Enumeration, characterization and identification of bacteria in soils of selected waste dumpsites in Rivers State, Nigeria

Abstract

Rapid population growth and industrialization have led to increased waste generation, while effective waste management remains a major challenge in Nigeria, where solid wastes are often indiscriminately disposed of. This study investigated the diversity and abundance of bacteria in soils from selected solid waste dump sites in Rivers State, Nigeria. Soil samples were collected monthly from three dump sites and three control locations between May 2023 and April 2024. Samples were analyzed using standard microbiological techniques and cultured on Nutrient Agar, MacConkey Agar, Starch Casein Agar, Salmonella–Shigella Agar, Thiosulfate Citrate Bile Salts Sucrose (TCBS) Agar, and Mannitol Salt Agar. Purified isolates were identified using morphological and biochemical characterization. Mean bacterial counts ranged as follows: total heterotrophic bacteria (THB), 2.9 ± 1.6 - 8.3 ± 2.2 × 10⁵ cfu/g; total coliforms, 4.1 ± 1.2 - 12.5 ± 2.4 × 10³ cfu/g; total actinomycetes, 0.6 ± 0.3 - 3.3 ± 1.4 × 10³ cfu/g; total Staphylococcus, 3.6 ± 2.1 - 16.1 ± 1.4 × 10³ cfu/g; total Salmonella, 0.1 ± 0.1 - 2.1 ± 0.3 × 10² cfu/g; total Shigella, 0.0 ± 0.0 - 0.9 ± 0.1 × 10² cfu/g; and total Vibrio, 0.0 ± 0.0 - 5.5 ± 0.5 × 10² cfu/g. No significant difference (p > 0.05) was observed in THB populations among the study locations, whereas other bacterial groups showed significant variations (p < 0.05) in some locations. Identified bacterial genera included Rhizobacter, Enterobacter, Citrobacter, Cronobacter, Kluyvera, Paraburkholderia, Serratia, Ralstonia, Vibrio, Aeromonas, Erwinia, Leclercia, Chryseomonas, Klebsiella, Pseudomonas, Salmonella, Shigella, Bacillus, Paenibacillus, Staphylococcus, Enterococcus, Salinococcus, Corynebacterium, Actinomyces, Rathayibacter, Microbacterium, Zhihengliuella, Sinomonas, Nesterenkonia, and Escherichia coli. THB counts were highest at the Boskel dumpsite, followed by the Aluu dumpsite, and lowest at the Elijiji dumpsite. Staphylococcus spp. were the most prevalent isolates across the sites. The high bacterial load and diversity observed indicate that solid waste dumpsites may serve as reservoirs of potentially pathogenic microorganisms, posing environmental and public health risks to waste workers and nearby residents. These findings highlight the need for improved waste management practices and the siting of dumpsites at safe distances from residential areas to minimize potential health hazards.

Keywords: Bacteria, soil, dumpsites, population, waste.