Assessing petroleum contamination in parts of the Niger Delta based on a sub-catchment delineated field assessment

Abstract

The Niger Delta in Nigeria is a complex and heavily contaminated area with over 150,000 interconnected contaminated sites. This intricate issue is compounded by the region's strong hydrological processes and high-energy environment, necessitating a science-based approach for effective contamination assessment and management. This study introduces the concept of sub-catchment contamination assessment and management, providing an overarching perspective rather than addressing each site individually. A description of the sub-catchment delineation process using the digital elevation model data from an impacted area within the Delta is provided. Additionally, the contamination status from the delineated sub-catchment is reported. Sediment, surface water and groundwater samples from the sub-catchment were analyzed for total petroleum hydrocarbons (TPH) and polycyclic aromatic hydrocarbons (PAHs), respectively. Surface sediment TPH concentrations ranged from 129 to 20,600 mg/kg, with subsurface (2-m depth) concentrations from 15.5 to 729 mg/kg. PAHs in surface and subsurface sediment reached 9.55 mg/kg and 0.46 mg/kg, respectively. Surface water exhibited TPH concentrations from 10 to 620 mg/L, while PAHs ranged from below detection limits to 1 mg/L. Groundwater TPH concentrations spanned 3 to 473 mg/L, with total PAHs varying from below detection limits to 0.28 mg/L. These elevated TPH and PAH levels indicate extensive petroleum contamination in the investigated sediment and water environment. Along with severe impacts on large areas of mangroves and wetlands, comparison of TPH and PAH concentrations with sediment and water quality criteria found 54 to 100% of stations demonstrated exceedances, suggesting adverse biological effects on aquatic and sediment biota are likely occurring.

Keywords: Environmental remediation; Hydrological analysis; Niger Delta; Petroleum contamination; Sub-catchment assessment.

Fig. 1

Digital elevation model derived sub-catchment. Data derived from Shuttle Radar Topography Mission (SRTM) 1 Arc-Second global dataset and OpenStreetMap. Sub-catchments shown along with types of samples collected (e.g. sediment, surface water, ground water)

Fig. 2

Petroleum contamination in the study area: a heavily oiled creek sediment exposed at the low tide mark, b floating crude oil at the low tide mark, c impacted mangrove shoots, and d mangrove substrates covered in oil with heavily impacted areas in the background

Fig. 3

Distribution of TPH and ∑PAHs in Kporghor River Estuary sediment: a surface TPH, b surface PAHs, c subsurface TPH, and d subsurface PAHs

Fig. 4

Comparative analysis using a whisker plot of sediment samples for individual PAH concentrations sorted by abundance: a surface sediment PAHs and b subsurface sediment PAHs. Error bars reflect the range of non-outlying values, the horizontal line is the median, and black diamonds are outliers

Fig. 5

Distribution of TPH and ∑PAHs in Kporghor River Estuary surface and groundwaters: a surface water TPH, b groundwater TPH, c surface water PAHs, and d groundwater PAHs

Fig. 6

Comparative analysis using a whisker plot of surface water samples for individual PAH concentrations sorted by abundance: a surface water PAHs and b groundwater PAHs. Error bars reflect the range of non-outlying values, the horizontal line is the median and black diamonds are outliers

Fig. 7

Stations in which a surface sediments, b surface waters or c groundwaters samples exceeded an ecological criterium. Subsurface sediment samples showed no exceedance, therefore are not included in the map