Toxic effects of Red-S3B dye on soil microbial activities, wheat yield, and their alleviation by pressmud application

This study examined the effect of Red-S3B textile dye on soil microbial activities, uptake of the dye by wheat plants and growth on the dye-contaminated soil. Moreover, pressmud (PM) application was investigated for its alleviative effect on wheat yield and dye uptake by plants. Preliminarily, soil was spiked with a wide concentration range (0, 100, 250, 500, 750 and 1000 mg kg^-1 soil) of Red-S3B dye and wheat was grown for 42-days. The dye did not suppress the activities of soil enzymes and growth of wheat seedlings at 100 mg kg^-1; however, beyond this level the dye had a linear negative effect on these attributes. With 1000 mg dye kg^-1 soil, wheat seedling biomass, viable microbial count, soil respiration, dehydrogenase, phosphatase, and urease activities decreased by 84%, 33%, 45%, 69%, 24%, and 11%, respectively as compared to uncontaminated soil. Moreover, phosphorus and potassium content in wheat shoot decreased, while the nitrogen content increased in Red-S3B contaminated soil. In the subsequent pot experiment, PM application (12.5 g kg^-1 soil) was assessed to alleviate the adverse effect of moderately toxic level of Red-S3B dye (500 mg kg^-1 soil) on wheat growth and yield. Root and straw biomass, and grain yield of wheat decreased by 13, 19 and 12%, respectively in Red-S3B contaminated soil as compared to uncontaminated soil. However, PM application to dye-contaminated soil retrieved the dye-induced reduction in root and straw biomass and grain yield to become statistically (p ≤ 0.05) at par with control plants. The color of Red-S3B was clearly visible in spikes depicting that plants absorbed Red-S3B but probably could not metabolize it. Amending the dye-contaminated soil with PM decreased Red-S3B content in awns from 78 to 37 mg kg^-1. Hence, it is concluded that Red-S3B textile dye is highly toxic to soil microbes and wheat plants at levels exceeding 100 mg kg^-1 soil. Soil application of PM alleviates the adverse effect of Red-S3B dye on wheat growth through reducing its uptake by plants.