Hydrocarbon and Metal Pollution of Eastern Niger Delta Ecosystems: Geographies of Impact and Contamination Assessment of Aquatic Foodchains in Rural Communities

Abstract

<p>Over six decades of crude oil exploration and exploitation in the Niger Delta region (NDR) of Nigeria has result in it being considered one of the most polluted regions of the globe. Despite the numerous reported crude oil spills and related gas flare/venting pollutants to the NDR environment, the full extent of related contamination is unknown. Information on the pre-impact and baseline concentrations, fate and behaviour of contaminants is important due to the possible detrimental influence on both ecosystem and human health. This study set out, to establish and understand the extent and impact of crude oil derived contamination, metals and hydrocarbons in aquatic and riparian ecosystems of the NDR, focussing on three rural locations (Abi, Bakassi and Ibeno Local Government Areas (LGAs)) in the eastern Niger Delta. These locations are on a pollution gradient based on existing local knowledge of oil production activities and are within two estuary systems of the Qua Iboe River (Ibeno)and Cross River (Abi and Bakassi) in the NDR. The gradient was Ibeno in close proximity to crude oil production operations, Bakassi possibly an oil impacted area but more distant from production sources, and Abi was a reference location for comparable studies.</p> <p>The thesis systematically examined existing data on the pollution status of metals and hydrocarbons in the aquatic ecosystem and foodchains from crude oil exploration and exploitation, through an extensive review of literature of existing available data from 2000. A detailed on the ground survey was then conducted to provide information on perceptions of rural communities and their knowledge of the impacts of crude oil exploration on livelihood and seafood quality, and safety and mitigation efforts by the inhabitants. This ground survey underpinned the design of ecological sampling. This was followed by an extensive ecological quality assessment that evaluated physicochemical parameters and nutrient (PCPN) status of abiotic environments - the riparian soils, mud flats surface sediments, and on surface water across the study locations. Further, the occurrence and distribution of ten metals (copper (Cu), cobalt (Co), chromium (Cr), cadmium (Cd), iron (Fe), manganese (Mn), nickel (Ni), lead (Pb), zinc (Zn) and vanadium (V)), total hydrocarbons (THC) and polycyclic aromatic hydrocarbon (PAHs) in abiotic (surface water, riparian top soil and mud flat sediment) samples and in a typical aquatic foodchain were sampled and assessed. Surface water samples were collected during ebb and flood tidal regimes, while the foodchain component organisms included water column bulk microplankton (BMP), shrimp species (<i>Macrobrachium</i> and <i>Penaeus</i> spp) and <i>Chrysichthys nigrodigitatus</i> (Silver catfish – live fish and market sold smoke dried fish) as the apex predator, including fish blood, gill, liver and bile fluid. Contaminant concentrations were compared with the Nigeria national and international acceptable standard and the ecological and human health risks associated with contaminants detected were assessed using the metal pollution index (MPI) and benzo[a]pyrene toxic equivalence quotient (BaP_TEQ), respectively. Finally, a range of biomarkers were assessed for the native sentinel catfish (including haematology, serum biochemical profile, histology, morphometric measurements, meristic counts, and proximate chemical composition) to evaluate sublethal impacts of exposure to contaminants.</p> <p>The literature review identified a need to ground truth contamination in the NDR because there has been little systematic evaluation of time and spatial trends in current concentration data. The local population survey showed that the major protein food sources for the inhabitants were of aquatic origin with 82% believing water and food resources were contaminated and presented numerous adverse socioeconomic and health effects. The distribution of the perceived contaminated food resources beyond the impacted locations was recognised. Local communities were adaptable to change, open to intervention strategies to improve their well-being/livelihood and were willing to be involved in decision making processes and assist in resource management using their local knowledge of the ecosystems. The survey showed the value of including the local populations in any decision making for a successful intervention programmes and this formed the basis used to identify the sample sites for this study. Results of the study location sampling showed similarities in PCPN for soils, sediments and water across the three sites (typical of the NDR) and over seasons with no significant tidal differences in the water samples. However, pH, DO, BOD, and EC in the dry season at Abi (the control site) and DO at Bakassi/Ibeno, intermittently exceed the appropriate national standards. This implies that at times, water quality in these communities is poor. The similar abiotic PCNPs across the sites, seasons and tide regimes (for water) provided a good basis for comparison of environmental contamination.</p> <p>The occurrence and distribution of the ten metals (Cu, Co, Cr, Cd, Fe, Mn, Ni, Pb, Zn and V) in abiotic (soil, sediment and water) matrices indicated generally comparable values over seasons but with high variability across the studied locations. Most metal concentrations in the foodchain/biological matrices significantly differed across locations and increased mostly during the dry season. The concentration trend of metals in sample matrices ranked in the order of: smoke-dried fish > whole shrimp > BMP ≥ liver > fresh fish tissue > bile fluid. A range of metals showed potential ecological/human health risks with sample concentrations above the permissible limits in various samples and locations such as: soil and sediment (Cd and Fe), surface water (Fe, Pb, Cd, Cu Mn, Ni, and Cr), microplankton (Cr), shrimp (Cd, Cr, Mn and Ni), fish muscle (Cd, Cr and Pb), liver (Cd and Cr), bile fluid (Cd, Cr and Pb) and, smoke dried fish tissue (Cd, Cr, Mn, Ni and Pb). Result showed that Cd and Cr were constantly detected above acceptable environment limits, and the MPI revealed major contamination in shrimps at Bakassi, although overall metal pollution index across the studied locations was low. </p> <p>The THC and ∑16PAH varied with seasons and tides, and according to location but indicated a possible pollution gradient increasing from Abi to Ibeno. The THC showed the greatest water concentration (7.70 mg L^-1 ) at Bakassi, while concentrations in soil (3.75 mg kg^-1 ), sediments (2.60 mg kg^-1 ), (BMP) (182.14 mg kg^-1 ), shrimps (4.82 mg kg^-1 ), fresh muscle/smoked fish tissue (5.98/16.17 mg kg^-1 ), liver (4.36 mg kg^-1 ) and bile fluid (0.38 mg kg^-1 ) were greatest at Ibeno. Similarly, ∑16PAH showed greatest concentration at Bakassi in water (2.03 mg L^-1 ), soil (0.02 mg kg^-1 ), microplankton (28.35 mg kg^-1 ), smoked fish (2.17 mg kg^-1 ) and liver (38.47 mg kg^-1 ), while Ibeno shrimps (7.78 mg kg^-1 ), fresh fish (7.23 mg kg^-1 ) and bile fluid (5.72 mg kg^-1ww) recorded the greatest ∑16PAH. Generally, elevated THC and ∑16PAH occurred more frequently usually in the wet season at either Bakassi or Ibeno, but elevated pollutants in biotic samples during the dry season is attributed to bioaccumulation of the pollutants. For source identification of detected PAHs, the molecular diagnostic ratios (DR) suggest a dominance of petrogenic sourced PAHs and the BaP_TEQ ecological assessment indicated a greater risk in aquatic foodchain samples where the US Environmental Protection Agency (USEPA) limit in fish for human consumption was exceeded. Biomarker responses of the sentinel catfish showed that haematological parameters and enzyme activities were significantly greater in the wet season, while serum lipid concentrations and biochemical metabolites indicated some significant differences over locations with greater concentrations either at Bakassi or Ibeno. Morphometric parameters mainly indicated similarities in the catfish population across the study locations. Gill and liver histology revealed pathological lesions in fish from all the study locations, irrespective of season but with increased lesions and tissue alterations in samples from the oil producing areas of Bakassi/Ibeno compared to the control area, Abi. Measured chemical composition of catfish from Ibeno indicated a low score on the food quality index. The biomarkers showed good potential as tools for evaluating impacts, including pollutants, on aquatic habitats. Further, the microplankton exposure, representing the primary trophic level in the foodchain, is reflective of the environmental health status and can provide a framework necessary for effective assessment, conservation and management of contamination in the aquatic ecosystems. This thesis provides the first systematic characterisation of pollutants including hydrocarbon pollution over a gradient of oil impacted areas in the eastern Niger Delta with evidence of pollutant distribution to areas with no pollution history. It, therefore, recommended the need for ecological monitoring and food safety assessment within and beyond the core oil producing communities.</p> <p>The baseline spatial and seasonal data combined with the effect biomarkers responses documented in this thesis provides a systematic integrated approach for understanding of current contamination and its impact in the region. It also provides some data to knowledge on possible ecological assessment tools in the eastern NDR aquatic ecosystems. Further multidisciplinary, comprehensive and high throughput omics-based research have been recommended.</p>