Biosurface properties and lead adsorption in a clone of Sphagnum palustre (Mosses): Towards a unified protocol of biomonitoring of airborne heavy metal pollution

Abstract

Although mosses are widely used for active biomonitoring of air pollution, a unified protocol for their treatment before exposure in bags is still lacking. Here we used field- and laboratory-grown Sphagnum palustre L. moss, respectively, treated by EDTA and devitalized by oven drying at 100 °C, to elaborate a consistent procedure of metal and proton adsorption on moss surfaces. Acid-base titrations and Pb²⁺ adsorption experiments at different pH values and Pb²⁺ concentrations in solution were performed with both field-collected and laboratory cloned mosses. Devitalization and EDTA treatments did not produce any measurable difference in terms of H⁺ and Pb²⁺ adsorption capacities of moss surfaces. The stability constants for Pb²⁺ adsorption onto moss surfaces as a function of pH (pH-dependent adsorption edge) and at constant pH (5.5 and 6.5) as a function of Pb²⁺ concentration ("langmuirian" adsorption isotherm) were rather similar between different treatments. A Linear Program Modeling (LPM) of adsorption reactions revealed high similarity of adsorption constants regardless of treatments for both field-grown and cloned mosses. Therefore, in view of the use of S. palustre clone for biomonitoring lead in the environment, we recommend devitalization at 100 °C as unique treatment to perform with the aim to preserve the biomonitor before and after its exposure in bags.

Keywords: Biosorption; Heavy metals; Kinetics; Langmuir isotherm; Moss-bags; Peat moss.