Biological toxicity of lanthanide elements on algae

生态毒理

2047–2048.

Biological toxicity of lanthanide elements on algae

Peidong Taia, Qing Zhaoa,b, Dan Sua,b, Peijun Lia

,a, and Frank Stagnittic Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110016, China Graduate University of Chinese Academy of Science, Beijing 100039, China b

c Pro Vice-Chancellor Research, University of Ballarat, University Drive, Mt Helen Campus, PO Box 663, Ballarat, Vic. 3353, Australia

Received 15 February 2010;

revised 12 May 2010;

accepted 19 May 2010.

Available online 14 June 2010.

Abstract The biological toxicity of lanthanides on marine monocellular algae was investigated. The specific objective of this research was to establish the relationship between the abundance in the seawater of lanthanides and their biological toxicities on marine monocellular algae. The results showed that all single lanthanides had similar toxic effects on Skeletonema costatum. High concentrations of lanthanides (29.04 ± 0.61 μmol L?1) resulted in 50% reduction in growth of algae compared to the controls (0 μmol L?1) after 96 h (96 h-EC50). The biological toxicity of 13 lanthanides on marine monocellular algae was unrelated with the abundance of different lanthanide elements in nature, and the “Harkins rule” was not appropriate for the lanthanides. A mixed solution that contained equivalent concentrations of each lanthanide element had the same inhibition effect on algae cells as each individual lanthanide element at the same total concentration. This phenomenon is unique compared to the groups of other elements in the periodic table. Hence, we speculate that the monocellular organisms might not be able to sufficiently differentiate between the almost chemically identical lanthanide elements.

Keywords:Biological toxicity; Abundance; Lanthanide elements; Algae

生态毒理

Article Outline

1.

Introduction

2.

Materials and methods

2.1. Chemicals

2.2. Algal incubation

2.3. Toxicity testing

2.4. Data analysis

3.

Results

3.1. Single lanthanides toxicity

3.2. Mixture lanthanides toxicity

3.3. The relationship between the toxicity of lanthanide elements and their abundance

3.4. Toxicities of Sc and Y

4.

Discussion

5.

Conclusions

Acknowledgements

References

1. Introduction

The lanthanide series comprises the 15 elements with atomic numbers 57 through 71, from lanthanum to lutetium. The lanthanides, together with No. 21 scandium and No. 39 yttrium, are also sometimes referred to by the trivial name of “rare-earth elements“. All of the rare earth metals are found in group 3 of the periodic table. The lanthanide series is named after lanthanum ([Spedding and Daane, 1971], [Subbarao and Wallace, 1980] and

[Yoshida et al., 1997]). Members of the series are often called lanthanides, because all of the members of the series very closely resemble the chemical properties of lanthanum. One of its members, promethium, is radioactive. Lanthanides are grouped because of their properties are tremendously similar, the same electronic layers and similar electronic configurations, their properties differing only slightly with atomic number ([Yoshida et al.,

生态毒理

1997] and [Greenwood and Earnshaw, 1997]).

From hydrogen to uranium, there are 85 stable elements in nature. More than 30 elements of which are called the essential elements for life and have a key function in helping living organisms live and healthy. In general, different essential elements have different functions for life and cannot be replaced with each other (Uchida, 2000). Some other elements, the nocuous elements, such as lead and tantalum, still have obviously different functions to life: their biological toxicities and inhibitions are different. Therefore, except for the inert gases, which have no observational functions for life because they do not form chemical compounds, living organisms can identify most elements, no matter how useful or toxic they are. It is well documented that those elements existing in large amounts in nature (lithosphere, crust and ocean) have low or little toxicity to living organisms. Generally speaking, high abundance of elements results in low the biological toxicity (Banin and Navrot, 1975). This is referred to as “Harkins rule” (Banin and Navrot, 1975). However, is the “Harkins rule” suitable for the lanthanides? No reported investigations were found in the scientific literature. Most of the stable chemical elements in nature can be identified in living organisms. However, no reported investigations for lanthanides were found in the available literature.

Algae are ecologically important organisms in the aquatic food chain and are frequently used in environmental studies for assessing the relative toxicity of various chemicals and/or waste discharges. Currently, batch technique is adopted by most standard algal test protocols for regulatory purposes ([Organization for Economic Cooperation, 1984],

[ISO 8692:2004 Wa, 2004], [American Society for Testing, 1994], US Environmental Protection Agency (US EPA)., 1996 and [ISO 14442:2006 W, 1444]). There are many compelling reasons for including algal indicators in environmental monitoring programs. One of the most important functions is that algae contribute substantially to total ecosystem primary production in most aquatic habitats. Because of their short response times, algae often provide one of the first signals of ecosystem impacts, thereby allowing for corrective regulatory and management actions to be taken before other undesirable impacts occur. Hence, algal tests are generally sensitive, rapid and cost effective ([Walsh, 1988] and [Nalewajko and Olaveson, 1998]). For these reasons they have been

生态毒理

frequently used in environmental studies and were applied in a number of different contexts, in screening test materials for the presence of toxicity, or as important parts of toxicity characterizations of test materials ([Walsh, 1988], [Peterson and Nyhol, 1993],

[Halling-Sorensen et al., 1996], [Lin et al., 2005], [Pavli? et al., 2005] and [Melo et al., 2006]).

The aim of this study was to evaluate toxic effects of 13 lanthanide elements on algae and study the relationship between the biological toxicity of lanthanide and their abundance in seawater.

2. Materials and methods

2.1. Chemicals

The following commercially available chemicals (purity >99.9%) were used: lanthanum chloride [LaCl3], cerium nitrate [Ce(NO3)3], neodymium chloride [NdCl3], samarium chloride [SmCl3], europium nitrate [Eu(NO3)3], gadolinium nitrate [Gd(NO3)3], terbium chloride[TbCl3], dysprosium chloride [DyCl3], holmium chloride [HoCl3], erbium nitrate

[Er(NO3)3], thulium chloride [TmCl3], ytterbium chloride [YbCl3], lutetium chloride [LuCl3], scandium chloride [ScCl3], and yttrium nitrate [Y(NO3)3]. All chemicals were bought from Acros Organics and Sterem Chemicals, USA. As a radioelement, Promethium was not included in our chemical list since we were unable to study it from the above chemical companies. Concentrations used in final tests were determined by carrying out a preliminary range-finding test covering several orders of magnitude of difference in test concentrations. Steps were uniform for all tested substances.

2.2. Algal incubation

Marine microalgae Skeletonema costatum was obtained from the key Laboratory of Mariculture, Ocean University of China, Qingdao. Inocula were taken from pre-cultures set up 3 d before the experiment and propagated under the same test conditions as the subsequent test. The initial cell densities were adjusted to approximately 104 cells mL?1 using plate count method. Obtained artificial seawater was enriched with a modification of f/2 medium, without EDTA. It has been demonstrated that EDTA greatly decreases the

生态毒理

toxicity of elements due to the chelating properties of the molecules (Sunda and Guillard, 1976).The modification f/2 media consisted of NaNO3 74.8 mg L?1, NaH2PO4 4.4 mg L?1, Trace metals stock solution 1.00 mL and Vitamin mix stock solution 1.00 mL, and was finally made up with filtered natural seawater, adjust pH to 8.0 with 1 M NaOH or HCl. The f/2 media contained all the essential elements and the trace element which were necessary for the algae growth. The trace metals stock solution was maintained in de-ionized water containing (L?1): 3.9 g FeC6H5O7·5H2O, 23 mg ZnSO4·4H2O, 10 mg CuSO4·5H2O, 178 mg MnCl2·4H2O; 7.3 mg Na2MoO4·2H2O, 12 mg CoCl2·6H2O. The vitamin mix stock solution was formulated by adding 0.5 mg Cyanocobalamin (B12), 0.5 mg Biotin (H), and 100 mg Thiamine (B1) to 1 L de-ionized water (Liang et al., 1998).

2.3. Toxicity testing

The toxicity of elements was assessed by measuring the ability of the elements to inhibit the growth of algae, as described in ISO 8692 (ISO, 2004).

The toxic effect of 13 lanthanide on S. costatum was conducted using 125 mL glass Erlenmeyer flasks that contained 30 mL of culture medium augmented with various concentrations of single lanthanides. Glassware used in the test and the nutrient solution sterilized with steam for 20 min at 105 °C, then sterilized by irradiating with ultraviolet for 20 min in Clean Room. Approximately 104 algal cells per mL from a late log phase culture were added into flasks and incubated for 72 h. Each concentration was triplicate. The vessels were randomly arranged in a photoautotrophic machine (Eyelatron FL1-160) during the toxicity tests. The cultures were incubated at 25 ± 1 °C, using a photoperiod of 14 h light and 10 h dark, lighting was supplied by white fluorescent lamps with a light intensity of 6000 lux (Voltcraft luxmeter FX-101). In order to avoid poor gas exchange conditions, the test flasks were shaken 5 min for each 12 h interval (110 rpm). The algae concentrations were measured at the beginning and at the end of the test by counting the cells with a hemacytometer.

For evaluating the toxic effects of mixed lanthanides on algae, a 13 lanthanides mixed solution that contained an equivalent concentration of each lanthanide element was used for another inhibition experiment. Single element solution, the lanthanum solution,