# Ba–Sr–V as Geogenic and Traffic Tracers in Paediatric Hair from Urban–Industrial Spain, with Co-Located Topsoil Vanadium

## TL;DR

This study analyzed barium, strontium, and vanadium in children's hair from an urban-industrial area in Spain to trace geogenic and traffic-related sources.

## Contribution

The study introduces a cautious tracer-based interpretation of Ba–Sr spatial patterns in hair, distinguishing geogenic and traffic influences in urban-industrial settings.

## Key findings

- Barium and strontium showed strong spatial gradients in adolescents, suggesting heterogeneous contact with dust and traffic materials.
- Vanadium levels in hair were low and not spatially discriminatory, indicating limited utility as a tracer in low-contrast urban settings.
- Soil–hair correspondence was weak overall but moderate in adolescent girls for vanadium.

## Abstract

Urban–industrial environments can generate mixed geogenic and traffic-related metal signatures in paediatric scalp hair, yet interpretation is challenged by left-censoring and limited health-based guidance values for hair. We quantified barium (Ba), strontium (Sr) and vanadium (V) in archived scalp hair collected in 2001 from children (6–9 years, n = 120) and adolescents (13–16 years, n = 97) residing in Alcalá de Henares (central Spain). Samples were washed, digested and quantified by Inductively coupled plasma mass spectrometry (ICP–MS; laboratory processing in 2025); results below the limit of detection (LoD) were treated as left-censored using NADA2 (no substitution). In children, Ba and Sr were frequently quantifiable (medians 0.193 and 0.412 µg/g; 38.3% and 23.3% <LoD), whereas V was heavily censored (74.2% <LoD; median 0.003 µg/g). Adolescents showed higher Ba and Sr and broader upper tails (Ba median 0.287 µg/g, P95 2.061 µg/g; Sr median 1.105 µg/g, P95 4.995 µg/g), while V remained low (median 0.011 µg/g, P95 0.052 µg/g). Ba and Sr displayed strong spatial gradients across four residential zones in adolescents (censored-data Peto–Peto tests p < 1 × 10−8), but V did not (p = 0.162). Co-located residential topsoils were available only for V and showed limited between-zone contrast; soil–hair correspondence was weak overall but moderate in adolescent girls (Spearman ρ = 0.433). These findings provide a historical baseline and support a cautious tracer-oriented interpretation in which the observed Ba–Sr spatial patterning is consistent with heterogeneous contact with dust- and traffic-influenced surface materials, while V appears less discriminatory in low-contrast community settings.