Lichens and particulate matter: Inter-relations and biomonitoring with lichens

In the last three decades, considerable attention was paid to the inter-relations of lichens and particulate matter. This chapter highlights the determinant factors of the entrapment of airborne particles by the lichen, e.g., the growth form of the thallus. The soil which provides the greater part of the particles adhered-to and/or entrappedin the thallus should be considered and characterized in biomonitoring studies which traditionally focus on airborne elements derived from anthropogenic activity, with an emphasis on heavy metals and radionuclides. Both visual data and analyses of coefficients of variation (CVs) contribute to knowledge of the nature of particulate matter entrapped by lichens. To date, a considerable number of laboratories studying the elemental content of lichens avoid the pre-treatment of thallial samples. A rough estimation based on a reviewof the relevant literature revealed that about 75 % of the laboratories used only dry cleaning and do not wash thalli prior to elemental determination. Other laboratories include in their protocol washing, sometimes several consecutive washings, combined with an ultrasonic treatment and/or shaking. This treatment has the potential to remove deposited material of natural and anthropogenic origin and induces the loss of elements. Lichenologists/bryologists need to face the dilemma of pre-treatment. In this context, scientists should determine whether the constituents of lichen are just and only algal and/or cyanobacterial cells and fungal hyphae, and particulates are “aliens.” The location of biomonitoring studies is of crucial importance: The increasing number of annual desert-dust storms especially in the Mediterranean basin and in southern Europe is the result of climate change. The temporal and spatial dimensions of bulk deposition are discussed, with relevance to change observed in biomonitoring studies.