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Content archived on 2024-05-29

Method development for determination of low Z elements in biofilms

Final Activity Report Summary - BIOFILM TXRF (Method development for determination of low Z elements in biofilms)

The analytical method to determine the low Z elements (Z=6 to 20, carbon to calcium) using low energy excitation total reflection X-ray fluorescence spectrometry was developed. The spectrometer consists of a Cr-anode X-ray tube, multilayer monochromator, vacuum chamber, movable sample support, and an ultrathin window Si(Li) detector. For the internal standardisation a double standard method was developed. The linearity range was investigated for all analytes. In the field, in the framework of two campaigns, the chemical characterisation of the colonisation process was performed using the above mentioned analytical method. This was made in the Velence Lake, Hungary. The bio-monitoring using biofilms was performed at Tiszaorveny / Tisza-Lake, Hungary, carrying out the monthly sampling of biofilms from different artificial growth supports. In these samples, the low Z elements, as well as the most abundant non-low Z trace metals were analysed, as a continuation of the previous work.

The first result was the development and of a low energy TXRF method for determination of low Z elements (carbon to calcium, Z=6 to 20). The reference material NIST1643c (trace elements in water) was used to check the linearity between analyte amount and analytical signal intensity. It has been established, that this linearity can be guaranteed for the elements C to F (Z=6 to 9) up to an absolute amount of 600 ng, above Na (Z=11) this limit lied at around 1000 ng. In this step, the obligate internal standard element was Ti.

Using direct growth of biofilms on the TXRF carrier plates for bio-monitoring, about six days cultivation time is recommended. As biofilms contain a considerable but variable amount of Ti, a two-stage internal standardisation has been used. Ag-L(alfa) was the primary internal standard, lying at 2.9 keV. This was used for determination of Ti, which was subsequently the internal standard for the low Z elements. This method makes it possible to map the whole plate, using a single Ag-spot.

Biofilms grown on different artificial sample holders (plexiglass and granithe) were used for the regular (monthly) bio-monitoring at Tiszaorveny, Tisza-Lake. The water phase at the sampling site was also regularly analysed chemically. The results show, that the water has a relatively low dissolved salt content, but a significant and strongly changing suspended matter. In the dissolved fraction, the most important trace elements were Cu, Zn, As, and Sr. In the suspended phase, considerable amounts of Mn, Fe, Ni, Cd, and Pb were found. From these trace elements, mostly the particulate bound ones were present in the biofilm samples, which indicates a high amount of embedded particles into the extracellular polymer matrix.

This statement was also proven by microscopic investigations. The trace element concentration data compared to those from the previous investigations (project MCIF-2002-01740) showed that, the concentration of Cu, Zn and Pb has increased by 61 %, 184 %, and 217 %, respectively, since 2000. This shows a considerable downstream transport of these polluting elements. The concentration of low Z elements did not show any considerable seasonal change from May to August. On the other hand, the last samples (mid-August to end of September) were completely different, containing about five times more Ca and P. The concentration of C was also increased, but the increase amounted to about 40 %. The concentration of the other elements remained almost constant. The support material did not affect strongly the low Z element contents.
As conclusion, the new equipment made possible to monitor the essential bio-elements C and P in biofilms.