Approaching mercury distribution in burial environment using PLS-R modelling

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.

Structural Equation Modelling of Mercury Intra-Skeletal Variability on Archaeological Human Remains

“…Diagenesis is a major issue when trace elemental composition is studied in osteoarchaeological records (Hedges, 2002). For the graves studied in this work, we addressed the factors controlling mercury content in soil/ sediments in a previous investigation (Álvarez-Fernández et al, 2021). This study showed that the buried individuals were the only source of mercury, and results agreed with previous work that found no evidence of diagenetic incorporation of mercury from soil to bone (Emslie et al, 2015;Kepa et al, 2012;Rasmussen et al, 2008Rasmussen et al, , 2013bWalser et al, 2019;Yamada et al, 1995).…”

“…The burial soils showed an enrichment in P and a decrease in alkalinity (from pH ~9 to 8), compared to the soil located from outside the burials. They also showed a secondary enrichment in silt+clay fractions and organic matter (Álvarez-Fernández et al, 2021), soil components able to retain mercury. T1 and T5 are not directly related to the funerary areas of the necropolis previously found, so the large number of bodies there was not expected to greatly influence the geochemistry of the two burials.…”

“…A total of 73 bulk powder bone samples were analysed: 11 for L01, 31 for L06 and 31 for L07. Since the present research is the continuation of previous work (Álvarez-Fernández et al, 2021), in which the distribution of mercury in the burial soil/sediment was assessed for these two graves, bulk bone sampling was intended to be in harmony with the soil/sediment sampling design, where samples were collected in two transectslongitudinal and transversealong each skeleton. The soil/sediment samples used here and in the previous research are the same, excluding those from outside burials that were not included in this study.…”

“…3. The latent constructs can be classified into three groups: i) those related to bone components, collagen and hydroxyapatite (HAP), to assess their role on the skeleton mercury content, and the degree of crystallinity of the mineral phase (HAPc), as it can affect the release of mercury from the bone tissue to the surrounding soil; ii) soil components SM 1. in the silt+clay fraction, among which mercury (Hg), primary silicates (psilicates) and clay were selected to assess the degree of interaction between bone and soil, as the bone was found to be a potential source of mercury to the soil; and iii) location, as it is susceptible to affect mercury content (Álvarez-Fernández et al, 2021).…”

Understanding Necrosol pedogenetical processes in post-Roman burials developed on dunes sands

“…To date, not much attention has been paid to the differences in the content of silt and clay fractions inside and outside the burials. To our knowledge, only our previous article Álvarez-Fernández, et al 59 analysed the silt and clay fraction apart from the ne earth. In this study, we encouraged the analysis of ne fractions, in particular when studying sandy soil/sediments, as they are the most reactive and have the largest potential to contain information about the interaction between buried bodies and burial environment.…”