To achieve the aim of the project, different work packages were designed: to develop and/or adapt biological methodology for biofilm (WP1), to study the biofilm responses to temperature (TºC) increase (WP2), to assess ENP impact on biofilms under current climate conditions (WP3) and the impact of warming on AgNP properties and toxicity to biofilms (WP4), and finally, to perform molecular analyses to get the broad biofilm microorganisms diversity (WP5).
Throughout a huge mesocosms experiment, the first of its kind at the University of Birmingham, biofilms were exposed to low concentration of ENPs with current and expected TºC (18ºC vs. 25ºC). The experiment involved 40 flumes of 60 L each, 20 set at 18ºC and 20 set at 25ºC, with 4 different pollutant treatments each: (i) control, (ii) silver ENPs (AgNP, pristine ENP), (iii) silver sulphide ENM (Ag2SNP, aged ENP) and (iv) silver nitrate (AgNO3, ionic control Ag+). To assess differences in temporal scales, water and biofilm samples were sampled just before adding the toxicants (0h) and after 1 and 3 days (acute effects), and after 14 and 30 days (chronic effects). Functional and structural analyses were performed according to the protocols stablished in the framework of the project. ENP ageing and characterisation were done in the University laboratories.
Project results highlight the ENP particulate effects compared to those from dissolved ions (AgNP vs. Ag+), despite the ENPs being agglomerated in the systems (e.g. ENP long term effects vs. Ag+ ephemeral effects on algal diversity). AgNPs cause negative effects on biofilm respiration and on all diatoms forms. However, AgNP kept or increased algal biomass and photosynthetic activity. Phosphatase activity (related with phosphate degradation) was affected by Ag2SNP. These results are important since in theory these aged and unreactive ENP “should not cause” any biological effects.
An increase of 6ºC caused an enhancement of algal biomass, photosynthetic activity, and some enzyme activities while others decreased. Microscopic images showed a homogenisation of biofilm community composition. These shifts should be taken seriously by river managers since they can modify the nutrient cycle in the freshwater systems and other ecosystem services, affecting the quality of water for the organisms who are living there but also for human health.
Finally, it is emphasised the need to review freshwater monitoring guidelines. It is extremely important to monitor water physicochemistry jointly with biological analyses to see if a system is polluted and how it is affected. For instance, biofilm is a powerful bioindicator of ecosystem health and can detect the bioaccumulation of metals even when levels are under the detection limit in water.
The plan for the dissemination of results included the publication of 3 research papers in international high impact journals. One will be submitted for publication soon. Results will continue to be disseminated in forthcoming conferences (i.e. SFS 2020), specific workshops (i.e. Biofilm workshop 2020) and public enjoyments activities organised (e.g. University Open days, Pint of Science, UoB Green Heart festival).
