## 2 Materials and Methods  
### Samplings and Gravimetric Analysis  
The sampling involved eight full-scale biomass treatment plants placed in Northern Italy (food waste, wastewater sludge, lignocellulosic, and agro-livestock residues) during the warm season in the same year. In particular, we sampled three composting plants processing the organic fraction of municipal solid waste (OFMSW) and other plant-based byproducts, three plants treating agro-livestock matrices, including both swine and bovine slurry and agricultural processing residues, one facility dedicated to the treatment of wastewater sludge, and one facility processing lignocellulosic waste.  
PM\({}_{10}\) sub-fractionated sampling was conducted in different areas of the plants, including areas where waste materials were received, treatment areas, and finally the areas where refinement of the effluents took place (some examples are shown in Figure 1). A high-volume cascade impactor sampler (High Volume Sampler, HVS; Airflow PM\({}_{10}\), Analitica Strumenti, Pesaro, Italy) was used, operating with a suction flow rate of 1.24 m\({}^{3}\)/min, in compliance with UNI EN 12341 standards [16]. The sampler employs a multistage impact mechanism, allowing airborne particles to pass through progressively narrower slits, thereby fractionating them based on their aerodynamic diameter onto sequentially arranged filters. The collected PM\({}_{10}\) was divided into six sub-fractions of equivalent aerodynamic diameter: 10-7.2 \(\upmu\)m, 7.2-3.0 \(\upmu\)m, 3.0-1.5 \(\upmu\)m, 1.5-0.95 \(\upmu\)m, 0.95-0.49 \(\upmu\)m, and <0.49 \(\upmu\)m. Slotted glass fiber filters (A/E type, 8 \(\times\) 10, Gelman Sciences, Bloomfield Twp, MI, USA; labeled as A) were used to collect PM\({}_{0.49\text{-}10}\), while A4-sized filters (203 \(\times\) 254 mm, Pall Corporation, New York, NY, USA; labeled as B) were used for PM\({}_{0.49}\)[17].  
Figure 1: Examples of some sampling areas involved in the work. From the reception of the organic materials through the composting and treatment stages to the last phase of refinement of the treated effluent.  
Each sampling session lasted at least 4 h and was generally conducted twice a day (morning and afternoon), except in specific cases where only one sampling per day was performed due to logistical and organizational constraints. Each filter underwent a pre- and post-sampling conditioning process for 48 h in a desiccator with silica gel to minimize any interference humidity might introduce into weight measurements. All membranes underwent a gravimetric analysis of particulate matter by pre- and post-sampling weighing with a five-decimal analytical balance (\(\pm\)0.00001 g), including a blank filter as a control to assess potential weight changes not attributable to sampling. The PM concentration on each filter was calculated considering the particulate mass and the volume of air passing through the filter. The PM concentration was expressed as \(\upmu\)g per m\({}^{3}\) of sampled air.  
The sampled filters were used to perform water-based and organic-based extractions, respectively, assess endotoxin levels and expose human embryonic lung fibroblasts (HELF) in order to evaluate the in vitro modulation of gene expression involved in DNA repair (XRCC1, ERCC1, XPA, XPF) [18] and IL-8 production [19].