Laor et al. [59] have tested the odour background from new bags and the impact of sample storage in both TedlarTM and NalophanTM bags, focusing on odours emitted from municipal sewage, aeration basins, sludge, livestock manure and coffee. They have verified that the odour background from new non-flushed TedlarTM and NalophanTM bags (in which fresh air have been stored for 24 h) is as high as 75–317 ou/m3 for TedlarTM or 36–43 ou/m3 for NalophanTM. For pre-flushed bags the background is reduced to 25–32 ou/m3 for TedlarTM or 19–22 ou/m3 for NalophanTM. This suggests that although new modern measurement systems allow us to detect very low odour concentrations, special caution is needed before considering values in the range of several to low tens of ou/m3.