New insight on occurrence of liquid crystal monomers: A class of emerging e-waste pollutants in municipal landfill leachate

Liquid crystal monomers (LCMs) have been proposed as a class of emerging organic pollutants, which were recently detected in indoor dust and sediment samples collected near electronic devices recycling facilities. However, there is a knowledge gap for analytical method, occurrence, and distribution of LCMs in aqueous sample. Herein, a robust method was developed to determine 38 target LCMs in landfill leachate. A combined ultrasonic enhanced liquid-liquid extraction, saponification and silica/florisil packed column purification method achieved recoveries of 76.9~127.1%, 84.5~114.6% and 81.3~104.6% at spiking levels of 2 ng, 10 ng and 50 ng in leachate, respectively. The developed method was validated through determination of target LCMs in leachate samples collected from municipal landfills in Hong Kong (HK) and Shenzhen (SZ), China. There were 23 and 20 LCMs detected in the HK (ΣLCMs=1120 ng/L) and SZ (ΣLCMs=409 ng/L) sample, respectively, with 6 LCMs newly detected in the environment. This study provided the first evidence suggesting that landfill leachate might be a potential sink of LCMs emitted from e-waste. Future study is urged to investigate the potential migration of LCMs from landfill leachate as a point source, and their occurrence, distribution, fate, and ecotoxicological risk in aquatic environments on regional and global scales.