Evaluation of uptake of eight metals by Sorghum bicolor grown in arable soil combined with sewage sludge based on prediction models

Contribution of molecular structures and quantum chemistry technique to root concentration factor: An innovative application of interpretable machine learning

Root concentration factor (RCF) is a significant parameter to characterize uptake and accumulation of hazardous organic contaminants (HOCs) by plant roots. However, complex interactions among chemicals, plant roots and soil make it challenging to identify underlying mechanisms of uptake and accumulation of HOCs. Here, nine machine learning techniques were applied to investigate major factors controlling RCF based on variable combinations of molecular descriptors (MD), MACCS fingerprints, quantum chemistry descriptors (QCD) and three physicochemical properties related to chemical-soil-plant system. Compared to models with variables including MACCS fingerprints or solitary physicochemical properties, the XGBoost-6 model developed by the variable combination of MD, QCD and three physicochemical properties achieved the most remarkable performance, with R2 of 0.977. Model interpretation achieved by permutation variable importance and partial dependence plots revealed the vital importance of HOCs lipophilicity, lipid content of plant roots, soil organic matter content, the overall deformability and the molecular dispersive ability of HOCs for regulating RCF. The integration of MD and QCD with physicochemical properties could improve our knowledge of underlying mechanisms regarding HOCs accumulation in plant roots from innovative structural perspectives. Multiple variables combination-oriented performance improvement of model can be extended to other parameters prediction in environmental risk assessment field.

Biosolids application enhances the growth of Aloe vera plants and provides a sustainable practice for nutrient recirculation in agricultural soils

In the present study, the fertilization potential of biosolids (sewage sludge; SS) for the cultivation of Aloe vera plants was investigated using block design. Pot experiments were conducted in this study using 50, 100, 150, and 200 g/kg of SS. Results showed that SS-fertilized soils significantly (p < 0.05) affected the proximate, biochemical, and heavy metal parameters of A. vera plants. In particular, the T4 treatment gave the best results with maximum plant height 62.21 ± 0.10 cm, number of leaves per plant 18.00 ± 4.00, shoot-to-root ratio 6:1, fresh weight 1972.10 ± 0.07 g per plant, dry weight 175.49 ± 0.15 g per plant, total chlorophyll content (TCC) 0.41 ± 0.02 mg/g fwt., carotenoids 0.25 ± 0.04 mg/g, total flavonoids 7.55 ± 0.05 mg/g, total tannins 3.87 ± 0.06 µg/g, ascorbic acid 532.14 ± 0.10 µg/g, superoxide dismutase (SOD) 46.28 ± 0.19 µg/g, catalase (CAT) 119.23 ± 0.17 µg/g, salicylic acid 3.05 ± 0.12 mg/ml and anthraquinones 0.45 ± 0.04 mg/ml, respectively. The proximate plant characteristics were 96.25 ± 2.71% moisture content, crude protein 0.93 ± 0.05%, crude fiber 5.78 ± 0.44%, crude lipid 3.25 ± 0.02%, lignin 10.74 ± 0.30%, cellulose 13.56 ± 1.06%, hemicellulose 7.24 ± 0.14%, ash 8.75 ± 0.03%, and carbohydrate contents 52.18 ± 1.10% in comparison with control treatment. The bioaccumulation factor showed that heavy metal accumulation was in the order of Cd < Ni < Cu < Pb < Cr < Zn < Fe. The prediction models developed on the basis of soil properties showed good fitness results for the prediction of heavy metal uptake by A. vera plants. The study presented a sustainable approach for managing SS in an eco-friendly way while producing good-quality A. vera plants.

Prediction Models Based on Soil Characteristics for Evaluation of the Accumulation Capacity of Nine Metals by Forage Sorghum Grown in Agricultural Soils Treated with Varying Amounts of Poultry Manure

Predictive models were generated to evaluate the degree to which nine metals (Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, and Zn) were absorbed by the leaves, stems and roots of forage sorghum in growing media comprising soil admixed with poultry manure concentrations of 0, 10, 20, 30 and 40 g/kg. The data revealed that the greatest contents of the majority of the metals were evident in the roots rather than in the stems and leaves. A bioaccumulation factor (BAF) < 1 was calculated for Cr, Fe, Ni, Pb and Zn; BAF values for Co, Cu, Mn and Cd were 3.99, 2.33, 1.44 and 1.40, respectively, i.e., > 1. Translocation factor values were < 1 for all metals with the exception of Co, Cr and Ni, which displayed values of 1.20, 1.67 and 1.35 for the leaves, and 1.12, 1.23 and 1.24, respectively, for the stems. The soil pH had a negative association with metal tissues in plant parts. A positive relationship was observed with respect to plant metal contents, electrical conductivity and organic matter quantity. The designed models exhibited a high standard of data precision; any variations between the predicted and experimentally observed contents for the nine metals in the three plant tissue components were nonsignificant. Thus, it was concluded that the presented predictive models constitute a pragmatic tool to establish the safety from risk to human well-being with respect to growing forage sorghum when cultivating media fortified with poultry manure.

Foliar use of TiO2-nanoparticles for okra (Abelmoschus esculentus L. Moench) cultivation on sewage sludge-amended soils: biochemical response and heavy metal accumulation

Considering its richness in organic and inorganic mineral nutrients, the recycling of sewage sludge (SS) is highly considered as a soil supplement in agriculture. However, the fate of hazardous heavy metal accumulation in the crops cultivated in SS amended soils is always a source of concern. Since nanoparticles are widely recognized to reduce heavy metal uptake by crop plants; thus, the present experiment deals with okra (Abelmoschus esculentus L. Moench) cultivation under the combined application of SS and TiO₂-nanoparticles (NPs). Triplicated pot experiments were conducted using different doses of SS and TiO₂-NPs such as 0 g/kg SS (control), 50 g/kg SS, 50 g/kg SS + TiO₂, 100 g/kg SS, and 100 g/kg SS + TiO₂, respectively. The findings of this study indicated that among the doses of treatment combinations investigated, 100 g/kg SS + TiO₂ showed a significant (p < 0.05) increase in the okra plant yield (287.87 ± 4.06 g/plant) and other biochemical parameters such as fruit length (13.97 ± 0.54 cm), plant height (75.05 ± 3.18 cm), superoxide dismutase (SOD: 110.68 ± 3.11 μ/mg), catalase (CAT: 81.32 ± 3.52 μ/mg), and chlorophyll content (3.12 ± 0.05 mg/g fwt.). Also, the maximum contents of six heavy metals in the soil and cultivated okra plant tissues (fruit, stem, and root regions) followed the order of Fe > Mn > Cu > Zn > Cr > Cd using the same treatment. Bioaccumulation and health risk assessment indicated that foliar application of TiO₂-NPs significantly reduced the fate of heavy metal accumulation under higher doses of SS application. Therefore, the findings of this study suggested that the combined use of SS and TiO₂-NPs may be useful in ameliorating the negative consequences of heavy metal accumulation in cultivated okra crops.

Biomass production, metal and nutrient content in sorghum plants grown on soils amended with sewage sludge

Sludge generation from wastewater treatment plants in Uruguay has increased in recent years. Agricultural soils may be a final destination. A greenhouse experiment was conducted to quantify the effect of this sludge on 1) plant biomass production and nutrient concentration of sorghum (Sorghum bicolor var. vulgare); 2) the chemical properties of amended soils; and 3) assess whether heavy metal concentrations in sludge are appropriate according to environmental regulations. Two soils (S1 and S2) were amended with pure sludge (PS) and limed sludge (LS), with low dose (LD) of 16.0 and 17.3 Mg ha⁻¹ and high dose (HD) of 32.0 and 34.6 Mg ha⁻¹, respectively. Sludge treatments increased plants' nutrient absorption and dry matter production. The LS treatments incremented plant biomass production, depending on soil pH and nutrient availability. The effect of sludge treatments on elemental concentration in aboveground biomass depended on the element, treatments, and soil type. Mineralized nitrogen (N) and plant available phosphorus (P-Bray 1) values increased with sludge addition without exceeding Uruguay's critical soil level of P-Bray 1 for the sorghum crop. The PS did not increase metal concentration in soils. The LS slightly decreased soil Pb and slightly increased Cr and Zn soil concentration; levels were according to Uruguayan environmental guidelines. Therefore, agriculture soils are a viable final destination for PS and LS. Land applied sludge has acceptable levels of metals and promotes crop development.