Endocrine-Disrupting Effects of Polycyclic Aromatic Hydrocarbons on Hypothalamic-Pituitary-Gonadal Axis Function in Cattle in the Niger Delta Region

Polycyclic aromatic hydrocarbons are persistent organic pollutants generated by petroleum extraction, crude oil spills, and gas flaring activities extensively documented in the Niger Delta region of Nigeria, encompassing Rivers, Bayelsa, and Delta states. Livestock grazing contaminated pastures and consuming polluted water in this region face chronic polycyclic aromatic hydrocarbon exposure with poorly characterised reproductive endocrine consequences. This study investigated the endocrine-disrupting effects of environmental polycyclic aromatic hydrocarbon exposure on hypothalamic-pituitary-gonadal axis function in cattle in the Niger Delta, using a mixed biomonitoring and experimental approach. Sixty cattle from oil-impacted farms in Rivers and Bayelsa states and 30 cattle from unexposed control farms in Anambra State were enrolled. Polycyclic aromatic hydrocarbon biomarkers including 1-hydroxypyrene and 2-naphthol in urine and 8-hydroxydeoxyguanosine as an oxidative DNA damage marker were quantified by liquid chromatography-mass spectrometry. Serum luteinising hormone, follicle-stimulating hormone, oestradiol, testosterone, and progesterone were measured. Aryl hydrocarbon receptor pathway activation in peripheral blood mononuclear cells was assessed by quantitative PCR of CYP1A1 and CYP1B1 gene expression. Cattle from oil-impacted farms showed significantly higher urinary PAH biomarker concentrations and elevated CYP1A1 expression, confirming aryl hydrocarbon receptor activation. LH pulse frequency and amplitude were significantly reduced in female cattle from impacted farms. Ovarian follicular counts by ultrasonography were significantly lower. Testosterone was significantly reduced in bulls from impacted areas. These mechanistic findings establish a biologically plausible endocrine disruption pathway mediated by polycyclic aromatic hydrocarbons in Niger Delta cattle, with implications for food security and animal welfare policy. Keywords: polycyclic aromatic hydrocarbons, endocrine disruption, hypothalamic-pituitary-gonadal, Niger Delta, cattle.