The Effect of Heavy Metals on Enzyme Activities in Sponge Iron Industry Polluted Soil

Present study assessed the effect of heavy metals on soil enzyme activities like amylase, invertase, dehydrogenase and urease of open shrub lands present at 1 km, 1.5 km, 2 km and 2.5 km distance away from Bhushan sponge iron industry, in Rengali block of Sambalpur district, Odisha. The heavy metals studied were Cd, Ni, and Cr, whose concentrations in the above sites were much more than the safety limits prescribed by WHO/FAO (2007). Highest amount of heavy metals were recorded in the site nearest to the plant i.e.1km away from the plant. Soil enzymes secreted by microorganisms, animals and plant roots below the soil play an important role in the biochemical functioning of soil like organic matter formation and degradation, nutrient cycling and energy transformation by catalyzing numerous chemical, physical and biological reactions. The site containing lowest heavy metals (5.6mg/Kg, 413.0mg/Kg, and 1006.3mg/kg of Cd, Ni, and Cr respectively) showed highest enzyme activities with respect to other experimental sites. A negative correlation was observed between heavy metal concentrations and soil enzyme activities. Further, the study indicated higher soil enzyme activities in the post-monsoon period in comparison to pre-monsoon period. When compared to the enzyme activities in the soil of open shrub lands present at the bottom of Dehari hill in Jyoti Vihar of Burla town, 32 km away from the present study site (control site), the enzyme activity of the present study was very low. The percentage inhibition of different enzyme activities in experimental sites with respect to control site were 91% and 80% for amylase, 93% and 91% for invertase, 97% and 96% for cellulase, 90% and 85% for dehydrogenase , 90% and 79.5% for urease activity in premonsoon and postmonsoon period respectively. The results indicate that the heavy metals in such high concentrations inhibit the activity of enzyme secreting flora and fauna in soil, as excessive amounts of heavy metals disrupt the homeostasis of soil by interfering with the control mechanisms at genetic level. Thus, the decline in soil enzyme activity reflects the soil degradation potential of the heavy metals released from sponge iron industry. Therefore, it is highly essential to take immediate remediation measure in order to protect the health of soil flora and fauna in these areas.