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Background.Port Harcourt is an oil-rich city in Nigeria's Niger delta region. For over two years, Port Harcourt experienced black soot deposition in the environment. In November 2016, residents woke up to black soot covering cars, clothes, houses, plants, etc. Soot concentrations continued to increase until the first quarter of 2017. After public outcry, the frequency and concentration of soot deposition began to decline.Objective.The present study was carried out to determine the presence and levels of heavy metals in soot along with a cancer risk assessment of heavy metals exposure in Port Harcourt, Nigeria.Method.Three residential locations were sampled: Aba road, Woji and Iwofe. Sampling was performed from 6:00 am to 6:00 pm, to simulate the estimated duration that most residents who do not work in offices are exposed to soot in places such as the open market and business areas. Five heavy metals (iron (Fe), nickel (Ni), chromium (Cr), cadmium (Cd) and lead (Pb)) were investigated. The data obtained were subjected to Pearson correlation and one-way analysis of variance using SPSS software to test the correlation and significant differences between metals concentrations.Results.Lead was found to have a significant correlation with Cd (0.808), indicating that both metals originated from the same source. Concentrations of heavy metals were higher than control values and the World Health Organization's specifications for ambient air. Chromium concentrations were the lowest. The order of concentration of heavy metals was Fe > Pb > Cd > Ni > Cr.Conclusions.Non-carcinogenic and carcinogenic health risks of these heavy metals were evaluated using the target hazard quotient (THQ) and the incremental lifetime cancer risk (ILCR). Obtained ILCR values were within the acceptable limits for cancer risks. However, the total ILCR values for Cd and Pb for children were 3 times higher than those for adults. This is a source of concern as their prevalence in ambient air puts children and residents in Port Harcourt metropolis at risk of various types of cancers.Competing Interests.The authors declare no competing financial interests.

Land use is one major factor that affects river water quality which is related to anthropogenic activities. Studies have shown that abandoned boats on watershed, petroleum and untreated wastewater from abattoirs can lead to anthropogenic pollution in surface waters. This study, therefore, was designed to assess spatial and temporal variation of selected heavy metals and level of pollution in Woji Creek. The study was carried out in the months of August, September and October 2018. Water samples were collected from five stations along the creek over a 3.2 km stretch. Water was collected to be analysed for heavy metals (Nickel, Cadmium, Copper, Lead and Iron). Results were subjected to ANOVA and heavy metal pollution index (HPI) was calculated using aquatic toxicity reference values (TRV) as threshold values. Heavy metal dominance in Woji was in the order of Pb>Ni>Fe>Cd>Cu. In the river, Ni had mean values ranging from 0.379±0.259 mg l −1 in August to 0.545±0.369 in October, while Pb with the highest concentration had mean values ranging from 0.229±0.333 mg l −1 in October to 1.534±0.103 mg l −1 in September. Concentrations of metals analysed were high than the TRV. Temporal analysis of HPI calculated for the study was above the critical heavy metal pollution index (100) (August=329.358, September=361.796, October=112.715). A correlation was observed between heavy metals analysed during the study. Spatial analysis of HPI showed higher pollution level at Station 3 with the highest anthropogenic activity along the creek. Cu showed a negative correlation to other metals analysed. Sources of pollution on this creek was identified to be both natural and majorly anthropogenic sources. This study, therefore, points out the need for proper environmental management as regards commercial activities around the waterways.

This is the first study related to PAHs distribution in the Woji Creek (Nigeria), that points out potential contaminant sources. The study involved sampling of water and sediment from five stations along the creek monthly (from August to October in 2018). Samples collected were analysed for the concentration of sixteen Polycyclic Aromatic Hydrocarbons (PAHs) using an Agilent 7890B Gas Chromatograph (GC-MS). Eleven (11) PAHs were identified in the water samples with five (5) below detectable limits (Naphthalene, Phenanthrene, Pyrene, Indeno (1, 2, 3, -cd) pyrene and Benzo [(g), (h), (i)] perylene). Results from the surface water showed that in the month of September, the concentration ranged from 6.029 ppm in S4 to 28.331 ppm in S5. October recorded a PAHs concentration ranging between 6.094 ppm at S1 and 29.257 ppm at S5. In the sediment highest concentration of PAHs was recorded in S5; 1809.08 ppm in August, 1810.05 ppm in September and 1821.5 ppm in October. The concentrations of PAHs in sediment were significantly greater than those in the water. In both sediment and water samples, the highest concentrations of total PAHs were recorded in station 5 and the lowest in station 4. The composition of PAH in water identified the dominance of 2 and 3 rings (Low Molecular Weight (LMW) PAHs) over 4, 5 and 6 rings (High Molecular Weight (HMW) PAHs). In the sediment samples analysed, LMW PAHs (2-3 rings) made up about 30% of the composition, while HMW PAHs (4-6 rings) made up about 70% of PAHs member groups. Cross plots showed that the PAHs could have come from petroleum and combustion.

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