Morphological abnormalities in periphytic diatoms as a tool for biomonitoring of heavy metal pollution in a river

In situ effect of heavy metal enrichment on periphytic diatom community of a river was studied using metal diffusing substrates. Periphytic algae growing on these substrates showed intracellular accumulation of test metals (Cu, Zn and Pb) which inhibited growth, as evidenced by reduced cell number, and increased morphological abnormalities in diatoms. In the case of Cu and Zn, percent deformed diatom frustules showed a strong relationship (r2 > 0.80) with intracellular metal content and metal release from the substrate. Frustule deformity was evident in 15 of the 19 common diatom taxa, occurring frequently in Fragilaria capucina, Gomphonema parvulum, Nitzschia palea, Pinnularia conica and Ulnaria ulna. Altered pattern of striations and changed outline of frustules were the only deformities in the control; however, raphe modification and mixed deformities (several deformities in the same frustule) were additionally observed under metal stress. Raphe modifications were more frequent in the case of Cu exposure, while abnormalities in striations and mixed deformities were more prevalent in diatoms exposed to Zn or Pb. The present study shows the utility of morphological abnormalities in diatom frustules as an effective tool for biomonitoring of heavy metal pollution in waterbodies.