Microbial Growth and Arsenic Tolerance Ability as Influenced by Inherent Arsenic Loading in Polluted Soils of West Bengal

The effect of inherent arsenic loading on microbial growth in polluted soils of Haringhata block in the district of Nadia, West Bengal as well as the arsenic tolerant ability of the composite cultures of the said soils in different concentrations of arsenate (As^V) and arsenite (As^III) at different hours of incubation were studied. Total arsenic loading in the affected soils ranged from 4.70 to 16.56 mg/kg and to that of Olsen extractable arsenic (available arsenic) from 0.74 to 2.98 mg/kg. Total and available arsenic loading adversely affected the bacterial and cyanobacterial population, but not the fungi and actinomycetes. Significant negative correlations were obtained between total soil arsenic and bacterial population (r = -0.798^** in CFU and -0.800^** in MPN method), available arsenic and bacterial population (r = -0.870^** in CFU and -0.783^** in MPN), total soil arsenic and cyanobacterial population (r = -0.853^**) as well as available arsenic and cyanobacterial population (r = -0.857^**). As^III was more toxic than As^V, the growth of the composite cultures appeared up to 20,000 mg/L in As^V enriched broth and up to 500 mg/L in As^III enriched broth in some of the soils after 168 hours of incubation. On an average, with increase in incubation period, arsenic tolerance ability increased and microbial growth appeared at the higher levels of As concentration. Microbial growth appeared at higher concentration of As^V and As^III with those soils having comparatively higher inherent As loading.