Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental pollutants that possess serious risks to human health and the environment. Forty riverbed sediments samples were collected in mangrove river bed sediments where artisanal refining of crude oil takes place in the Niger Delta of Nigeria. The concentration, occurrence, distribution, toxicity and health risk of sixteen priority PAHs (16PAHs) were analysed in the samples. Apart from Nap, Acy, BkF, InP and DbE, all the other PAHs were present in all the sampled points of the studied area with BbF and BaA recording the highest mean values. The range and mean of the total PAHs (∑16PAHs) of this study are 23.461–89.886 mg/kg and 42.607 ± 14.30 mg/kg dry weight (dw), which is classified as heavily contaminated when compared to the European classification of PAHs pollution in soil (>1.0 mg/kg). The range of the effect range factors used to assess the risk of PAHs in an ecosystem (Effect rang-low (ER-L) and Effect range-median ER-M) of this study is from 0.953 to 8.80 mg/kg. PAHs below ER-L (4.0 mg/kg) indicate no toxic effect, but values above ER-M (44.79 mg/kg) indicate toxic effects to the sediments, its resources and, ultimately, the public that consumes the resources thereof; hence, the study area falls within the contaminated category. The occurrence of the high molecular weight (HMW) PAHs (73.4%) supersedes those of the lower molecular weight (LMW) PAHs (26.6%). The diagnostic ratios and principal component analysis suggest that the main contributors of PAHS into the sediments are the combustion of biomass, fossil fuel (crude oil) and pyrogenic sources. The toxic equivalent quotient (TEQ) and mutagenic equivalent quotient (MEQ) of PAHs ranged from 2.96 to 23.26 mgTEQ/kg dw and 4.47 to 23.52 mgMEQ/kg dw, and the total mean toxic equivalency quotient (∑TEQ) (15.12 ± 8.4 mg/kg) is also greater than the safe level of 0.6 mg/kg, which indicates high toxicity potency. The mean incremental lifetime cancer risks (ILCRs) of human exposure to PAHs shows that both adults TotalILCR adults (6.15 × 10−5) and children TotalILCR children (2.48 × 10−4) can be affected by dermal contact rather than ingestion and inhalation. Based on these findings, the appropriate regulatory bodies and other organs of government in the region should enforce outright stoppage of the activities of these illegal artisans who do not have control mechanisms for loss control at the site and carry out appropriate clean-up of the area.

The impact of artisanal refining of crude oil on the river bed sediments of the study area was investigated by assessing some quality properties. The result showed some consistency across the stations of the study area; however there were some differences between the values of the test stations and control station indicating some level of impacts on the quality of the sediments. .383 and 0.2610.128, respectively. The result indicated that the said activities affected the pH, PO4 3-, SO4 2-, NO 3-, Cl -etc. of the study area; as these values were consistently lower than that of the control station. Again some of the quality properties were higher or lower than those of the control station and some related studies within and outside the region of the study area indicating some impacts which could be mostly anthropogenic. These impacts if not checked and the makeshift refining of the crude oil stopped by the appropriate regulatory bodies could have some adverse effects on the aquatic life quality of the ecosystem.

The major aim of the present study was to evaluate the concentration levels of some heavy metals and their relationships between the bottom sediments, its overlaying (bottom) water and the surface water of the study area in Andoni local Government of Rivers State, Nigeria (Long.7° 20' 48.639''E and Lat.4 29 20.169N) using standard methods of analysis. The mean result showed variation patterns (P<0.05) of the metals in each of the medium as - surface water – Mg>N=Cu=Zn>Pb=Cd>V; bottom water – Mg>Cu>Ni=Zn>Pb=Cd>V and bottom sediments – Mg=Zn>Pb>Cd>Cu=Ni>V, while that of the media for each metal is Sediment >> Bottom water=Surface water. The sediments of the study area had more positive significant correlations among metal pairs than others indicating that metals were more bound to the sediments than in the water columns. V-Cd, V-Pb and V-Ni showed significant positive correlations in the water columns indicating that their input sources may likely be the same, which could have been from petroleum related activities. The level of contamination of the study area is relatively high when compared to related studies within and outside the region. It is therefore recommended that the activities of this make-shift refining of crude oil in the area should be stopped by the relevant regulatory agencies and also further studies on other media should be carried out.