Novel method for determining DDT in vapour and particulate phases within contaminated indoor air in a malaria area of South Africa

The organochlorine insecticide DDT (1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane) is still used for malaria vector control in certain areas of South Africa. The strict Stockholm Convention on Persistent Organic Pollutants (POPs) allows spraying on the inside of traditional dwellings with DDT. In rural villages contaminated dust presents an additional pathway for exposure to DDT. We present a new method for the determination of DDT in indoor air where separate vapour and particulate samples are collected in a single step with a denuder configuration of a multi-channel open tubular silicone rubber (polydimethylsiloxane (PDMS)) trap combined with a micro quartz fibre filter. The multi-channel PDMS trap section of the denuder concentrates vapour phase insecticide whereas particle associated insecticide is transferred downstream where it is collected on a micro-fibre filter followed by a second multi-channel PDMS trap to capture the blow-off from the filter. The multi-channel PDMS trap and filter combination are designed to fit a commercial thermal desorber for direct introduction of samples into a GC–MS. The technique is solvent-free. Analyte extraction and sample clean-up is not required. Two fractions, vapour phase and particulate phase p,p′-DDT, o,p′-DDT; p,p′-DDD, o,p′-DDD; p,p′-DDE and o,p′-DDE in 4 L contaminated indoor air, were each quantitatively analysed by GC–MS using isotopically labelled ring substituted ¹³C₁₂ – p,p′-DDT as an internal standard. Limits of detection were 0.07–0.35 ng m⁻³ for p,p′-DDT, o,p′-DDT, p,p′-DDD, o,p′-DDD, p,p′-DDE and o,p′-DDE. Ratios of airborne p,p′-DDD/p,p′-DDT and of o,p′-DDT/p,p′-DDT are unusual and do not match the ideal certified ingredient composition required of commercial DDT. Results suggest that the DDT products used for indoor residual spraying (IRS) prior to, and during 2007, may have been compromised with regards to insecticidal efficacy, demonstrating the power of this new environmental forensics tool.