重金屬鉻 ( Chromium ) 因工業蓬勃發展而產生，又因工廠不當排放鉻污染大量存在於環境中，其中鉻最常以Cr (Ⅵ) 與Cr (III) 的氧化態存在於水環境中，Cr (Ⅵ) 具有劇毒性，水環境中Cr (Ⅵ) 濃度若過高會導致水生動植物中毒、停止生長甚至是死亡，若Cr (Ⅵ) 被人體吸收則會形成體內的基因突變與致癌物質的產生。生物修復作為目前最具有經濟效益的污染處理方式，其中以小球藻作為去除水中重金屬為處理效率快、生態風險低的方法。為了實際應用在污水處理系統，本研究探討了小球藻除鉻的基本性質影響、環境中共存污染物對小球藻除鉻的影響、鉻在藻體內的型態變化與小球藻對鉻的去除機制與其生態風險。
研究表明，生物累積與生物還原為小球藻除鉻的主要機制，實驗得知小球藻去除水中鉻的效率隨著鉻濃度升高而呈現下降的趨勢，5000 μg Cr/L為小球藻除鉻的耐受度極限，過高濃度的鉻無法被小球藻吸收。且在加入相同濃度的硒研究發現，鉻與共存污染物的同時存在時，小球藻去除鉻的效率與鉻在藻體內的累積都有下降的趨勢，這是因為鉻與硒在小球藻體內會競爭相同的硫酸鹽載體。使用X射線吸收光譜 ( XAS ) 來了解鉻在藻體內的型態轉化，大部分的Cr (Ⅵ) 與都能轉化成毒性較低的Cr (III) 型態，代表小球藻不僅能降低環境中污染物濃度還能降低生態風險。
使用穿透式電子顯微鏡 ( TEM ) 觀察鉻在藻類細胞內對於藻細胞的超微結構影響與小球藻對抗金屬的機制，發現鉻離子進入藻類細胞後會形成大小20-40nm的圓形顆粒且聚集在細胞外圍細胞壁中，藻類細胞對污染物的解毒機制為藻細胞體內與細胞壁上的還原酶與穀胱甘肽還原金屬鉻污染並降低其毒性，若環境中污染物濃度過高，藻類細胞為了保持細胞內的濃度平衡會把形成的金屬顆粒排出細胞外。此外，富含鉻的小球藻在後續處置中若沒處理好可能導致環境的二度污染，實驗研究了小球藻作為生質油的可行性，發現加入鉻的小球藻體能產生更多的油脂，能用於生質能的飽和脂肪酸含量也有提升，如此推測，小球藻處理完環境中鉻污染後，再作為生質能原料不失為一種對環境友善的選擇。

Chromium (Cr) pollution has posed a significant impact on our environment and natural resources, in particular water and soil, all over the world. Excessive exposure could lead to toxic and detrimental health effects on humans and animals. As algae have been applied as an environmentally benign and economically viable means to treat Cr-contamianted water, this study tested Chlorella sorokiniana for its performance in Cr removal and sensitivity to Cr toxicity either in the presence or absence of selenium as an antagonist. Tested at various Cr levels, C. sorokiniana displayed the greatest removal efficiency (67.4%) at 500 μg Cr/L, with a remarkable decline in performance at 5000 μg Cr/L and above. The lowest Cr removal efficiency was observed for the alga simultaneously exposed to Cr(VI) and Se (VI), exhibiting greater antagonism between both species. Speciation analysis conducted using X-ray absorption spectroscopy (XAS) shows most of the absorbed Cr (VI) by the alga was transformed to Cr(III) in less than 72hr. High resolution transmission electron microscope (HRTEM) images display nano-particles inside the sectioned algal cells, using an ultra-microtome, possibly through the synthesis by the reductase and glutathione contents as part of defense mechanism against Cr toxicity. In order to prevent the accumulated Cr in algal cells from being released back to the environment, Cr-laden algal biomass was further recycled for the greater lipid production, compared to the control and group that was coexposed to Cr and Se. Overall, our results suggest C. sorokiniana shows great potential to efficiently remove and biotranform Cr (VI) to lower toxic forms, and then can be used as a better fuel source than the unexposed alga.

1. Wang, X., et al., Processes of chromium (VI) migration and transformation in chromate production site: A case study from the middle of China. Chemosphere, 2020. 257: p. 127282.
2. Haney, J.T., et al., Development of an inhalation unit risk factor for hexavalent chromium. Regulatory Toxicology and Pharmacology, 2014. 68(2): p. 201-211.
3. Tseng, C.-H., C. Lei, and Y.-C. Chen, Evaluating the health costs of oral hexavalent chromium exposure from water pollution: A case study in Taiwan. Journal of Cleaner Production, 2018. 172: p. 819-826.
4. Murthy, M.K., P. Khandayataray, and D. Samal, Chromium toxicity and its remediation by using endophytic bacteria and nanomaterials: A review. Journal of Environmental Management, 2022. 318: p. 115620.
5. Genchi, G., et al. The Double Face of Metals: The Intriguing Case of Chromium. Applied Sciences, 2021. 11, DOI: 10.3390/app11020638.
6. Sandana Mala, J.G., D. Sujatha, and C. Rose, Inducible chromate reductase exhibiting extracellular activity in Bacillus methylotrophicus for chromium bioremediation. Microbiological Research, 2015. 170: p. 235-241.
7. Oruko, R.O., et al., Contemporary and future direction of chromium tanning and management in sub Saharan Africa tanneries. Process Safety and Environmental Protection, 2020. 133: p. 369-386.
8. Genchi, G., et al., The double face of metals: The intriguing case of chromium. Applied Sciences, 2021. 11(2): p. 638.
9. Jobby, R., et al., Biosorption and biotransformation of hexavalent chromium [Cr (VI)]: a comprehensive review. Chemosphere, 2018. 207: p. 255-266.
10. Coetzee, J.J., N. Bansal, and E.M.N. Chirwa, Chromium in Environment, Its Toxic Effect from Chromite-Mining and Ferrochrome Industries, and Its Possible Bioremediation. Exposure and Health, 2020. 12(1): p. 51-62.
11. Singh, S., et al., Ecological effects, remediation, distribution, and sensing techniques of chromium. Chemosphere, 2022. 307: p. 135804.
12. Joutey, N.T., et al., Mechanisms of hexavalent chromium resistance and removal by microorganisms. Rev Environ Contam Toxicol, 2015. 233: p. 45-69.
13. Tang, X., et al., Study on detoxification and removal mechanisms of hexavalent chromium by microorganisms. Ecotoxicology and Environmental Safety, 2021. 208: p. 111699.
14. Sen, M. and M.G. Dastidar, Chromium removal using various biosorbents. Journal of Environmental Health Science & Engineering, 2010. 7(3): p. 182-190.
15. Park, D., Y.-S. Yun, and J.M. Park, XAS and XPS studies on chromium-binding groups of biomaterial during Cr(VI) biosorption. Journal of Colloid and Interface Science, 2008. 317(1): p. 54-61.
16. Kapoor, R.T., et al., Accumulation of chromium in plants and its repercussion in animals and humans. Environmental Pollution, 2022. 301: p. 119044.
17. Wu, Q., et al., Remediation of high-concentration Cr(VI)-contaminated soils with FeSO4 combined with biostimulation: Cr(VI) transformation and stabilization. Journal of Hazardous Materials Advances, 2022. 8: p. 100161.
18. Çimen, A., Removal of chromium from wastewater by reverse osmosis. Russian Journal of Physical Chemistry A, 2015. 89(7): p. 1238-1243.
19. Xing, X., et al., A comprehensive review on emerging natural and tailored materials for chromium-contaminated water treatment and environmental remediation. Journal of Environmental Chemical Engineering, 2022. 10(2): p. 107325.
20. Di Natale, F., et al., Equilibrium and dynamic study on hexavalent chromium adsorption onto activated carbon. Journal of Hazardous Materials, 2015. 281: p. 47-55.
21. Schneider, R.M., et al., Adsorption of chromium ions in activated carbon. Chemical Engineering Journal, 2007. 132(1): p. 355-362.
22. Han, X., et al., Biosorption and bioreduction of Cr(VI) by a microalgal isolate, Chlorella miniata. Journal of Hazardous Materials, 2007. 146(1): p. 65-72.
23. Owlad, M., et al., Removal of Hexavalent Chromium-Contaminated Water and Wastewater: A Review. Water, Air, and Soil Pollution, 2009. 200(1): p. 59-77.
24. Mamais, D., et al., Biological groundwater treatment for chromium removal at low hexavalent chromium concentrations. Chemosphere, 2016. 152: p. 238-244.
25. Sharma, P., et al., Health hazards of hexavalent chromium (Cr (VI)) and its microbial reduction. Bioengineered, 2022. 13(3): p. 4923-4938.
26. Abdelfattah, A., et al., Microalgae-based wastewater treatment: Mechanisms, challenges, recent advances, and future prospects. Environmental Science and Ecotechnology, 2023. 13: p. 100205.
27. Greeshma, K., H.-S. Kim, and R. Ramanan, The emerging potential of natural and synthetic algae-based microbiomes for heavy metal removal and recovery from wastewaters. Environmental Research, 2022. 215: p. 114238.
28. Sibi, G., Biosorption of chromium from electroplating and galvanizing industrial effluents under extreme conditions using Chlorella vulgaris. Green Energy & Environment, 2016. 1(2): p. 172-177.
29. Singh, V., et al., Isolation and characterization of Pseudomonas resistant to heavy metals contaminants. International Journal of Pharmaceutical Sciences Review and Research, 2010. 3(2): p. 164-167.
30. Foucault, Y., et al., Green manure plants for remediation of soils polluted by metals and metalloids: Ecotoxicity and human bioavailability assessment. Chemosphere, 2013. 93(7): p. 1430-1435.
31. Yun, H.-S., Y.-S. Kim, and H.-S. Yoon, Characterization of Chlorella sorokiniana and Chlorella vulgaris fatty acid components under a wide range of light intensity and growth temperature for their use as biological resources. Heliyon, 2020. 6(7): p. e04447.
32. Fu, F. and Q. Wang, Removal of heavy metal ions from wastewaters: A review. Journal of Environmental Management, 2011. 92(3): p. 407-418.
33. Day, J.G., E.E. Benson, and R.A. Fleck, In vitro culture and conservation of microalgae: Applications for aquaculture, biotechnology and environmental research. In Vitro Cellular & Developmental Biology - Plant, 1999. 35(2): p. 127-136.
34. Siddiki, S.Y.A., et al., Microalgae biomass as a sustainable source for biofuel, biochemical and biobased value-added products: An integrated biorefinery concept. Fuel, 2022. 307: p. 121782.
35. Song, Y., et al., The promising way to treat wastewater by microalgae: Approaches, mechanisms, applications and challenges. Journal of Water Process Engineering, 2022. 49: p. 103012.
36. Khanna, P., A. Kaur, and D. Goyal, Algae-based metallic nanoparticles: Synthesis, characterization and applications. Journal of Microbiological Methods, 2019. 163: p. 105656.
37. Ahmed, J. and V. Kumar, Effect of high-pressure treatment on oscillatory rheology, particle size distribution and microstructure of microalgae Chlorella vulgaris and Arthrospira platensis. Algal Research, 2022. 62: p. 102617.
38. Safi, C., et al., Morphology, composition, production, processing and applications of Chlorella vulgaris: A review. Renewable and Sustainable Energy Reviews, 2014. 35: p. 265-278.
39. Abdelnour, S., et al., The application of the microalgae Chlorella spp. as a supplement in broiler feed. World's Poultry Science Journal, 2019. 75(2): p. 305-318.
40. Chugh, M., et al., Algal Bioremediation of heavy metals: An insight into removal mechanisms, recovery of by-products, challenges, and future opportunities. Energy Nexus, 2022. 7: p. 100129.
41. Volland, S., et al., Intracellular chromium localization and cell physiological response in the unicellular alga Micrasterias. Aquatic Toxicology, 2012. 109: p. 59-69.
42. Cervantes, C., et al., Interactions of chromium with microorganisms and plants. FEMS Microbiology Reviews, 2001. 25(3): p. 335-347.
43. Barrera-Díaz, C.E., V. Lugo-Lugo, and B. Bilyeu, A review of chemical, electrochemical and biological methods for aqueous Cr(VI) reduction. Journal of Hazardous Materials, 2012. 223-224: p. 1-12.
44. Pradhan, D., et al., Recent bioreduction of hexavalent chromium in wastewater treatment: A review. Journal of Industrial and Engineering Chemistry, 2017. 55: p. 1-20.
45. Hulkoti, N.I. and T.C. Taranath, Biosynthesis of nanoparticles using microbes—A review. Colloids and Surfaces B: Biointerfaces, 2014. 121: p. 474-483.
46. Gong, B., et al., Induction of zincophore pseudopaline secretion by Cr(VI) and intracellular formation of granules from nanocrystal aggregation by Cr(III) in Pseudomonas aeruginosa. Journal of Environmental Management, 2022. 323: p. 116201.
47. Wong, P. and J. Trevors, Chromium toxicity to algae and bacteria. Chromium in the natural and human environments, 1988. 305.
48. Jin, Z., et al., Metal-free selenium doped carbon nanotube/graphene networks as a synergistically improved cathode catalyst for oxygen reduction reaction. Nanoscale, 2012. 4(20): p. 6455-60.
49. Fukushi, K. and D.A. Sverjensky, A surface complexation model for sulfate and selenate on iron oxides consistent with spectroscopic and theoretical molecular evidence. Geochimica et Cosmochimica Acta, 2007. 71(1): p. 1-24.
50. Rayman, M.P., Selenium and human health. The Lancet, 2012. 379(9822): p. 1256-1268.
51. Sors, T.G., D.R. Ellis, and D.E. Salt, Selenium uptake, translocation, assimilation and metabolic fate in plants. Photosynthesis Research, 2005. 86(3): p. 373-389.
52. Pereira, Y., et al., Chromate Causes Sulfur Starvation in Yeast. Toxicological Sciences, 2008. 106(2): p. 400-412.
53. Wang, Y., et al., Feasibility of using Chlorella vulgaris for the removal of selenium and chromium in water: Competitive interactions with sulfur, physiological effects on algal cells and its resilience after treatment. Journal of Cleaner Production, 2021. 313: p. 127939.
54. Kong, W., et al., Sediment and residual feed from aquaculture water bodies threaten aquatic environmental ecosystem: Interactions among algae, heavy metals, and nutrients. Journal of Environmental Management, 2023. 326: p. 116735.
55. Neal, A.L., What can be inferred from bacterium–nanoparticle interactions about the potential consequences of environmental exposure to nanoparticles? Ecotoxicology, 2008. 17(5): p. 362-371.
56. Jain, M.S., S. Paul, and A.S. Kalamdhad, Kinetics and physics during composting of various organic wastes: Statistical approach to interpret compost application feasibility. Journal of Cleaner Production, 2020. 255: p. 120324.
57. Chen, J., et al., Elucidating the mechanism of Cr (VI) formation upon the interaction with metal oxides during coal oxy-fuel combustion. Journal of hazardous materials, 2013. 261: p. 260-268.
58. Du, Z., et al., Microwave-assisted pyrolysis of microalgae for biofuel production. Bioresource Technology, 2011. 102(7): p. 4890-4896.
59. Agathokleous, E., J. Guo, and J. Peñuelas, Low doses of toxicants can enhance algae potential as biodiesel and biomass feedstocks. Renewable and Sustainable Energy Reviews, 2022. 168: p. 112858.
60. Sathya, A.B., et al., Microalgal biofuel production: Potential challenges and prospective research. Fuel, 2023. 332: p. 126199.
61. McKendry, P., Energy production from biomass (part 1): overview of biomass. Bioresource Technology, 2002. 83(1): p. 37-46.
62. Medipally, S.R., et al., Microalgae as Sustainable Renewable Energy Feedstock for Biofuel Production. BioMed Research International, 2015. 2015: p. 519513.
63. Ahmed, S.F., et al., Utilization of nanomaterials in accelerating the production process of sustainable biofuels. Sustainable Energy Technologies and Assessments, 2023. 55: p. 102894.
64. Zhu, L., et al., Using microalgae to produce liquid transportation biodiesel: What is next? Renewable and Sustainable Energy Reviews, 2017. 78: p. 391-400.
65. Liu, J., et al., Biomass pyrolysis mechanism for carbon-based high-value products. Proceedings of the Combustion Institute, 2022.
66. Lepage, G. and C.C. Roy, Improved recovery of fatty acid through direct transesterification without prior extraction or purification. Journal of Lipid Research, 1984. 25(12): p. 1391-1396.
67. Shanker, A.K., et al., Chromium toxicity in plants. Environment International, 2005. 31(5): p. 739-753.
68. Zhang, B., et al., Selenium(Ⅳ) alleviates chromium(Ⅵ)-induced toxicity in the green alga Chlamydomonas reinhardtii. Environmental Pollution, 2021. 272: p. 116407.
69. Schiavon, M., et al., Selenium accumulation and metabolism in algae. Aquatic Toxicology, 2017. 189: p. 1-8.
70. Hu, M., et al., Preferential uptake of Se(IV) over Se(VI) and the production of dissolved organic Se by marine phytoplankton. Marine Environmental Research, 1997. 44(2): p. 225-231.
71. Vriens, B., et al., Selenium Uptake and Methylation by the Microalga Chlamydomonas reinhardtii. Environmental Science & Technology, 2016. 50(2): p. 711-720.
72. Pagnanelli, F., et al., Biosorption-mediated reduction of Cr(VI) using heterotrophically-grown Chlorella vulgaris: Active sites and ionic strength effect. Chemical Engineering Journal, 2013. 231: p. 94-102.
73. Zayed, A., et al., Chromium accumulation, translocation and chemical speciation in vegetable crops. Planta, 1998. 206(2): p. 293-299.
74. Qing, X., et al., Selenium alleviates chromium toxicity by preventing oxidative stress in cabbage (Brassica campestris L. ssp. Pekinensis) leaves. Ecotoxicology and Environmental Safety, 2015. 114: p. 179-189.
75. <BIOSYNTHESIS OF.pdf>.
76. Lai, C.-Y., et al., Microbial selenate reduction in membrane biofilm reactors using ethane and propane as electron donors. Water Research, 2020. 183: p. 116008.
77. Wang, Y., et al. Selenite Reduction and the Biogenesis of Selenium Nanoparticles by Alcaligenes faecalis Se03 Isolated from the Gut of Monochamus alternatus (Coleoptera: Cerambycidae). International Journal of Molecular Sciences, 2018. 19, DOI: 10.3390/ijms19092799.
78. Gojkovic, Ž., et al., Effect of Selenate on Viability and Selenomethionine Accumulation of <i>Chlorella sorokiniana</i> Grown in Batch Culture. The Scientific World Journal, 2014. 2014: p. 401265.
79. Zheng, Y.-M., et al., Characterization of hexavalent chromium interaction with Sargassum by X-ray absorption fine structure spectroscopy, X-ray photoelectron spectroscopy, and quantum chemistry calculation. Journal of Colloid and Interface Science, 2011. 356(2): p. 741-748.
80. Bunaciu, A.A., E.g. Udriştioiu, and H.Y. Aboul-Enein, X-Ray Diffraction: Instrumentation and Applications. Critical Reviews in Analytical Chemistry, 2015. 45(4): p. 289-299.
81. Oukarroum, A., et al., Inhibitory effects of silver nanoparticles in two green algae, Chlorella vulgaris and Dunaliella tertiolecta. Ecotoxicology and Environmental Safety, 2012. 78: p. 80-85.
82. Liu, S., et al., Analysis of intracellular copper ions content and distribution in algae by gold nanorods method. Chemosphere, 2020. 259: p. 127512.
83. Das, R.K., et al., Biological synthesis of metallic nanoparticles: plants, animals and microbial aspects. Nanotechnology for Environmental Engineering, 2017. 2(1).
84. Li, S.-N., R. Wang, and S.-H. Ho, Algae-mediated biosystems for metallic nanoparticle production: From synthetic mechanisms to aquatic environmental applications. Journal of Hazardous Materials, 2021. 420: p. 126625.
85. Mehta, S.K. and J.P. Gaur, Use of Algae for Removing Heavy Metal Ions From Wastewater: Progress and Prospects. Critical Reviews in Biotechnology, 2005. 25(3): p. 113-152.
86. Watanabe, K., et al., Symbiotic association in Chlorella culture. FEMS Microbiology Ecology, 2005. 51(2): p. 187-196.
87. Costa, C.H.d., et al., Effect of chromium oxide (III) nanoparticles on the production of reactive oxygen species and photosystem II activity in the green alga Chlamydomonas reinhardtii. Science of The Total Environment, 2016. 565: p. 951-960.
88. Farias, D.R., et al., In situ assessment of Ulva australis as a monitoring and management tool for metal pollution. Journal of Applied Phycology, 2017. 29(5): p. 2489-2502.
89. LeBlanc, K.L., et al., Selenium analysis in waters. Part 2: Speciation methods. Science of The Total Environment, 2018. 640-641: p. 1635-1651.
90. Al Ketife, A.M.D., F. Al Momani, and S. Judd, A bioassimilation and bioaccumulation model for the removal of heavy metals from wastewater using algae: New strategy. Process Safety and Environmental Protection, 2020. 144: p. 52-64.
91. Daud, M.K., et al., Differential physiological, ultramorphological and metabolic responses of cotton cultivars under cadmium stress. Chemosphere, 2013. 93(10): p. 2593-2602.
92. Vitória, A.P., M. Da Cunha, and R.A. Azevedo, Ultrastructural changes of radish leaf exposed to cadmium. Environmental and Experimental Botany, 2006. 58(1): p. 47-52.
93. Wasastjerna, J.A., On the radii of ions. 1923: Soc. Scientiarum Fennica.
94. Liu, S. and J. Xiao, Migration mechanism of microcystin-LR synergism with Cu2+ from algal cell to water environment using modified nano system. Materials Science and Engineering: B, 2022. 284: p. 115920.
95. Zhang, Z., G. Chen, and Y. Tang, Towards selenium recovery: Biocathode induced selenate reduction to extracellular elemental selenium nanoparticles. Chemical Engineering Journal, 2018. 351: p. 1095-1103.
96. Prajitha, N., S.S. Athira, and P.V. Mohanan, Bio-interactions and risks of engineered nanoparticles. Environmental Research, 2019. 172: p. 98-108.
97. Arvidsson, R., S.F. Hansen, and A. Baun, Influence of natural organic matter on the aquatic ecotoxicity of engineered nanoparticles: Recommendations for environmental risk assessment. NanoImpact, 2020. 20: p. 100263.
98. Abdolahpur Monikh, F., et al., The stochastic association of nanoparticles with algae at the cellular level: Effects of NOM, particle size and particle shape. Ecotoxicology and Environmental Safety, 2021. 218: p. 112280.
99. Greenwell, H.C., et al., Placing microalgae on the biofuels priority list: a review of the technological challenges. Journal of The Royal Society Interface, 2010. 7(46): p. 703-726.
100. Ma, F. and M.A. Hanna, Biodiesel production: a review1Journal Series #12109, Agricultural Research Division, Institute of Agriculture and Natural Resources, University of Nebraska–Lincoln.1. Bioresource Technology, 1999. 70(1): p. 1-15.