Comparative Toxicological Profiles of Copper, Zinc, and Lead in Urban Environments. Exposure Pathways and Long-Term Public Health Implications. A Systematic Review

Transport activity, industrial emissions, waste, atmospheric deposition, contaminated water systems, and dust resuspension have resulted in persistently redistributing copper (Cu), zinc (Zn), and lead (Pb) in urban environments as they are continuously redistributed in the air, dust, soil, water, food, and interior surfaces. This paper systematically reviewed the toxicological comparison of Cu, Zn, and Pb in urban environments, with reference to exposure pathways and long-term effects on the population. The study adopted the PRISMA 2020 framework and followed a comparative narrative synthesis design. A search of the literature was conducted in Scopus, Web of Science Core Collection, PubMed/MEDLINE, ScienceDirect, and Google Scholar using Boolean combinations of metal-specific, urban-exposure, and toxicological keywords. The search generated 1,248 records (36 of which were identified by hand), of which 268 were duplicates, leaving 980 distinct records. Among them, 671 failed on the title stage, 167 on the abstract stage, and 62 on the full-text eligibility assessment; thus, 80 peer-reviewed studies were retained in the final synthesis. Data were systematically obtained on the type of study location, environmental matrix, types of metal contamination, sources of contamination, exposure pathways, toxicological endpoints, biomarkers, and the effects of contamination on public health. Findings indicated that the most frequently encountered media of exposure were road dust, street dust, and urban soils; drinking water; indoor dust; and food systems, but the most prevalent routes of exposure were inhalation, dust ingestion, water ingestion, dietary intake, dermal contact, and occupational exposure. The best result was that Pb was the most consistently risky metal, and became not only essential but also toxic when exposed in a chronic excess manner, while Cu and Zn displayed the dual essential yet toxic quality. Generally, exposure to urban metals is cumulative, multipathway and a key long-term community health issue.