Abstract
<title>Abstract</title> <p> Mercury (Hg) and lead (Pb) are persistent, toxic trace metals whose pollution legacy from industrial activities can remain in the environment for centuries until reaching long-term sinks. This study reconstructs the history of Hg and Pb accumulation in Lake Estanya (NE Spain), a karstic lake system located 30 km downwind of the industrial complex of Monzón, known for hosting chlor-alkali, metallurgical and chemical industries. Two gravity cores retrieved in 2023 were analysed at sub-decadal resolution, spanning the last 330 years of evolution in Hg and Pb concentrations, enrichment factors, accumulation fluxes, and Pb isotopic composition. Analysis of atmospheric deposition samples from Monzón further enabled characterisation of the pollution processes currently affecting the Estanya catchment, allowing a comparison between legacy contamination and present-day trends. The sedimentary record reveals a rise in Hg and Pb accumulation during the second half of the twentieth century, synchronous with the establishment and expansion of the chemical industry in Monzón, the intensification of metallurgical activity, and the widespread use of leaded gasoline together with growing road traffic in Spain prior to its ban in 2001. Hg and Pb enrichment factors and accumulation fluxes increased exponentially from 1950 onward, followed by a marked decline at the turn of the 21 <sup>st</sup> century, attributed to the effectiveness of environmental regulations and the resulting reduction in primary Hg and Pb emissions. This trend is supported by the Pb isotopic signature, which shifts toward more radiogenic values in recent decades, indicating incipient system recovery. Nonetheless, Pb and especially Hg concentrations and enrichment factors remain elevated, reflecting the persistence of these trace metals and the formation of reservoirs that sustain their recycling decades after primary emissions ceased. Source apportionment of recent atmospheric deposition attributes Hg and Pb inputs to a mixture of industrial emissions, road traffic, and dust from regional sources and Saharan outbreaks. These results show that, while emission inputs are rapidly reflected in lake sediment records, system recovery is delayed by the long-term persistence and remobilisation of legacy Hg and Pb. This finding highlights the relevance of high-resolution lake records for tracking industrial pollution trajectories, enabling assessment of the effectiveness of environmental regulations and ecosystem recovery. </p>