Physiological Effects of Exposure to Arsenic, Mercury, Antimony and Selenium in the Aquatic Moss Fontinalis antipyretica Hedw.

Abstract

Laboratory experiments were carried out to determine the effects of exposure to different concentrations of As, Hg, Sb and Se on photosynthetic and respiratory rates and on photosynthetic efficiency in the aquatic bryophyte Fontinalis antipyretica Hedw. Specimens of the moss, collected from a clean site, were incubated in solutions of As, Hg, Sb and Se (at concentrations ranging from 0.1 μg l−1 to 10,000 μg l−1) for up to 22 days. The photosynthetic and respiratory rates were then determined by the light/dark bottle technique, and the photosynthetic efficiency was measured by the saturation pulse method. Although different responses were observed in relation to the concentration of the elements, clear responses in net photosynthesis and photosynthetic efficiency were generally only observed in the moss exposed to the highest concentrations of these elements in solution. Mercury was apparently the most toxic of the elements studied. Net photosynthesis and photosynthetic efficiency were also related to tissue concentrations of these elements in the moss. Despite the higher toxicity of Hg, this element can be accumulated at high concentrations in moss, probably at extracellular sites. For Sb, the same tissue concentration had very different physiological effects depending on the initial concentration to which the moss was exposed in solution. Temporal trends in chlorophyll fluorescence were more stable than trends in net photosynthesis. The respiratory rate was very variable and was not clearly related to the concentration of elements in solution or in moss tissues.