Earliest evidence of pollution by heavy metals in archaeological sites.

Guadalupe Monge,Nadine Mattielli,Antonio García-Alix,Francisca Martínez-Ruiz,Jordi Rosell,Jose María Bermúdez De Castro,Clive Finlayson,Joaquín Rodríguez-Vidal,Ruth Blasco,Miguel Cortés Sánchez,José Carrión,Geraldine Finlayson,Francisco J Jimenez-Espejo,Naohiko Ohkouchi

doi:10.1038/srep14252

Abstract

Homo species were exposed to a new biogeochemical environment when they began to occupy caves. Here we report the first evidence of palaeopollution through geochemical analyses of heavy metals in four renowned archaeological caves of the Iberian Peninsula spanning the last million years of human evolution. Heavy metal contents reached high values due to natural (guano deposition) and anthropogenic factors (e.g. combustion) in restricted cave environments. The earliest anthropogenic pollution evidence is related to Neanderthal hearths from Gorham's Cave (Gibraltar), being one of the first milestones in the so-called “Anthropocene”. According to its heavy metal concentration, these sediments meet the present-day standards of “contaminated soil”. Together with the former, the Gibraltar Vanguard Cave, shows Zn and Cu pollution ubiquitous across highly anthropic levels pointing to these elements as potential proxies for human activities. Pb concentrations in Magdalenian and Bronze age levels at El Pirulejo site can be similarly interpreted. Despite these high pollution levels, the contaminated soils might not have posed a major threat to Homo populations. Altogether, the data presented here indicate a long-term exposure of Homo to these elements, via fires, fumes and their ashes, which could have played certain role in environmental-pollution tolerance, a hitherto neglected influence.

Highlights

Increases of these pollutants can be expected from long-term human activities, especially combustion, which has been reported in connection with ash biomass[8] and demonstrated to show variable toxicity
In order to reach this objective several cave deposits have been geochemically analysed, including representative archaeological sites from the Iberian Peninsula persistently occupied by Homo populations during the last 1.4 Ma13–15
The studied sites fail to develop soil sensu stricto because endokarstic deposits undergo different sedimentary processes from those affecting conventional soils. They can experience either post-depositional geogenic or pedogenic effects, it is noteworthy that these environments are less subaerially exposed and less affected by atmospheric weathering processes

Summary

Introduction

Caves are persistently restricted environment and heavy metal bio-mediated accumulations, such as those caused by natural organic sources (bird and bat guano)[4,5], or by inorganic sources pertinent to the geological context of the cavern[6,7], may reach relatively high levels. Increases of these pollutants can be expected from long-term human activities, especially combustion, which has been reported in connection with ash biomass (heavy metal enrichment mainly dealing with Cu, Zn and Mn)[8] and demonstrated to show variable toxicity. Zn isotopic analysis have been carried out in order to evaluate whether element accumulation is derived from sea spray or affected by diagenetic processes

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Conclusion