Fungal laccases: an effective new treatment against micropollutants in municipal wastewaters

Pollution of surface waters is increasingly becoming a topic of major discussion, especially considering that it is not only caused by individual and sporadic sources of contamination but also from unexpected ones. Besides classical and well-known pollutants, new contaminants have been discovered including several pharmaceuticals, pesticides, herbicides, personal care products (PCPs), plasticizers, flame retardant, etc. Many of them pose a serious environmental awareness, due to their capability to mimic hormones, altering the endocrine system: they are so-called Endocrine Disrupting Chemicals (EDCs). Few efforts have been already performed, to limit or restrict the use of these harmful compounds, but commonly in use processes are only partially effective, causing their progressive and constant accumulation into the environment and allowing them to get in contact with aquatic organisms and human beings. The present study focused on the municipal water treatment plant (MWTP) of the Torino district (Italy) where, at the end of the process, many of these molecules were still widely present, at high concentrations (ng/l or even μg/l), including the well-known bisphenol A, ketoprofen, 4-n-nonylphenol, alachlor. Facing this problematic a fungal laccase-mediated system was used for the treatment of model and real solutions containing several EDCs. A multishot stir bar sorptive extraction with targeted in-situ derivatisation and a gaschromatography-mass spectrometric were used, enabling the detection and the quantification of target analytes at ppt level (ng/l). Laccases of Trametes pubescens MUT 2400 were able to degrade many EDCs, belonging to different chemical classes. Preliminary experiments were set up in model solutions to evaluate the most proper laccase concentration, able to carry out extensive and fast degradation reactions. The treatment of the complex real municipal water sample was set with 100 U/l of fungal laccases. Most of the detected compounds were widely degraded (35-93%) within 24 h. The ecotoxicological analyses and the oestrogenic activity tests clearly showed that the decrease of micropollutants corresponds to a strong reduction of the toxicity and estrogenic activity of the wastewater reducing its environmental impact. Further studies are in progress to optimize the operative parameters of the treatment (i.e. working pH, laccase concentration, enzyme immobilization), in order to enhance the stability and the efficiency of the laccase-mediated system.