Irrigation and phosphorous fertilization management to minimize rice grain arsenic content.

This research sought to minimize inorganic arsenic levels in polished rice grain by using different irrigation and phosphorous fertilization practices while also maintaining crop yield and water productivity. Two experiments were conducted during seasons 2018-2019 and 2019-2020 using a split-plot design with three blocks, five irrigation treatments (main-plots) and two phosphorous levels (sub-plots). Irrigation treatments consisted of a traditional continuous flood (CF) control and four alternatives irrigation techniques with one or two drying events during the irrigation cycle. The phosphorous fertilization levels investigated were an unfertilized control (0 kg P2O5 ha-1) and the recommended fertilization level of 50 kg P2O5 ha-1. Soil pH and redox potentials were measured in each treatment. Strategically-timed, low severity drying events were effective at achieving aerobic soil conditions, resulting in Eh values over 50 mV. The alternative irrigation treatment with two drying events, implemented at panicle initiation and full flowering, was the most effective in reducing inorganic arsenic in grain without affecting grain yield or the amount of irrigation water applied. This irrigation technique could be considered as an alternative management to the traditional continuous flooded to reach minimal inorganic arsenic accumulation in grain in order to attend special quality standards or specific market requirements. Accumulated inorganic arsenic in grain was below international maximum levels in all analyzed samples, with an average value of 0.084 mg kg-1.

Regional variability of arsenic content in Uruguayan polished rice.

Characterization of the country internal variability of arsenic (As) accumulation in rice grain across different rice production regions is very important in order to analyze its compliance with international and regional limits. A robust sampling study scheme (n = 150 samples) was performed to determine total arsenic (tAs) and inorganic (iAs) levels from polished rice grain covering all rice producing regions along two growing seasons. The mean and median concentration of tAs were 0.178 mg kg-1 and 0.147 mg kg-1, with a minimum and maximum value of 0.015 mg kg-1 and 0.629 mg kg-1, respectively and a coefficient of variation of 63.6%. The mean and median concentration of iAs were 0.062 mg kg-1 and 0.055 mg kg-1 respectively ranging from 0.005 mg kg-1 up to a maximum of 0.195 mg kg-1 and a coefficient of variation of 51.5%. A moderate correlation was revealed within iAs and tAs. Levels of iAs in all of the samples were below the international limits of 0.2 mg kg-1 according to the international limits for human health by the Codex Alimentarius (FAO and WHO, 2019). Rice fields cultivated on soils originated from igneous geological material reported lower arsenic levels accumulated in rice grain in relation to sedimentary soils. Japonica cultivars presented significantly lower tAs and iAs concentrations than Indica ones (p = 0.0121 and p < 0.0001; respectively). Consumption of rice by male and female adults in Uruguay is safe according to its level of annual consumption and based on the mean iAs levels determined in this study.