Element determination in natural biofilms of mine drainage water by total reflection X-ray fluorescence spectrometry

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Abstract

Human impacts like mining activities lead to higher element concentration in surface waters. For different pollution levels, the consequences for aquatic organisms are not yet investigated in detail. Therefore, the aim of this investigation is to determine the influence of mining affected surface waters on biofilms.

Elements like heavy metals can be absorbed on cell walls and on polymeric substances or enter the cytoplasm of the cells. Thus, they are important for the optimization of industrial biotechnological processes and the environmental biotechnology. Beyond this, biofilms can also play an important role in wastewater treatment processes and serve as bioindicators in the aquatic environment.

The presented total reflection X-ray fluorescence spectroscopic investigation was performed to compare the element accumulation behavior of biofilms grown on natural or on artificial materials of drainage water affected by former copper mining activities. A high salt and heavy metal pollution is characteristic for the drainage water. For an assessment of these results, samples from stream Schlenze upstream the confluence with the drainage water, a small tributary of the Saale River in central Germany, were analyzed, too.

Introduction

Element analysis of different freshwater biota (e.g. biofilm, zooplankton) is an important task in today's environmental sciences. Such investigations help to understand the element uptake mechanisms into the trophic chain [1]. In general, at lowest trophic aquatic level, biofilms are complex, heterogeneous, thin and slimy layers formed by bacteria, fungi or algae, which are attached to a boundary surface. The organisms are embedded in a matrix of extracellular polymeric substances (EPS) (Fig. 1). Because of the adhesion of microorganisms on the EPS, stable synergistic communities (microconsortia) can build up [2]. Since biofilms can settle on nearly all boundary surfaces in the water, they are actively involved in the sorption and desorption processes of elements. As shown in Table 1, biofilms can have positive as well as negative effects in environment, medicine and industry [3], [4], [5].

Biofilms can adsorb elements like heavy metals [6]. For that reason, they can be used as bioindicators in the environmental sciences. The metal ions can be bound to the bacterial extracellular polymeric substances (EPS) or by the cytoplasm, as well as to the cell walls [3], [4], [7].

This study presents element concentrations of biofilms, which grew in a nutrient-limited, high saline (Table 2) and heavy metal contaminated water, the adit named Schlüsselstollen (engl. Key adit), which is influenced by drainage water from former mining activities. For comparison, biofilms from the stream Schlenze downstream the confluence with the adit with a lower contamination levels were analyzed.

At the same time, the macrostructure of the biofilm was investigated.

Elemental analysis of biofilms using conventional atomic spectrometric methods such as atomic absorption spectrometry (AAS) or inductively coupled plasma atomic emission/mass spectrometry (ICP-AES/MS) [8], [9] needs large amounts of biological materials in the milligram range (mg range). Therefore, the accumulation of heavy metals in the biofilm matrix was determined with the total reflection X-ray fluorescence spectrometry (TXRF) [10], [11], [12], which offers the advantage to analyze even a small amount of a sample material in the microgram range [13].

Section snippets

Sampling sites

Samplings of water and biofilms were carried out in the adit Schlüsselstollen (total length 31.6 km) and the stream Schlenze. The adit is a dewatering system that drains a former mining district (Mansfelder Land, copper shale mining). It enters the stream Schlenze and significantly influences its water quality [14], [15], [16]. The Schlenze flows into the Saale River. Besides the Rivers Schwarze Elster, Mulde and Havel, the Saale is one of the main tributaries of the Elbe River (Fig. 2).

Surface water samples

All

Biofilm structure

The biofilms of the adit were very different in relation to other surface water biofilms due to their remarkable structure. As visible in Fig. 7a, the rust-colored biofilms exhibit a sponge-like structure. Further on, it is interesting that the biofilms show gas inclusions, which are similar to vacuoles embedded in EPS. Normally, biofilms forming in rivers have flat structures, which are adapted in consistency and surface to the flow of the river (Fig. 7b). The reason for the different

Conclusions

The TXRF is suitable to determine the element content in biofilms grown in adit and drainage waters.

The artificial supports, described in the article, can be used to characterize the element accumulation of biofilms in adits or drainage waters. No significant differences were observed between the element accumulations of biofilms grown on natural or artificial supports.

First results of element investigation on biofilms from the adit Schlüsselstollen have shown high accumulation rates on lead,

Acknowledgements

We thank Mrs. Andrea Hoff who has worked with us during the sampling campaigns and has done the water analysis, and Mr. Karsten Rahn for taking the underwater photos.

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This paper was presented at the 11th International Conference on Total Reflection X-ray Fluorescence Spectrometry and Related Methods (TXRF-2005), held in Budapest, Hungary, 18­22 September 2005, and is published in the special issue of Spectrochimica Acta Part B, dedicated to that conference.

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