Recoveries of trace pseudoephedrine and methamphetamine residues from impermeable household surfaces: Implications for sampling methods used during remediation of clandestine methamphetamine laboratories

Evaluation of the risk posed by contaminants present during and after decontamination of clandestine methamphetamine laboratories requires a connection between the levels of contaminants measured and those actually present at the scene. The recoveries of pseudoephedrine and methamphetamine from glass, stainless steel, and a range of impermeable surfaces likely to be found in a clandestine laboratory were examined, using GC-MS of derivatized samples as the analytical method. When surfaces had been cleaned prior to drug deposition, wiping with water-dampened filter paper can recover 60–80% of pseudoephedrine immediately after deposition, and at least 50% of the pseudoephedrine still present on a surface after 2 days when deposited at a surface concentration of 2.5 μg/100 cm2. Wiping with methanol-dampened filter paper could recover 60–90% of the methamphetamine immediately after deposition, and could recover at least 50–60% of the methamphetamine still present after 2 days when 0.6 μg/100 cm2 was initially deposited on the surface. Recoveries were lower for surfaces that had not been pre-cleaned. Methamphetamine and pseudoephedrine showed significant volatility in both the free base and hydrochloride forms, with experiments in an enclosed format showing up to half the recovered drug being present on a glass plate held about 4 mm above a substrate contaminated with one of the drugs at the above surface concentrations after 2 days. It is therefore important to remove any visible bulk contaminants and remove obvious pseudoephedrine or methamphetamine-contaminated surfaces prior to heating, ventilation or sealing of a clandestine laboratory to avoid redistribution of material around the site. A revised method for pseudoephedrine analysis was developed that could also detect the pseudoephedrine–formaldehyde adduct that can form from trace pseudoephedrine present at clandestine laboratories.