Seasonal distribution of radionuclides and metal(loid)s in mining-contaminated soils: an integrated multivariate and risk assessment approach
摘要
Unregulated artisanal mining increases soil contamination, while seasonal changes further worsen the distribution of potentially toxic elements (PTEs), including radionuclides and toxic metals. This study examined the seasonal variation of Zn, Ba, Bi, La, Sc, Sb, Sr, Pb, Th, U, and K in soils from a lead/zinc mining district in southeastern Nigeria. PTEs were measured using ICP–MS, and activity concentrations of 238U, 232Th, and 40 K were calculated from mass concentrations and natural specific activities. Results were compared to regulatory standards, and ecological, radiological, carcinogenic, and non-carcinogenic health risks were evaluated with multiple models. Source apportionment was conducted using multivariate analyses, while spatial variability was evaluated using the coefficient of variance (CV%). The average soil PTE concentrations were Pb > K > Zn > Ba > La > Th > Sr > Sc > U > Sb > Bi (dry), and K > Pb > Zn > Ba > La > Sr > Th > Sc > Sb > U > Bi (wet), while the mean activity concentrations followed ATh-232 > AK-40 > AU-238. Regulatory benchmarks for Zn and Pb were consistently exceeded, and ATh–232 surpassed the world average (45 Bq/kg) in 50% of dry season locations and 56.25% of wet season locations. Health risks were higher for children during the dry season, with non-carcinogenic and carcinogenic risks from cumulative exposure observed in all groups and seasons. Multivariate analysis linked Ba/La/Sc/Sr/U to natural sources and Pb/Zn/Th/Sb to mixed anthropogenic/geogenic sources. Locations L9 (dry) and L5 (wet) were the most ecologically degraded, with Pb posing the greatest ecological hazard. Urgent remediation and sustainable mining practices are recommended to protect the environment and public health.