Phytoremediation of Cadmium Polluted Soils: Current Status and Approaches for Enhancing

Cadmium (Cd) is a heavy metal present in atmosphere, rocks, sediments, and soils without a known role in plants. It is relatively mobile and can easily enter from soil into groundwater and contaminate the food chain. Its presence in food in excess amounts may cause severe conditions in humans, therefore prevention of cadmium entering the food chain and its removal from contaminated soils are important steps in preserving public health. In the last several years, several approaches for Cd remediation have been proposed, such as the use of soil amendments or biological systems for reduction of Cd contamination. One of the approaches is phytoremediation, which involves the use of plants for soil clean-up. In this review we summarized current data on the use of different plants in phytoremediation of Cd as well as information about different approaches which have been used to enhance phytoremediation. This includes data on the increasing metal bioavailability in the soil, plant biomass, and plant accumulation capacity as well as seed priming as a promising novel approach for phytoremediation enhancing.

Selenium Decreases the Cadmium Content in Brown Rice: Foliar Se Application to Plants Grown in Cd-contaminated Soil

Cadmium (Cd) contamination in agricultural soils has become a serious issue owing to its high toxicity threat to human health through the food chain. The purpose of this paper is to explore the availability of foliar selenium (Se) application in reducing Cd enrichment in brown rice. A field experiment from 2017 to 2019 was conducted to investigate the effects of foliar Se application on the physiology and yields of three rice cultivars and their accumulation of Cd in low-Cd and high-Cd soils. The grain protein contents and yields of rice plants grown in the high-Cd soil were lower than those of plants cultivated in the low-Cd soil by 27.85% and 6.82%, whereas the malondialdehyde (MDA) and Cd contents were higher by 66.06% and 91.47%, respectively. Se application reduced Cd translocation from the stems and leaves to the spikes, decreasing the Cd content in brown rice by 40.36%. Additionally, Se enhanced the antioxidative activity, glutathione and protein contents, and rice yield (7.58%) and decreased the MDA and proline contents. However, these Se effects weakened under the high-Cd soil. Foliar Se application can alleviate Cd-induced physiological stress in brown rice while improving its yield and reducing its Cd content.

Nanoparticles Induced Restricted Cadmium Mobility and Accumulation in Wheat From Contaminated Soil

Nanotechnology has gained importance over conventional technologies to enhance crop yield and environmental sustainability. In agricultural soil, cadmium (Cd) contamination has been a serious issue, impacting food security and quality and caused serious human health and environmental problems. Nanoparticles (NPs) have large surface area and high adsorption capacity, due to which they are efficiently used to remediate Cd-contaminated agricultural soils. The aims to conduct this experiment were to evaluate the effects of iron (Fe), silicon (Si) and zinc (Zn) NPs on the growth, physiology, and accumulation of Cd in various parts of plants. Soil in bulk was collected and spiked with different Cd levels (0, 5, 10, 20 mg kg-1), and NPs @ 60 mg kg-1 of soil were applied at the time of wheat sowing. Plants showed significant increase in shoot length and grain yield with the NPs application compared to control (no NPs application). The results illustrated that NPs have a positive effect on stomatal conductance, transpiration rate, photosynthetic rate compared to control. The Cd concentration in roots, shoot and grains were reduced by 36%, 50% and 69% with the application of NPs. However, this reduction was more pronounced at 5 mg kg-1 Cd with Fe-NPs followed by Zn-NPS and Si-NPs. Overall, it was concluded that NPs play an important role in the enhancement of plant biomass, increase in nutrients availability, and decreasing the Cd accumulation in different plant parts.

Cadmium concentration in water and sediment from lake Lau Kawar, North Sumatra

Heavy metals are easy to bind organic matter and settle to the bottom of the waters and unite with sediments, which is cadmium. Cadmium (Cd) is found from volcanic eruptions, from various human activities, and is carcinogenic. This study aims to analyze the concentration of cadmium in water and sediment in Lake Lau Kawar. Water samples were collected by purposive sampling at three stations using Horizontal Bottle samples. Sediment samples were collected compositely using an Eckmann grab then analyzed by the Atomic Absorption Spectrophotometer method. Descriptive data analysis used comparative quantitative methods, namely comparing the level of cadmium in water and sediment in Lau Kawar Lake with the quality standards set by WHO and IADC/CEDA. The water quality in Lake Lau Kawar is in good condition. The concentration of heavy metal Cd in water and sediment still meets the established water quality standard criteria. The source of Cd contamination in the lake, which comes from the volcanic ash of Mount Sinabung, is only carried in low quantities. The largest source of contamination comes from the activities of residents as fertilizers and pesticides used on agricultural land.

Coupled Metabolome With Physiology Unveiled Mechanisms for Cadmium Affecting Active Ingredients Synthesis in Salvia Miltiorrhiza, A Non-cd-hyperaccumulator

BackgroundCadmium (Cd) poses threats to human health by affecting the safety (Cd accumulation) and quantity (contents of active ingredients) of Salvia miltiorrhiza due to human activities and Cd characteristics. It remains largely unknown how Cd stress affects the synthesis of active ingredients in S. miltiorrhiza. ResultsHere we investigated physiologies (contents of Cd, malondialdehyde (MDA) and proline, and activities of superoxide dismutase, peroxidase (POD) and catalase (CAT)), transfer factor (TF), bioconcentration factor (BCF) and metabolites of S. miltiorrhiza at different levels of Cd contamination with a pot experiment. The results revealed that Cd concentration, as it rose in soil, increased significantly in roots and leaves with TFs and BCFs below 1 in the Cd addition groups; POD and CAT activities and proline content increased and then declined significantly. Besides, amino acids and organic acids (especially D-glutamine (D-Gln), L-aspartic acid (L-Asp), L-phenylalanine (L-Phe), L-tyrosine (L-Try), geranylgeranyl-PP (GGPP), and rosmarinic acid (RA)) contributed more than other metabolites in discriminating roots under different levels of Cd contamination. With Cd concentration rising, the relative content of GGPP declined and then increased significantly; RA content rose significantly; content of L-Phe and L-Try increased and then declined significantly, while the content of D-Gln and L-Try decreased and then increased significantly. Conclusions These results suggested that S. miltiorrhiza belonged to a non-Cd-hyperaccumulator with most Cd accumulated in roots; Cd enhanced the RA synthesis via regulating amino acid metabolism but inhibited the tanshinone synthesis mainly by declining the GGPP content, with proline, POD and CAT playing vital roles in resisting Cd stress.

Ecological Risk Assessment of Heavy Metals in Adjoining Sediment of River Ecosystem

The present study was focused on heavy metal distribution patterns and the associated ecological risk assessment in the adjoining sediment of the Hindon River in Muzaffarnagar Region (U.P.), India. Lead (Pb), zinc (Zn), copper (Cu), cadmium (Cd), nickel (Ni), iron (Fe), aluminum (Al), sodium (Na), and potassium (K) were estimated from six sediment samples (Atali A and B, Budhana A and B, and Titavi A and B). The concentration of the heavy metals Zn, Pb, Cu, Ni, and Cd ranged from 25.5–74.7 mg kg−1, 29.8–40.6 mg kg−1, 7.0–29.2 mg kg−1, 14.7–21.8 mg kg−1, and 0.96–1.2 mg kg−1, respectively and followed the sequence Zn > Pb > Cu > Ni > Cd, while major elements followed the sequence Na > Fe > Al > K. The enrichment factor (EF) and geo-accumulation index (Igeo) revealed that Atali A showed the highest enrichment and followed the sequence Zn > Cu > Pb > Ni > Cd. Contamination factor (CF) and contamination degree (CD) depicted that all of the sites (except Titavi B) were moderately to considerably contaminated. The highest degree of contamination (CF, CD, and PLI, pollution load index) was observed at Titavi A followed by Atali A and Budhana A. Eco-toxicological risk assessment (RI) indicated that the sites were moderately contaminated, predominantly by Ni and Pb and Zn. The results revealed that the metal contamination in sediment is alarming and might pose an adverse threat to ecosystem health.

Supplemental Effects of Biochar and Foliar Application of Ascorbic Acid on Physio-Biochemical Attributes of Barley (Hordeum vulgare L.) under Cadmium-Contaminated Soil

Biochar, prepared from organic waste materials, can improve the quality of contaminated soil areas. Biochar can be used as an economic centerpiece over other available resources and can properly utilize large amounts of waste. Soil contaminated with cadmium (Cd) is a worldwide problem that poses potential agricultural and human health hazards. Moreover, Cd toxicity causes serious problems for sustainable food production, especially in food crops like barley. High cadmium concentration in soil is phytotoxic and decreases plant growth and ultimately yields. Biochar and ascorbic acid in ameliorating Cd stress are economically compatible and consistent approaches in agriculture. The present study aimed to evaluate biochar’s and foliar-applied ascorbic acid’s influence on some growth and biochemical characteristics of barley (Hordeum vulgare L.) to Cd stress. The soil was supplemented with biochar 2% w/w and 20 mg Cd kg−1. The foliar application of 30 mM ascorbic acid was done on plants. The results revealed that Cd stress decreased chlorophyll a, chlorophyll b, total chlorophyll, and carotenoids. It also increased oxidative stress indicators, i.e., APX, COD, POD, flavonoids, anthocyanin, phenolics, and electrolyte leakage, in barley with Cd-contamination. A significant enhancement in root and shoot length, gas exchange attributes, and chlorophyll contents validated the effectiveness of Bio + Asa treatments over all other treatments under Cd contamination. In conclusion, the sole applications of biochar and Asa in Cd contamination are also effective, but Bio + Asa is a better amendment for Cd stress alleviation in barley plants.

Risk Assessment of Arsenic and Cadmium in Groundwater of Talukas Ghorabari and Mirpur Sakro, Sindh, Pakistan

The current study was carried out for quantitative and risk assessment of cadmium (Cd) and arsenic (As) from Talukas Ghora Bari and Mirpur Sakro. The concentration of Cd was determined using Atomic Absorption Spectroscopy instrument. The As concentration was measured with the help of the Arsenic Kit Method. For analysis of Cd, samples were prepared by the Microwave digestion method, whereas for As analysis, water samples were analyzed directly. The range of Cd content was observed from the studied areas as 1 – 10 μg/L and 1.2 – 11.2 μg/L, respectively. The groundwater water of Talukas Ghorabari and Mirpur Sakro showed the mean Cd content of 5 μg/L and 6.1 μg/L, respectively. The Cd contamination of 56% and 80% was found in Ghorabari and Mirpur Sakro, respectively. The range of As content of 0.00 – 50 μg/L and 10 – 80 μg/L was determined from Ghorabari and Mirpur Sakro, respectively. Hazard Quotient for Cd > 1 was found in 40% of both children and infants in the groundwater of the study area, which may cause non-carcinogenic risk. About 48% of water samples declared HQ values > 1 for adults in the water of Ghorabari. Since 84% of samples showed the HQ values > 1 for children and infants. The HQ values of As for Adults of the Mirpur Sakro were observed in 63.3% samples, whereas for children and infants, HQ values were found in 100% samples. It is therefore strongly recommended that groundwater must be treated before consumption by the people of the area under study.