Dendrochronological and dendrochemical approaches to assess lindane contamination in pine tree rings at the Bailín landfill site (Sabiñánigo, Huesca, Spain)

Dendrochronology-the scientific method of dating tree rings-has been widely applied to reconstruct past environmental events such as paleoclimatic variation, climate change, wildfire history, droughts, floods, and glacial dynamics. However, its application to track the historical deposition of persistent organic pollutants remains underexplored. In this study, we analyzed annual growth rings of Pinus sylvestris to reconstruct the temporal dynamics of hexachlorocyclohexane (HCH) isomer contamination at the Bailín landfill site (Sabiñánigo, northeastern Spain) over the period 1979-2018. Our results indicated an average tree age of 49.5 years and an average tree-ring width of 1.60 mm. Mean sensitivity values revealed greater tree-ring growth variability during the 1986-1992 interval compared to the remaining periods. The ring width index exhibited a heterogeneous pattern and non-linear growth dynamics in radial tree development over the 78-year analysis period. The lowest HCH concentrations were recorded during 1979-1985, prior to the use of the site for HCH waste disposal. In contrast, the highest concentrations occurred during 2016-2018, following the large-scale relocation of HCH-contaminated material from the old landfill to a newly constructed secure cell. This pattern is consistent with known site management history and suggests that HCH, once absorbed and translocated from the roots to the trunk, exhibits low mobility and high persistence within P. sylvestris tissues. Our findings support, at least for Scotch pine, the use of dendrochemical analysis as a valuable tool for reconstructing temporal trends in environmental contamination by persistent organic pollutants.