CONTAMINATION OF ENVIRONMENTAL-SAMPLES PREPARED FOR PCB ANALYSIS

Archived air-dried soil that had been collected, stored, and sealed in 1914, before the commercial manufacture of PCBs, together with wet freshly sampled ancient peat, which contained little or no PCBs, were exposed to contemporary air in a laboratory. Measurable increases in the concentration of PCBs, particularly the low molecular weight congeners,were detectable after exposure for as little as a few hours. Concentrations after a few days exposure to laboratory air were similar to those measured in contemporary field surface soils (similar to 20-30 mu g of Sigma PCB kg(-1)). Laboratory air concentrations ranged between 4.7 and 8.2 ng of Sigma PCB m(-3) during the period of exposure, markedly higher than routinely detected in outdoor U.K. urban air. The calculated average net dry deposition flux from air-soil in the laboratory over 25 days was 5 mu g of Sigma PCB m(-2) day(-1). Indoor air concentrations might be expected to be, higher than those routinely measured outside, exacerbating the potential problems of sample contamination. Extreme caution is needed in the preparation and handling of samples which contain inherently low concentrations of PCBs and before ascribing the presence of these compounds in certain samples to 'natural production' mechanisms.