Bioconcentration potential and microbial toxicity of onium cations in photoacid generators.

Despite the widespread utilization of onium salts as photoacid generators (PAGs) in semiconductor photolithography, their environmental, health, and safety (EHS) properties remain poorly understood. The present work reports the bioconcentration potential of five representative onium species (four sulfonium and one iodonium compound) by determining the octanol-water partition coefficient (P) and lipid membrane affinity coefficient (K); microbial toxicity was evaluated using the bioluminescent bacterium Aliivibrio fischeri (Microtox bioassay). Four of the oniums exhibited varying degrees of hydrophobic (lipophilic) partitioning (log P: 0.08-4.12; K: 1.70-5.62). A strong positive linear correlation was observed between log P and K (K = log P + 1.76, R = 0.99). The bioconcentration factors (log BCF) estimated from P and K for the four oniums ranged from 0.13 to 3.67 L kg. Bis-(4-tert-butyl phenyl)-iodonium and triphenylsulfonium had 50% inhibitory concentrations (IC) of 4.8 and 84.6 μM, whereas the IC values of the other three oniums were not determined because these values were higher than their aqueous solubility. Given the increased regulatory scrutiny regarding the use and potential health impacts from onium PAGs, this study fulfills critical knowledge gaps concerning the EHS properties of PAG oniums, enabling more comprehensive evaluation of their environmental impacts and potential risk management strategies.