Effect of various azo dyes on soil organic matter cycling in three soils of varying texture.

Little is known regarding effects of azo-dyes on soil organic matter cycling in soil. Therefore, this lab study was carried out in Government College University Faisalabad to understand effects of varying concentrations (100, 200, 400 mg kg-1 ) of reactive black (RB5), direct red (DR) and, acid yellow (AY) on soil organic matter cycling in a sandy loam, a clay loam, and a loam. Soils were mixed with the aforementioned dyes and incubated in lab for 636 hrs. Results revealed that DR induced change of -52 to +53%, -8 to -58%, and -50 to +8% on soil respiration rate in sandy loam, loam and clay loam soils respectively in first 160 h of incubation. RB5 induced a change of -52 to +49%, -38 to +9%, and -67 to -15% whereas, the AY induced a change of -54 to +36%, -34 to +24%, and -75 to -6% in respiration rate in sandy loam, loam and clay loam soils respectively during the same incubation time. The microbial biomass C (MBC) did not show any significant change in response to any azo dye in loam soil. Metabolic quotient indicated that the clay loam soil experienced the highest toxicity in response to DR and RB5 among the three soils. Overall, our study shows that not all the dyes are toxic to SOM cycling and that is dependent on the type of the azo dye as well as the intrinsic characteristics of the soils. [ABSTRACT FROM AUTHOR]