Determination of Some Selected Heavy Metals in Effluents from Lubricants Manufacturing and Associated Contamination of Oysters (Crassostrea cucullata) and Soil near Discharge Points in Mombasa, Kenya

Abstract

Purpose: Available reports on heavy metal contamination along the Kenyan coastal zone focused on concentration levels in marine and coastal waters, sediments and biota, with indications of potential sources. However, information on contribution of specific sources to the heavy metal load into the marine and coastal environment is scanty or unavailable. Thus, this study addressed the need to assess specific potential sources and their contribution to heavy metal contamination. The generated data can be applied for monitoring discharge loads of heavy metals from lubricant manufacturing processes into the environment, its level of contamination to the environment and the potential risk to man through food chain.

Materials and Methods: Concentrations of selected heavy metals Cd, Cr, Cu, Pb, and Hg in effluents filtrates, residues (SPM), Oysters (Crassostrea cucullata) and soil samples were determined using ICP-OES. The procedures of the analytical methods and instruments used were validated with analysis of a multi-element certified reference material (CRM IAEA-452) for the elements Cd, Cr, Cu, Pb and Hg in the effluent samples and standard reference material (SRM 1566b) from National institute standards and technology for the elements Cd, Cr, Cu, Pb and Hg in the marine bivalve tissues. Physico – chemical parameters Temperature, P^H, Conductivity, Dissolved oxygen and Total organic carbon were also determined in the effluent samples.  Sampling was done in the year 2021 and 2022. Effluent samples were collected from OLA energy Kenya limited, VIVO energy Kenya limited and TOTAL energy Kenya limited. Oyster samples and soil sediment samples were collected from Makupa creek. Data analysis was carried out using (SPSS) for Windows (Version 16) and one way analysis of variance (ANOVA) at 95% confidence level. The difference in mean concentrations of heavy metals within and between groups were considered significant at P˂0.05. The interrelationships of heavy metals contamination in the samples were determined using the Pearson correlation coefficient. It was considered significant at P value ˂0.05.

Findings: This study showed presence of heavy metals that varied in concentrations in effluents samples, soils samples and Oyster samples. The mean concentrations of heavy metals in the effluents filtrates ranged as follows Pb = 0.0038±0.0004 mg/l – 0.0025 ± 0.003 mg/l, Cu = 0.0054±0.0038 mg/l – 0.0019±0.0002 mg/l, Cr = 0.0071±0.0021mg/l – 0.0045±0.0022 mg/l, Cd = 0.0041±0.0026 mg/l – 0.0013±0.0001 mg/l and Hg = 0.0063±0.0018 mg/l – 0.0026±0.0004 mg/l. The range of values for the mean concentrations of the heavy metals in the Oysters showed that Pb = 0.0227±0.0091mg/kg – 0.019 ± 0.006 mg/kg, Cu = 0.0618±0.0171mg/kg – 0.0601±0.0168 mg/kg, Cr = 0.0265 ± 0.0277 mg/kg – 0.0152 ± 0.0009 mg/kg, Cd = 0.0464±0.0282 mg/kg – 0.0273 ± 0.0117 mg/kg and Hg = 0.0264±0.0158 mg/kg – 0.025±0.0080 mg/kg. The range of values for the mean concentrations of the heavy metals in the soil samples showed that Pb = 0.0523 ± 0.0189 mg/kg – 0.0447±0.0181 mg/kg, Cu = 0.3010 ± 0.0282 mg/kg – 0.2437 ± 0.2690 mg/kg, Cr = 0.6564 ± 0.1468 mg/kg – 0.5862 ± 0.3073 mg/kg, Cd = 0.5434 ± 0.2207 mg/kg – 0.3506±0.2157 mg/kg and Hg = 0.2679 ± 0.1923 mg/kg – 0.2366±0.1584 mg/kg. The range values for the Physico-chemical parameters in the effluent samples were P^H = 7.31±0.198 – 6.53±0.459, Temperature = 27.53±0.378^oC – 23.3±0.2^oC, Dissolved oxygen = 6.81±0.191mg/l – 3.11±0.242 mg/l, conductivity = 2740.0±901.041 uS/cm – 1523.33±55.075 uS/cm, Total organic carbon = 15.18±1.2750 mg/l – 0.92±0.1026 mg/l. Concentrations of heavy metals were at safe limits set by WHO, US – EPA and NEMA (2017) except Hg in soil samples was slightly above permissible limits. Concentration of mercury was lower in effluent filtrates and effluents residues samples than in soil and Oysters samples.  

Implications to Theory, Practice and Policy: This study recommends that frequent inspection be carried out on wastes emanating from industries, at its disposal sites and in living organisms at the vicinity of the wastes disposal sites. Industrialists should adopt best practices of wastes disposal and management to reduce emissions of harmful substances into the environment. Public education and awareness should be carried out to enlighten the residents about the impacts on health upon interaction with the polluted environment and feeding on organisms that reside in such contaminated environments.