Evaluation of brick kiln operation impact on soil microbial biomass and enzyme activity

Heavy metal emission from brick kiln operation in developing countries is one of the major sources of environmental pollution. The present study evaluated the intensity of Cd and Pb pollution and the impact on soil microbial activity in agricultural soils in the vicinity of the brick kiln cluster of Hathazari, Chattogram, Bangladesh. It is a major concern as anthropogenic stress on soil microorganisms is directly related to crop productivity. Soil samples were collected from 21 sites covering 7 locations including the reference sites for the assessment of the toxic impact on soil biota. Soil samples were analyzed using standard procedures. In some of the sampling sites, Cd and Pb concentrations were signifi cantly higher than the reference sites. Metal concentration indicates that the anthropogenic input in the soils was in the range of 0.27 to 1.07 mg∙kg–1 of Cd and 19.07 to 52.07 mg∙kg–1 of Pb. However, the concentrations of Pb were not in toxic concentration when compared to the standard level by Chinese environmental quality standards for soil. The highest contamination degree (PER) of the soils was 200.87 and the lowest was 115.83. The contamination factor demonstrated that the soils were in the moderate to considerable level of contamination. The results showed that the number of soil microbial population, microbial activity, microbial biomass carbon, dehydrogenase, urease, acid phosphatase and arylsulfatase activities in the reference soil were all higher than in the agricultural soil in the vicinity of brick kiln cluster. Exponential curves showed a signifi cant positive correlation between heavy metal and microbial metabolic quotient (qCO2) indicating metal stress and high concentration of heavy metals decreased microbial biomass and enzyme activity. Soil pH and Cd content were identifi ed as the key infl uential factors controlling soil biological functions. A signifi cantly high correlation was observed for Cd and Pb (r = 0.89, p < 0.001), it suggests the same source of contamination input. Contamination of Cd and Pb is attributed to heavy input of aerial deposits of metal-enriched fumes from brick kiln operation. A signifi cant negative impact of Cd and Pb on soil microbial activities and enzyme activities was also profound from correlation studies and PCA analysis. However, regular application of fertilizer in agricultural soils may have supported adaptation to long-term Cd stress mainly through the maintenance of microbial activity. The study is important in eco-toxicological and biomonitoring aspects as the data on heavy metal toxicity to the soil environment can act as guidelines for the continuation of brick kiln operation and the sustainable utilization of natural resources. Keywords