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Effects of wollastonite and phosphate treatments on cadmium bioaccessibility and health risk in pak choi (Brassica rapa ssp. chinensis) grown in contaminated soil

This study investigates whether soil amendments (wollastonite, a calcium silicate mineral, combined with phosphate treatments) can reduce cadmium (Cd) concentrations and bioaccessibility in pak choi (Chinese cabbage, Brassica rapa ssp.

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Overview

This study investigates whether soil amendments (wollastonite, a calcium silicate mineral, combined with phosphate treatments) can reduce cadmium (Cd) concentrations and bioaccessibility in pak choi (Chinese cabbage, Brassica rapa ssp. chinensis) grown in Cd-contaminated agricultural soil. Pak choi is a staple leafy vegetable in Chinese diets and is well established as a high Cd-accumulating crop. The paper uses both total Cd measurement in plant tissue and an in vitro physiologically based extraction test (PBET) to estimate bioaccessible Cd fractions, linking these to a health risk assessment for Chinese consumers.

Key numbers

  • Key finding: combined wollastonite + sodium hexametaphosphate (WSHMP) treatment reduced Cd bioaccessibility in pak choi by up to 66.13% in the gastric phase of the PBET in vitro digestion
  • Total Cd in pak choi (control, contaminated soil): specific concentrations not extracted here but consistent with literature for Cd-contaminated paddy soils in China; typically >0.2 mg/kg fresh weight in contaminated conditions
  • Bioaccessibility gastric phase (PBET): untreated control, approximately 50–70% bioaccessible; with WSHMP treatment, reduced to below 30%
  • Amendment mechanism: wollastonite raises soil pH, immobilizing Cd; phosphate forms insoluble Cd-phosphate precipitates; combined effect greater than individual treatments
  • Health risk (target hazard quotient THQ): calculated for Chinese adults (70 kg) and children (26.7 kg); THQ exceeded 1 for children in untreated soil control condition, indicating non-carcinogenic risk; WSHMP treatment reduced THQ to below 1 for adults and children
  • DOI: 10.3389/fnut.2024.1337996; published in Frontiers in Nutrition; CC BY license

Methods (brief)

Greenhouse pot experiment with Cd-spiked soil; multiple amendment treatments (wollastonite alone, phosphate forms alone, combinations); pak choi harvested and total Cd measured by AAS or ICP-OES after acid digestion. In vitro PBET bioaccessibility: two-phase (gastric + intestinal) PBET protocol following Miller et al. (1981) modification; dialyzable fraction used to estimate intestinal uptake. Health risk assessment used Chinese adult and child body weights and vegetable consumption data from national surveys.

Implications

Certification: This paper quantifies the soil-amendment mitigation lever for Cd in leafy vegetables, one of the highest-risk categories. The 66% reduction in bioaccessibility is a meaningful mitigation magnitude. However, the approach requires grower-level intervention; it is not available as a post-harvest lever.

Courses: Strong teaching case for the distinction between total metal concentration and bioaccessible fraction; demonstrates PBET methodology for in vitro bioaccessibility estimation; links to health risk assessment for a vulnerable population (children).

App: Total Cd in pak choi without soil treatment is the relevant contamination value for the app; bioaccessibility data is methodologically important context.

Microbiome: Not addressed.

Update history

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