Watering regime influences Cd concentrations in cultivated spinach

The Response of Cd Chemical Fractions to Moisture Conditions and Incubation Time in Arable Land Soil

Heavy metal pollution in soils is an issue of global concern, and many scholars have focused on Cadmium (Cd) because of its strong biological migration and toxicity. This study explored arable land soil, changes in external Cd contamination processes and its response to soil moisture conditions, and indoor simulation. After adding an external source of 5 mg/kg d.w., the distribution of soil Cd fractions content, EXC-Cd, CAB-Cd, FMO-Cd, OM-Cd, and RES-Cd, were continuously monitored under different water management regimes, and correlation analysis and regression equations were calculated. The results show that after external Cd entered arable land soils, the binging strength of pollutants and soil gradually increased with incubation time, and the distribution of Cd chemical forms was more stable under different water management regimes. The oversaturated water content promotes the transformation of EXC-Cd to other forms. The transformation of CAB-Cd fractions can be accelerated to other fractions by field capacity, and the active conversion period was 30–60 d. Not all Cd fractions correlated between each other, under the four water management regimes, but it seems that the reducibility of the soil environment was more conducive to external Cd fixation and stability. The response surface design method (RSM) was used to establish quantitative regimes between Cd fractions with incubation time and soil moisture, and the soil moisture content and incubation time had an obvious effect on FMO-Cd content, with R2 = 0.9542.

Cadmium uptake by onions, lettuce and spinach in New Zealand: Implications for management to meet regulatory limits

Paired soil and plant samples collected from the main commercial growing areas for onions (Allium cepa), lettuce (Lactuca sativa) and spinach (Spinacia olearacea) in New Zealand were used to assess the influence of plant and soil factors on cadmium (Cd) uptake in these crops. Differences in Cd concentration between eight lettuce sub-types were not consistent across sites, nor were differences in Cd concentrations in three crisphead cultivars assessed at two sites. Similarly, differences in Cd concentrations between four onion cultivars were inconsistent across sites. Mean lettuce Cd concentrations in eight lettuce varieties (range 0.005-0.034 mg∙kg-1 (fresh weight, FW) were markedly lower than those in baby leaf and bunching spinach, (range 0.005-0.19 mg∙kg-1 FW). Significant regional variation was observed in Cd concentrations in one onion cultivar (mean range 0.007-0.05 mg∙kg-1 FW). Soil Cd concentration, pH and region were statistically significant predictors of onion Cd concentration, explaining low (38% for soil Cd and pH) to moderate (50% for all three parameters) percentage of the variation. Soil Cd concentration and exchangeable magnesium or total carbon were statistically significant predictors of Cd concentration in baby leaf and bunching spinach, respectively, explaining a moderate percentage (49% and 42%) of the variation in Cd concentration. Increasing pH and soil carbon may assist in minimising Cd uptake in onion and bunching spinach, respectively. The low to moderate proportion of explained variation is partly attributable to the narrow range in some measured soil properties and indicates factors other than those assessed are influencing plant uptake. This highlights a challenge in using these relationships to develop risk-based soil guideline values to support compliance with food standards. Similarly, the inconsistency in Cd concentrations in different cultivars across sites highlights the need for multi-site assessments to confirm the low Cd accumulation status of different cultivars.

Rice straw- and rapeseed residue-derived biochars affect the geochemical fractions and phytoavailability of Cu and Pb to maize in a contaminated soil under different moisture content

Management of toxic elements contaminated upland and wetland soils using biochar is of great concern from both agricultural and environmental points of view. The impact of rice straw- and rapeseed residue-derived biochars produced under 300 °C and 550 °C (added to the soil at 2% and 5%; w/w) on the geochemical fractions, phytoavailability, and uptake of Cu and Pb in a contaminated mining soil under different moisture contents (80%, 60%, and 40% of soil field capacity) was investigated in a greenhouse pot experiment using maize. The higher rate of rice straw-derived biochar pyrolyzed at 550 °C caused a significant reduction in the mobile (soluble + exchangeable) fraction of Cu (59.42%) and Pb (75.4%) and increased the residual fractions of Cu (37.8%) and Pb (54.7%) in the treated soil under the highest moisture content (80%) as compared to the untreated soil. Therefore, this biochar significantly decreased the phytoavailability (CaCl₂-extractable form) of Cu by 59.5% and Pb by 67.6% under the highest moisture content. Also, at the same moisture level (80%), the higher rate of rapeseed residue-derived biochar pyrolyzed at 550 °C decreased significantly the phytoavailability of Cu by 46.5% and Pb by 60.52% as compared to the untreated soil. The 5% rate of the higher temperature pyrolyzed rice straw and rapeseed biochars decreased the uptake of Cu and Pb by the roots and shoots of maize up to 51% for Cu and 45% for Pb. Immobilization of Cu and Pb in the biochar-treated soil at 80% moisture content may possibly due to the associated increase of soil pH and poorly-crystalline Fe oxides content, and/or the metals precipitation with sulfides. These results indicated that application of high temperature pyrolyzed rice straw- and rapeseed residue-derived biochars at 5% could immobilize Cu and Pb and decrease their uptake by maize under high levels of moisture content; consequently, they can be used for phyto-management of Cu and Pb contaminated wetland soils.

Effects of ferrous sulfate amendment and water management on rice growth and metal(loid) accumulation in arsenic and lead co-contaminated soil

Arsenic (As) and lead (Pb) commonly co-exist with high concentrations in paddy soil mainly due to human activities in south of China. This study investigates the effect of ferrous sulfate (FeSO₄) amendment and water management on rice growth and arsenic (As) and lead (Pb) accumulation in rice plants. A paddy soil co-contaminated with As and Pb was chosen for the pot experiment with three FeSO₄ levels (0, 0.25, and 1%, on a dry weight basis) and two water managements (flooded, non-flooded). The concentrations of As and Pb in iron plaques and rice plants were determined. Application of FeSO₄ and non-flooded conditions significantly accelerated the growth of rice plants. With the addition of FeSO₄, iron plaques were significantly promoted and most of the As and Pb were sequestered in the iron plaques. The addition of 0.25% FeSO₄ and non-flooded conditions did not significantly change the accumulation of As and Pb in rice grains. The practice also significantly decreased the translocation factor (TF) of As and Pb from roots to above-ground parts which might have been aided by the reduction of As and Pb availability in soil, the preventing effect of rice roots, and the formation of more reduced glutathione (GSH). Flooded conditions decreased the Pb concentration in rice plants, but increased As accumulation. Moreover, rice grew thin and weak and even died under flooded conditions. Overall, an appropriate FeSO₄ dose and non-flooded conditions might be feasible for rice cultivation, especially addressing the As issue in the co-contaminated soil. However, further detailed studies to decrease the accumulation of Pb in edible parts and the field application in As and Pb co-contaminated soil are recommended.