Chemical Preservation of Semi-volatile Polycyclic Aromatic Hydrocarbon Compounds at Ambient Temperature: A Sediment...

Site investigations require the collection and analysis of representative environmental samples to delineate impacts, risks, and remediation options. When environmental samples are collected, concentrations of semi-volatile polycyclic aromatic hydrocarbons (PAHs) begin to change due to several processes, such as evaporation, adsorption, precipitation, photo, and microbial degradation. Preservation techniques are used to minimize these changes between collection and analysis. The most common techniques are refrigeration, freezing, and acidification. In the mid 1970 s, regulatory agencies developed a holding time limit of 14 days for PAHs in soil/sediment samples stored at < 6 °C. The technical basis for this limit is not well defined yet failing to meet this limit may force resampling. This study examined the effectiveness of preservatives at maintaining PAH concentrations in sediment samples to 60 days. Sediment samples were collected at three sites that were impacted with petrogenic and pyrogenic PAHs. Chemically preserved (sodium azide, NaN₃) and unpreserved samples were analyzed at defined time intervals from 0 to 60 days. Statistical analysis indicated acceptable preservation of PAHs in the sediment samples preserved with sodium azide for 60 days when maintained at either ambient laboratory temperature or 4 ± 2 °C, and for up to 21 days with no preservative when maintained at 4 ± 2 °C.