Metal adsorption on mosses: Toward a universal adsorption model

Area of Science:

• Environmental Science
• Biogeochemistry
• Materials Science

Background:

• Mosses are increasingly utilized in biomonitoring for heavy metal pollution.
• Understanding the adsorption mechanisms of heavy metals on moss species is crucial for effective environmental monitoring.
• Four common moss species, Hypnum sp., Sphagnum sp., Pseudoscleropodium purum, and Brachytecium rutabulum, are widely used in moss bag techniques.

Purpose of the Study:

• To quantify the adsorption of five heavy metals (Cu2+, Cd2+, Ni2+, Pb2+, Zn2+) on four typical moss species.
• To investigate the influence of pH and metal concentration on heavy metal adsorption by mosses.
• To determine the adsorption constants and the number of surface binding sites using a Linear Programming Model (LPM).

Main Methods:

• Batch reactor experiments were conducted across a wide pH range (1.3-11.0) and metal concentrations (1.6μM-3.8mM).
• Surface acid-base titration was performed to assess proton-binding sites.
• A Linear Programming Model (LPM) was applied to experimental data to derive equilibrium constants and binding site densities.
• pH-edge experiments and constant pH Langmuirian isotherms were used to analyze adsorption behavior.

Main Results:

• Sphagnum sp. exhibited the highest number of proton-binding sites (0.65 mmol g-1), indicating high adsorption potential.
• Brachytecium rutabulum showed the highest percentage of metal adsorption for most studied metals.
• Sphagnum sp. was identified as the strongest adsorbent based on Langmuirian isotherms, with differences within 20% among species.
• The LPM accurately modeled the experimental data across the studied parameters.
• Similar adsorption patterns were observed for all five metals across different moss species and conditions.

Conclusions:

• Mosses are highly efficient natural adsorbents for heavy metals.
• A universal adsorption edge and constant pH adsorption isotherm can be recommended for the four studied moss species.
• The findings support the use of these moss species for effective environmental monitoring of heavy metal contamination.