Sun et al. 2025 - Biochar-alginate composite for cadmium-contaminated lettuce soil

Sun and colleagues tested a modified biochar-calcium alginate hydrogel composite (MB-CA) as an in situ passivation material for cadmium-contaminated agricultural soil. The study reports adsorption, soil-fraction, pot, and field endpoints, including reduced cadmium in lettuce edible parts. This is mitigation evidence for crop supply-chain controls; its soil and amendment-performance values must not be pooled as consumer-product occurrence concentrations.

Key numbers

The PDF abstract reports that 7.0% of sampled Chinese agricultural-soil sites exceeded the GB 15618-2018 soil environmental quality standard for cadmium. In this study, adsorption of Cd2+ by MB-CA fit the Freundlich isotherm better than the Langmuir model, and the authors describe the effective pH range as pH 4-6.

In the pH experiment, adsorption capacity increased from 3.65 mg/g at pH 2 to 32.59 mg/g at pH 4. The isotherm discussion reports a highest calculated maximum adsorption capacity of 25.94 mg/g at 40 degrees C.

The test soil had pH 6.77 +/- 0.20, soil organic matter 40.6 g/kg, cation-exchange capacity 9.1 mol/kg, and Cd content 0.73 mg/kg. The authors state that the pot and field test soil was approximately 0.75 mg/kg Cd, above the GB15618-2018 agricultural-land risk-screening value of 0.3 mg/kg for 6.5 < pH ⇐ 7.5.

After MB-CA treatment and removal of the composite material, soil Cd decreased from 0.76 mg/kg to 0.35 mg/kg and 0.25 mg/kg in the reported experiments. In field experiments, exchangeable Cd decreased from 27.3% to 19.26%, while residual Cd increased; the pot-experiment narrative reports residual Cd increasing from 58.13% to 67.4%.

For lettuce, MB-CA reduced cadmium content in edible parts by 63.11% and 76.92% in the field and pot experiments, respectively, compared with controls. The modified-biochar comparator reduced lettuce Cd by 33.10%.

Methods (brief)

The study cross-linked modified biochar and calcium alginate hydrogels to make MB-CA, then evaluated adsorption isotherms, pH response, soil Cd fractions, lettuce Cd, and soil microbial indicators. Pot treatments used 50 g Cd-contaminated soil per treatment, added composite material equivalent to 2% of soil weight, included modified-biochar and deionized-water controls, and used three replicates. Lettuce was harvested after 40 days. The field experiment applied MB-CA at 1 kg/m2 and used a deionized-water control. Soil Cd fractions were analyzed by Tessier sequential extraction, and total Cd was measured by graphite furnace atomic absorption spectrometry.

Implications

Certification: Exclude the spiked-solution, soil, and lettuce-reduction endpoints from occurrence-threshold pools. The paper supports cadmium mitigation and supplier-control context for contaminated growing environments.

Courses: Useful for agronomic-remediation modules because it links pH control, adsorption isotherms, soil Cd speciation, and edible-crop Cd reduction.

App: No direct product-risk distribution. The lettuce result can support a mitigation note that passivating Cd-contaminated soil may reduce crop uptake when validated for the farm and crop.

Wiki pages this source may touch

• agronomic
• remediation-evidence
• cadmium
• atomic-absorption-spectrophotometry

Verification notes

This page was built from the PDF title page, abstract, results sections on pH, isotherms, soil Cd fractions, lettuce Cd, soil physicochemical properties, and pot/field methods. The auto-fetch filename’s “fabric-protectants” label is not supported by the paper content. Products and ingredients are intentionally empty because the source is mitigation evidence, not a direct survey of a finished consumer product.

Page history

The five most recent substantive edits to this page. The full version history lives in git; when DOI minting comes online (see schema docs), each entry below will also link to a version-pinned DataCite DOI.