Geochemical characteristics and health risk assessment of rare earth elements in water from Edo and Cross River States, Niger Delta

Abstract

Water resources in the Niger Delta are increasingly threatened by anthropogenic activities. This study assessed the rare earth elements (REEs) in water from 22 communities in Edo and Cross River States, Nigeria, focusing on their geochemical characteristics and associated health risks. A total of 113 water samples were analysed using Agilent 7700x ICP-MS. The concentration of most REEs excluding scandium and dysprosium exceeded natural background levels. Chondrite-normalized patterns showed strong enrichment with distinct anomalies for cerium (Ce/Ce* = 2.11 - 3.54), europium (Eu/Eu* = 0.49 - 1.01), and gadolinium (Gd/Gd* = 0.80 - 1.65), indicating oxic aquifer conditions, active fractionation, and possible anthropogenic contributions. The Pollution Load (1.12 - 1.38) and Nemerow indices (2.25–2.58) indicated moderate pollution, while the Degree of Contamination (30.68 - 42.04) and very high Water Quality Index values (3,111.55 - 4,055.47) identified them as unsuitable for consumption without treatment. Despite this contamination, non-carcinogenic and carcinogenic risks were negligible across all age groups, with hazard indices (3.34 × 10⁻² - 4.87 × 10⁻²) below 1 and cancer risks (1.64 × 10⁻¹² - 2.39 × 10⁻¹²) within USEPA’s acceptable range. Oral ingestion accounted for 98.5% of total chronic exposure. Principal component analysis showed that bedrock weathering (PC1: 76.14%) is the dominant source of REEs, followed by secondary geochemical fractionation and limited anthropogenic influence (PC2: 13.21%). Although immediate health risks are minimal, the elevated contamination indices and poor water quality underscore the need for sustained monitoring, targeted treatment interventions, and proactive management of water resources in the Niger Delta.