Lead accumulation and distribution in different rice cultivars

Translocation pattern of heavy metals in soil-rice systems at different growth stages: A case study in the Taihu region, Eastern China

Rice production is crucial for human nutrition and food safety globally. However, it has been a significant sink for potentially harmful metals because of intensive anthropogenic activities. The study was conducted to characterize heavy metal translocation from soil to rice at the filling, doughing and maturing stages, and influencing factors of their accumulation in rice. The distribution and accumulation patterns varied for metal species and growth stages. Cd and Pb accumulation mainly occurred in roots, Cu and Zn were readily transported to stems. Cd, Cu, and Zn accumulation in grains had a descending order of filling > doughing > maturing. Soil heavy metals, TN, EC, and pH exerted important impacts on heavy metals uptake by roots during the period from filling stage to maturing stage. Concentrations of heavy metals in grains were positively correlated with the translocation factors TF_stem-grain (from stem to grain) and TF_leaf-grain (from leaf to grain). Grain Cd exhibited significant correlations with total Cd and DTPA-Cd in the soil at each of the three growth stages. Moreover, Cd in maturing grain could be effectively predicted by soil pH and DTPA-Cd at the filling stage.

Varietal differences influence arsenic and lead contamination of rice grown in mining impacted agricultural fields of Zamfara State, Nigeria

In Zamfara state, Nigeria, rice is cultivated in fields contaminated with Pb (lead) from artisanal and illicit mining activities. Rice grown in such contaminated agricultural areas risks not only Pb contamination but also contamination from other toxic elements, like arsenic (As); co-contamination of Pb and As in rice cultivated in mining impacted areas has been previously reported and rice is a hyperaccumulator of As. A field study was conducted with ten different commonly-cultivated Nigerian rice varieties in the mining-impacted farmlands of Dareta village, Zamfara State. The aim was to determine the optimal rice variety for cultivation on these contaminated farmlands; an optimal variety would have the lowest contaminant concentrations and highest essential elements concentrations in the rice grains. A total of 300 paired soil and rice plants were collected. The mean As and Pb concentrations in paddy soils were 0.91 ± 0.82 mg kg^-1 and 288.5 ± 464.2 mg kg^-1, respectively. Mean As (30.4 ± 15.1 μg kg^-1) content in rice grains was an order of magnitude lower than the Codex recommendation of 200 μg kg^-1 (for milled rice) while the Pb content in all the rice varieties (overall mean of 743 ± 327 μg kg^-1) was approximately four times higher than the Codex recommendation of 200 μg kg^-1. Contrary to previous studies, a negative correlation was observed between As and Pb in rice grains across all the varieties. Rice variety Bisalayi was the variety with the lowest Pb transfer factor (TF = 0.08), but the average Pb concentration in rice grain was still above the Codex recommendation. Bisalayi also had the highest TF for iron. Variety ART_15, which had the lowest As uptake (TF = 0.10), had the highest TF for essential elements (magnesium, potassium, manganese, zinc, and copper). In areas of Pb contamination, Bisalayi rice may therefore be a suitable variety to choose for cultivation.

Lead Toxicity: Health Hazards, Influence on Food Chain, and Sustainable Remediation Approaches

Lead (Pb) toxicity has been a subject of interest for environmental scientists due to its toxic effect on plants, animals, and humans. An increase in several Pb related industrial activities and use of Pb containing products such as agrochemicals, oil and paint, mining, etc. can lead to Pb contamination in the environment and thereby, can enter the food chain. Being one of the most toxic heavy metals, Pb ingestion via the food chain has proven to be a potential health hazard for plants and humans. The current review aims to summarize the research updates on Pb toxicity and its effects on plants, soil, and human health. Relevant literature from the past 20 years encompassing comprehensive details on Pb toxicity has been considered with key issues such as i) Pb bioavailability in soil, ii) Pb biomagnification, and iii) Pb- remediation, which has been addressed in detail through physical, chemical, and biological lenses. In the review, among different Pb-remediation approaches, we have highlighted certain advanced approaches such as microbial assisted phytoremediation which could possibly minimize the Pb load from the resources in a sustainable manner and would be a viable option to ensure a safe food production system.

Lead toxicity in plants: Impacts and remediation

Lead (Pb) is the second most toxic heavy metal after arsenic (As), which has no role in biological systems. Pb toxicity causes a range of damages to plants from germination to yield formation; however, its toxicity is both time and concentration dependent. Its exposure at higher rates disturbs the plant water and nutritional relations and causes oxidative damages to plants. Reduced rate of seed germination and plant growth under stress is mainly due to Pb interference with enzymatic activities, membrane damage and stomatal closure because of induction of absicic acid and negative correlation of Pb with potassium in plants. Pb induced structural changes in photosynthetic apparatus and reduced biosynthesis of chlorophyll pigments cause retardation of carbon metabolism. In this review, the noxious effects of Pb on germination, stand establishment, growth, water relations, nutrient uptake and assimilation, ultra-structural and oxidative damages, carbon metabolism and enzymatic activities in plants are reported. The Pb dynamics in soil rhizosphere and role of remediation strategies i.e. physical, chemical and biological to decontaminate the Pb polluted soils has also been described. Among them, biological strategies, including phytoremediation, microbe-assisted remediation and remediation by organic amendments, are cost effective and environmentally sound remedies for cleaning Pb contaminated soils. Use of organic manures and some agricultural practices have the potential to harvest better crops yield of good quality form Pb contaminated soils.

Effects and mechanisms on the reduction of lead accumulation in rice grains through lime amendment

The influence of lime amendment on the absorption and accumulation of lead (Pb) in the grains of three rice cultivars ((Dong Lian 5 (DL-5, Indica), TeYou 009 (TY-009, Hybrid Indica), and YiYou 673 (YY-673, Hybrid Indica)) was investigated and the associated mechanisms were explored. Pot experiment was conducted in heavily Pb-polluted paddy soil. The transformation of Pb species in soil and roots under different levels of lime application was studied by Pb L3-edge X-ray absorption spectroscopy (Pb L3-XAS) and BCR sequential extraction. The results showed that lime amendment significantly increased soil pH and decreased DTPA-extractable Pb in soil. When the additional ratio of Liming was lower than 32 g kg^-1, the Pb accumulation in rice plants, particularly in the grains was remarkably reduced. Moreover the biomass of rice was not significantly affected. Among the three cultivars, the lowest Pb content in rice grains occurred in YY-673. The cultivation of rice cultivar with low Pb accumulation will reduce the Pb content in the grains. Liming significantly inhibited the translocation of Pb from the roots to the aboveground parts, and from the stems and leaves to grains. Pb L3-XAS and BCR s sequential extraction method analysis revealed that lime amendment increased Pb²⁺ association with Fe oxides (Pb-Ferr), the precipitation of 2PbCO₃·Pb(OH)₂, the residual fraction of paddy soil, and also promoted the transformation of Pb(NO₃)₂ and Pb-pectin to 2PbCO₃·Pb(OH)₂ and Pb-Ferr in rice roots. The suitable lime addition (> 4 g kg^-1, under this pot experiment) could effectively reduce Pb accumulation in rice grains.