Abstract
Azo dyes are one of the largest classes of synthetic dyes being used in textile industries. It has been reported that 15–50% of these dyes find their way into wastewater that is often used for irrigation purpose in developing countries. The effect of azo dyes contamination on soil nitrogen (N) has been studied previously. However, how does the azo dye contamination affect soil carbon (C) cycling is unknown. Therefore, we assessed the effect of azo dye contamination (Reactive Black 5, 30 mg kg−1 dry soil), bacteria that decolorize this dye and dye + bacteria in the presence or absence of maize leaf litter on soil respiration, soil inorganic N and microbial biomass. We found that dye contamination did not induce any change in soil respiration, soil microbial biomass or soil inorganic N availability (P > 0.05). Litter evidently increased soil respiration. Our study concludes that the Reactive Black 5 azo dye (applied in low amount, i.e., 30 mg kg−1 dry soil) contamination did not modify organic matter decomposition, N mineralization and microbial biomass in a silty loam soil.
Highlights
Azo dyes, which contain one or more than one -N=N- groups, constitute the largest class of synthetic dyes that are used in a wide range of commercial applications, i.e., textile, food, paper printing, cosmetics with textile industry as the largest consumer (O’Neill et al, 1999)
Reactive Black 5 azo dye contamination did not have any effect on cumulative soil respiration (Fig. 1A)
Availability of water extractable organic carbon (WEOC) or soluble C did not differ between control and treated soils (Figs. 2A & 2B, P > 0.05)
Summary
Azo dyes, which contain one or more than one -N=N- groups, constitute the largest class of synthetic dyes that are used in a wide range of commercial applications, i.e., textile, food, paper printing, cosmetics with textile industry as the largest consumer (O’Neill et al, 1999). The concentration of the azo dyes in textile wastewaters vary from 10 to 250 mg L−1 (O’Neill et al, 1999). Presence of azo dyes in water bodies causes aesthetic problems and obstruct light penetration and oxygen transfer into water thereby affecting aquatic life (Sponza, 2006; Li et al, 2012; Zhang et al, 2012). Azo dyes and their degradation intermediates may be mutagenic and carcinogenic for living organisms (Weisburger, 2002).
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