z.H., He, B., Pan, X.J., Zhang, K.G., Wang, C., Sun, J., Yun, Z.J., Jiang, G.B., 2010. Levels, trends and risk assessment of arsenic pollution in Yangzonghai Lake. Yunnan Province, China. Sci. China Chem. 53 (8), 1809–1817.
Kai Liu School of Life Science, Yunnan University, Kunming 650091, Yunnan Province, PR China Received 24 April 2015 12 June 2015 16 June 2015 Available online 27 June 2015
n
Corresponding author. Fax: þ86 0871 65311210.
Contents lists available at ScienceDirect
Ecotoxicology and Environmental Safety journal homepage: www.elsevier.com/locate/ecoenv
Response to the Commentary on “Arsenic mobility in the arsenic-contaminated Yangzonghai Lake in China”
art ic l e i nf o Keywords: Arsenic distribution Stratification Microorganism Sediment Arsenic release
a b s t r a c t This is the response to “Commentary on ‘Arsenic mobility in the arsenic-contaminated Yangzonghai Lake in China’ by Changliang Yang et al. [Ecotoxicology and Environmental Safety, 107(2014)321-327]” (by Jing Chen et al.). To doubts and questions raised by Chen et al., we give further explanations and provide more relevant evidences. The water temperature stratification existed in Lake Yangzonghai in summer, and affected by which arsenic concentration with water depth was uneven and peaked in the bottom layer in summer. In the case of adding carbon source (glucose) and maintaining anerobic state, enhanced microbial activity promoted the release of arsenic from sediment to water which was observed in the laboratory experiments. Errors might exist in sampling, determination and calculation, but they would not change the main conclusions of the article. & 2015 Elsevier Inc. All rights reserved.
We would like to thank Professor Jing Chen and his research team for their commentary on our article “Arsenic mobility in the arsenic-contaminated Yangzonghai Lake in China” (Liu et al., 2014). As the responsible person who proposed and implemented the project of purifying arsenic pollution with the flocculants of ferric trichloride in Lake Yangzonghai, Professor Jing Chen has been paying special attention on any publication related to the arsenic pollution of the lake. We would like to show our respect to him for his efforts and contribution to the arsenic removal from water of the lake. After reading the commentary carefully, we realize that there are some misunderstandings and some misinterpretations in the commentary which we would like to clarify as follows:
1. About the concentration distribution of As in the lake To understand the spatial distribution of As in Yangzonghai Lake, we made two thorough field investigations on August 31, 2012, and January 8, 2013, respectively. Among 31 sampling sites in the lake, we chose five sites (A-E) (Fig. 1) to collect samples at different depths (from the first one at 0.5 m below the surface to the last one at 0.5 m from the bottom, a sample every other meter down along the water column). The water temperature, pH, and dissolved oxygen (DO) at each depth were recorded simultaneously by a multi- functional parameters instrument (YSI Inc). Distinct water temperature stratification was observed on August 31, 2012, but not found on January 8, 2013. We noticed that total arsenic concentration changed with depth, which showed little difference from 0.5 m to 10.5 m depth, but increased beyond 10.5 m and peaked at the bottom (Fig. 2). As now well known, water temperature stratification of lakes generally forms in http://dx.doi.org/10.1016/j.ecoenv.2015.06.026 0147-6513/& 2015 Elsevier Inc. All rights reserved.
summer and disappear in winter. The commentators try to deny the fact that total arsenic concentration changed with depth in their commentary by quoting the investigation results of Wang et al. (2010). Unfortunately, none of the four investigations made by Wang et al. were in the same month as we did. It is inappropriate to compare the investigation results obtained in different seasons and different years, especially comparing the investigation results obtained before and after the remediation (Wang et al. made the investigations before September 2009, and the remediation took place between October 2009 and December 2011). And furthermore, Wang et al. did find that arsenic concentration increased with water depth at some sampling sites ( Figs. 3 and 4), but the commentators did not draw attention to this. According to the article by Wang et al., all the water samples were filtered before acidation and determination, which means they examined the dissoluble arsenic in water column when they investigated the changes of arsenic concentration with water depth. As for other evidence the commentators quoted (data from Kunming Environmental Monitoring Center and Professor Jing Chen’s research team), we decline to comment on them since they are not from publications.
2. About microorganisms role in As release Our conclusions in the article that “In the case of glucose supplementation, microbial activity promoted the release of As from sediment to solution, resulting in authigenic secondary As pollution.” was derived based on the experiments which were done under the following conditions: maintaining the incubators an aerobic condition and enhancing microbial activity by adding a
S. Li et al. / Ecotoxicology and Environmental Safety 120 (2015) 468–472
469
Fig. 1. Schematic graph of the sampling sites in Lake Yangzonghai in southwest China (Liu et al., 2014).
carbon source (glucose). It does not imply by any means that the release of As is happening or will certainly happen in the natural system of Lake Yangzonghai in the same way as the experiments showed, which we should have made clearer. However, despite the different conditions between laboratory experiment and the natural system, one cannot deny that the microorganisms plays an important role in the transformation and mobilization of As from sediment to water, which has been widely accepted now. It is generally thought that the microbially mediated reductive dissolution of iron-bearing minerals in water environments leads to the release of As. The amount released depends on the valence state of As and the mineralogical characteristics of Fe within the environment (Islam et al., 2004; Campbell et al., 2006). Most researchers believe that, as the carrier of As in sediment, the catalytic reduction of iron (hydr)oxide minerals in an anaerobic environment is the main driver of As release (Smedley and Kinniburgh, 2002; Islam et al., 2004). Both the microbially mediated reductive dissolution of iron (hydr)oxides and the direct reduction of As by microorganisms can lead to the activation of As, resulting in an increase in As concentration in water (Islam et al., 2004). Our experiments arrived at the same conclusions.
3. About sampling and determination Firstly, sampling water with a suction pump in a deep lake like Yangzonghai Lake is practical and feasible when a large amount of water is needed. The local environmental monitoring institution employs the same method to investigate the arsenic concentration distribution with depth. We noticed the possible disturbance of the sediment when we took the sample from the bottom of the lake. We had taken necessary measures to avoid sucking the sediment. We should point out that the arsenic concentration
changed little in hypolimnion compared with that in thermocline. The hypolimnion occurred from 16.5 m depth to the bottom of the lake. Since the arsenic concentrations from 16.5 m depth to the bottom changed little, the disturbance effect from the sampling was quite slight. Concerning the determination of As, we made a mistake in our article when we described the water sample treatment. Actually, we displayed only total arsenic in this study, and all the arsenic concentrations in the article refer to total arsenic. We are very sorry about the mistake which has confused readers. The determination method of total arsenic in our study is so called Atomic Fluorescence Spectrum (AFS) which is widely used to detect arsenic in water and waste water in environmental monitoring sector in China. The limit of detection of the method is 0.1 μg L-1. To determine the total arsenic in water sample from Yangzonghai Lake, 20 ml well-mixed water sample without filtration pretreatment was put into a 50 ml beaker, and was mixed evenly with 3 ml HCL (1 mol/l) and 2 ml 10% thiocarbamide. After 20 minutes, 5 ml solution was taken from the beaker with bottletop dispenser and was injected into hydride-generator of AFS. After adding 4 ml 0.7% potassium borohydride (PBH), the water sample was detected with AFS. In the study, we added a little HNO3 into the water sample to adjust the pH o2, which is the common method to preserve water sample, and should not affect the determination of total arsenic.
4. About arsenic reserve in the lake Since the water level of the lake changed day by day, and the distribution of the arsenic concentrations in the lake water in summer was uneven, the accurate calculation of the arsenic reserve in the lake water was not easy, and further verification will be needed. The arsenic reserve was not the important question
470
S. Li et al. / Ecotoxicology and Environmental Safety 120 (2015) 468–472
Fig. 2. The ranges of As concentration, water temperature, pH, and DO at sample sites A, B, C and E at various water depths in Lake Yangzonghai (Liu et al., 2014).
which we aimed to answer in our study, and the possible error in the calculation did not affect the main conclusions of the study.
5. About competitive anion exchange In our study, based on the research findings of others, we
discussed the functions of the competitive anion, and concluded that “although studies have confirmed that the presence of competing anions promoted As leaching from sediment, whether competitive anions promote desorption of As on iron(oxy)(hydr) oxides in the sediment of a lake contaminated by As and then treated with a flocculent such as Yangzonghai Lake requires verification”. It is an obvious misinterpretation to say that “the
S. Li et al. / Ecotoxicology and Environmental Safety 120 (2015) 468–472
471
Fig. 3. Map of sampling sites in Yangzonghai (▲ lake water and sediments; ◆ soil; ● well water and spring water) (Wang et al., 2010).
Fig. 4. Relation between arsenic concentrations and depth of lake water in Yangzonghai (Wang et al., 2010).
authors attribute the As release in summer to the high concentration of HCO3- without any support of experimental data”.
6. Summary Based on investigations of total arsenic distribution in vertical direction in Lake Yangzonghai, we found that the total arsenic concentration increased with depth and peaked at the bottom layer because of water temperature stratification in summer, but the same phenomenon was not found in winter. The same
phenomenon of the lake was discovered and reported by other researchers. Laboratory experiments displayed that in the case of adding a carbon source (glucose) and maintaining an anerobic state, enhanced microbial activity promoted the release of arsenic from sediment to water, which implied that microorganism played an important role in the mobilization of As in the sediment. Besides microorganism’s function, whether competitive anions also promoted desorption of As on iron(oxy)(hydr)oxides in the sediment of the lake needs further verification.
472
S. Li et al. / Ecotoxicology and Environmental Safety 120 (2015) 468–472
Shiyu Li, Changliang Yangn Engineering Technology Institute, Yunnan University, Kunming 650091, Yunnan Province, PR China E-mail address: [email protected] (C. Yang)
References Campbell, K.M., Malasarn, D., Saltikov, C.W., Newman, D.K., Hering, J.G., 2006. Simultaneous microbial reduction of iron(III) and arsenic(V) in suspensions of hydrous ferric oxide. Environ. Sci. Technol. 40 (19), 5950–5955. Islam, F.S., Gault, A.G., Boothman, C., Polya, D.A., Charnock, J.M., Chatterjee, D., 2004. Role of metal reducing bacteria in arsenic release from Bengal delta sediments. Nature 430, 68–71. Liu, R.B., Yang, C.L., Li, S.Y., Sun, P.S., Shen, S.L., Li, Z.Y., Liu, K., 2014. Arsenic mobility in the arsenic-contaminated Yangzonghai Lake in China. Ecotoxicol. Environ. Saf. 107, 321–327. Smedley, P.L., Kinniburgh, D.G., 2002. A review of the source, behavior and distribution of arsenic in natural waters. Appl. Geochem. 17, 517–568. Wang, Z.H., He, B., Pan, X.J., Zhang, K.G., Wang, C., Sun, J., Yun, Z.J., Jiang, G.B., 2010. Levels, trends and risk assessment of arsenic pollution in Yangzonghai Lake. Yunnan Province, China. Sci. China Chem. 53 (8), 1809–1817.
Kai Liu School of Life Science, Yunnan University, Kunming 650091, Yunnan Province, PR China Received 24 April 2015 12 June 2015 16 June 2015 Available online 27 June 2015
n
Corresponding author. Fax: þ86 0871 65311210.
