The effects of tread rubber and road dust particles on stress, immunity and digestive biomarkers in the larvae of the mealworm Tenebrio molitor

Airborne road and abrasive car parts particles penetrate into aquatic and soil environments, but also, settling on vegetation along highways, enter trophic chains as a result of consumption by herbivorous invertebrates. The effects of this exposure are poorly recognized. The study aimed to assess the toxicity of two traffic-connected materials: tread rubber (TR) particles and environmentally relevant field-collected road dust (RD), to the Tenebrio molitor larvae under laboratory conditions using a set of protective (heat shock protein - HSP70, metallothionein - Mts levels), immunity (lysozyme - Lys, defensin - Def levels) and digestive (protease, amylase, and celulase activities) biomarkers. ELISA assay was used for protein levels, while fluorimetric and spectrophotometric methods were used for enzymatic activity studies. RD and TR particles were characterized by SEM/EDS techniques. The representative TR particle sizes were within the range of 31 µm and 274 µm. For the RD, the size of the particles were 153-587 µm. Fat body HSP70 levels were, on average, twice lower in groups exposed to RD particles. For fat body Mts, RD and TR caused the decrease while in the gut, the effect depended on the particle type. Gut lysozyme levels increased for both particles while in fat body this effect was made by RD. Digestive enzyme activity did not reflect exposure to TR and RD particles. RD induced changes in more experimental groups than TR. This may be due to the greater complexity of their composition. Further studies focusing on material type, concentration, exposure duration, and particle size are necessary to understand the effects of traffic-connected material on terrestrial herbivores.