Nemerow Pollution Index and Inter-Variable Relationships in Esuk Oro River, Southern Nigeria

<title>Abstract</title> <p>Pollution indices can condense multivariable water-quality data, but incorrect normalization can produce misleading classifications. This study recalculated single-factor pollution indices and the composite Nemerow pollution index for three stations in Esuk Oro River using station means for nine indicators. Pearson correlations were independently recomputed from five monthly means. Each single-factor index was expressed as the measured value divided by its operational benchmark; for dissolved oxygen, a minimum-objective ratio was used. The composite index combined the maximum and mean single-factor indices. Composite values were 3.015, 3.118, and 3.200 at the upstream, midstream, and downstream stations, respectively. Phosphate was the dominant contributor (single-factor indices 4.172–4.438), while alkalinity marginally exceeded its screening value (1.110–1.162); upstream total suspended solids also slightly exceeded its benchmark (1.054). Significant monthly correlations included alkalinity–nitrate (r=0.987,p=0.002), alkalinity–chloride (r=0.967,p=0.007), and total dissolved solids–nitrate (r=-0.936,p=0.019). The results identify nutrient enrichment as the principal index driver. Because only five monthly observations were available and some benchmarks are operational rather than health-based limits, the index is a screening tool and not a declaration of drinking-water safety.</p>