Development and Validation of a Box and Flux Model to Describe Major, Trace and Potentially Toxic Elements (PTEs) in Scottish Soils

Luigi Gallini,Antonio Scopa,Andrew Hursthouse

doi:10.3390/ijerph18178930

Abstract

The box and flux model is a mathematical tool used to describe and forecast the major and trace elements perturbations of the Earth biogeochemical cycles. This mathematical tool describes the biogeochemical cycles, using kinetics of first, second and even third order. The theory and history of the box and flux modeling are shortly revised and discussed within the framework of Jim Lovelok’s Gaia theory. The objectives of the investigation were to evaluate the natural versus anthropic load of Potentially Toxic Elements (PTEs) of the Scottish soils, investigate the soil components adsorbing and retaining the PTEs in non-mobile species, evaluate the aging factor of the anthropic PTEs and develop a model which describes the leaching of PTEs in layered soils. In the Scottish land, the soil-to-rock enrichment factorinversely correlates with the boiling point of the PTEs. The same is observed in NW Italy and USA soils, suggesting the common source of the PTEs. The residence time in soils of the measured PTEs linearly correlates with the Soil Organic Matter (SOM). The element property which mostly explains the adsorption capacity for PTEs’ is the ionic potential (IP). The downward migration rates of the PTEs inversely correlate with SOM, and in Scottish soil, they range from 0.5 to 2.0 cm·year−1. Organic Bentoniteis the most important soil phase adsorbing cation bivalent PTEs. The self-remediation time of the polluted soil examined ranged from 50 to 100 years. The aging factor, the adsorption of PTEs’ into non-mobile species, and occlusion into the soil mineral lattice was not effective. The box and flux model developed, tested and validatedhere does not describe the leaching of PTEs following the typical Gaussian shape distribution of the physical diffusion models. Indeed, the mathematical model proposed is sensitive to the inhomogeneity of the layered soils.

Highlights

In the geodynamic earth system, elements cycle between several compartments, most relevant of which are the atmosphere, hydrosphere, pedosphere, biosphere and lithosphere, and across ecosystems in biogeochemical equilibria with these principal planetary reservoirs
We evaluate the chemical–physical processes and kinetics that phous precipitates in non-bioavailable phases occluded in the soil, forming amorphous crystalline remove low-mobileand anthropogenic
These variations are common in soils with high vertical flushing by soil water and assisted by organic colloids from the surface layers

Summary

Introduction

In the geodynamic earth system, elements cycle between several compartments, most relevant of which are the atmosphere, hydrosphere, pedosphere, biosphere and lithosphere, and across ecosystems in biogeochemical equilibria with these principal planetary reservoirs. As demonstrated by Jim Lovelock’s Gaia theory, many of the important driving forces of the earth’s dynamic biogeochemical system, as well as most of the relevant geochemical reaction kinetics, rule the flux of elements between the different earth reservoirs, modulated by the biological activity of living organism [1,2]. Most of the chemical equilibria controlling geodynamics are modulated by simple and multiple retroactive feedback, which ensures some buffering capacity to earth ecosystem and some degree of homeostasis to overall planet earth [3].

Methods

Results

Conclusion