A geospatial assessment of human exposure pathways to chemical contaminants in the environment: a cause for action in Owerri, Imo State, Nigeria

Nwachukwu, Joseph Ikechukwu (2018) A geospatial assessment of human exposure pathways to chemical contaminants in the environment: a cause for action in Owerri, Imo State, Nigeria. Doctoral thesis (PhD), Manchester Metropolitan University.

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Abstract

The indiscriminate dumping of refuse and its potential threat to groundwater in Owerri, Nigeria remain a public health concern. This thesis applied multi-disciplinary techniques (environmental chemistry, health studies, geospatial statistics, social sciences, soil science and horticulture) to assess various pathways through which humans can be exposed to contaminants. A bi-seasonal random geospatial sampling of environmental matrices (groundwater, river water, dumpsites leachates, soil, and plant samples) impacted by urbanisation and anthropogenic activities was carried out between 2015 and 2017. Laboratory analysis reveals that concentration of nitrate in groundwater is above the maximum concentration limit (MCL) of 50μg/mL stipulated by the Nigerian Standard for Drinking Water Quality (NSDWQ) in approximately 12% of sampled wells. This presents nitrate as a critical contaminant in groundwater. Concentrations of Pb and Cd exceeded the MCL by about 1.6% and 0.25% respectively. All measured parameters in the river samples were within the acceptable threshold limits, whereas Pb concentration in soil measured above the 85 μg/g target value stipulated by the Nigeria Department of Petroleum Resources in about 0.9% of sampled soils. Pb measured above the thresholds of 0.3 μg/g and 0.1μg/g specified by the Food and Agricultural Organisation (FAO) in 99.8% of pumpkin leaf (Telfaiara occidentalis) and 51.6% of cassava tuber (Manihot occidentalis) samples respectively. Findings suggest review of groundwater risk evaluation techniques such as DRASTIC to incorporate more relevant soil and climatic attributes. In Owerri, urbanisation appears to have influenced groundwater nitrification as reflected in wells close to various contaminant sources, such as landfills and septic tanks. The wider implication of this study lies on the application of redox chemistry in the mini catchment assessment of contaminants behaviour that could help in the formulation of large-scale groundwater exploitation programmes and water management policies. Health risk assessment shows that children are significantly more vulnerable to contaminant exposure.