Lead bioavailability and effects to periphyton

Toxic metals such as lead and cadmium may be present in natural waters at elevated concentrations above the natural background, due to inputs from wastewater, industrial and mining effluents. Lead has been distributed in the environment for many years because of its use as gasoline additive and is considered as a global pollutant which is detected even in remote areas. Accumulation of lead in aquatic organisms and effects of elevated Pb concentrations on those are yet poorly understood. Interactions of lead with algae and with periphyton, the natural algae community growing on solid substrates, should be examined under the complex conditions of natural waters.

The aims of the present project are to examine bioavailability and effects of lead to algae and periphyton under natural freshwater conditions, in particular to better understand how its distribution in periphyton and its intracellular speciation in algae influence effects on algae and on the periphyton community. The major questions to be answered are:

• How is lead bound and distributed in periphyton ? What is the role of the embedding extracellular matrix in binding lead ?
• What is the intracellular speciation of lead in algae, as determined by X-ray absorption spectroscopy (XAS) ? What does this speciation imply with respect to toxic effects and detoxification of Pb in algal cells ?
• Which are the toxic effects of lead on periphyton, with respect to photosynthesis, community structure and tolerance