Foliar application of lead and arsenic solutions to Spinacia oleracea: biophysiochemical analysis and risk assessment

Distribution and ecological risk assessment of trace elements in the paddy soil-rice ecosystem of Punjab, Pakistan

Trace elements (TEs) contamination of agricultural soils requires suitable criteria for regulating their toxicity limits in soil and food crops, which depends on their potential ecological risk spanning regional to global scales. However, no comprehensive study is available that links TE concentrations in paddy soil with ecological and human health risks in less developed regions like Pakistan. Here we evaluated the data set to establish standard guidelines for defining the hazard levels of various potentially toxic TEs (such as As, Cd, Co, Cu, Cr, Fe, Mn, Ni, Pb, Se, Zn) in agricultural paddy soils of Punjab, Pakistan. In total, 100 topsoils (at 0-15 cm depth) and 204 rice plant (shoot and grain) samples were collected from five ecological zones of Punjab (Gujranwala, Hafizabad, Vehari, Mailsi, and Burewala), representing the major rice growing regions in Pakistan. The degree of contamination (C_d) and potential ecological risk index (PERI) established from ecological risk models were substantially higher in 100% and 97% of samples, respectively. The positive matrix factorization (PMF) model revealed that the elevated TEs concentration, notably Cd, As, Cr, Ni, and Pb, in the agricultural paddy soil was attributed to the anthropogenic activities and groundwater irrigation. Moreover, the concentration of these TEs in rice grains was higher than the FAO/WHO's safe limits. This study provided a baseline, albeit critical knowledge, on the impact of TE-allied ecological and human health risks in the paddy soil-rice system in Pakistan; and it opens new avenues for setting TEs guidelines in agro-ecological zones globally, especially in underdeveloped regions.

The significance of eighteen rice genotypes on arsenic accumulation, physiological response and potential health risk

Rice is an important food crop that is susceptible to arsenic (As) contamination under paddy soil conditions depending on As uptake characteristics of the rice genotypes. Here we unveiled the significance of eighteen (fine and coarse) rice genotypes against As accumulation/tolerance, morphological and physiological response, and antioxidant enzymes-enabled defense pathways. Arsenic significantly affected rice plant morphological and physiological attributes, with relatively more impacts on fine compared to coarse genotypes. Grain, shoot, and root As uptake were lower in fine genotypes (0.002, 0.020, and 0.032 mg pot^-1 DW, respectively) than that of coarse (0.031, 0.60, and 1.2 mg pot^-1 DW, respectively). Various biochemical (pigment contents, hydrogen peroxide, lipid peroxidation) and defense (antioxidant enzymes) plant parameters indicated that the fine genotypes, notably Kainat and Basmati-385, possessed the highest As tolerance. Arsenic-induced risk indices exhibited greater hazard quotient (up to 1.47) and carcinogenic risk (up to 0.0066) for coarse genotypes compared to the fine ones, with the greatest risk for KSK-282. This study elaborates the pivotal role of genotypic variation among rice plants in As accumulation, which is crucial for mitigating the associated human health risk. Further research is required on molecular aspects, e.g., genetic sequencing, to examine rice genotypes variation in defense mechanisms to As contamination.

Elucidating the Potential of Vertical Flow-Constructed Wetlands Vegetated with Different Wetland Plant Species for the Remediation of Chromium-Contaminated Water

Water scarcity is one of the key global challenges affecting food safety, food security, and human health. Constructed wetlands (CWs) provide a sustainable tool to remediate wastewater. Here we explored the potential of vertical flow-CWs (VF-CWs) vegetated with ten indigenous wetland plant species to treat chromium (Cr)-contaminated water. The wetland plants were vegetated to develop VF-CWs to treat Cr-contaminated water in a batch mode. Results revealed that the Cr removal potential of VF-CWs vegetated with different wetland plants ranged from 47% to 92% at low (15 mg L−1) Cr levels and 36% to 92% at high (30 mg L−1) Cr levels, with the maximum (92%) Cr removal exhibited by VF-CWs vegetated with Leptochloa fusca. Hexavalent Cr (Cr(VI)) was reduced to trivalent Cr (Cr(III)) in treated water (96–99 %) of all VF-CWs. All the wetland plants accumulated Cr in the shoot (1.9–34 mg kg−1 dry weight (DW)), although Cr content was higher in the roots (74–698 mg kg−1 DW) than in the shoots. Brachiaria mutica showed the highest Cr accumulation in the roots and shoots (698 and 45 mg kg−1 DW, respectively), followed by Leptochloa fusca. The high Cr level significantly (p < 0.05) decreased the stress tolerance index (STI) percentage of the plant species. Our data provide strong evidence to support the application of VF-CWs vegetated with different indigenous wetland plants as a sustainable Cr-contaminated water treatment technology such as tannery wastewater.

The potential of microbes and sulfate in reducing arsenic phytoaccumulation by maize (Zea mays L.) plants

Arsenic (As) contamination in soil-plant system is an important environmental, agricultural and health issue globally. The microbe- and sulfate-mediated As cycling in soil-plant system may depend on soil sulfate levels, and it can be used as a potential strategy to reduce plant As uptake and improve plant growth. Here, we investigated the role of soil microbes (SMs) to examine As phytoaccumulation using maize as a test plant, under varying sulfate levels (S-0, S-5, S-25 mmol kg^-1) and As stress. The addition of sulfate and SMs promoted maize plant growth and reduced As concentration in shoots compared to sulfate-treated plants without SMs. Results revealed that the SMs-S-5 treatment proved to be the most promising in reducing As uptake by 27% and 48% in root and shoot of the maize plants, respectively. The SMs-S treatments, primarily with S-5, enhanced plant growth, shoot dry biomass, Chl a, b and total Chl (a + b) contents, and gas exchange attributes of maize plants. Similarly, the antioxidant defense in maize plants was increased significantly in SMs-S-treated plants, notably with SMs-S-5 treatment. Overall, the SMs-S-5-treated plants possessed improved plant growth, dry biomass, physiology and antioxidant defense system and decrease in plant shoot As concentration. The outcomes of this study suggest that sulfate supplementation in soil along with SMs could assist in reducing As accumulation by maize plants, thus providing a sustainable and eco-friendly bioremediation strategy in limiting As exposure.

The potential of using Cedrus atlantica as a biomonitor in the concentrations of Cr and Mn

Air pollution is becoming increasingly dangerous which is quite a significant issue of today's world, especially air pollution from heavy metal, whose emission increases with industrial and traffic activities. This is of great importance in terms of environmental pollution and human health. Heavy metals do not deteriorate and disappear easily on earth. They are liable to bioaccumulate within cells in organisms. Most of them demonstrate harmful effects in addition as a result of advanced accumulation, and thus they emerge as toxic and carcinogenic. Therefore, it is of great importance to observe the changes in heavy metal concentrations in the air. One of the most effective techniques for monitoring the change of heavy metal concentrations in the atmosphere is the use of annual rings of trees as biomonitors. In this study, in the annual rings of the Cedrus atlantica Manetti tree cut at the Kastamonu province at the end of 2019, the variation of the concentrations of some of the heavy metals most associated with traffic density was tried to be determined. Within the scope of the study, Cr and Mn concentration in the outer bark and the inner bark was compared with the direction and wood for the variation of heavy metal concentrations. Also, variance analysis and Duncan test were applied and evaluated. As a result of the study, while the highest values in many heavy metals are generally obtained in the outer bark, the transfer of metals in the wood is limited, and some heavy metal concentrations change significantly depending on the direction, especially in the wood. This change is related to the traffic density, so Cedrus atlantica Manetti annual rings are very suitable as biomonitors for air pollution control.

Effectiveness of plants and green infrastructure utilization in ambient particulate matter removal

Air pollution is regarded as an increasingly threatening, major environmental risk for human health. Seven million deaths are attributed to air pollution each year, 91% of which is due to particulate matter. Vegetation is a xenobiotic means of removing particulate matter. This review presents the mechanisms of PM capture by plants and factors that influence PM reduction in the atmosphere. Vegetation is ubiquitously approved as a PM removal solution in cities, taking various forms of green infrastructure. This review also refers to the effectiveness of plant exploitation in GI: trees, grasslands, green roofs, living walls, water reservoirs, and urban farming. Finally, methods of increasing the PM removal by plants, such as species selection, biodiversity increase, PAH-degrading phyllospheric endophytes, transgenic plants and microorganisms, are presented.

Risk assessment of heavy metal(loid)s via Spinacia oleracea ingestion after sewage water irrigation practices in Vehari District

The use of sewage water as an irrigation source can be beneficial in agricultural practices, however, it may result in human health risks due to the consumption of heavy metal(loid)-contaminated food. This study evaluated the suitability of using sewage water (SW), freshwater (FW), and groundwater (GW) for vegetable irrigation in District Vehari. Spinach (Spinacia oleracea) plants were grown in pots irrigated with FW, GW, and SW in different proportions and combinations. The results indicated the substantial lesser buildup of heavy metal(loid)s (As (- 0.8%), Cd (- 38%), Cr (- 6.2%), Cu (- 20%), Fe (- 9.2%), Mn (- 13%), Ni (- 16%), Pb (- 19%), and Zn (-15%)) in soil after S. oleracea cultivation compared to unirrigated soil possibly due to high metal(loid) uptake by S. oleracea. Irrigation with all types of waters resulted in metal(loid) accumulation in S. oleracea predominantly in roots. The combinations of FW, GW, and SW resulted in high metal(loid) accumulation (As, Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn) in the edible S. oleracea leaves than their alone application. Owing to high metal(loid) buildup, plants showed a linear trend in physiological imbalance in terms of reduced pigment content, induction of peroxidation, and oxidation of lipids. The severe oxidative stress was observed in S. oleracea plants under FW and GW irrigation due to high metal(loid) accumulation. The risk indices showed possible carcinogenic risk (CR > 0.0001) and non-carcinogenic risk (HI > 1) from the consumption of metal(loid)-contaminated S. oleracea leaves. Results revealed unsuitability of all waters and their combinations for S. oleracea irrigation. Moreover, this study does not encourage the use of mixed water for vegetable irrigation in Vehari District. Therefore, it is of utmost importance to monitor the quality of irrigation waters to ensure food safety and prevent chronic health risks to the exposed population.

Foliar uptake and transport of atmospheric trace metals bounded on particulate matters in epiphytic Tillandsia brachycaulos

Epiphytic Tillandsia species are uniquely suitable for the study of foliar uptake of atmospheric trace metals (ATM) because these plants can only rely on their leaves for this purpose. Therefore, we analyzed the uptake and transport of different metals (Fe, Al, Zn, Mn, Ba, Ti, Cu, Ni, Cr, Sn, Pb, Co, As, and Se) bounded on atmospheric particulate matters (APM) in Tillandsia brachycaulos Schltdl. The results showed that the metal contents inside leaves significantly (p < .05) increased after APM exposure. There was a significant (p < .05) positive correlation between the content of 14 trace metals accumulated on the leaf surface and inside the leaf, which indicated that APM is the main source of ATM uptake. The subcellular analysis showed that the Pb, Cu, Ni, Zn, and Cr absorbed by T. brachycaulos were stored primarily in the cell walls and organelles. After the removal of foliar trichomes of T. brachycaulos, the metal contents on the leaf surface decreased, whereas the contents of most metals inside the leaf increased. This is an evidence that foliar trichomes serve a protective function by intercepting ATM onto the leaf surface.Novelty statementsThere was a significant positive correlation between the contents of 14 trace metals accumulated on the leaf surface and in the leaf of T. brachycaulos, which indicated that atmospheric particulate matters are the main source of trace metals in the leaves.After the removal of foliar trichomes of T. brachycaulos, the trace metal contents on the leaf surface decreased, whereas the contents of most trace metals inside the leaf increased. This is an evidence that foliar trichomes serve a protective function by intercepting atmospheric trace metals onto the leaf surface.