Cadmium contamination in agricultural soils of Bangladesh and management by application of organic amendments: evaluation of field assessment and pot experiments

Microplastics increase cadmium absorption and impair nutrient uptake and growth in red amaranth (Amaranthus tricolor L.) in the presence of cadmium and biochar

Microplastic (MP) pollution in terrestrial ecosystems is gaining attention, but there is limited research on its effects on leafy vegetables when combined with heavy metals. This study examines the impact of three MP types-polyethylene (PE), polyethylene terephthalate (PET), and polystyrene (PS)-at concentrations of 0.02, 0.05, and 0.1% w/w, along with cadmium (Cd) and biochar (B), on germination, growth, nutrient absorption, and heavy metal uptake in red amaranth (Amaranthus tricolor L.). We found that different MP types and concentrations did not negatively affect germination parameters like germination rate, relative germination rate, germination vigor, relative germination vigor, and germination speed. However, they increased phytotoxicity and decreased stress tolerance compared to an untreated control (CK1). The presence of MPs, particularly the PS type, reduced phosphorus and potassium uptake while enhancing Cd uptake. For example, treatments PS0.02CdB, PS0.05CdB, and PS0.1CdB increased Cd content in A. tricolor seedlings by 158%, 126%, and 44%, respectively, compared to the treatment CdB (CK2). Additionally, MP contamination led to reduced plant height, leaf dry matter content, and fresh and dry weights, indicating adverse effects on plant growth. Moreover, the presence of MPs increased bioconcentration factors and translocation factors for Cd, suggesting that MPs might act as carriers for heavy metal absorption in plants. On the positive side, the addition of biochar improved several root parameters, including root length, volume, surface area, and the number of root tips in the presence of MPs, indicating potential benefits for plant growth. Our study shows that the combination of MPs and Cd reduces plant growth and increases the risk of heavy metal contamination in food crops. Further research is needed to understand how different MP types and concentrations affect various plant species, which will aid in developing targeted mitigation strategies and in exploring the mechanisms through which MPs impact plant growth and heavy metal uptake. Finally, investigating the potential of biochar application in conjunction with other amendments in mitigating these effects could be key to addressing MP and heavy metal contamination in agricultural systems.

Effect of Organic Amendments on Cadmium Bioavailability in Soil and its Accumulation in Rice Grain

A pot trial was conducted during the boro (dry) season to evaluate the impact of six traditional organic amendments (OAs) on the growth of SL-8 rice variety in both agricultural and cadmium (Cd) stressed soil at 2% and 4% application rates. Traditional OAs used in the study were cow dung, mustard oil cake (MOC), rice husk, saw dust, tea leaf and vermi compost (VC). Except for cow dung all other OAs were found to remove 99% of Cd from the aqueous solution, while cow dung removed 95%. Rice grain grown in OA-added soil in all application rates contained less Cd than the control. A 2% application rate was found to be more effective in reducing both Cd bioavailability and Cd in grain. OA application in soil significantly influenced soil pH in all cases. Though both bioavailable Cd in soil and grain Cd were reduced by the OA addition, the Cd uptake tendency of SL-8 rice variety markedly increased because of Cd spiking in soil.

A state-of-the-art review on cadmium uptake, toxicity, and tolerance in rice: From physiological response to remediation process

Cadmium (Cd), a major contaminant of concern, has been extensively reviewed and debated for its anthropogenic global shifts. Cadmium levels in rice grains raise wide food safety concerns. The aim of this review is therefore to capture the dynamics of Cd in paddy soil, translocation pathways of Cd from soil to consumption rice, and assess its bio-accessibility in human consumption. In crop plants, Cd reduces absorption of nutrients and water, triggers oxidative stress, and inhibits plant metabolism. Understanding the mechanisms and behaviour of Cd in paddy soil and rice allows to explain, predict and intervene in Cd transferability from soil to grains and human exposure. Factors affecting Cd movement in soil, and further to rice grain, are elucidated. Recently, physiological and molecular understanding of Cd transport in rice plants have been advanced. Morphological-biochemical characteristics and Cd transporters of plants in such a movement were also highlighted. Ecologically viable remediation approaches, including low input cost agronomic methods, phytoremediation and microbial bioremediation methods, are emerging.

A soybean based-diet prevents Cadmium access to rat cerebellum, maintaining trace elements homeostasis and avoiding morphological alterations

Cadmium (Cd) is one of the most dangerous heavy metals that exists. A prolonged exposure to Cd causes toxic effects in a variety of tissues, including Central Nervous System (CNS), where it can penetrate the Blood Brain Barrier (BBB). Cd exposure has been linked to neurotoxicity and neurodegenerative diseases. Soy isoflavones have a strong antioxidant capacity, and they have been shown to have positive effects on cognitive function in females. However, the mechanisms underlying Cd neurotoxicity remain completely unresolved. The purpose of this study was to characterize the potential protective effect of a soy-based diet vs. a casein-based diet against Cd toxicity in rat cerebellum. Female Wistar rats were fed with casein (Cas) or soybean (So) as protein sources for 60 days. Simultaneously, half of the animals were administered either 15 ppm of Cadmium (CasCd and SoCd groups) in water or regular tap water as control (Cas and So groups). We analyzed Cd exposure effects on trace elements, oxidative stress, cell death markers, GFAP expression and the histoarchitecture of rat cerebellum. We found that Cd tissue content only augmented in the Cas intoxicated group. Zn, Cu, Mn and Se levels showed modifications among the different diets. Expression of Nrf-2 and the activities of CAT and GPx decreased in Cas and So intoxicated groups,while 3-NT expression increased only in the CasCd group. Morphometry analyses revealed alterations in the purkinje and granular cells morphology, decreased number of granular cells and reduced thickness of the granular layer in Cd-intoxicated rats, whereas no alterations were observed in animals under a So diet. In addition, mRNA expression of apoptotic markers BAX/Bcl-2 ratio and p53 expression increased only in the CasCd group, a finding confirmed by positive TUNEL staining in the cerebellum granule cell layer in the same group. Also, Cd intoxication elicited overexpression of GFAP by astrocytes, which was prevented by soy. White matter alterations were only subtle and characterized by intramyelinic edema in the CasCd group. Overall, these results unmask an irreversible toxic effect of a subchronic Cd intoxication on the cerebellum, and identify a protective role by a soy-based diet with potential as a therapeutic strategy for those individuals exposed to this dangerous environmental contaminant.

Comparative evaluation of cadmium phytoremediation potential of five varieties of Helianthus annuus L

Helianthus annuus is a potential metal accumulator plant, which can find application in cadmium (Cd) phytoremediation and provide economic gains in terms of oil yield. This study is focused on Cd accumulation analysis, physiological and biochemical responses of five varieties of H. annuus (DRSF-108, DRSF-113, LSFH-171, Phule Bhaskar and KBSH-44). Plantlets of all varieties were treated with various Cd concentrations (10, 50, 100, 300 and 500 mg kg^-1) for 20, 40 and 60 days. DRSF-108 showed the maximum total Cd accumulation (430.52 mg kg^-1) in whole plant while minimum accumulation was observed in KBSH-44 (150.66 mg kg^-1) at 500 mg kg^-1 Cd after 60 days. The highest level of proline and polyphenol in DRSF-108 were 27.206 µmol g^-1 fw and 6.86 mg g^-1 fw, respectively. Antioxidant enzymes (catalase, ascorbate peroxidase and glutathione reductase) also showed increased activity in response to Cd treatment. SEM-EDX analysis of potential accumulator genotype, DRSF-108, showed the distribution of intracellular Cd into plant tissues. Therefore, it is concluded that among five varieties, DRSF-108 was the most potential Cd accumulator and had a higher capacity for Cd tolerance compared to other varieties. Our findings may allow us to extend variety DRSF-108 for sustainable farming and Cd remediation.

Variations in cadmium accumulation among amon rice cultivars in Bangladesh and associated human health risks

Rice consumption is one of the major cadmium (Cd) exposure routes for human. Bangladeshi people have historically subsisted on a rice-based diet; however, only a few reports have investigated Cd accumulation by different rice cultivars in Bangladesh. This study was designed to investigate the uptake and accumulation of Cd in different rice cultivars and associated health risks to humans eating rice. A pot experiment was conducted to grow eight amon rice varieties under control, 5 and 10 mg Cd/kg soil under open air conditions. After harvesting the Cd fractionation, bioavailable Cd and rice grain Cd content were determined. Cd spiked as Cd²⁺ enriched the Cd bioavailability to plant by 35% (in 5 mg/kg stress) and 85% (in 10 mg/kg stress). There were variations among the rice varieties in their ability to accumulate Cd in grain and this was found to be 15-fold higher under control conditions. Grain Cd content significantly differed among the rice varieties at each level of soil Cd. In this study, BR-52 emerged as the most Cd-safe cultivar followed by BR-75, Rani salut, BR-71, BR-49, BR-76, BR-87 and lastly, BINA-7. Most of the agronomic parameters of rice concerning yield were affected by both rice varieties and soil Cd level. In different rice varieties, rhizosphere pH increased through root exudation which ultimately produced equilibria among the five major soil Cd fractions so that Cd became bioavailable to plants. All rice varieties showed high hazard quotient (HQ) values under Cd stress conditions and posed a risk to human health. For noncarcinogenic health risk assessment through HQ, we recommend 0.1 mg Cd/kg rice grain be used as the maximum allowable concentration (MAC) in calculating health risk for Bangladeshi people.