Determination of chlorinated pesticides and PCB in pine needles - Improved method for the monitoring of airborne organochlorine pollutants

A method to determine organochlorine pollutants in pine needles is described. Fresh, whole needles have been extracted for 48 h in dichloromethane to obtain the epicuticular wax fraction. The remainder has been cut into small pieces and again extracted with dichloromethane to obtain the internal lipids. Prior to gas chromatography, both the wax and the internal lipid extracts have been fractionated on two columns: first a silica gel/silica gel:sulphuric acid 2:1 column with dichloromethane as eluent and then a nitrophenyl silica column with hexane as eluent. Three fractions have been collected, fraction 1 containing hexachlorobenzene (HCB), fraction 2 containing polychlorinated biphenyls (PCB) and 1,1-dichloro-2,2-bis(4-chlorophenyl)ethene (DDE), and fraction 3 containing the remaining, more polar, organochlorine pesticides. For some pine species, the nitrophenyl silica column has been combined with a short aminopropyl silica column to obtain chromatograms of the PCB fraction free from negative peaks. The precision is in the range of 4-12% relative standard deviation, and the overall recovery is around 65-90%.