Comparative Effects of Car Wash Detergents and Biosurfactants (Rhamnolipids) on the Soil Environment: In Search of a Greener Alternative

Abstract

Aims: This study investigates the comparative effects of synthetic car wash and a bio-based surfactant detergent, biotensidon, on the soil environment.
 Study Design: Evaluation studies.
 Place and Duration of Study: Geology and Woodland laboratory at William Smith Building, University of Keele, in 2018.
 Methodology: 1000 g of Topsoil purchased from a local store was dried in the oven at 1100C for 24 hours and its moisture content was determined. 100 g of the soil was irrigated with diluted detergents and cleaning solutions for 5 days. The leachates were then collected and analyzed for pH and Electrical Conductivity (EC) and further analyzed with Infrared Spectroscopy (IR) while the soil sample pellets were with X-Ray Fluorescence (XRF) machine.
 Results: The colour of soil leachate when physically observed was consistently almost clear for tap water, light yellow for the biotensidon detergent and dark brown for the car wash detergent. For the pH for the same period, the soil leachates were between neutral and mildly alkaline among the different samples. However, for EC, the maximum EC recorded was in soil irrigated with Car Wash Detergent (1157, 1181, 1242, 1390 and 1876 µS/cm) for all of the 5 days. This is followed by soil irrigated with BioTensidon (732, 757, 796, 799 and 836 µS/cm) for the same period while the minimum EC was recorded in soil irrigated with tap water (456, 487, 500, 505 and 553 µS/cm) for the 5 days. The IR analysis of soil leachates showed peak values that did not differ with all the three leachates collected each day, while the XRF analysis showed the major elements SiO2, Al2O3 and Fe2O3 to be the most dominant for analyzed samples.
 Conclusion: Both detergents examined had similar compositions of ingredients for making detergents. Some of these ingredients are well known to be harmful to humans, soil, water and plants, and these compositions vary between the detergents. Both detergents also have similar compositions of microelements that are essential for plant growth and some that are toxic to plants. However, the car wash detergents showed no amount of the element Lead (Pb). The car wash detergents significantly bleached organic fractions of the topsoil when examined physically. An 8% soil pH increase and 43% soil EC increase were recorded after 5 days of testing by car wash detergents when compared to the biosurfactants. Also, biosurfactants were shown to contain some toxic concentrations that may be unsafe.