Short-Term Aging of Pod-Derived Biochar Reduces Soil Cadmium Mobility and Ameliorates Cadmium Toxicity to Soil Enzymes and Tomato.

Contamination of agricultural soil with cadmium (Cd) has become a global concern because of its adverse effects on ecohealth and food safety. Soil amendment with biochar has become one of the phytotechnologies to reduce soil metal phyto-availability and its potential risks along the food chain. Biochar, derived from cocoa pod, was evaluated in soil Cd fractions (exchangeable, reducible, oxidizable, and residual) by modified Commission of the European Communities Bureau of Reference sequential extraction and its efficacy to ameliorate Cd toxicity to soil enzymes and leaf bioactive compounds. A pot experiment was conducted using Cd-spiked soil at 10 mg/kg with tomato (Solanum lycopersicum L.) at a biochar application rate of 1 and 3% (w/w) for 6 wk. The addition of biochar significantly reduced (p < 0.05) the exchangeable, reducible, and residual fractions by at least approximately 23%, with a consequential decrease in Cd root uptake and transport within tomato tissues. The activity of soil enzymes (catalase, dehydrogenase, alkaline phosphatase, and urease) was affected by Cd toxicity. However, with the exception of dehydrogenase, biochar application significantly enhanced the activity of these enzymes, especially at the 3% (w/w) rate. As for the secondary metabolites we studied, Cd toxicity was observed for glutathione, terpenoids, and total phenols. However, the biochar application rate of 1% (w/w) significantly ameliorated the effects of toxicity on the secondary metabolites. In conclusion, biochar demonstrated the potential to act as a soil amendment for Cd immobilization and thereby reduce the bioavailability of Cd in soil, mitigating food security risks. Environ Toxicol Chem 2021;40:3306-3316. © 2020 SETAC.

Cadmium toxicity in cowpea plant: Effect of foliar intervention of nano-TiO2 on tissue Cd bioaccumulation, stress enzymes and potential dietary health risk.

The study was conducted to investigate the effects of foliar-intervention of nano-TiO2 on Cd toxicity in cowpea plants. Cowpea plants were exposed to Cd toxicity at 10 mg/kg soil for 21 days and afterwards, subjected to six episodes of foliar application of nano-TiO2 intervention. Results showed that foliar-applied nano-TiO2 significantly promoted chlorophyll b and total chlorophyll contents after Cd stress as compared to Cd-stressed plants without the intervention. Interestingly, Cd contents of roots, shoots and grains were significantly reduced (p < 0.05) after nano-TiO2 sprays compared to Cd-stressed plants. However, the Cd contents in edible tissues (leaves and seeds) after interventions remained above recommended threshold. Furthermore, nano-TiO2 interventions promoted stress enzymes activity in both roots and leaves as well as increased Zn, Mn and Co levels in seeds compared to Cd-stressed plants without intervention. Estimated daily intake of Cd in leaves and seeds for adult subpopulation exceeded the WHO recommended daily intake by some folds in Cd-stressed and nano-TiO2-treated plants. The health risk quotient (HQ) for adult subpopulation exceeded unitary in seeds from nano-TiO2 treatments (HQ = 1.75 and 1.96, respectively) while no potential risk was obtained for leaves. Overall, foliar application of nano-TiO2 portends significant ameliorative potential for Cd toxicity in cowpea plants.

Bioaccumulation and associated dietary risks of Pb, Cd, and Zn in amaranth (Amaranthus cruentus) and jute mallow (Corchorus olitorius) grown on soil irrigated using polluted water from Asa River, Nigeria.

Dietary uptake of heavy metals through the consumption of vegetables grown on polluted soil can have serious human health implications. Thus, the study presented in this paper investigated the bioaccumulation and associated dietary risks of Pb, Zn, and Cd present in vegetables widely consumed in Nigeria, namely amaranth and jute mallow, grown on soil irrigated with polluted water from Asa River. The study found that the soil was polluted with Zn, Pb, and Cd with Pb and Cd being contributed by polluted river, while Zn was from geogenic sources. The metal concentration in amaranth and jute mallow varied in the order of Zn > Pb > Cd and Zn > Pb ≈ Cd, respectively. Jute mallow acts as an excluder plant for Pb, Cd, and Zn. Consequently, the metal concentrations in jute mallow were below the toxic threshold levels. Furthermore, non-cancer human health risk of consuming jute mallow from the study site was not significant. In contrast, the concentrations of Pb and Cd in amaranth were found to be above the recommended safe levels and to be posing human health risks. Therefore, further investigation was undertaken to identify the pathways of heavy metals to amaranth. The study found that the primary uptake pathway of Pb and Cd by amaranth is foliar route, while root uptake is the predominant pathway of Zn in amaranth.