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.

The mechanistic pathways of arsenic transport in rice cultivars: Soil to mouth.

Rice cultivars are major conduit of arsenic (As) poisoning to human. We quantified transferability of fifteen rice cultivars representing three groups i.e., high yielding variety (HYV), local aromatic rice (LAR) and hybrid for As from soil to cooked rice and its ingestion led health risk, elucidating the processes of its unloading at five check points. Conducting a field experiment with those cultivars, we sampled roots and shoots at tillering, booting and maturity (with grains), separated the grains into husk, bran and polished rice, cooked it through different methods and analyzed for As. Of the tested groups, As restriction from root to grain followed the order: LARs (94%) > HYVs (88.3%) > hybrids (87.2%). The low As sequestration by LARs was attributed to their higher root biomass (10.20 g hill-1) and Fe-plaque formation (2421 mg kg-1), and lower As transfer coefficients (0.17), and higher As retention in husk and bran (84%). On average, based on calculated four major risk indices, LARs showed 4.7-6.8 folds less As toxicity than HYVs and hybrids. These insights are helpful in advocating some remedies for As toxicity of the tested rice cultivars.