Heavy metal concentrations and its impact on soil microbial and enzyme activities in agricultural lands around ship yards in Chattogram, Bangladesh

Abstract

The present endeavor was to evaluate the spatial distribution and ecological risk of heavy metals, released from ship scrap processing activities in agricultural soils of Sitakunda, Bangladesh. Soil samples were collected from 19 sites located in the vegetable garden, vegetable field and paddy field soils. The studied soils have the texture of sandy clay loam, extremely acidic to moderately acidic pH (4.23–5.88), soil organic matter was in the range from 0.79 to 1.43%. The mean concentrations of all the heavy metals were higher than the standard limit value. Heavy metal concentrations ranged from 1.77 to 8.10 mg∙kg–1 Cd, 102.75 to 262.00 mg∙kg–1 Cr, 90.52 to 662.33 mg∙kg–1 Cu, 26.66 to 227.47 mg∙kg–1 Ni, 148.33 to 1483.33 mg∙kg–1 Pb and 270.37 to 1416.13 mg∙kg–1 Zn. The toxicity level of heavy metals in agricultural soils was, in order of decreasing concentration: Cd > Pb > Cu > Zn > Ni > Cr. The principal component analysis evidenced that the heavy metal contaminants in agricultural soils may originate from the ship scrap dismantling and processing operations. All the heavy metals had shown a very high significant negative correlation with the number of cultivable bacteria and fungi, soil microbial biomass carbon, and microbial activity as well as the dehydrogenases, urease, acid phosphatase and arylsulfatase enzyme activities. Dehydrogenases activity was a very responsive enzymatic assay (p < 0.001) to ascertain the effect of contamination on the physiologically active soil microorganisms. The positively correlated quadratic relationship between metabolic quotient and heavy metal concentration designate adapted and metabolically less efficient microbial population developed due to long-term heavy metal pollution in these agricultural soils.