Evaluating the Effects of Effluent and Heavy-Metals on the Physicochemical Parameters of Ikpoba River Benin City, Nigeria

Abstract

Around the world, water bodies are the primary location for the disposal of waste. Down the Ikpoba river gradient, water samples were taken from stations A1, A2, B1, and B2. Atomic Absorption Spectrometry (AAS) was used to measure the concentrations of heavy metals, like Iron (Fe), Zinc (Zn), Copper (Cu), Lead (Pb), and Cadmium (Cd) and the physicochemical characteristics of the water detected. The results revealed varying concentrations of contaminants, which can cause deterioration of aquatic ecosystem, waterborne illnesses from ingestion of contaminated aquatic life. The ANOVA result, revealed a strong positive relationship between BOD and COD across the full dataset which confirms that organic waste is the dominant driver of both parameters. Notably, the COD values are disproportionately higher than the corresponding BOD values at downstream. The high BOD at downstream drives microbial oxygen consumption, explaining the dissolved oxygen depletion observed at B1 and B2. The extreme COD at B1, points to a direct effluent discharge point in close proximity to this station. The COD:BOD ratio of 10:1 to 28:1 at downstream confirms that a substantial fraction of the organic load is refractory, meaning it will persist in the river long after the readily biodegradable fraction has been consumed. Upstream stations show considerably higher EC values than their downstream counterparts: A1 records 497 and 459 mS/m, and A2 records 466 and 233 mS/m. The slightly elevated iron at A2 (0.621-0.780mg/L) and the anomalous alkalinity at A1(pH 9.65-9.9) B1 records the most extreme values across nearly every parameter (BOD up to 20mg/L, COD up to 560mg/L, iron up to 2.687mg/L) indicating it is the proximity to the discharge point. B2, located further downstream, shows partial attenuation (mean COD 311 vs 388mg/L at B1), which is consistent with dilution and self-purification processes operating between the two stations. High levels of iron in both station A1, this 6:2 split means that 75% of all samples collected from the Ikpoba River exceeded the WHO guideline. The pH in upstream station A1 clearly exceeds the WHO limit: its two readings of 9.9 and 9.65, shows alkalinity and above the safe maximum for drinking water. The existence of heavy metals is harmful to aquatic life, and does move up in the food chain; even when present at a steady rate. This indicates the pressing need for reinforcement of systematic effluent treatment and pollution control measures to preserve the Ikpoba river and protect human health.