Effectiveness of Bryophytes and Cicada Shells as a Bio-Index for Heavy Metal Contamination of River Water and Soil

Abstract

Metal concentrations of sampled bryophytes varied widely and increased depending on the metal contamination conditions. The highest values in bryophytes were several 10,000 ppm for Cu and Zn, 100,000 ppm for Pb, several 1,000 for As and a few 100 ppm for W. Bryophytes are therefore considered to be an effective index of Cu, Zn, Pb, As, and W contaminations. However, the heavy metal concentration in bryophytes at a W mine was low and the heavy metal concentration in other plants showed a higher concentration than that of bryophytes. The presence of W is thought to be the cause of the decrease in the heavy metal concentrations in bryophytes. The other possibility is that only bryophytes with a low copper concentration can grow. The highest Zn concentrations in a cruciferous species reached several 10,000 ppm among sampled plants. The Cu and Zn concentrations in both cicada shells and adult cicadas were not always high at metal mines. Therefore, Cu and Zn concentrations of cicada shells were not effective as a Cu and Zn contamination index. Pb and As concentrations in cicada shells at Pb and As mines were higher than those for non-Pb and non-As contaminated areas and were higher than those in cicada adults. Therefore, cicadas were thought to release Pb and As into their shells during molting and maintain high concentrations of Pb and As in their cicada shells. Pb and As concentrations in cicada shells were thought to be an effective contamination index.