Cr and Hg toxicity assessed in situ using the structural and functional characteristics of algal communities
Singh, A.K. | Rai, L.C.
The toxicity of mercury and chromium on algal community structure have been assessed using in situ N2ase activity, pigment diversity, autotrophic index, and 14C uptake of algae. The location was in the river Ganga and controlled ecosystem pollution experiment enclosures were used. Maximum inhibition of algal number was observed at 0.8 micrograms Hg mL-1 followed by 8.0 micrograms Cr mL-1. Unicellular forms, except for Anorthoneis excentrica, were very sensitive to test metals used. The decline in algal number was concentration dependent and metal specific at generic and species levels. Complete elimination of three and six species was observed respectively at 8.0 micrograms Cr mL-1 and 0.8 micrograms Hg mL-1 after 12 days' exposure. Likewise, a concentration-dependent and metal-specific increase in autotrophic index and pigment diversity of phytoplankton was recorded for Hg and Cr. Inhibition of 14C uptake of phytoplankton in Ganga water was almost equal (79%) at 0.8 micrograms Hg mL-1 and 8.0 micrograms Cr mL-1 (78%). Although complete inhibition of in situ N(2)ase was observed at 0.8 micrograms Hg mL-1, it was only 80% with 8.0 micrograms Cr mL-1. Our study suggests that heavy metals inhibit both structural and functional variables of phytoplankton in field microcosms. Hence this technique seems to hold potential for the biomonitoring of heavy metal toxicity in the field.
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