Effect of arsenic contamination on microbial biomass and its activities in arsenic contaminated soils of Gangetic West Bengal, India A.K. Ghosh a , P. Bhattacharyya a, * , R. Pal b a NBSS and LUP (ICAR), Block-DK, Sector-II, Salt Lake City, Kolkata-700091, West Bengal, India b Department of Agricultural Chemicals, Bidhan Chandra Krishi Viswavidyalaya, Mohanpur, West Bengal, Pin-741235, India Received 24 June 2003; accepted 27 September 2003 Abstract A study was conducted to see the effect of arsenic contamination on soil quality indicators, viz., microbial biomass, soil respiration, fluorescein diacetate and dehydrogenase (DHG) activity in arsenic contaminated soils of West Bengal. All the parameters were significantly and negatively correlated with all the form of arsenic (bioavailable and total) but the microbial metabolic quotient was significantly and positively correlated with all forms of arsenic, indicating arsenic induced stress to the soil microbial community. This may be due to part of the microbial biomass, which is located in the inner parts of the micro-aggregates of soil, which is affected by arsenic accumulates present in soil particles. Linear regression analysis revealed that the bioavailable arsenic exerted greater inhibitory effect on the soil microbial population than the total arsenic content of soils. Water-soluble arsenic showed more inhibitory effect than NaHCO 3 extractable form, in their association with biological properties of the contaminated soils. Water-soluble form of arsenic was much more toxic than insoluble forms. This signified that with increase in bioavailability, the arsenic exerted more inhibitory effect on these parameters. It is thus suggested that the microbial biomass, fluorescein diacetate and dehydrogenase activity alone and expressed on a soil organic matter basis along with the soil respiration parameters can be helpful in assessing the effects of arsenic on the size and activity of microbial biomass in soils. D 2003 Elsevier Ltd. All rights reserved. Keywords: Arsenic; Microbial biomass; Soil respiration; Fluorescein diacetate; Dehydrogenase activity 1. Introduction Arsenic contamination of groundwater in West Bengal is very widespread. Presently, 5 million people in 978 villages from eight districts and southern part of capital city, Kolkata (Chakraborti et al., 1999) are drinking As contaminated water having As concentration above 0.01 mg As/l (WHO, 1996). In some areas of Bangladesh and West Bengal (India), concentration of arsenic (As) in groundwater exceeds the guideline concentration set internationally and nationally at 10 to 50 Ag As/l and may reach concentrations in the mg As/l range. Such groundwater is also used for irrigation and this makes it possible for As to enter the human food chain through locally grown food crops and vegetables. Soil acts as a principal sink of As in the environment, which comes from the contaminated ground- water aquifers, and as most of the arsenical residues have low solubility and low volatility, they generally accumulate in the topsoil layers (Woolson et al., 1973). The concentra- tion of As in soil generally ranges from 5 to 30 mg As/kg. The importance of the microbial study lied in the fact that microbes are the source and sink of plant nutrients and are instrumental in nutrient cycling and therefore, indicators of soil quality. Arsenic pollution in groundwater in India and Bangla- desh is considered to be the largest contamination problem in the world. Arsenic may have a direct influence on the microbial populations present in the soil. Decreases have been reported in microbial populations in soils that have been polluted with As compounds (Maliszewska et al., 1985; Hiroki, 1993; Bardgett et al., 1994; Simon, 2000). Arsenic is toxic to almost all bacteria, by inhibiting basic cellular functions, which are linked with energy metabo- lism (Walker et al., 2000). Recent study suggests that the long-term contamination by As adversely affected micro- bial biomass C and respiration (Edvantoro et al., 2003; Van Zwieten et al., 2003). Microbial parameters appear to be very useful in monitoring soil pollution by metals, but no 0160-4120/$ - see front matter D 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.envint.2003.10.002 * Corresponding author. Tel.: +91-33-2359-0727. E-mail address: b _ pradip@rediffmail.com (P. Bhattacharyya). www.elsevier.com/locate/envint Environment International 30 (2004) 491 – 499