Optimized extraction of environmentally persistent free radicals from clays contaminated by polycyclic aromatic hydrocarbons

Environmentally persistent free radicals (EPFR) are emerging contaminants of health concern. Their levels in the environment are not well known because few studies have optimized EPFR extraction. Therefore, here we studied the extraction and decay of EPFR that are formed on the surfaces of Cu(II)-montmorillonite clay contaminated by polycyclic aromatic hydrocarbons (PAH) including benzo[a]pyrene and anthracene. EPFR were analyzed by electron paramagnetic resonance. Results show that acetone or dichloromethane/acetone effectively extract benzo[a]pyrene-EPFR. By contrast, CCl4, acetonitrile or methanol do not extract benzo[a]pyrene-EPFR, but extract residual benzo[a]pyrene at 62.2% for CCl4, 77.8% for acetonitrile and 59.1% for methanol. EPFR concentration decreases with ultrasonic intensity and time, from 60 s at 16 kHz to 1200 s at 40 kHz. The decay of PAH–EPFR in acetone displays two steps, a fast decay from 0 to about 5 h, then a slower decay from 5 to 50 h. The 1/e lifetime during the slow decay period was about 168 h for benzo[a]pyrene-EPFR and 180 h for anthracene-EPFR.