Should moss samples used as biomonitors of atmospheric contamination be washed

When terrestrial mosses are used to monitor atmospheric contamination, the samples are usually analysed without first being washed, so that the contaminants deposited on the moss can be quantified. However, when the aim is to evaluate phyto-toxic effects and the risks associated with increased concentrations of contaminants, it is the bioconcentrated fraction that is of interest. In such cases, the samples are washed to remove deposited material adhering to the surface of the moss. In the present study, the efficacy of the washing step was evaluated, by electron microscopy and microanalysis, in samples exposed to different levels of contamination. The results obtained show that washing is not effective at removing particles deposited on the moss surface, so that an alternative cleaning method is required. Until such a method becomes available, use of the Sequential Elution Technique is recommended for precise determination of the bioconcentrated contaminants.