Reaction Pathways and Kinetics of a Cyanobacterial Neurotoxin β-N-Methylamino-L-Alanine (BMAA) during Chlorination

β-N-Methylamino-L-alanine (BMAA), a probable cause of the amyotrophic lateral sclerosis/parkinsonism-dementia complex (ALS/PDC), or Alzheimer's disease, has been identified in more than 20 cyanobacterial genera. However, its removal and fate in drinking water has never been reported before. In this study, the reaction of BMAA with chlorine, a common drinking-water oxidant/disinfectant, was investigated. A liquid chromatograph coupled with a triple quadrupole mass spectrometer was employed to quantify BMAA and its intermediates. Upon chlorination, four chlorinated intermediates, each with one or two chlorines, were identified. The disappearance of BMAA caused by chlorine follows a second-order reaction, with the rate constant k₁ is 5.0 × 10⁴ M^-1 s^-1 at pH ∼7.0. The chlorinated intermediates were found to further react with free chlorine, exhibiting a second-order rate constant k₃ = 16.8 M^-1 s^-1. After all free chlorine was consumed, the chlorinated intermediates autodecomposed slowly with a first order rate constant k₂ = 0.003 min^-1 when a reductant was added, these chlorinated intermediates were then reduced back to BMAA. The results as described shed a useful light on the reactivity, appearance, and removal of BMAA in the chlorination process of a drinking-water system.