Assessment of Soil Degradation, Soil and River-Water Contamination, Modeled Human Health Risks, and Vegetation Indicators at Impacted and Reference Sites in Wasit and Baghdad Governorates, Central Iraq

Abstract

Soil and water quality were assessed at four anthropogenically disturbed land-use sites (petroleum refinery, industrial zone, abandoned agricultural land and municipal waste dump) and one undisturbed reference site in Wasit and Baghdad Governorates, central Iraq, during 2025. Surface soils were analysed for Pb, Cd, Zn, Cu, Ni, pH, electrical conductivity (EC) and organic matter; Tigris River water was monitored upstream and downstream of contamination sources; non-carcinogenic and carcinogenic health risks were modeled following USEPA procedures; and vegetation structure was surveyed. The refinery site (S1) had the highest mean soil concentrations of Pb (312.4 mg/kg), Cd (12.8 mg/kg) and Ni (248.4 mg/kg), corresponding to 4.5, 16.0 and 7.1 times the comparison values used. Mean downstream total dissolved solids (TDS) reached 4,218 ± 386 mg/L in the wet season, 322% above the 1,000 mg/L drinking-water standard, and petroleum hydrocarbons exceeded the 0.05 mg/L guideline by 37- to 85-fold. The modeled hazard index for children at S1 was 1.58, driven mainly by Pb ingestion (HQ = 1.14), whereas the adult hazard index (0.18) and the inhalation cancer risks for Cd and Ni (< 10⁻⁷) were within acceptable limits. Plant species richness at the impacted sites ranged from 3 to 18 species per plot, compared with 34 at the reference site, representing reductions of 47–91%. These results provide site-specific baseline information for the selected land uses and support prioritizing confirmatory monitoring and remediation planning at the refinery and waste-dump sites.