Cadmium enrichment in topsoil: Separating diffuse contamination from biosphere-circulation signals

Area of Science:

• Environmental Science
• Geochemistry
• Soil Science

Background:

• Cadmium (Cd) is a toxic heavy metal with significant environmental implications.
• Soil Cd concentrations vary between topsoil and subsoil layers, influenced by soil properties and anthropogenic activities.
• Understanding Cd distribution is crucial for assessing ecological risks and managing soil contamination.

Purpose of the Study:

• To compare the statistical distribution of cadmium (Cd) concentrations in topsoil and subsoil across diverse regional datasets.
• To investigate the influence of soil organic matter on Cd accumulation and distribution.
• To estimate diffuse Cd contamination levels and identify potential anthropogenic sources.

Main Methods:

• Analysis of eight regional to continental scale datasets of Cd concentrations in subsoil (C horizon) and topsoil.
• Statistical comparison of Cd concentration ratios (CdTOP/CdSUB) between mineral and organic soil horizons.
• Examination of cumulative distribution functions (CDFs) to assess Cd accumulation and contamination.

Main Results:

• Topsoil is invariably enriched in Cd compared to subsoil, with higher ratios observed when comparing mineral subsoil to organic topsoil.
• Organic topsoil's Cd distribution reflects plant accumulation, differing from lead (Pb) which shows a linear shift.
• Estimated diffuse Cd contamination ranged from below 0.03 mg/kg to 0.28 mg/kg, with some datasets indicating large-scale anthropogenic sources.

Conclusions:

• Natural processes significantly influence Cd distribution, particularly in organic topsoil, leading to selective accumulation.
• Topsoil enrichment of Cd is a consistent observation, with organic horizons playing a key role in its biosphere interactions.
• Further research is needed to address analytical limitations in subsoil Cd assessment and fully understand natural Cd accumulation processes.