This dataset is the result of an experimental series that was carried out in September/October 2022 at GFZ German Research Centre for Geosciences, Potsdam, Germany to observe biosorption of lead under extreme conditions. Synthetic solutions, simulating the geothermal fluids from the Heemskerk geothermal power plant were were prepared in 30 ml glass vials (Rotalibo screw neck ND24 EPA). To prepare the stock solutions, sodium chloride (NaCl, 99.8 %, Cellpure, Merck, DE) was added at 265 g/L and Pb(II), in form of lead nitrate (Pb(NO3 )2 , Merck, DE), at 1 g/L to ultrapure water. To assess the impact of acetic acid on lead biosorption, two treatments were done: one without acetic acid and one where acetic acid (100 %, Merck, DE) was added at 60 mg/L. Finally, dead biomass of the fungus Penicillium citrinum was added in the samples at a concentration of 4 g/L (Wahab et al., 2017). The samples were incubated in an autoclave at a pressure of 8 bars on a rotative shaker. The temperature was set at 25 °C, 60 °C or 98 °C with three contact times (1, 2 and 3 h). All treatments were performed in triplicates. For each treatment, two controls without biomass were done. Control samples without the addition of NaCl were done in duplicate, at 25 °C and for 2 h. After incubation, samples were filtered through a 0.22 µm nitrocellulose filter (Sartorius Stedim Biotech, FR) to separate the biomass from the liquid. The biomass on the filters was dried for 24 h at 45 °C before being scraped from the filter and kept in a Falcon tube at room temperature.