Bioaccumulation of Zinc in Bermuda Grass Cynodon dactylon

Bioaccumulation of Zinc in Bermuda Grass (Cynodon dactylon) Drew Fisher, H. Marie Surratt, Louise Gebauer, and Andrew Palaski Natural Science Division, Pepperdine University 24255 Pacific Coast Highway, Malibu, California 90263 Abstract Materials & Methods Discussion Phytoremediation is the plant based process to remove toxins such as heavy metals from the soil. In this experiment, we hypothesized Bermuda grass (Cyndon dactylon) will absorb a detectable level of zinc, a nontoxic metal, from the soil. We grew two separate groups of grass: the control and the experimental, which was watered with zinc acetate. Neither of the groups produced enough yield within the weeks given to the experiment, but if it went according to plan, we would have used flame atomic absorption spectroscopy to evaluate the relative concentrations of zinc. Significant uptake of zinc could reveal a possible use of bermuda grass to phytoextract other toxic heavy metals from the soil and reduce anthropogenic impact on the earth. The methods of our experiment would be following the methods of Bidar and colleague’s article to find the heavy metal concentration in both the plant and the soil if we had more time to finish. For each sampling, plants (shoots and roots) would be collected from each group of grown grass. After harvesting shoots using a pair of scissors, roots and soils were sampled between 0 and 15 cm deep. In the laboratory, half of each grass sample would be washed three times with deionized water; the second part remained unwashed. Roots were gently separated from soils, then abundantly washed with tap water to eliminate soil particles, and rinsed three times with deionized water. Root and washed shoot samples would be divided into two parts. The first would be immediately stocked at − 80°C until further biochemical analysis, and the second would be dried at 105°C, crushed with liquid nitrogen using a mortar, and 315 -μm-sieved for metal concentration determination. Metal concentrations were also determined on unwashed shoot samples which were prepared as washed shoots. Root-surrounding soil samples were air-dried, crushed, and 2 -mm-sieved for agronomic parameter measurements. Then, a small part of soil was crushed again and passed through a 315 -μm sieve for soil dissolution (Bidar, 2009). For each sampling group, a homogenous composite soil sample would be constituted from the two groups. For the total metal concentrations, acid digestions would be performed on three replicates for each soil plot sample. The soil would be basic potting soil so there would be no need to test soil texture. Soil p. H were measured in deionized water with a soil/water ratio of 1: 2 (NF ISO 10390 method). Total carbonates would be determined by measuring the CO 2 release after HCl treatment (NF ISO 10693 method). Organic carbon concentrations would be determined by measuring the volume of CO 2 formed after samples would be burned at 1, 000°C in the presence of O 2 (NF ISO 10694 method). Total nitrogen concentrations would be determined using NF ISO 13878 method, which consists in burning samples at 1, 000°C in the presence of O 2 and thereafter measuring reduced nitrogen amounts. The cation exchange capacity (CEC) would be analyzed after exchange with a 1 -M ammonium acetate solution (NF X 31 -130 method). Available phosphorus concentrations would be determined by the method of Joret. Hébert (NF X 31 -161), which consists in extracting phosphorus with a 0. 1 -M ammonium oxalate solution. Magnesium, potassium, and sodium would be extracted in a 1 -M ammonium acetate solution according to NF X 31 -108 method. Magnesium concentrations would be measured using atomic absorption flame; potassium and sodium concentrations would be measured using emission absorption flame. Concentrations of the Zn in roots and shoots would be measured after microwave digestion. Five milliliters of HNO 3 (70%) would be added to 250 mg of dry roots or shoots (Mc. Grath, 1996). After their 0. 45 -μm-filtration, digestion products were adjusted to a volume of 25 ml with ultra pure water. As for the soil samples, acid digestions would be performed on three replicates for each plant sample. Metal concentrations were determined by using atomic absorption spectrometry (Bidar, 2009). Within the experiment being performed, positive results of zinc uptake will allow us to further explore bioremediation through perennial grasses. Although the experiment is not yet completed, results from previous experiments can be examined. According to the results published by Bidnar et al. (2009), bioaccumulation of zinc is present in much higher concentrations in the roots than in the shoots (see Figure 1). This indicates bioaccumulation of zinc in the soil into the roots. As we can see from the projected results in Figure 2, the zinc concentration was higher in zinc treated plants versus the control group. Therefore, since bermuda grass is also a perennial grass, we predict there would be a similar result of successful zinc accu This relates to the experiment being performed because zinc uptake in the soil could point to the ability of bermuda grass to phytoremediate heavy metals introduced from industrial processes such as mining. Anthropogenic metal contamination is a prevalent issue which impacts the earth. Not only is industry affecting the planet through greenhouse gases, they are also contaminating the land that surrounds these processes. Introduction With the development of mining and other industrial processes, ground contamination with heavy metals has become a major concern. Plants are a focus of this concern, since they are at the base of the food chain and extract toxic heavy metals through a process known as phytoextraction (Deram et al. 2005). Heavy metals can be introduced through both air transport and transport through streams from mining sites (Hong et al. 2016). These heavy metals can be found in concentrations much higher than what is known to be safe for biological organisms (Ernst 1990). Phytoextraction is one of the most important ways that these metals can be removed from the soil. In this study, the ability of bermuda grass (Cynodon dactylon) to phytoextract zinc (Zn) is explored. Within southern California, bermuda grass is a fast growing, perennial plant species that is very abundant. According to Wolf et al. in 2015, Bermuda grass can be grown and harvested within nine weeks. This makes bermuda grass a possible tool for phytoremediation because it can (1) be grown quickly and (2) be extracted from the soil. If bermuda grass shows bioaccumulation of Zn, it is possible it could be used to extract other toxic, heavy metals from the soil. Zinc is a non-toxic heavy metal that is used in small concentrations in plants. Zinc acts as a great model for assessing the bioaccumulation of heaving metals in perennial grasses (Deram et al. 2005). Zinc reacts in much similar pathways to other heavy metals such as lead and cadmium, both of which are toxic to biological organisms. By performing flame atomic absorption spectroscopy (FAAS), relative concentrations of zinc extraction can be compared between a control and a zinc-treated group. By examining these results, important information about the phytoextraction abilities of bermuda grass will be found. Results Conclusion Bioremediation of zinc in bermuda grass provides an indication of how well a plant will accumulate dangerous heavy metals from soils and groundwater. This is important to consider, since mining and other industrial processes have increased heavy metal pollution. By uptaking pollutants, grasses such as bermuda grass are a powerful aid in reducing soil contamination, which in turn can help keep groundwater clean. In terms of climate change, finding ways to remove chemicals in a clean and sustainable way is paramount. This can help make various forms of energy more eco-friendly. The next step in this experiment is to continue growing the bermuda grass, and test the uptake of zinc using flame atomic absorption spectroscopy. Acknowledgments This research was supported by the Seaver College Natural Science Division. We thank Stephen Davis and David Green who provided insight and expertise that greatly aided in the composition of the research. We would also like to thank Talia Cao for her guidance and support. Figure 1: Two sets of perennials that went through zinc bioaccumulation tests for three seasons (S 1, S 2, S 3) under conditions of excess heavy metals. The first graph is of the species Trifolium repens and the second graph is of the Lolium perenne. Results, which corresponded to the Bioaccumulation factor (BF) calculated as follows: metal concentrations in roots or shoots/metal concentrations in soil, are expressed as the mean value and standard deviation. Comparisons were carried between values in spring 2005 (S 2) and autumn 2005 (S 3) (p < 0. 05, p < 0. 01, p < 0. 001; Mann–Whitney U test) and between values in autumn 2005 (S 3) and autumn 2004 (S 1) (p < 0. 05, p < 0. 01, p < 0. 001; Mann–Whitney U test). Comparisons were also carried out between roots and shoots BF (Bidar, 2009). Study Sites Works Cited Bidar, G. , Pruvot, C. , Garçon, G. , Verdin, A. , Shirali, P. , & Douay, F. (2009). Seasonal and annual variations of metal uptake, bioaccumulation, and toxicity in Trifolium repens and Lolium perenne growing in a heavy metalcontaminated field. Environmental Science and Pollution Research, 16(1), 42 -53. The experiment was performed in the Natural Science Department’s student projects laboratory on Pepperdine University Seaver main campus. The bermuda grass was grown in a growth chamber, set to 25 °C at 100% RH. The growth chamber offered an ideal control for optimal growth of the grass and uptake of zinc. Deram, Annabelle & Denayer, Franck-Olivier & Petit, Daniel & Van Haluwyn, Chantal. (2006). Seasonal variations of cadmium and zinc in Arrhenatherum elatius, a perennial grass species from highly contaminated soils. Environmental pollution (Barking, Essex : 1987). 140. 62 -70. 1016/j. envpol. 2005. 06. 025. Dushenkov, Vyacheslav & B. A. Nanda. Kumar, P & Motto, Harry & Raskin, Ilya. (1995). Rhizofiltration: The Use of Plants to Remove Heavy Metals from Aqueous Streams. Environmental science & technology. 29. 1239 -45. 1021/es 00005 a 015. Ernst WHO (1990) Mine vegetation in Europe. In: Heavy Metal Tolerance in Plants: Evolutionary Aspects (ed. Shaw AJ), pp. 21– 37. CRC Press, Boca Raton, FL. Mc. Grath D (1996) Application of single and sequential extraction procedures to polluted and unpolluted soils. Sci Total Environ 178: 37– 44 Figure 2: This is what we would expect from our tests if the data for our C. dactylon was completed, since the researched article’s perennials growing under excess heavy metals showed significance. We would expect our data to reflect a similar conclusion since perennials usually absorb nutrients in the same root location. Wolf, D. C. , Brye, K. R. , & Gbur, E. E. (2015). Using Soil Amendments to Increase Bermuda Grass Growth in Soil Contaminated with Hydraulic Fracturing Drilling Fluid. Soil & Sediment Contamination, 24(8), 846 -864. Hong, S. , Radnexhad, H. , Abari, M. F. , Sadeghi, M. , & Zaeimdar, M. (2016). Assessment of Contamination of the Industrial Region Soils Caused by Heavy Metals. Oxidation Communications, 39(4 -II), 3313 -3323.