Radiation Protection Dosimetry Advance Access published May 1, 2015 Radiation Protection Dosimetry (2015), pp. 1–4
doi:10.1093/rpd/ncv242
ENVIRONMENTAL RADIOACTIVITY OF WATER SAMPLES COLLECTED IN HIGASHI-HIROSHIMA CAMPUS, HIROSHIMA UNIVERSITY, JAPAN S. Nakashima1, *, A. Sasai2, K. Koga2, H. Yasuhara2, A. Matsushima1 and K. Inada1 1 Natural Science Center for Basic Research and Development, Hiroshima University, Higashi-Hiroshima, Japan 2 Graduate School of Science, Hiroshima University, Higashi-Hiroshima, Japan *Corresponding author: [email protected]
INTRODUCTION Environmental radioactivity of water samples has been studied in Higashi-Hiroshima Campus, Hiroshima University, Japan to check that radioactive nuclides discharged from the radiation facility of Hiroshima University are extremely low compared with regulation values. In the course of the study, an interesting seasonal change in the total b-activity was observed in the sewage sample(1). It was suggested that the total bactivity is mainly due to 40K concentration(2), and the coexisting chemical substances or microorganisms affect the change of total b-activity(3). MICROBIAL MAT Brownish yellow microbial mats are growing at the pond and river in Higashi-Hiroshima Campus, Hiroshima University. The microbial mats are produced through biomineralisation. Water samples were collected every month from the river in Higashi-Hiroshima Campus. One was collected at (A) upper stream of the microbial mat, and the other was at (B) lower reaches of the mat. For the comparison, (C) the water far from microbial mat was also collected. The total b-activity, g-rays and metal concentrations were measured using 2p gas flow counter, HPGe detector and inductively coupled plasma atomic emission spectroscopy (ICP-AES), respectively(4). The concentrations of Fe and Mn in Samples A and B were relatively low in summer, while the concentrations were relatively high in winter. That is, the concentrations decrease with increasing water temperature and increase with decreasing temperature. It may be thought that microbial mat affects the concentration of Fe and Mn in Point A as well as in Point B, because the flow of the river is slow and the sampling point A is very near to the microbial mat.
The results suggest that microbial mats become active in summer and adsorb more Fe and Mn in summer. Total b-activity showed an opposite temperature dependence with Fe and Mn concentrations, i.e. the activity increased with an increase in water temperature and decreased with a decrease in water temperature. On the other hand, the concentrations of Fe and Mn in Sample C are very low for every month, although the seasonal change in the total b-activity was observed in Sample C. It was suggested that the total b-activity was mainly explained by water temperature. However, question whether microbial mat activity contributes or not to seasonal change in the total bactivity remains. In the present study, the iron and aluminium concentrations were investigated in water around microbial mat region in the water samples of HigashiHiroshima Campus, Hiroshima University to know the formation condition of microbial mat. It was also investigated what kinds of elements are included in the microbial mats. The metal adsorption by the microorganism was checked in microbial mat and by substances in microbial mat. From these experiments, the seasonal change in the total b-activity in the river sample was discussed.
IRON AND ALUMINIUM ION CONCENTRATIONS IN WATER WITH AND WITHOUT MICROBIAL MATS There are many microbial mat spots in the river of Higashi-Hiroshima Campus as shown in Figure 1. Microbial mat includes iron hydroxide through biomineralisation. The river water samples in the campus were collected three times for 10 spots along the stream in summer. Filtration was not performed. The iron and aluminium concentrations of the samples
# The Author 2015. Published by Oxford University Press. All rights reserved. For Permissions, please email: [email protected]
Downloaded from http://rpd.oxfordjournals.org/ at East Carolina University on July 10, 2015
The relation between concentration of elements and microbial activity in the water samples of Higashi-Hiroshima Campus, Hiroshima University was investigated. Energy dispersive X-ray spectroscopy revealed that microbial mat contains iron, aluminium, silicon and phosphorus. Model experiment revealed that the potassium was adsorbed by living microorganism in the microbial mats, while it was not adsorbed by dead microbial mat. Iron was adsorbed by both living and dead microbial mats. The present results explain the increase in the total b-radioactivity of water sample in summer and the decrease in winter.
S. NAKASHIMA ET AL.
Figure 3. Aluminium concentration of water sample.
Figure 4. EDX of microbial mat obtained from the campus river.
ENERGY DISPERSIVE X-RAY SPECTROSCOPY (EDX) Figure 2. Iron concentration of water sample.
were measured by using ICP-AES. The river flows from 1 to 10. There were microbial mats in Spots 2 – 8 and 10, while there were no microbial mats in Spots 1 and 9. Iron concentration in each point is shown in Figure 2. Aluminium concentration in each spot is shown in Figure 3. Iron concentration is ca. 50 times higher than that of aluminium. It was shown that iron ion concentrations of sampling points with microbial mats are higher than those of sample points without microbial mat. Aluminium ion concentrations for sample points with microbial mats are also higher than those for sample points without microbial mats. It is thought that high metal concentration is an important factor for the formation of microbial mat, because the mat is composed of iron hydroxide. The assumption in the present study is that the metal concentration in water changes depending on the microbial activity. Potassium concentration did not show such trend. There is a slight trend that the potassium concentration of the lower stream is relatively lower than that of upper stream. The results suggest that the mechanism of adsorption/desorption is different between iron and potassium.
The microbial mats were gathered to take an electron micrograph of the microbial mats. Some microbial mats were collected from the spots shown in Figure 1. After collected microbial mats were dried, the sample for electron microscope was made by using epoxy resin or carbon tape. Figure 4 shows the result of EDX. It can be seen that the microbial mat in the campus included some aluminium and iron as metal. The results agreed with the existence of iron and aluminium in the water sample. The microbial mats also included silicon, phosphorous as well as iron and aluminium. EDX of the microbial mat obtained outside of the campus revealed the existence of calcium, manganese as well as aluminium, iron, silicon and phosphorous. Element map of the microbial mat was also obtained. The electron map revealed that iron and silicon distributed uniformly. The result shows that the iron compound is not adduct. MODEL EXPERIMENTS A model experiment of adsorption was performed by using microbial mat. Living microbial mat was gathered and was used as it is for the model experiment (living microbial mat). On the other hand, the microbial mat was autoclaved
Page 2 of 4
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Figure 1. Sampling points 1 –10 of water sample in HigashiHiroshima Campus, Hiroshima University. Painted portions show the points where we can find microbial mats.
ENVIRONMENTAL RADIOACTIVITY OF WATER SAMPLES COLLECTED IN HIGASHI-HIROSHIMA CAMPUS
increases. That is, the dry microbial mats discharged some potassium ion in the potassium solution, whereas the living microbial mats adsorbed potassium ion in the potassium solution. The difference between living and dead microbial mats in the behaviour for adsorption is due to the difference between the microorganism in microbial mat and substances in microbial mat. From the model experiment, the difference in behaviour of adsorption was shown between iron and potassium, suggesting the difference in adsorption mechanism between them. In this article, the seasonal change in b-radioactivity from the point of adsorption of microbial mat is discussed. The present results suggest that in summer, the microbial mats become active and adsorb iron. In this situation, the microbial mats have no capacity for adsorbing potassium ion. That is, the potassium concentration in water increases in summer. Therefore, the radioactivity of 40K in water increases in summer. On the other hand, in winter, microbial mat becomes less active, so the adsorption of iron ion will be decelerated; therefore, potassium will be adsorbed onto the microbial mat. There might be a difference in adsorption mechanism between iron and potassium. Therefore, the concentration of potassium in water decreases in winter. And, the radioactivity of 40K in water decreases in winter. This may explain the
Figure 5. Iron concentration change of the solution with living microbial mat.
Figure 7. Potassium concentration of the solution with living microbial mat.
Figure 6. Iron concentration change of the solution with dead microbial mat.
Figure 8. Potassium concentration of the solution with dead microbial mat.
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and dried. This microbial mat was also used for the model experiment (dead microbial mat). Iron(III) chloride, aluminium chloride and potassium chloride were dissolved in 200 ml of water to make a concentration of 10 –25 ppm. About 2 g of living or dead microbial mats were put into each solution. The 5 ml solutions of water samples were collected every day. The concentrations of these samples were measured by using ICP-AES. The results are shown in Figures 5–8. Figure 5 shows the iron concentration change of the solution with time having living microbial mat. The concentration decreases soon initially, and then the concentration decreases gradually. Figure 6 shows the iron concentration change of the solution with time having dead microbial mat. The concentration decreases soon almost perfectly. The similar trends were observed in the aluminium concentration change of the solution with and without microbial mat. The dead microbial mat adsorbed metals more than the living one. Figure 7 shows the potassium concentration change of the solution with living microbial mat. The concentration decreases soon after mixing, after that the concentration does not change. Figure 8 shows the potassium concentration change of the solution with dead microbial mat. The concentration does not decrease. It may be seen that the concentration
S. NAKASHIMA ET AL.
seasonal change of radioactivity in the environmental river sample in Higashi-Hiroshima Campus, Hiroshima University. CONCLUDING REMARKS
We thank the Ministry of Education, Culture, Sports, Science and Technology of Japan for supporting a part of this work under a Grant-in-Aid for Scientific Research (#24550176). REFERENCES 1. Inada, K., Matsushima, A., Nakashima, S., Takahashi, Y., Saito, T., Iwatani, K. and Shizuma, K. Proceedings of the Seventh Workshop on Environmental Radioactivity, 191– 193 (2006). 2. Matsushima, A., Nakashima, S., Inada, K., Takahashi, T. and Shizuma, K. Proceedings of the Eighth Workshop on Environmental Radioactivity, 127–129 (2007). 3. Inada, K., Matsushima, A., Koba, R., Teramoto, H., Yamasaki, N. and Nakashima, S. Proceedings of the Ninth Workshop on Environmental Radioactivity, 26– 28 (2008). 4. Koga, K., Kawai, S., Matsushima, A., Inada, K. and Nakashima, S. Proceedings of the 13th Workshop on Environmental Radioactivity, 138– 143 (2012).
Page 4 of 4
Downloaded from http://rpd.oxfordjournals.org/ at East Carolina University on July 10, 2015
In this study, the relation between environmental radioactivity and microbial mat was investigated in the river samples of Higashi-Hiroshima Campus, Hiroshima University. The metal adsorption by living microbial mats or by dead mats shows a difference between iron and potassium. Both the living and the dead microbial mats adsorbed iron and aluminium. On the other hand, the living microbial mats adsorbed the potassium, whereas the dead microbial mats did not adsorb the potassium in the potassium solution. The adsorption phenomenon of potassium to microbial mat changed depending on the activity of microbial mat and the amount of iron. This may explain the increase in the total b-radioactivity in summer and the decrease in winter.
ACKNOWLEDGEMENTS
doi:10.1093/rpd/ncv242
ENVIRONMENTAL RADIOACTIVITY OF WATER SAMPLES COLLECTED IN HIGASHI-HIROSHIMA CAMPUS, HIROSHIMA UNIVERSITY, JAPAN S. Nakashima1, *, A. Sasai2, K. Koga2, H. Yasuhara2, A. Matsushima1 and K. Inada1 1 Natural Science Center for Basic Research and Development, Hiroshima University, Higashi-Hiroshima, Japan 2 Graduate School of Science, Hiroshima University, Higashi-Hiroshima, Japan *Corresponding author: [email protected]
INTRODUCTION Environmental radioactivity of water samples has been studied in Higashi-Hiroshima Campus, Hiroshima University, Japan to check that radioactive nuclides discharged from the radiation facility of Hiroshima University are extremely low compared with regulation values. In the course of the study, an interesting seasonal change in the total b-activity was observed in the sewage sample(1). It was suggested that the total bactivity is mainly due to 40K concentration(2), and the coexisting chemical substances or microorganisms affect the change of total b-activity(3). MICROBIAL MAT Brownish yellow microbial mats are growing at the pond and river in Higashi-Hiroshima Campus, Hiroshima University. The microbial mats are produced through biomineralisation. Water samples were collected every month from the river in Higashi-Hiroshima Campus. One was collected at (A) upper stream of the microbial mat, and the other was at (B) lower reaches of the mat. For the comparison, (C) the water far from microbial mat was also collected. The total b-activity, g-rays and metal concentrations were measured using 2p gas flow counter, HPGe detector and inductively coupled plasma atomic emission spectroscopy (ICP-AES), respectively(4). The concentrations of Fe and Mn in Samples A and B were relatively low in summer, while the concentrations were relatively high in winter. That is, the concentrations decrease with increasing water temperature and increase with decreasing temperature. It may be thought that microbial mat affects the concentration of Fe and Mn in Point A as well as in Point B, because the flow of the river is slow and the sampling point A is very near to the microbial mat.
The results suggest that microbial mats become active in summer and adsorb more Fe and Mn in summer. Total b-activity showed an opposite temperature dependence with Fe and Mn concentrations, i.e. the activity increased with an increase in water temperature and decreased with a decrease in water temperature. On the other hand, the concentrations of Fe and Mn in Sample C are very low for every month, although the seasonal change in the total b-activity was observed in Sample C. It was suggested that the total b-activity was mainly explained by water temperature. However, question whether microbial mat activity contributes or not to seasonal change in the total bactivity remains. In the present study, the iron and aluminium concentrations were investigated in water around microbial mat region in the water samples of HigashiHiroshima Campus, Hiroshima University to know the formation condition of microbial mat. It was also investigated what kinds of elements are included in the microbial mats. The metal adsorption by the microorganism was checked in microbial mat and by substances in microbial mat. From these experiments, the seasonal change in the total b-activity in the river sample was discussed.
IRON AND ALUMINIUM ION CONCENTRATIONS IN WATER WITH AND WITHOUT MICROBIAL MATS There are many microbial mat spots in the river of Higashi-Hiroshima Campus as shown in Figure 1. Microbial mat includes iron hydroxide through biomineralisation. The river water samples in the campus were collected three times for 10 spots along the stream in summer. Filtration was not performed. The iron and aluminium concentrations of the samples
# The Author 2015. Published by Oxford University Press. All rights reserved. For Permissions, please email: [email protected]
Downloaded from http://rpd.oxfordjournals.org/ at East Carolina University on July 10, 2015
The relation between concentration of elements and microbial activity in the water samples of Higashi-Hiroshima Campus, Hiroshima University was investigated. Energy dispersive X-ray spectroscopy revealed that microbial mat contains iron, aluminium, silicon and phosphorus. Model experiment revealed that the potassium was adsorbed by living microorganism in the microbial mats, while it was not adsorbed by dead microbial mat. Iron was adsorbed by both living and dead microbial mats. The present results explain the increase in the total b-radioactivity of water sample in summer and the decrease in winter.
S. NAKASHIMA ET AL.
Figure 3. Aluminium concentration of water sample.
Figure 4. EDX of microbial mat obtained from the campus river.
ENERGY DISPERSIVE X-RAY SPECTROSCOPY (EDX) Figure 2. Iron concentration of water sample.
were measured by using ICP-AES. The river flows from 1 to 10. There were microbial mats in Spots 2 – 8 and 10, while there were no microbial mats in Spots 1 and 9. Iron concentration in each point is shown in Figure 2. Aluminium concentration in each spot is shown in Figure 3. Iron concentration is ca. 50 times higher than that of aluminium. It was shown that iron ion concentrations of sampling points with microbial mats are higher than those of sample points without microbial mat. Aluminium ion concentrations for sample points with microbial mats are also higher than those for sample points without microbial mats. It is thought that high metal concentration is an important factor for the formation of microbial mat, because the mat is composed of iron hydroxide. The assumption in the present study is that the metal concentration in water changes depending on the microbial activity. Potassium concentration did not show such trend. There is a slight trend that the potassium concentration of the lower stream is relatively lower than that of upper stream. The results suggest that the mechanism of adsorption/desorption is different between iron and potassium.
The microbial mats were gathered to take an electron micrograph of the microbial mats. Some microbial mats were collected from the spots shown in Figure 1. After collected microbial mats were dried, the sample for electron microscope was made by using epoxy resin or carbon tape. Figure 4 shows the result of EDX. It can be seen that the microbial mat in the campus included some aluminium and iron as metal. The results agreed with the existence of iron and aluminium in the water sample. The microbial mats also included silicon, phosphorous as well as iron and aluminium. EDX of the microbial mat obtained outside of the campus revealed the existence of calcium, manganese as well as aluminium, iron, silicon and phosphorous. Element map of the microbial mat was also obtained. The electron map revealed that iron and silicon distributed uniformly. The result shows that the iron compound is not adduct. MODEL EXPERIMENTS A model experiment of adsorption was performed by using microbial mat. Living microbial mat was gathered and was used as it is for the model experiment (living microbial mat). On the other hand, the microbial mat was autoclaved
Page 2 of 4
Downloaded from http://rpd.oxfordjournals.org/ at East Carolina University on July 10, 2015
Figure 1. Sampling points 1 –10 of water sample in HigashiHiroshima Campus, Hiroshima University. Painted portions show the points where we can find microbial mats.
ENVIRONMENTAL RADIOACTIVITY OF WATER SAMPLES COLLECTED IN HIGASHI-HIROSHIMA CAMPUS
increases. That is, the dry microbial mats discharged some potassium ion in the potassium solution, whereas the living microbial mats adsorbed potassium ion in the potassium solution. The difference between living and dead microbial mats in the behaviour for adsorption is due to the difference between the microorganism in microbial mat and substances in microbial mat. From the model experiment, the difference in behaviour of adsorption was shown between iron and potassium, suggesting the difference in adsorption mechanism between them. In this article, the seasonal change in b-radioactivity from the point of adsorption of microbial mat is discussed. The present results suggest that in summer, the microbial mats become active and adsorb iron. In this situation, the microbial mats have no capacity for adsorbing potassium ion. That is, the potassium concentration in water increases in summer. Therefore, the radioactivity of 40K in water increases in summer. On the other hand, in winter, microbial mat becomes less active, so the adsorption of iron ion will be decelerated; therefore, potassium will be adsorbed onto the microbial mat. There might be a difference in adsorption mechanism between iron and potassium. Therefore, the concentration of potassium in water decreases in winter. And, the radioactivity of 40K in water decreases in winter. This may explain the
Figure 5. Iron concentration change of the solution with living microbial mat.
Figure 7. Potassium concentration of the solution with living microbial mat.
Figure 6. Iron concentration change of the solution with dead microbial mat.
Figure 8. Potassium concentration of the solution with dead microbial mat.
Page 3 of 4
Downloaded from http://rpd.oxfordjournals.org/ at East Carolina University on July 10, 2015
and dried. This microbial mat was also used for the model experiment (dead microbial mat). Iron(III) chloride, aluminium chloride and potassium chloride were dissolved in 200 ml of water to make a concentration of 10 –25 ppm. About 2 g of living or dead microbial mats were put into each solution. The 5 ml solutions of water samples were collected every day. The concentrations of these samples were measured by using ICP-AES. The results are shown in Figures 5–8. Figure 5 shows the iron concentration change of the solution with time having living microbial mat. The concentration decreases soon initially, and then the concentration decreases gradually. Figure 6 shows the iron concentration change of the solution with time having dead microbial mat. The concentration decreases soon almost perfectly. The similar trends were observed in the aluminium concentration change of the solution with and without microbial mat. The dead microbial mat adsorbed metals more than the living one. Figure 7 shows the potassium concentration change of the solution with living microbial mat. The concentration decreases soon after mixing, after that the concentration does not change. Figure 8 shows the potassium concentration change of the solution with dead microbial mat. The concentration does not decrease. It may be seen that the concentration
S. NAKASHIMA ET AL.
seasonal change of radioactivity in the environmental river sample in Higashi-Hiroshima Campus, Hiroshima University. CONCLUDING REMARKS
We thank the Ministry of Education, Culture, Sports, Science and Technology of Japan for supporting a part of this work under a Grant-in-Aid for Scientific Research (#24550176). REFERENCES 1. Inada, K., Matsushima, A., Nakashima, S., Takahashi, Y., Saito, T., Iwatani, K. and Shizuma, K. Proceedings of the Seventh Workshop on Environmental Radioactivity, 191– 193 (2006). 2. Matsushima, A., Nakashima, S., Inada, K., Takahashi, T. and Shizuma, K. Proceedings of the Eighth Workshop on Environmental Radioactivity, 127–129 (2007). 3. Inada, K., Matsushima, A., Koba, R., Teramoto, H., Yamasaki, N. and Nakashima, S. Proceedings of the Ninth Workshop on Environmental Radioactivity, 26– 28 (2008). 4. Koga, K., Kawai, S., Matsushima, A., Inada, K. and Nakashima, S. Proceedings of the 13th Workshop on Environmental Radioactivity, 138– 143 (2012).
Page 4 of 4
Downloaded from http://rpd.oxfordjournals.org/ at East Carolina University on July 10, 2015
In this study, the relation between environmental radioactivity and microbial mat was investigated in the river samples of Higashi-Hiroshima Campus, Hiroshima University. The metal adsorption by living microbial mats or by dead mats shows a difference between iron and potassium. Both the living and the dead microbial mats adsorbed iron and aluminium. On the other hand, the living microbial mats adsorbed the potassium, whereas the dead microbial mats did not adsorb the potassium in the potassium solution. The adsorption phenomenon of potassium to microbial mat changed depending on the activity of microbial mat and the amount of iron. This may explain the increase in the total b-radioactivity in summer and the decrease in winter.
ACKNOWLEDGEMENTS
