Heavy metal contamination in agricultural soils poses a growing global threat to food safety, particularly in rapidly urbanising and industrial regions. Despite widespread documentation of soil pollution, few studies have experimentally linked land-use stratification with plant metal uptake and human health risk using integrated field-based approaches. This study conducted a controlled assessment of heavy metal accumulation and associated dietary health risks across urban, peri-urban, and rural zones in the North Kazakhstan Region. A total of 36 composite topsoil samples (0–20 cm) and corresponding Lactuca sativa and Lolium perenne specimens were collected from 12 georeferenced plots and analysed for eight heavy metals. Urban soils exhibited significantly elevated concentrations of lead (131.2 ± 19.8 mg/kg) and cadmium (12.6 ± 2.7 mg/kg), exceeding national maximum permissible concentrations by 4.4 and 3.6 times, respectively (p < 0.01). Bioconcentration and transfer factors were highest for Cd (BCF = 1.82, TF = 1.27 in lettuce), confirming its strong phytoavailability. Health risk assessments revealed that children consuming urban-grown lettuce exceeded US EPA thresholds for non-carcinogenic risk (HRI = 1.75 for Cd; 1.38 for Pb). Strong correlations were observed between soil contamination levels and both plant uptake (r = 0.87 for Cd) and estimated daily intake (r = 0.81), reinforcing the direct link between contaminated soils and dietary exposure.