Scoping Review on Soil Contamination from Pb–Zn Slag and Environmental Assessment Methods

Pb–Zn slag and smelting activities represent a persistent global source of soil contamination, releasing toxic heavy metals—lead (Pb), zinc (Zn), cadmium (Cd), and arsenic (As)—with documented risks to ecosystems and human health. Although previous reviews have addressed heavy metal contamination near smelters and pollution indices as assessment tools, no review has specifically mapped environmental assessment methods for Pb–Zn slag-contaminated soils, and evidence from Central Asia remains absent. This scoping review, following PRISMA-ScR 2018 guidelines, maps the global evidence base on soil contamination from Pb–Zn slag and associated assessment methods. Searches across Dimensions, PubMed, and OpenAlex identified 410 records; 56 studies (2010–2025) met the inclusion criteria. Studies were concentrated in China (35.7%), Poland (8.9%), and Brazil (7.1%); no studies from Kazakhstan were identified despite major Pb–Zn smelting operations in the Shymkent region. All studies reported heavy metal concentrations exceeding regulatory thresholds, with cadmium as the primary ecological risk driver and lead posing the greatest health risk to children. Assessment methods included pollution indices (73.2%), ecological risk assessment (67.9%), GIS-based spatial analysis (57.1%), human health risk frameworks (51.8%), and source apportionment models (50.0%). Post-2018 studies increasingly applied integrated multi-method frameworks. Critical gaps include the absence of Central Asian research, limited predictive modeling, and a lack of standardized protocols. Findings provide a structured evidence map to guide environmental monitoring and remediation at slag-contaminated sites globally.