Cadmium and lead pollution in environmental and food matrices in Kakamega Town of Kenya highlighting risks in rapidly urbanizing regions of Africa

Environmental contamination from toxic heavy metals poses severe risks to public health, ecological, and food safety risks around the world. Many studies have reported elevated heavy metal levels in multiple environmental media. Yet, many potentially polluted sites remain unexplored. The current study assessed heavy metal pollution in agricultural soils, water, and pumpkin leaves of peri-urban areas of Kakamega town, Kenya. Samples of the three matrices were collected from 21 sites across three zones and analyzed for arsenic (As), cadmium (Cd), nickel (Ni), lead (Pb), copper (Cu), and zinc (Zn) using atomic absorption spectrophotometry. Measured metal levels were evaluated against international and national standards (FAO/WHO, European Union (EU), and Kenya’s National Environmental Management Authority (NEMA)) for agricultural soils, drinking water, and leafy vegetables. Sequential soil extraction and correlation analyses were deployed to determine soil metal speciation, bioavailability, and inter-matrix relationships. The findings depicted Cd pollution in all water samples, and Pb and Ni in sections of soil and leafy vegetable samples. Pb pollution was most prevalent in sites next to town center and along major traffic corridors, highlighting vehicular emissions as the dominant pollution source. Cd enrichment was prominent in populated informal settlements—implicating inadequate waste management as the key contributor. Sequential extraction showed that 31–35% of soil Cd occurred in exchangeable fractions, posing risk of bioavailability, while Pb was immobilized within organic and sulfide-bound soil phases. These results highlight persistent heavy metal contamination with implications for public health, environmental sustainability, and agricultural productivity. The study emphasizes need for extended investigations to similar landscapes, strengthened urban waste management, stricter environmental regulations, and tailored strategies to mitigate pollution propagation through vulnerable urban–agricultural interfaces.