Spatial distribution of heavy metals in seawater and age-specific health risks to swimmers at Tirang Beach, Indonesia.

River-influenced urban beaches require spatially and temporally resolved monitoring to assess contaminant exposure during recreational activities. This study examined how dissolved heavy metals are distributed in seawater and the health risks they pose to swimmers at Tirang Beach in Semarang City, Indonesia, and evaluated age-specific non-carcinogenic risks from incidental ingestion by adult and child swimmers. Four sampling campaigns at five locations produced 20 station-campaign observations. Metal concentrations were determined using flame atomic absorption spectrophotometry, and their spatial distributions were visualised using geographic information system mapping. Average daily ingestion dose, ingestion hazard quotient, and cumulative hazard index were calculated for the recreational exposure scenarios. Nickel had the highest mean concentration at 0.485 mg L-1 and the widest observed range at 0.120-1.740 mg L-1. The five metals showed distinct temporal maxima and non-coincident spatial patterns. However, these concentration patterns could not identify specific rivers or industrial facilities as confirmed sources. The maximum hazard index was 8.49 × 10-4 for adults and 1.24 × 10-2 for children. Child estimates were approximately 14.64 times higher because of the ingestion-volume and body-weight assumptions applied to the exposure scenario. Nickel contributed most to the cumulative index. The findings support repeated multi-station monitoring, event-based sampling, and source investigation before location-specific public-health measures are implemented.