The Shymkent–Saryagash–Abay (A-15) international highway is a major Kazakhstan–Uzbekistan freight corridor that runs through the irrigated horticultural belt of the Turkestan Region in South Kazakhstan, where adjacent fields supply vegetables and cucurbits to the regional market. Composite soil samples (n = 18) were taken at six distances (2–300 m) from the road edge across three locations during 2022–2023, along with edible fruits of tomato, cucumber, watermelon, and melon (n = 12) from the adjoining fields. Pb, Zn, and Cd were measured via flame atomic absorption spectrometry after HNO₃/H₂O₂ digestion. Soil concentrations decreased sharply with distance (Pb: 26.3 → 5.98 mg kg⁻¹; Zn: 21.29 → 4.16; Cd: 0.47 → 0.01 mg kg⁻¹), exceeding the national soil MPCs by 1.5–3 times within 2–10 m. Pb and Zn exceeded the Kazakhstani food-safety MPCs in all four crops, and Cd in three of four (tomato, cucumber, and melon). Transfer factors followed the order of Cd (2.90–4.40) > Zn (1.99–3.00) > Pb (0.16–0.30), and the Cd geo-accumulation index ranged from 1.05 to 1.65 at 2–5 m. Adult dietary risk was acceptable (HI = 0.029–0.052; CR < 1.7 × 10⁻⁶), yet food-safety exceedances support a precautionary sanitary buffer and combined soil-and-crop monitoring along the corridor.

The purpose of the proposed research work is to determine the number of heavy metals (Pb, Zn, Cd) in soils and agricultural crops located near highways in South Kazakhstan (Turkestan region, Saryagash district) and to evaluate their transfer into plants. Soil samples along the highway and vegetables (tomatoes, cucumbers) and cucurbits (watermelon, melon) grown in this area were selected as the objects of the research. The concentrations of heavy metals were determined by atomic absorption spectroscopy. The transfer factor (TF) was calculated to characterize the rate of element transfer into plants. This study provides new data on heavy metal distribution and transfer in agricultural systems of South Kazakhstan, a region where roadside contamination of crops remains insufficiently studied. According to the research results, the concentrations of Pb, Zn and Cd in the soil along the road were found to be 1.5–3 times higher than the permissible limit values. The spread of heavy metals in the soil was determined in a decreasing order: Pb > Zn > Cd. The transfer factor into plants were within the following limits: Pb — 0.16–0.32; Zn — 1.99–3.0; Cd — 2.9–4.4. The highest migration ability was characteristic of the Cd element, which indicated its high bioavailability. As a result of the correlation analysis, positive relationship (r > 0.90) was revealed between all indicators, especially between Zn and Cd (r = 0.99). The conducted research showed that the migration of heavy metals to agricultural crops poses a significant threat to human health. Therefore, it is recommended to conduct regular monitoring, maintain sanitary distances and apply bioremediation measures aimed at reducing soil contamination to prevent the accumulation of heavy metals in products grown along roads.