Disappearance kinetics of 56 toxic semi-volatile organic compounds under common storage conditions

Synthetic semi-volatile organic compounds (SVOCs) are widely distributed in the environment due to their ever expanding uses. But because some are hazardous, their presence in matrices such as indoor air, wastewater, fish tissue and marine sediment samples (where they could adversely impact public health and the environment) is carefully monitored. To do so, samples are collected, stabilized for transport to laboratories (which are often off-site) and purified for analysis. In-between purification and analysis, the stability of SVOCs in storage is largely assumed. In this study, we test this assumption by assessing the collective stability of 56 SVOCs (amines, halo ethers, nitrobenzenes, phenols, phthalate esters, polycyclic aromatic hydrocarbons and chlorinated compounds) in mixtures stored at -20 °C, 4 °C or 22 °C over a 53 day period. Results show that (i) SVOCs are stable in darkened Amber vials, (ii) that constant temperature is more important than fluctuating temperature in maintaining the integrity of samples in storage, and (iii) that the collective disappearance of SVOCs in colorless 1 mL vials follow first-order kinetics with half-lives (in days) of 28 ± 8, 26 ± 3 and 31 ± 7 at -20 °C, 4 °C or 22 °C, respectively. PAHs (and phthalate esters) were mostly stable with dibenz[a,h]anthracene, indeno[1,2,3-cd]pyrene and 1,12-benzoperylene showing the longest half-lives (57 ± 2 days at -20 °C and 65 ± 6 days at 4 °C, respectively). The degree of substitution on phenols by deactivating groups appears to introduce stability differences. While mono-substituted phenols (chloro and nitro) were sensitive to temperature changes, di- and tri-substituted phenols (dinitro, dichloro and trichloro) were not. Overall, light was found to be the most important factor in the disappearance of SVOCs in colorless vials.