Soil Structural and Chemical Conditions After Disposal of Fabric Dye on a Loamy Sand Soil in Southwestern Nigeria

The indiscriminate disposition of dye waste water from the age-long “Adire” industry of Abeokuta, southwest Nigeria is a major concern as the movement of such contaminants in the soil needs to be monitored. This study investigated the effect of fabric dye on soil physical and chemical properties. Treatments were local concentration, spent local-concentration, half local- concentration and twice local-concentration of the dye; and control (no contaminant). Sixteen litres of the dye concentrations were applied on field plots every two days to maintain the soil at 10% field capacity for 3 months. Soil samples were collected from 0-10 cm, 10-20 cm and 20-30 cm depths at the termination of application of dyes (3 months) and 12 months after the application of treatments. Results show that macroaggregates (>0.25 mm) were dominant in the control while microaggregates (<0.25 mm) were more in dye polluted plots at 3 months. The mean-weight diameter (MWD) for control was about two times higher (1.73 mm) than that of the treated plots (0.77-0.87 mm). Twelve months after the termination of dye application, macroaggregates (5-2 mm) and microaggregates (<0.25 mm) had similar distributions for the control and treated plots (9.70-25.44 mm). Bulk density for treated plots (1.99-2.10 g/cm3) was significantly (p ≤0.05) higher than control (1.83 g/cm3). Saturated hydraulic conductivity (Ks) was higher in control (12.6 cm/hr) than treated plots (0.6-10.2 cm/hr). Infiltration rate declined in dye treated plots (2.33- 30.53 cm/hr) at -2 cm water head compared to control (88.00 cm/hr); whereas, at -1 cm water head it ranged from 1.13-23.60 cm/hr in treated plots compared to control (71.87 cm/hr). Sorptivity at -2 cm and -1 cm water head (2.94 cm/hr1/2 and 1.60 cm/hr1/2) for control was significantly higher than dye plots (0.00003-0.00006 mm/hr1/2). Exchangeable acidity was significantly higher in the control (6.02-6.17 cmol/kg) than 0.37-0.77 cmol/kg observed in dye plots. However, Na+ (21.53-90.23 cmol/kg), phosphorus (13.68-39.92 mg/kg), K+ (20-49.67 cmol/kg), Mg2+ (97.57-100.63 cmol/kg) and sulphur (4.67-8.93 mg/kg) contents were significantly higher with dye treatment. The pH was more acidic in contaminated plots (6.13-6.53) than near neutral (6.97- 7.00) for control. In conclusion, significant physical and chemical degradation was observed following treatment with the dye and it's waste-water indicating a negative impact on the soil.