Cultivable bacterial diversity, physicochemical profiles, and toxicity determination of car wash effluents

Carwash effluents contain potentially toxic chemical and microbiological pollutants which may pose public health and ecotoxicological threats if directly discharged into surface waters. This work was aimed at determining the microbiological, physicochemical, and toxicological parameters of carwash effluents. Toxicity assays were determined using whole effluent toxicity (WET) using Danio rerio and Daphnia pulex. For microbiological analysis, sample aliquots were spread plated onto R2A Agar for the isolation of heterotrophic bacteria followed by DNA extraction from axenic cultures for sequencing analysis. The pH of effluent samples lay in the alkaline range, and ranged from pH 7 to pH 10. Sample salinity ranged from 0.2 to 0.3 g/Kg. Electrical conductivity values ranged from 274 to 554 μS/cm. Concentrations of Co, Pb, and Ni were < 1 mg/L in all samples while the concentrations of Cu ranged from 0.94 to 3.8 mg/L and Zn from 1.15 to 3 mg/L. Oil and grease concentrations ranged from 5 to 24 mg/L. The concentrations of TPH-GRO were low at < 1 mg/L in all samples. All the carwash effluents were categorised as acutely toxic, with ≥ 75% mortality recorded for both test organisms within the first 24 h of exposure to the test solutions. Heterotrophic bacteria counts ranged from 2800 to 4600 CFU/100 ml. Sequencing analysis revealed that 57% of the isolates were closely related to Aeromonas species, with 43% closely related to Pseudomonas species. We conclude that carwash effluents are veritable sources of microbiological contaminants and potentially toxic chemical pollutants of public health and ecotoxicological concern.