Assessment of Heavy Metal Contamination in Scratch-Off Coatings of Prepaid Mobile Phone Cards in Saudi Arabia: Analytical Determination, Exposure Pathways, and Human Health Risk Evaluation.

Prepaid mobile phone recharge cards remain widely used consumer products in many low- and middle-income settings, yet the scratch-off coatings that conceal personal identification numbers (PINs) have received little attention as potential sources of trace-metal exposure. The present study quantified lead (Pb), cadmium (Cd), and copper (Cu) in scratch-off coatings collected from three major telecommunications brands marketed in Saudi Arabia and evaluated potential health risks using conservative and realistic exposure models. Thirty cards from each brand were purchased from retail outlets in Taif city. Scratch-off coatings were mechanically removed, homogenized, and digested using nitric/perchloric acid prior to analysis by flame atomic absorption spectrometry (AAS). Quality assurance procedures included blank correction, triplicate analysis, calibration verification, and recovery assessment (> 90% for all analytes). Measured concentrations ranged from 16.12 to 17.62 mg/kg for Pb, 0.26 to 0.52 mg/kg for Cd, and 9.69 to 13.13 mg/kg for Cu, with Pb consistently representing the dominant contaminant. Exposure was assessed by the daily intake of metals (DIM), average daily intake (ADI), and dermal absorbed dose (DAD) approaches. Under the conservative DIM scenario, Pb yielded values of 0.0248-0.0271 mg/kg/day and corresponding Health Risk Index (HRI) values of 6.20-6.78, exceeding the safety threshold. In contrast, ingestion-based ADI estimates (10-6 mg/kg/day) and DAD estimates (10-8-10-9 mg/kg/day) were markedly lower, indicating that realistic exposure is substantially less than the upper-bound scenario. Target hazard quotient (THQ) values exceeded unity for Pb but not for Cd or Cu; however, the cumulative Hazard Index (HI) ranged from 7.08 to 7.76, indicating possible noncarcinogenic concern dominated by Pb. Target cancer risk (TCR) values for Cd (1.52 × 10-6-3.04 × 10-6) fell within the generally acceptable regulatory range but still indicate a measurable lifetime cancer risk. Overall, the findings identify scratch-off coatings as a previously underrecognized consumer-product exposure pathway and support the need for improved quality control, regulatory oversight, and safer coating formulations.