Central nervous system concentrations of nano- and microplastics and risk of amyotrophic lateral sclerosis

Growing evidence suggests that microplastics, particularly nanoplastics, may be neurotoxic. However, there are few studies of neurologic diseases, especially amyotrophic lateral sclerosis (ALS). In a hospital-based case-control study, we measured in vivo concentrations of nano- and microplastics (size 0.1–10 µm) in serum and CSF among 24 newly diagnosed cases of ALS and 20 controls. Adjusting for sex and age, we found a strong positive association between serum and CSF microplastic concentrations and higher microplastic concentrations in the CSF and serum of ALS cases compared with controls. In spline regression analyses, CSF microplastic concentrations showed a positive monotonic association with odds of ALS. Serum microplastic concentrations also showed a positive association with ALS, but only above a certain threshold. Among ALS cases, serum—but not CSF—microplastic concentrations were positively associated with neurofilament light chain, a biomarker of neuroaxonal damage. Given the case-control design, we cannot rule out reverse causation (i.e. that ALS-related factors caused greater bioaccumulation of microplastics) or the possibility that the association reflects changes in lifestyle or other chemical exposures. However, the observed pattern raises the possibility of an aetiologic role of nano- and microplastics in motor neuron degeneration and indicates higher CNS concentrations of these chemicals in ALS cases.