Levels and risk assessment of polycyclic aromatic hydrocarbons in water and fish of Rivers Niger and Benue confluence Lokoja, Nigeria.

Abstract

As from last decade, the pollution of water bodies by chemical toxicants has become a topic of public discourse and concern in many countries. Polycyclic aromatic hydrocarbons (PAHs) are carcinogens and being ubiquitous in nature, are daily being released into water bodies as a result of anthropogenic sources. The water samples were collected with plastic bottles/containers by dipping the sampler below the water surface to minimize the contamination of water sample by surface films and cocked below water surface to avoid air entrapment while the fish samples namely Clarias spp (Catfish) and Oreochromis spp (Tilapias) were purchased from fishermen at the bank of the river confluence. Three water samples each were collected from five sample points [A], [B], [C], [D] and [E] created for that purpose at each visit monthly for a period of six months and taken in an ice-cooler box to the laboratory. In all a total of 90 water samples and 20 fish samples were analysed. The water samples were preserved in a refrigerator below 4°C prior to analysis. The concentrations of the sixteen US EPA priority polycyclic aromatic hydrocarbons (PAHs) were investigated using Gas chromatography coupled with Mass Spectrometer detector (GC-MS) after liquid-liquid and solid-liquid extractions. The concentrations of the six detected PAHs in water were of the following ranges: Nap(Not Detected {ND} to 0.543), Ph(ND to 0.083) Ant (ND to 0.083), BbF(0.080 to 0.093), BkF(0,083 to 0.093) and BaP(0.083 to 0.113) mg/L with distribution pattern of Nap>BaP > BbF=BkF > Ant = Ph. The mean concentration value of PAHs in Catfish and Tilapia were Nap(2.383 and 1.947), Ph(0.050 and 0.057), Ant(0.057 and 0.057), BbF(0.043 and ND), BkF(0.043 and ND) and BaP(0.050 and ND). The health risk assessment showed that the concentration of Benzo[a]pyrene, a known indicator of the presence of carcinogenic PAHs is of health risk concern. The PAHs were not significantly different in the water and fish respectively and the correlation studies showed that the PAHs were from the same source. The study showed clearly that the levels of PAHs in the samples are of concern due to increasing pollution.