Effect of two different rice dehusking procedures on total arsenic concentration in rice

A critical analysis of various post-harvest arsenic removal treatments of rice and their impact on public health due to nutrient loss

Rice (Oryza sativa L.) is particularly susceptible to arsenic (As) accumulation. Currently, to decrease the level of As accumulated in rice, various post-harvest methods, i.e., polishing, parboiling, pH-dependent soaking, washing, and cooking at different rice-to-water ratios (r/w), are being focused, because it removes significant amount of As from rice grain. Depending upon the rice variety and type, i.e., rough (with husk), husked (without husk/brown), or polished rice, these methods can remove 39-54% As by parboiling, 38-55% by polishing, 37-63% by soaking, and 6-80% by washing and cooking. Infants are highly vulnerable to As exposure; thus, these methods can be helpful for the production of rice-based infant foods. Although concern arises during the use of these methods that apart from decreasing the level of As in rice grain, they also lead to a significant loss of nutrients, such as macro- and micro-elements present in rice. Among these discussed methods, parboiling curtails 5-59%, polishing curtails 6-96%, soaking curtails 33-83%, and washing and cooking in different r/w reduce 8-81% of essential nutrients resulting in 2-90% reduction in contribution to the RDI of these nutrients through rice-based diet. Thus, these post-harvest arsenic removal methods, although reduce arsenic induced health hazard, but may also lead to malnutrition and compromised health in the population based on rice diet. There is a need to explore another way to reduce As from rice without compromising the nutrient availability or to supplement these nutrients through grain enrichment or by introducing additional dietary sources by changing eating habits; however, this may impose an extra economic burden on people.

Evaluating the efficacy and feasibility of post harvest methods for arsenic removal from rice grain and reduction of arsenic induced cancer risk from rice-based diet

Food-chain arsenic (As) contamination is a severe environmental and health problem worldwide, and its intake through rice affects billions of people. In this review, we have summarized the post harvest As removal methods from rice and their efficacy and feasibility. Rice grain subspecies (indica and japonica), size (short, medium and long), type (husked, parboiled or polished), soaking time, temperature and rice to water ratio (r/w) during washing and cooking are the major factors that affect the removal of total arsenic (tAs) from rice grain. The reduction in tAs was greater in japonica than indica rice and was directly proportional to As in husked rice. For the removal of As, a low water volume (1:2 r/w) was more effective during washing due to friction between rice grains, while high water (≥4 times water) during cooking was more effective. Up to 80 % As was removed by cooking in 1:10 (rice: water). Soaking rice in edible acids such as vinegar, acetic and ascorbic acid was not effective, except citric acid, which removes tAs up to 63 %. Human-health risk assessment showed that these post harvest and cooking methods reduce the non-carcinogenic and incremental lifetime cancer risk by up to 5-fold, as calculated on the basis of bioaccessible inorganic As. These post harvest methods also remove nutrient elements and vitamins. The recommended dietary intake (RDI) of Zn and Cu was particularly affected (up to 40 and 83 %). The levels of P, Mo, Mn and Co were still sufficient to meet the RDI through the rice-based diet, while rice is already poor in the RDI of Ca, K, Fe and Se, and their levels were further reduced by 0.22-44 %. In conclusion, these post harvest and cooking methods may significantly reduce As induced health risks; however, other dietary sources of nutrients need to be carefully evaluated and supplemented.

Living with arsenic in the environment: An examination of current awareness of farmers in the Bengal basin using hybrid feature selection and machine learning

High levels of arsenic in drinking water and food materials continue to pose a global health challenge. Over 127 million people alone in Bangladesh (BD) and West Bengal (WB) state of India are exposed to elevated levels of arsenic in drinking water. Despite decades of research and outreach, arsenic awareness in communities continue to be low. Specifically, very few studies reported arsenic awareness among low-income farming communities. A comprehensive approach to assess arsenic awareness is a key step in identifying research and development priorities so that appropriate stakeholder engagement may be designed to tackle arsenic menace. In this study, we developed a comprehensive arsenic awareness index (CAAI) and identified key awareness drivers (KADs) of arsenic to help evaluate farmers' preferences in dealing with arsenic in the environment. The CAAI and KADs were developed using a questionnaire survey in conjunction with ten machine learning (ML) models coupled with a hybrid feature selection approach. Two questionnaire surveys comprising of 73 questions covering health, water and community, and food were conducted in arsenic-affected areas of WB and BD. Comparison of CAAIs showed that the BD farmers were generally more arsenic-aware (CAAI = 7.7) than WB farmers (CAAI = 6.8). Interestingly, the reverse was true for the awareness linked to arsenic in the food chain. Application of hybrid feature selection identified 15 KADs, which included factors related to stakeholder interventions and cropping practices instead of commonly perceived factors such as age, gender and income. Among ML algorithms, classification and regression trees and single C5.0 tree could estimate CAAIs with an average accuracy of 84%. Both communities agreed on policy changes on water testing and clean water supply. The CAAI and KADs combination revealed a contrasting arsenic awareness between the two farming communities, albeit their cultural similarities. Specifically, our study shows the need for increasing awareness of risks through the food chain in BD, whereas awareness campaigns should be strengthened to raise overall awareness in WB possibly through media channels as deemed effective in BD.

Modifying the Parboiling of Rice to Remove Inorganic Arsenic, While Fortifying with Calcium

Using village-based rice processing plants in rural Bangladesh, this study considered how parboiling rice could be altered to reduce the content of the carcinogen inorganic arsenic. Parboiling is normally conducted with rough rice (i.e., where the husk is intact) that is soaked overnight at ambient temperatures, and then either steamed or boiled for ∼10 min, followed by drying. Across 13 geographically dispersed facilities it was found that a simple alteration parboiling wholegrain, instead of rough rice, decreased the inorganic arsenic content by 25% ( P = 0.002) in the final polished grain. Also, parboiling wholegrain had little impact on milling quality of the final polished rice. The wholegrain parboiling approach caused statistically significant median enrichment of calcium, by 213%; and a reduction in potassium, by 40%; with all other nutrient elements tested being unaffected. Milled parboiled rough rice had an enriched inorganic arsenic compared to nonparboiled milled rice, but parboiling of wholegrain rice did not enrich inorganic arsenic in the final milled product. Polished rice produced from the parboiling of both rough and wholegrain rice significantly reduced cadmium compared to nonparboiled polished rice, by 25%. This study also identified that trimethylarsine oxide and tretramethylarsonium are widely elevated in the husk and bran of rice and, therefore, gives new insights into the biogeochemical cycling of arsenic in paddy ecosystems.

Impact of arsenic contaminated groundwater used during domestic scale post harvesting of paddy crop in West Bengal: Arsenic partitioning in raw and parboiled whole grain

The role of post harvesting procedures for producing parboiled rice grain using arsenic (As) contaminated groundwater in rural Bengal was investigated. Considerable high concentrations of As (mean: 186 μg/kg) were found in about 82% of parboiled rice grain samples compared to raw or non-parboiled rice grain samples (66 μg/kg in 75% samples) obtained from Deganga, a highly As affected zone located in West Bengal, India. This observation instigated to study the additional entry of As at various stages of parboiling. A maximum increase of 205% of As content in parboiled rice grain was observed. Significant increase in parboiled whole grain As concentration was dependent upon the large difference between As concentrations of the water and the raw whole grain used for parboiling. Arsenic concentrations of water samples collected at raw, half boiled and full boiled stages of parboiling increased, irrespective of their initial concentration due to reduction in final volume during parboiling process. Principle component analysis shows a positive correlation of As concentration of rice grain to that in the groundwater being used in post harvesting procedure. Moreover, partitioning studies of As in whole grain indicated higher accumulation of As content in individual rice grain than that in their respective husks implying higher risk of exposure on ingestion of these contaminated rice grains. It is therefore, suggested to employ novel methods such as rain water harvesting or surface water channelling to make As free water available for parboiling process to curtail the entry of additional As in parboiled rice.

Opportunities and Challenges for Dietary Arsenic Intervention

The diet is emerging as the dominant source of arsenic exposure for most of the U.S. population. Despite this, limited regulatory efforts have been aimed at mitigating exposure, and the role of diet in arsenic exposure and disease processes remains understudied. In this brief, we discuss the evidence linking dietary arsenic intake to human disease and discuss challenges associated with exposure characterization and efforts to quantify risks. In light of these challenges, and in recognition of the potential longer-term process of establishing regulation, we introduce a framework for shorter-term interventions that employs a field-to-plate food supply chain model to identify monitoring, intervention, and communication opportunities as part of a multisector, multiagency, science-informed, public health systems approach to mitigation of dietary arsenic exposure. Such an approach is dependent on coordination across commodity producers, the food industry, nongovernmental organizations, health professionals, researchers, and the regulatory community. https://doi.org/10.1289/EHP3997.

Inorganic arsenic contents in rice-based infant foods from Spain, UK, China and USA

Spanish gluten-free rice, cereals with gluten, and pureed baby foods were analysed for total (t-As) and inorganic As (i-As) using ICP-MS and HPLC-ICP-MS, respectively. Besides, pure infant rice from China, USA, UK and Spain were also analysed. The i-As contents were significantly higher in gluten-free rice than in cereals mixtures with gluten, placing infants with celiac disease at high risk. All rice-based products displayed a high i-As content, with values being above 60% of the t-As content and the remainder being dimethylarsinic acid (DMA). Approximately 77% of the pure infant rice samples showed contents below 150 μg kg(-1) (Chinese limit). When daily intake of i-As by infants (4-12 months) was estimated and expressed on a bodyweight basis (μg d(-1) kg(-1)), it was higher in all infants aged 8-12 months than drinking water maximum exposures predicted for adults (assuming 1 L consumption per day for a 10 μg L(-1) standard).

Processing conditions, rice properties, health and environment

Rice is the staple food for nearly two-thirds of the world’s population. Food components and environmental load of rice depends on the rice form that is resulted by different processing conditions. Brown rice (BR), germinated brown rice (GBR) and partially-milled rice (PMR) contains more health beneficial food components compared to the well milled rice (WMR). Although the arsenic concentration in cooked rice depends on the cooking methods, parboiled rice (PBR) seems to be relatively prone to arsenic contamination compared to that of untreated rice, if contaminated water is used for parboiling and cooking. A change in consumption patterns from PBR to untreated rice (non-parboiled), and WMR to PMR or BR may conserve about 43–54 million tons of rice and reduce the risk from arsenic contamination in the arsenic prone area. This study also reveals that a change in rice consumption patterns not only supply more food components but also reduces environmental loads. A switch in production and consumption patterns would improve food security where food grains are scarce, and provide more health beneficial food components, may prevent some diseases and ease the burden on the Earth. However, motivation and awareness of the environment and health, and even a nominal incentive may require for a method switching which may help in building a sustainable society.

Effect of cooking method and rice type on arsenic concentration in cooked rice and the estimation of arsenic dietary intake in a rural village in West Bengal, India

Arsenic (As) contamination of rice plants can result in high total As concentrations (t-As) in cooked rice, especially if As-contaminated water is used for cooking. This study examines two variables: (1) the cooking method (water volume and inclusion of a washing step); and (2) the rice type (atab and boiled). Cooking water and raw atab and boiled rice contained 40 microg As l(-1) and 185 and 315 microg As kg(-1), respectively. In general, all cooking methods increased t-As from the levels in raw rice; however, raw boiled rice decreased its t-As by 12.7% when cooked by the traditional method, but increased by 15.9% or 23.5% when cooked by the intermediate or contemporary methods, respectively. Based on the best possible scenario (the traditional cooking method leading to the lowest level of contamination, and the atab rice type with the lowest As content), t-As daily intake was estimated to be 328 microg, which was twice the tolerable daily intake of 150 microg.

Speciation and distribution of arsenic and localization of nutrients in rice grains

Arsenic (As) contamination of rice grains and the generally low concentration of micronutrients in rice have been recognized as a major concern for human health. Here, we investigated the speciation and localization of As and the distribution of (micro)nutrients in rice grains because these are key factors controlling bioavailability of nutrients and contaminants. Bulk total and speciation analyses using high-pressure liquid chromatography (HPLC)-inductively coupled plasma mass spectrometry (ICP-MS) and X-ray absorption near-edge spectroscopy (XANES) was complemented by spatially resolved microspectroscopic techniques (micro-XANES, micro-X-ray fluorescence (micro-XRF) and particle induced X-ray emission (PIXE)) to investigate both speciation and distribution of As and localization of nutrients in situ. The distribution of As and micronutrients varied between the various parts of the grains (husk, bran and endosperm) and was characterized by element-specific distribution patterns. The speciation of As in bran and endosperm was dominated by As(III)-thiol complexes. The results indicate that the translocation from the maternal to filial tissues may be a bottleneck for As accumulation in the grain. Strong similarities between the distribution of iron (Fe), manganese (Mn) and phosphorus (P) and between zinc (Zn) and sulphur (S) may be indicative of complexation mechanisms in rice grains.

Arsenic speciation in food and estimation of the dietary intake of inorganic arsenic in a rural village of West Bengal, India

Arsenic (As) species were quantified by HPLC-HG-AFS in water and vegetables from a rural area of West Bengal (India). Inorganic species predominated in vegetables (including rice) and drinking water; in fact, inorganic arsenic (i-As) represented more than 80% of the total arsenic (t-As) content. To evaluate i-As intake in an arsenic affected rural village, a food survey was carried out on 129 people (69 men and 60 women). The data from the survey showed that the basic diet, of this rural population, was mainly rice and vegetables, representing more than 50% of their total daily food intake. During the periods when nonvegetarian foods (fish and meat) were scarce, the importance of rice increased, and rice alone represented more than 70% of the total daily food intake. The food analysis and the food questionnaires administrated led us to establish a daily intake of i-As of about 170 microg i-As day (-1), which was above the tolerable daily intake of 150 microg i-As day (-1), generally admitted. Our results clearly demonstrated that food is a very important source of i-As and that this source should never be forgotten in populations depending heavily on vegetables (mainly rice) for their diet.