Translocation of Soil Arsenic towards Accumulation in Rice: Magnitude of Water Management to Minimize Health Risk

Globally, the risk of arsenic (As) contamination in soil and rice is well documented across the globe. In Bangladesh, drinking water and rice are two major exposure pathways of As to humans. Therefore, the efficiency of recent technologies to reduce rice As and associated human health risks still need to be deeply investigated. In this direction, a pot experiment was performed to investigate the impact of soil As and agronomic irrigation management on rice (cv. BRRI dhan28) growth, yield, As accumulation, and finally, health risks to humans from consuming rice. Treatment combinations were made with three levels of As (0, 20, and 40 mg kg−1) having two irrigation procedures, including alternate wetting and drying (AWD) and traditional continuous flooding (CF). According to the findings, As pollution in the soil lowered the yield contributing features and rice yield, including panicle length, filled grains per panicle, sterile grains per panicle, 1000-grain weight, grain yield, and straw yield. AWD water management significantly improved the growth performance and productivity of rice. Grain yield was increased by 13% in AWD compared to CF. Rice grain and straw As concentrations were increased to 0.56 mg kg−1 and 15.10 mg kg−1, respectively, in soil with 40 mg kg−1 As and CF water management. AWD treatment significantly reduced grain and straw As contents by 16% and 28%, respectively. Increased grain, straw, and total As uptake was noticed with higher soil As concentrations. The study also found that rising soil As raised non-carcinogenic risks (HQ > 1) and carcinogenic risks (CR > 1.010–4) while AWD lowered health risks compared to CF. Thus, rice farming using AWD irrigation could be a viable and long-term solution for reducing As contamination in rice and associated human health hazards.

Sustainable removal of soil arsenic by naturally-formed iron oxides on plastic tubes

Arsenic (As) pollution in paddy fields is a major threat to rice safety. Existing As remediation techniques are costly, require external chemical addition and degrade soil properties. Here, we report the use of plastic tubes as a recyclable tool to precisely extract As from contaminated soils. Following insertion into flooded paddy soils, polyethylene (PE) tube walls were covered by thin but massive Fe coatings of 76.9-367 mg Fe m-2 in 2 weeks, which adsorbed significant amounts of As as well as lead and antimony. The formation of tube-wall Fe oxides was driven by local Fe-oxidizing bacteria with oxygen produced by oxygenic phototrophs (e.g., Cyanobacteria) or diffused from air through the tube wall. The tubes with As-bound Fe oxides can be easily separated from soil and then recycled. We tested the As removal efficiency in a pilot experiment to remove As from ~ 20 cm depth / 80 kg soils in a two-year experiment and achieved an overall efficiency of 152 mg As m-2 soil year-1. The As accumulated in rice tissues was significantly decreased in the treatment. This work provides a low-cost and sustainable soil remediation method for the targeted removal of As from soils and a useful tool for the study and management of the biogeochemical Fe cycle in paddy soils.

Soil Chemical Properties and Maize (Zea mays L.) Yield influenced by Lime and Fern (Pteris vittata)

This study aimed to investigate the influence of liming and fern on reducing the absorption of arsenic (As) by maize and As content in the soil. The single-factor experiment was designed in a completely random block (4 treatments and 4 replicates). Treatments were followed: Treatment 1 (NT1) liming (3tons CaO.ha-1); NT2: Plant ferns alternately with maize (without liming); NT3: Plant ferns alternately with maize and liming (3 tons CaO.ha-1); NT4: Control (no liming or ferns). The results showed that the applications of liming and ferns have positive influences on the soil pH, EC, OM, yield, and yield components of the maize tested in this study. The yield difference between the application of liming and intercropped ferns was increased from 5.4 to 22.3 %. Moreover, the arsenic contents in soil, stems, and seeds were 25.7, 32.0 and 50 % lower than that of the control, respectively. soil to roots and stems, which significantly caused reduction of a large amount of As content in soils. Therefore, to reduce the production cost, and enhance soil and maize quality, application of lime (3 ton.ha-1) and intercropped ferns is recommended. HIGHLIGHTS Increasing pH, EC and organic matter by the lime application combined with ferns Decreasing the soil arsenic concentration by intercroping maizes and ferns The lime application combined with ferns raising the yield components and yield of maize The high As accumulation of stems and shoots of ferns intercroping maizes and ferns The lowest As accumulation of stems and seeds of maizes applying the lime combined with ferns