Abstract
Mercury environmental cycle and toxicology have been widely researched. Given the long history of mercury pollution, researching mercury trends in the past can help to understand its behaviour in the present. Archaeological skeletons have been found to be useful sources of information regarding mercury loads in the past. In our study we applied a soil multi-sampling approach in two burials dated to the 5th to 6th centuries AD. PLRS modelling was used to elucidate the factors controlling mercury distribution. The model explains 72% of mercury variance and suggests that mercury accumulation in the burial soils is the result of complex interactions. The decomposition of the bodies not only was the primary source of mercury to the soil but also responsible for the pedogenetic transformation of the sediments and the formation of soil components with the ability to retain mercury. The amount of soft tissues and bone mass also resulted in differences between burials, indicating that the skeletons were a primary/secondary source of mercury to the soil (i.e. temporary sink). Within burial variability seems to depend on the proximity of the soil to the thoracic area, where the main mercury target organs were located. We also conclude that, in coarse textured soils, as the ones studied in this investigation, the finer fraction (i.e. silt + clay) should be analysed, as it is the most reactive and the one with the higher potential to provide information on metal cycling and incipient soil processes. Finally, our study stresses the need to characterise the burial soil environment in order to fully understand the role of the interactions between soil and skeleton in mercury cycling in burial contexts.
Highlights
Mercury is a global pollutant that is released to the environment from both anthropogenic and non-anthropogenic sources
As it has different chemical species that do not necessary share absorption pathways neither behaviour inside the o rganism[5,6]. This variability leads to a wide range of target organs and clinical symptomatology, which can be affected by dose, time, and route of exposure[7]
There is a handful of studies that deal with mercury in past p opulations[13,20,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41], and only a few assessed mercury diagenesis in burial c ontext[13,22,23,31,36,41] by analysing punctual soil samples associated with the bones and graves. 42approached mercury distribution vertically and horizontally in soil with respect to femur in three burials (nv = 5–6, nh = 5–6, per individual) in a medieval cemetery in Denmark
Summary
Mercury is a global pollutant that is released to the environment from both anthropogenic and non-anthropogenic sources. We have proposed archaeological human remains as suitable archives[13,20] to investigate the impact that changing mercury loads to the environment had in past-populations, especially on pre-industrial times These w orks[13,20] show the same trend previously found b y18 in their paleo-reconstruction of Hg atmospheric levels, with Roman populations showing significantly higher mercury (and Pb) concentrations in skeletal remains than post-Roman populations. Preserved archaeological human remains are mainly skeletons that have been buried for long periods of time—much longer than the individual’s life At this point, two aspects have to be considered: (1) bones are not the target organ for mercury, and (2) bones can be affected by diagenetic processes in the burial environment. Since bone is not a mercury target, as it mainly accumulates in liver and kidney[5], a question remains opens: how is mercury distributed in burials contexts and which are the factors controlling its distribution?
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